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Article

Effects of Light Intensity and Photoperiod on the Feeding Behavior of Rainbow Trout Oncorhynchus mykiss (Walbaum, 1792)

by
Xiao Liu
,
Liuyi Huang
*,
Qiqing Liu
,
Run Wang
,
Bo Liu
,
Zhaomin Li
,
Yacai Song
and
Ziyi Huang
College of Fisheries, Ocean University of China, Qingdao 266003, China
*
Author to whom correspondence should be addressed.
Fishes 2026, 11(3), 183; https://doi.org/10.3390/fishes11030183
Submission received: 25 February 2026 / Revised: 13 March 2026 / Accepted: 18 March 2026 / Published: 19 March 2026
(This article belongs to the Special Issue Engineering Solutions for Sustainable Offshore Aquaculture and Fisheries)
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Abstract

Light is a critical factor influencing fish behavior, yet the low-light conditions in deep-sea cages may impair feeding in visual species like rainbow trout Oncorhynchus mykiss (Walbaum, 1792). This study investigated the effects of light intensity and photoperiod on the feeding behavior of rainbow trout. Using green light, a factorial design tested three light intensities (10, 100, and 1000 lx) and three photoperiods (8L:16D, 16L:8D, and 24L:0D), alongside a complete darkness control (0 lx and 0L:24D). Key behavioral parameters during feeding were quantified via video analysis. The results showed significant main and interactive effects of light intensity and photoperiod on feeding behaviors. Feeding activity was substantially suppressed under continuous darkness. On the initial experimental day, exploratory movement was greatest under 10 lx and 8L:16D. Following 50 days of exposure, fish in light groups exhibited more focused swimming trajectories near the feeding point, indicating behavioral adaptation and spatial learning. Correlation analyses suggested a strategic shift from broad exploration to precise, efficient localization over time. In conclusion, specific lighting conditions, notably low intensity under a regular photoperiod, promote efficient feeding behavior in rainbow trout, whereas darkness or extreme light regimens are inhibitory. These findings reveal adaptive behavioral plasticity in this species and provide a scientific basis for optimizing light management in offshore salmonid aquaculture.
Keywords:
Oncorhynchus mykiss; feeding; behavior; swimming; fish welfare
Key Contribution: This study finds that specific lighting conditions, especially low light intensity under a regular photoperiod, can effectively promote efficient feeding behavior in rainbow trout by facilitating behavioral adaptation and spatial learning, whereas darkness or extreme light regimens are inhibitory, thereby providing a scientific basis for optimizing light management in offshore salmonid aquaculture.

1. Introduction

With the progressive saturation of nearshore aquaculture space and increasing environmental pressures, expanding marine aquaculture into offshore and deep-sea areas has become an inevitable trend for modern fisheries [1,2]. Large-scale deep-sea aquaculture cages independently developed in China, such as Deep Blue No. 1 and its successor, have successfully achieved commercial-scale farming of rainbow trout (Oncorhynchus mykiss (Walbaum, 1792)) in the Yellow Sea Cold Water Mass [3,4], marking a significant advancement in Chinese offshore cold-water fish aquaculture.
Light is one of the most important environmental factors regulating physiological rhythms and shaping behavioral patterns in fish [5,6,7,8]. For visually feeding fish [9,10,11], light availability directly determines the prey-detection efficiency [8,12,13,14], spatial orientation [15], and predation success [16]. Specifically, appropriate light intensity is fundamental for visual function, as both insufficient and excessive illumination can constrain visual field and food discrimination capabilities, leading to reduced feeding efficiency [17,18,19]. Meanwhile, photoperiod (including light–dark alternation and duration) acts as the primary zeitgeber for feeding rhythms in fish [20,21,22], significantly influencing both the duration and intensity of feeding [23,24]. Almazán-Rueda et al. [25] reported that continuous light and higher light intensity (150 lx) increased swimming and aggressive behaviors in juvenile African catfish (Clarias gariepinus) compared to a 12L:12D or lower light intensity (15 lx), with photoperiod and light intensity interacting significantly. Similarly, Gao et al. [26] observed a distinct circadian feeding rhythm in Haliotis discus hannai, with feeding rates highest under 12L:12D and significantly reduced under continuous light, reflecting a strong link to the light/dark cycle. In addition to regulating feeding behavior, light conditions may also influence social interactions, stress levels, and overall welfare status in cultured fish species, particularly in socially structured species such as salmonids [27,28]. Behavioral changes such as alterations in swimming activity, feeding anticipation, and aggressive interactions are widely considered important indicators of welfare in farmed fish [29].
Unlike land-based or nearshore aquaculture systems, offshore deep-sea cages such as Deep Blue No. 1 are typically deployed at deeper waters (below 20 m) from June to October, where incident light undergoes substantial physical attenuation during transmission through the water column. This results in long-term low-light or near-dark conditions inside cages, which differ markedly from the natural habitats of salmonids [30,31]. This mismatch poses potential challenges to production efficiency and fish welfare in deep-offshore salmonid farming. Therefore, elucidating the effects of light on the feeding behavior of cultured species is particularly important under the unique deep-sea aquaculture light environment. Feeding behavior refers to the actions such as finding, selecting, and consuming food [32]. Currently, behavioral characteristics of fish, such as feeding behavior and swimming patterns, are predominantly analyzed using video and image monitoring technologies [29,33,34], behavior recognition models [35,36], and acoustic monitoring [37,38]. However, there remains a lack of systematic behavioral observation and quantitative analysis concerning the dynamic responses and adaptive changes in the detailed feeding behavior of rainbow trout under varying light intensities and photoperiods. Based on these considerations, the present study employs a controlled experimental setup combined with behavioral monitoring methods, focusing on the effects of different lighting conditions on the feeding behavior of rainbow trout. The aim is to identify the most favorable photoperiod and light intensity for feeding, thereby providing a scientific basis for optimizing light management in offshore deep-sea aquaculture of cold-water fish species.

2. Materials and Methods

2.1. Experimental Materials

Juvenile rainbow trout (O. mykiss) were purchased from a commercial aquaculture facility in Rizhao, Shandong Province, China. All fish were healthy and free of disease. The initial body weight and total length of the fish were 139.23 ± 27.67 g and 23.64 ± 1.89 cm, respectively. The experimental fish were in a stable phase of salinity acclimation prior to seawater transfer, in preparation for subsequent stocking in offshore net-cage culture systems. Fish were reared in brackish water, with water exchanged twice daily (at 8:00 AM and 6:00 PM). Each water exchange replaced approximately two-thirds of the total water volume. Water quality parameters were monitored daily using a YSI multiparameter water quality analyzer (Yellow Springs Instrument Co., Yellow Springs, OH, USA) and a portable multiparameter water quality meter (Xiamen Pantian Biotechnology Co., Ltd., Xiamen, China). To ensure stable culture conditions throughout the experiment, salinity, water temperature (T), pH, nitrate (NO3−-N), ammonium nitrogen (NH4+-N), phosphate (PO43−), and dissolved oxygen (DO) were maintained at 21.76 ± 0.20 ppm, 19.61 ± 0.64 °C, 8.38 ± 0.70, 0.035 ± 0.02 mg/L, 0.03 ± 0.02 mg/L, 0.10 ± 0.01 mg/L, and 6.96 ± 0.55 mg/L, respectively. Based on practical aquaculture experience, the feeding ration was set at 2% of the fish body weight per day, corresponding to a daily total feed intake of 3.07 g per fish. Fish were fed once daily at 8:00 AM with a commercial diet (Miaozhibao Feed Co., Ltd., Rizhao, China) containing moisture ≤ 10.0%, crude protein ≥ 50.0%, crude lipid ≥ 9.0%, crude fiber ≤ 5.0%, and crude ash ≤ 14.0%.

2.2. Experimental Setup

In the aquaculture tank (6 m × 6 m), a total of 10 rearing compartments (1 m × 1 m × 0.8 m) were assembled using steel wire ropes (ø = 10 mm), net panels (mesh size 2a = 16 mm), and stainless-steel frames (ø = 5 mm) (Figure 1a). A camera (C1HC 1080P, EZVIZ Network Co., Ltd., Hangzhou, China) was installed directly above each rearing compartment. The vertical distance between the camera and the rearing compartment was adjusted to ensure that the video frame fully covered the entire rearing compartment (Figure 1a). The experimental light source was placed 0.2 m above the water surface, with a rearing water depth of 0.6 m. Light-shading cloth was installed between the rearing compartments to effectively prevent light penetration between adjacent units, thereby ensuring independent lighting control (Figure 1c). The overall experimental setup is shown in Figure 1b.

2.3. Light Source Control

The light intensity and photoperiod were automatically regulated by the Fish Farming Intelligent Lighting System (Figure 1d), which was developed in collaboration with the Ocean University of China and Shanghai Taoming Marine Technology Co., Ltd. (TOMAN®, Shanghai, China). The system consists of a lighting control cabinet, a controllable light source, and a control software interface. The intelligent control software was capable of performing automatic timing, positioning, and brightness control functions. The system is powered by a 220 V AC supply. The control software communicates with the control software interface via Ethernet cable using the TCP protocol for control. The controllable light source emits green illumination. In this experiment, the light intensity of each controllable light source was manually adjusted using the left interface of the intelligent control software, allowing precise brightness settings for each lamp to the required experimental levels (10 lx, 100 lx, and 1000 lx). Photoperiod control was implemented through the automatic strategy function on the right side of the software, enabling independent setting of the on and off times for each light source. The on/off schedule for the light sources in each treatment group is shown in Table 1. Specifically, the 0L:24D group was set to constant darkness, the 8L:16D group was set to turn on at 8:00 AM and off at 4:00 PM, the 16L:8D group was set to turn on at 8:00 AM and off at 12:00 PM, and the 24L:0D group was set to constant illumination.

2.4. Experimental Design

Based on comprehensive findings from studies by Liu et al. [39], Luchiari and Pirhonen [40], and Karakatsouli et al. [41,42], rainbow trout exhibits a pronounced phototaxis toward green light and demonstrates superior physiological status and growth performance under such lighting conditions. In accordance with these results, green light (wavelength range 492–577 nm) was selected as the rearing light source in this experiment. The experimental lighting conditions comprised two factors: light intensity (10 lx, 100 lx, and 1000 lx, approximately equivalent to 0.15 μmol/m2/s, 1.54 μmol/m2/s, and 15.38 μmol/m2/s, respectively) and photoperiod (8L:16D, 16L:8D, and 24L:0D). A fully orthogonal two-factor design was adopted, resulting in a total of nine treatment groups (L1–L9, Table 1). An additional control group was maintained under complete darkness (L0, i.e., 0 lx, 0L:24D, Table 1). Light intensity was measured at the center of the rearing compartment floor directly beneath the light source (indicated by the red dot in Figure 2) using a spectroradiometer (OHSP-350, Hopoo color Technology Co., Ltd., Hangzhou, China). The target light intensities for the experiment were calibrated based on the readings obtained at this red measurement point (Figure 2). The light intensity values recorded at various measurement points on the bottom of the rearing compartment are presented in Table 2.
The experiment was conducted at Huali Ocean Technology Co., Ltd. in Rizhao City, Shandong Province, lasting 50 days from 24 July to 11 September 2024. Prior to the experiment, the fish were acclimated in the rearing compartments for 7 days. Each treatment group consisted of three replicate compartments, with 10 fish stocked per compartment, resulting in a total of 300 experimental fish. The stocking density was 2.32 kg/m3. Feed was provided daily at 8:00 AM at the water surface directly below the light source, corresponding to the central area of the rearing compartment. Thus, the feeding location remained fixed at the center of each compartment during the experiment. The first 10 min of the feeding process were recorded for subsequent analysis of feeding behavior.

2.5. Swimming Behavior Analysis

Swimming behavior was analyzed for three randomly selected fish from each treatment group. A 30 s video segment following feed provision was extracted for analysis. Based on the methodologies of Kane et al. [43] and Yalsuyi et al. [44], changes in feeding behavior of the experimental fish were characterized by analyzing variations in swimming patterns, including average swimming speed (AS), total movement (TM), fastest movement (FM), average angular change of movement (AC), and average distance from the center (DC) (see Table 3).
The selected video data were analyzed on a Windows platform (Windows 11, Microsoft Corporation, Redmond, WA, USA) using Adobe After Effects software (Adobe After Effects CS6, Adobe Inc., San Jose, CA, USA; version CS6). Total movement and Distance from the center were measured on the Windows platform using Digimizer software (MedCalc Software Ltd., Ostend, Belguim; version 6.4.5). Swimming trajectories were generated using the open-source behavioral tracking software Tracker (Tracker Video Analysis and Modelling Tool, Open Source Physics project; version 6.2.0; https://physlets.org/tracker/, accessed on 17 March 2026). To minimize tracking error, manual point tracking was performed throughout the video sequence, using the tip of the fish’s snout as the positional marker. The step frame interval was set to 1, resulting in approximately 476 tracked points per trajectory. Definitions of the swimming behavior are provided in Table 3, and the tracking and calculation process for swimming behavior is illustrated in Figure 3.

2.6. Statistical Analysis

All data analyses were performed using SPSS software (IBM SPSS Statistics, IBM Corp., Armonk, NY, USA; version 26.0). Statistical significance was set at p < 0.05. Data are presented as mean ± standard deviation. Data normality and homogeneity of variance were assessed using the Kolmogorov–Smirnov test and Levene’s test, respectively. If the data met the assumptions of normality and homogeneity of variance, a two-way analysis of variance (Two-way ANOVA) was conducted. When significant main effects of light intensity and photoperiod were detected, pairwise comparisons with Bonferroni correction were performed. If a significant interaction between light intensity and photoperiod was found, simple effect analysis was further conducted. If the data violated the assumptions of normality and homogeneity of variance, a logarithmic transformation was applied to achieve a normal distribution and homoscedasticity. If the transformed data still did not meet these assumptions, the non-parametric Kruskal–Wallis H test was used, followed by pairwise comparisons with the Wilcoxon rank-sum test.
For comparisons across different time points within the same light treatment group, an independent samples t-test was used if the data were normally distributed. If normality was violated for any group, the non-parametric Mann–Whitney U test was applied.
The relationships among the various swimming behavior parameters were examined using Spearman’s rank correlation analysis. The correlation coefficient r was used to evaluate the monotonic association between parameters, ranging from −1 to 1, where 1 indicates a perfect positive correlation, −1 a perfect negative correlation, and 0 no correlation. The corresponding p-values were calculated to determine the statistical significance of the correlation coefficients. A statistically significant correlation was defined as p < 0.05 (or p < 0.01).

3. Results

3.1. Average Swimming Speed

A two-way ANOVA indicated that light intensity (F(2, 24) = 8.20, p < 0.01), photoperiod (F(3, 24) = 13.04, p < 0.001), and their interaction (F(6, 24) = 5.23, p < 0.01) all had a significant effect on AS at D1 (Table 4). The results of simple effect analysis (Figure 4a) showed that when the photoperiod was fixed, under the 16L:8D, AS at D1 was significantly higher at 1000 lx than at 100 lx (p = 0.023). Under the 24L:0D, AS at D1 was significantly higher at both 10 lx and 1000 lx compared to 100 lx (both p = 0.049). When light intensity was fixed at 10 lx, AS at D1 under the 24L:0D was significantly higher than under both 0L:24D (p = 0.006) and 16L:8D (p = 0.004). At 100 lx, AS at D1 under the 8L:16D was significantly higher than under all other photoperiods (vs. 0L:24D, p = 0.025; vs. 16L:8D, p < 0.001; vs. 24L:0D, p = 0.001). At 1000 lx, AS at D1 under the 24L:0D was significantly higher than under 0L:24D (p = 0.035).
Kruskal–Wallis test analysis revealed that light intensity (H = 1.36, p = 0.507) had no significant effect on AS at D50, whereas photoperiod (H = 22.55, p < 0.001) exerted a significant influence (Table 5). As shown in Figure 4b, at 10 lx light intensity, AS at D50 under both the 16L:8D and 24L:0D was significantly higher than under the 8L:16D (p < 0.001) and 0L:24D (p = 0.028). At 100 lx, AS at D50 under both the 8L:16D and 24L:0D was significantly higher than under the 16L:8D and 0L:24D (p < 0.001). At 1000 lx, AS at D50 under the 0L:24D was significantly lower than under the 8L:16D (p = 0.002), 16L:8D (p < 0.001), and 24L:0D (p < 0.001).
As shown in Figure 4c, on experimental day 1 (D1), the AS in L3 was significantly higher than in groups L0, L2, L5, and L6 (p < 0.05, Table 6). On experimental day 50 (D50), the AS in the control group L0 was significantly lower than in all other light treatment groups (L1–L9) (p < 0.05, Table 6). With the exception of the complete darkness environment (L0), the AS of rainbow trout at D50 was significantly higher than at D1 in all remaining groups (p < 0.05, Table 6).

3.2. Average Angular Change

The two-way ANOVA indicated that light intensity (F(2, 24) = 5.57, p = 0.010), photoperiod (F(3, 24) = 8.23, p = 0.001), and their interaction (F(6, 24) = 14.32, p < 0.001) all had a significant effect on AC at D1 (Table 4). The results of the simple effect analysis (Figure 4d) showed that when the photoperiod was fixed, under the 8L:16D, AC at D1 was significantly higher at 1000 lx than at both 10 lx (p = 0.001) and 100 lx (p = 0.006). In contrast, under the 16L:8D, AC at D1 at 1000 lx was significantly lower than at both 10 lx and 100 lx (both p ≤ 0.001). Under the 24L:0D, AC at D1 at 100 lx was significantly higher than at both 10 lx (p < 0.001) and 1000 lx (p < 0.001).
When light intensity was fixed at 10 lx, AC at D1 under the 16L:8D was significantly higher than under 0L:24D (p = 0.001), 8L:16D (p < 0.001), and 24L:0D (p = 0.011). At 100 lx, AC at D1 under the 16L:8D was significantly higher than under all other photoperiods (vs. 0L:24D, p = 0.037; vs. 8L:16D, p = 0.017; vs. 24L:0D, p = 0.041). At 1000 lx, AC at D1 under the 8L:16D was significantly higher than under 0L:24D (p = 0.026), 16L:8D (p = 0.026), and 24L:0D (p = 0.041).
The two-way ANOVA indicated that light intensity (F(2, 24) = 13.80, p < 0.001), photoperiod (F(3, 24) = 12.78, p < 0.001), and their interaction (F(6, 24) = 3.44, p = 0.014) all had a significant effect on AC at D50 (Table 4). The results of the simple effect analysis (Figure 4e) showed that when the photoperiod was fixed, under the 16L:8D, AC at D50 was significantly higher at 1000 lx than at 10 lx (p < 0.001). Under the 24L:0D, AC at D50 at 10 lx was significantly higher than at both 100 lx (p < 0.001) and 1000 lx (p = 0.009).
When light intensity was fixed at 10 lx, AC at D50 under the 24L:0D was significantly higher than under both 0L:24D (p = 0.001) and 8L:16D (p < 0.001). At 1000 lx, AC at D50 under the 8L:16D was significantly higher than under both 0L:24D (p = 0.046) and 24L:0D (p = 0.004).
As shown in Figure 4f, on experimental day 1 (D1), the average angular change (AC) in treatment groups L2 and L6 was significantly higher than in groups L0, L1, L4, L8, and L9 (p < 0.05, Table 6). On experimental day 50 (D50), the AC in groups L7 and L8 was significantly higher than in groups L2, L3, and L9 (p < 0.05, Table 6). With the exception of groups L2, L5, and L6, the AC of rainbow trout at D50 was significantly higher than at D1 (p < 0.05, Table 6).

3.3. Total Movement

The two-way ANOVA indicated that light intensity (F(2, 24) = 15.74, p < 0.001), photoperiod (F(3, 24) = 13.52, p < 0.001), and their interaction (F(6, 24) = 4.93, p = 0.002) all had a significant effect on TM at D1 (Table 4). The results of the simple effect analysis (Figure 4g) showed that when the photoperiod was fixed, under the 8L:16D, TM at D1 was significantly higher at 10 lx than at both 100 lx and 1000 lx (both p = 0.003). Under the 16L:8D, TM at D1 was significantly higher at 1000 lx than at 100 lx (p = 0.007). Under the 24L:0D, TM at D1 was significantly higher at both 10 lx and 1000 lx compared to 100 lx (both p ≤ 0.001).
When light intensity was fixed at 10 lx, TM at D1 under both the 8L:16D and 24L:0D was significantly higher than under the 0L:24D and 16L:8D (p < 0.01). At 100 lx, TM at D1 under the 8L:16D was significantly higher than under both the 16L:8D (p = 0.005) and 24L:0D (p = 0.022). At 1000 lx, TM at D1 under the 24L:0D was significantly higher than under the 0L:24D (p = 0.045).
Kruskal–Wallis test analysis revealed that light intensity (H = 2.42, p = 0.298) had no significant effect on TM at D50, whereas photoperiod (H = 20.70, p < 0.001) exerted a significant influence (Table 5). As shown in Figure 4h, at 10 lx light intensity, TM at D50 under the 0L:24D was significantly lower than under the 8L:16D (p = 0.001), 16L:8D (p < 0.001), and 24L:0D (p < 0.001). At 100 lx, TM at D50 under both the 8L:16D and 24L:0D was significantly higher than under the 16L:8D and 0L:24D (all p < 0.05). At 1000 lx, TM at D50 under the 0L:24D was significantly lower than under the 8L:16D (p = 0.010), 16L:8D (p = 0.007), and 24L:0D (p = 0.025).
As shown in Figure 4i, on experimental day 1 (D1), the total movement (TM) in treatment groups L1 and L3 was significantly higher than in groups L0, L2, L5, and L6 (p < 0.05, Table 6). On experimental day 50 (D50), the TM in groups L4 and L8 was significantly higher than in groups L0, L1, L5, and L9 (p < 0.05, Table 6). With the exception of the complete darkness environment (L0), the TM of rainbow trout at D50 was significantly higher than at D1 in all other groups (p < 0.05, Table 6).

3.4. Average Distance from the Center

The two-way ANOVA showed that photoperiod had a significant main effect on DC at D1 (F(3, 24) = 19.14, p < 0.001), and there was a significant interaction between light intensity and photoperiod (F(6, 24) = 5.07, p = 0.002), while the main effect of light intensity was not significant (F(2, 24) = 0.01, p = 0.986) (Table 4). The results of the simple effect analysis (Figure 4j) showed that when the photoperiod was fixed, under the 8L:16D, DC at D1 was significantly lower at 10 lx than at 100 lx (p = 0.002). Under the 24L:0D, DC at D1 at 10 lx was significantly higher than at 100 lx (p = 0.041).
When light intensity was fixed at 10 lx, DC at D1 under the 24L:0D was significantly higher than under 0L:24D (p < 0.001) and 8L:16D (p = 0.01). At 100 lx, DC at D1 under the 0L:24D was significantly lower than under 8L:16D (p < 0.001) and 24L:0D (p = 0.027). At 1000 lx, DC at D1 under the 0L:24D was significantly lower than under 8L:16D (p = 0.044), 16L:8D (p = 0.002), and 24L:0D (p = 0.017).
The two-way ANOVA indicated that light intensity (F(2, 24) = 38.44, p < 0.001), photoperiod (F(3, 24) = 9.73, p = 0.001), and their interaction (F(6, 24) = 3.61, p = 0.011) all had a significant effect on DC at D50 (Table 4). The results of the simple effect analysis (Figure 4k) showed that when the photoperiod was fixed, under the 8L:16D, DC at D50 was significantly lower at 10 lx than at both 100 lx (p = 0.001) and 1000 lx (p = 0.001). Under the 16L:8D, DC at D50 at 100 lx was significantly lower than at 1000 lx (p = 0.017). Under the 24L:0D, DC at D50 at 10 lx was significantly lower than at 100 lx (p = 0.047).
When light intensity was fixed at 10 lx, DC at D50 under 0L:24D was significantly higher than under 8L:16D (p = 0.034) and 16L:8D (p = 0.002). At 100 lx, DC at D50 under 0L:24D was significantly lower than under 8L:16D (p < 0.001), 16L:8D (p = 0.015), and 24L:0D (p < 0.001). At 1000 lx, DC at D50 under 0L:24D was significantly lower than under 8L:16D (p < 0.001), 16L:8D (p = 0.001), and 24L:0D (p < 0.001).
As shown in Figure 4l, on experimental day 1 (D1), the average distance from the center (DC) in treatment groups L3 and L4 was significantly higher than in groups L0, L1, and L5 (p < 0.05, Table 6). On experimental day 50 (D50), the DC in groups L4 and L8 was significantly higher than in groups L0, L1, L3, and L5 (p < 0.05, Table 6). With the exception of groups L0, L3, and L4, the DC of rainbow trout at D50 was significantly higher than at D1 (p < 0.05, Table 6).

3.5. Fastest Movement

The two-way ANOVA indicated that light intensity (F(2, 24) = 8.72, p = 0.001), photoperiod (F(3, 24) = 19.71, p < 0.001), and their interaction (F(6, 24) = 6.95, p < 0.001) all had a significant effect on FM at D1 (Table 4). The results of the simple effect analysis (Figure 4m) showed that when the photoperiod was fixed, under the 16L:8D, FM at D1 was significantly higher at 1000 lx than at 100 lx (p = 0.004). Under the 24L:0D, FM at D1 was significantly higher at both 10 lx and 1000 lx compared to 100 lx (p ≤ 0.005).
When light intensity was fixed at 10 lx, FM at D1 under both the 8L:16D and 24L:0D s was significantly higher than under the 0L:24D and 16L:8D s (all p < 0.05). At 100 lx, FM at D1 under the 8L:16D was significantly higher than under all other photoperiods (vs. 0L:24D, p = 0.023; vs. 16L:8D, p < 0.001; vs. 24L:0D, p = 0.001).
The Kruskal–Wallis test revealed that light intensity (H = 1.05, p = 0.593) had no significant effect on FM at D50, whereas photoperiod (H = 21.03, p < 0.001) exerted a significant influence (Table 5). As shown in Figure 4n, at 10 lx intensity, FM at D50 under the 0L:24D was significantly lower than under the 8L:16D, 16L:8D, and 24L:0D s (all p < 0.001). At 100 lx intensity, FM at D50 under both the 8L:16D and 24L:0D s was significantly higher than under the 16L:8D and 0L:24D s (all p < 0.05). At 1000 lx intensity, FM at D50 under the 0L:24D was significantly lower than under the 8L:16D (p = 0.002), 16L:8D (p < 0.001), and 24L:0D (p = 0.001).
As shown in Figure 4o, on experimental day 1 (D1), the fastest movement (FM) in L1, L3, and L4 was significantly higher than in L0, L2, L5, and L6 (p < 0.05, Table 6). On experimental day 50 (D50), the FM in groups L4, L6, L8, and L9 was significantly higher than in groups L0 and L5 (p < 0.05, Table 6). With the exception of groups L0, L1, L3, and L4, the FM of rainbow trout at D50 was significantly higher than at D1 in all other groups (p < 0.05, Table 6).

3.6. Swimming Trajectory

As shown in Figure 5 and Figure 6, on experimental day 1 (D1), compared to the other light treatment groups, the swimming trajectories and the distribution of trajectory density of rainbow trout during feeding were more concentrated in the central area of the rearing compartment (i.e., the feeding point) in treatment groups L0 (Figure 5j and Figure 6j), L6 (Figure 5f and Figure 6f), and L7 (Figure 5g and Figure 6g). This central region corresponded to the feeding point, where feed was delivered at the water surface directly beneath the light source. Because the feeding location was fixed at the center of each rearing compartment, fish tended to aggregate in this area during feeding periods, which may partially influence the spatial distribution of swimming trajectories.
As shown in Figure 7 and Figure 8, on experimental day 50 (D50), compared with the other light treatment groups, the swimming trajectories and the density distribution of trajectories of rainbow trout during feeding were more concentrated in the central area of the rearing compartment in group L0 (Figure 7j and Figure 8j). Compared with D1, the swimming trajectories and trajectory density distribution during feeding at D50 were more concentrated toward the central area of the rearing compartment (i.e., the feeding point). Overall, the swimming trajectories observed on D50 showed a stronger spatial concentration around the feeding point than those recorded on D1.

3.7. Correlation Analysis of Feeding Behavior

As shown in Table 7, on experimental day 1 (D1), average swimming speed (AS) showed a significantly negative correlation with average angular change (AC) (r = −0.47, p < 0.01), while it was positively correlated with total movement (TM) (r = 0.85, p < 0.01), average distance from the center (DC) (r = 0.41, p < 0.01), and fastest movement (FM) (r = 0.89, p < 0.01). AC was significantly negatively correlated with TM (r = −0.50, p < 0.01) and FM (r = −0.51, p < 0.01). TM exhibited a significantly positive correlation with FM (r = 0.79, p < 0.01). DC was positively correlated with FM (r = 0.40, p < 0.05).
As shown in Table 8, on experimental day 50 (D50), average swimming speed (AS) showed significantly positive correlations with total movement (TM) (r = 0.81, p < 0.01), average distance from the center (DC) (r = 0.54, p < 0.01), and fastest movement (FM) (r = 0.82, p < 0.01). AC exhibited a significantly positive correlation with FM (r = 0.60, p < 0.01). TM was significantly positively correlated with DC (r = 0.63, p < 0.01) and FM (r = 0.81, p < 0.01). DC was also significantly positively correlated with FM (r = 0.52, p < 0.01).

4. Discussion

This study investigated the effects of different light intensities and photoperiods on the swimming behavior metrics and spatial distribution of rainbow trout during feeding. The results indicate that light is a key environmental factor influencing the feeding behavior of rainbow trout, with light intensity and photoperiod jointly affecting feeding behavior characteristics through complex interactions.
Under complete darkness (L0), the activity metrics of the fish during feeding were significantly reduced, and their swimming trajectories were highly concentrated around the feeding point. This pattern suggests that fish relied heavily on the localized food source when visual cues were limited, which is consistent with the characteristics of rainbow trout as a visually oriented species [45,46]. The absence of sufficient visual information under dark conditions likely restricts the ability of fish to detect and track food items over a broader spatial range, thereby reducing exploratory movement and confining swimming trajectories to the immediate vicinity of the feeding location [47]. Notably, during the initial experimental phase (D1), similar behavioral suppression was observed in groups exposed to high-intensity light (L7) or a long photoperiod (L6). These findings indicate that both insufficient illumination and excessive light exposure may disrupt visual perception and spatial orientation during feeding, thereby affecting the ability of fish to efficiently locate food targets [48]. Together, these results imply that rainbow trout may require an appropriate range of light intensity and photoperiod to maintain effective visual detection and coordinated foraging movements. In addition to influencing feeding efficiency, light regimes may also affect fish welfare and social behavior in salmonids. Rainbow trout can exhibit territoriality and intraspecific aggression under certain environmental conditions, and previous studies suggest that social interactions and aggressive behavior are common features in salmonids and can influence growth and welfare status in cultured populations [28,49,50]. Photoperiod and light conditions are also known to regulate physiological rhythms and behavioral processes in salmonids [51]. Excessively long photoperiods or continuous illumination may alter behavioral activity and social interactions, potentially increasing aggressive encounters that can lead to fin damage or bite wounds in aquaculture systems [49]. Although aggression was not directly quantified in this study, the lighting conditions tested here may influence broader behavioral dynamics within fish groups. Therefore, optimizing light intensity and photoperiod may contribute not only to improved feeding behavior but also to maintaining stable social interactions and welfare conditions in rainbow trout aquaculture.
In natural ecosystems, aquatic organisms experience diurnal cycles and have evolved corresponding physiological senses and behavioral activities to adapt to changes in light intensity and photoperiod [52,53]. In the present study, during the initial phase (D1), the interaction between light intensity and photoperiod significantly affected all measured swimming behavior parameters (AS, AC, DC, TM, and FM) during feeding, highlighting the importance of the synergistic regulation by these two light factors. Specifically, under a short photoperiod (8L:16D) on D1, TM was markedly higher at 10 lx than at 100 lx and 1000 lx, suggesting that low light intensity promotes a wider exploration range for food localization. This pattern may also reflect the natural feeding ecology of rainbow trout. Wild populations of rainbow trout and other salmonids commonly exhibit crepuscular feeding behavior, with peaks in feeding activity occurring around dawn and dusk when ambient light levels are relatively low [54,55]. The 8L:16D photoperiod applied in the present study is comparable to winter photoperiod conditions in the Northern Hemisphere (approximately November–December), which may coincide with seasonal metabolic rhythms in salmonids [56]. Under such dim-light conditions, reduced visibility may provide fish with a predatory advantage by allowing them to detect prey while simultaneously reducing exposure to predators, thereby promoting more extensive exploratory swimming during feeding [57,58]. Under constant light (24L:0D), DC was significantly greater at 10 lx compared with other photoperiods, indicating that continuous illumination may influence the swimming range during feeding. By D50, compared to complete darkness, fish exposed to low light intensity under a short photoperiod exhibited more precise localization of the feeding area, reflected in increased AS and FM relative to the complete darkness condition (0L:24D).
Furthermore, this study revealed a clear behavioral adaptation and learning capacity in rainbow trout following long-term exposure to different light environments. Specifically, except for the complete darkness group (L0), fish in all light-treatment groups showed significantly higher movement activity (e.g., AS and TM) on D50 than on D1, indicating enhanced overall activity after prolonged exposure. By D50, swimming trajectories became more tightly concentrated around the feeding point, suggesting that fish progressively refined their spatial orientation toward the feeding location over time. This pattern may reflect the development of spatial learning and feeding habituation, enabling individuals to optimize their food searching strategy and reduce unnecessary exploratory movements during feeding events [59]. Such behavioral adjustments are commonly interpreted as adaptive responses that improve foraging efficiency under stable environmental conditions.
Correlations among different behavioral metrics changed noticeably over the course of the experiment. On D1, AS was significantly negatively correlated with AC (r = −0.47), implying that high-speed swimming was often accompanied by lower turning angles, reflecting a fast, relatively straight-line exploratory strategy. By D50, AC was significantly positively correlated with FM (r = 0.60), indicating that fish could change direction more flexibly during high-speed movement. This shift in correlation structure suggests a transition in behavioral strategy, from an initial “extensive search” pattern characterized by rapid exploration to a later “target-oriented localization” pattern with more flexible directional adjustments. Such a behavioral shift may represent an optimization of feeding strategy under prolonged exposure to the experimental light regimes, ultimately contributing to improved feeding efficiency.

5. Conclusions

This study demonstrates that light conditions, including intensity and photoperiod, are key environmental factors regulating the feeding behavior of rainbow trout. Appropriate illumination is essential for efficient visual foraging, whereas extreme conditions such as darkness, excessive intensity, or prolonged photoperiods suppress exploratory behavior during feeding. In this experiment, low light intensity (10 lx) combined with a regular photoperiod (8L:16D) promoted favorable swimming behavior during feeding while potentially maintaining feeding efficiency with reduced energy expenditure. More importantly, rainbow trout also exhibited clear behavioral adaptation to the light environment. With prolonged exposure, fish showed increased activity, improved spatial use around the feeding area, and a shift from broad exploratory searching to more precise feeding localization. These findings improve understanding of how light regulates fish feeding behavior and provide a scientific basis for optimizing lighting strategies in rainbow trout aquaculture, which may help enhance feeding efficiency, production performance, and fish welfare.

Author Contributions

Conceptualization, X.L. and L.H.; methodology, X.L.; validation, Q.L., R.W., B.L., Z.L., Y.S. and Z.H.; formal analysis, X.L.; investigation, X.L., L.H., Q.L., R.W., B.L., Z.L., Y.S. and Z.H.; resources, L.H.; data curation, X.L., Q.L., R.W., B.L., Z.L., Y.S. and Z.H.; writing—original draft preparation, X.L.; writing—review and editing, L.H.; visualization, X.L.; supervision, L.H.; project administration, L.H.; funding acquisition, L.H. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Key Research and Development Program of China (grant number 2020YFD0901205), under the project “Demonstration of New Resource Development and Integrated Processing Models for Distant-Water Fisheries”.

Institutional Review Board Statement

All experimental procedures involving animals complied with the Guidelines for the Ethical Review of Laboratory Animal Welfare (GB/T 35892-2018, China). This study was reviewed and approved by the Scientific Ethics Committee of Ocean University of China (Qingdao, China) (Approval Code: OUC-AE-2025-285; Approval Date: 25 September 2025).

Data Availability Statement

The data that support the findings of this study are available on request from the corresponding author, upon reasonable request.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
ASAverage Swimming Speed
TMTotal Movement
FMFastest Movement
ACAverage Angular Change of Movement
DCAverage Distance from the Center

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Figure 1. Schematic diagram of the experimental system. (a) Structure of the rearing compartments (1 m × 1 m× 0.80 m) installed in the aquaculture tank (6 m × 6 m) and the camera positioned above each compartment for behavioral recording; (b) overall layout of the experimental setup in the aquaculture tank; (c) arrangement of the controllable light source above the water surface (20 cm) and installation of light-shading cloth between adjacent compartments to prevent light interference among treatments; and (d) Fish Farming Intelligent Lighting System used to regulate light intensity and photoperiod, including the control software interface, lighting control cabinet, and controllable light sources. The schematic diagram was created using Microsoft PowerPoint (Microsoft Corp., Redmond, WA, USA).
Figure 1. Schematic diagram of the experimental system. (a) Structure of the rearing compartments (1 m × 1 m× 0.80 m) installed in the aquaculture tank (6 m × 6 m) and the camera positioned above each compartment for behavioral recording; (b) overall layout of the experimental setup in the aquaculture tank; (c) arrangement of the controllable light source above the water surface (20 cm) and installation of light-shading cloth between adjacent compartments to prevent light interference among treatments; and (d) Fish Farming Intelligent Lighting System used to regulate light intensity and photoperiod, including the control software interface, lighting control cabinet, and controllable light sources. The schematic diagram was created using Microsoft PowerPoint (Microsoft Corp., Redmond, WA, USA).
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Figure 2. Schematic diagram of the illuminance measurement points. (a) Overall measurement points within the rearing compartment, and (b) measurement points at the compartment bottom. The solid blue and red dots represent the location of illuminance sensors in each rearing compartment. The red dot marks the center of the tank bottom, directly below the light source; the target illuminance for the experiment was calibrated based on the readings from this point.
Figure 2. Schematic diagram of the illuminance measurement points. (a) Overall measurement points within the rearing compartment, and (b) measurement points at the compartment bottom. The solid blue and red dots represent the location of illuminance sensors in each rearing compartment. The red dot marks the center of the tank bottom, directly below the light source; the target illuminance for the experiment was calibrated based on the readings from this point.
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Figure 3. Swimming behavior tracking and calculation. (a) Orange dots mark three randomly selected experimental fish (No. 1–3), tracked by snout position. White dotted lines between red points show swimming trajectories between frames. White points are starting positions; orange points are endpoints. The distance between them is the total movement distance, TM. (b) Average distance of the fish snout points from the origin ( x ¯ = ( x 1 + x 1 + ⋯ + x i ) / i ) . (c) Average change in movement angle ( α ¯ = ( α 1 + α 2 + ⋯ + α i ) / i ).
Figure 3. Swimming behavior tracking and calculation. (a) Orange dots mark three randomly selected experimental fish (No. 1–3), tracked by snout position. White dotted lines between red points show swimming trajectories between frames. White points are starting positions; orange points are endpoints. The distance between them is the total movement distance, TM. (b) Average distance of the fish snout points from the origin ( x ¯ = ( x 1 + x 1 + ⋯ + x i ) / i ) . (c) Average change in movement angle ( α ¯ = ( α 1 + α 2 + ⋯ + α i ) / i ).
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Figure 4. The effects of light intensity, photoperiod, and treatment duration on the swimming behavior parameters of rainbow trout. (a) AS, D1, (b) AS, D50, (c) AS, D1 vs. D50, (d) AC, D1, (e) AC, D50, (f) AC, D1 vs. D50, (g) TM, D1, (h) TM, D50, (i) TM, D1 vs. D50, (j) DC, D1, (k) DC, D50, (l) DC, D1 vs. D50, (m) FM, D1, (n) FM, D50, and (o) FM, D1 vs. D50. Different lowercase indicates significant differences between treatment groups of different photoperiods under the same light intensity (p < 0.05), and * indicates significant differences between treatment groups of different light intensities within the same photoperiod (p < 0.05).
Figure 4. The effects of light intensity, photoperiod, and treatment duration on the swimming behavior parameters of rainbow trout. (a) AS, D1, (b) AS, D50, (c) AS, D1 vs. D50, (d) AC, D1, (e) AC, D50, (f) AC, D1 vs. D50, (g) TM, D1, (h) TM, D50, (i) TM, D1 vs. D50, (j) DC, D1, (k) DC, D50, (l) DC, D1 vs. D50, (m) FM, D1, (n) FM, D50, and (o) FM, D1 vs. D50. Different lowercase indicates significant differences between treatment groups of different photoperiods under the same light intensity (p < 0.05), and * indicates significant differences between treatment groups of different light intensities within the same photoperiod (p < 0.05).
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Figure 5. Swimming trajectories of experimental fish (D1). (a–i) represent L1–L9, and (j) represents L0. A, B, and C are the randomly selected trajectories of experimental fish from each treatment.
Figure 5. Swimming trajectories of experimental fish (D1). (a–i) represent L1–L9, and (j) represents L0. A, B, and C are the randomly selected trajectories of experimental fish from each treatment.
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Figure 6. Distribution density map of the swimming trajectories of the experimental fish (D1). (a–i) represent L1–L9, and (j) represents L0.
Figure 6. Distribution density map of the swimming trajectories of the experimental fish (D1). (a–i) represent L1–L9, and (j) represents L0.
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Figure 7. Swimming trajectories of experimental fish (D50). (a–i) represent L1–L9, and (j) represents L0. A, B, and C are the randomly selected trajectories of experimental fish from each treatment.
Figure 7. Swimming trajectories of experimental fish (D50). (a–i) represent L1–L9, and (j) represents L0. A, B, and C are the randomly selected trajectories of experimental fish from each treatment.
Fishes 11 00183 g007
Fishes 11 00183 g008
Figure 8. Distribution density map of the swimming trajectories of the experimental fish (D50). (a–i) represent L1–L9, and (j) represents L0.
Figure 8. Distribution density map of the swimming trajectories of the experimental fish (D50). (a–i) represent L1–L9, and (j) represents L0.
Fishes 11 00183 g008
Table 1. Light condition treatments and the on/off schedule.
Table 1. Light condition treatments and the on/off schedule.
Light TreatmentLight IntensityPhotoperiodLight ON/OFF Timing
L00 lx0L:24DConstant darkness
L110 lx8L:16D08:00 ON/16:00 OFF
L210 lx16L:8D08:00 ON/00:00 OFF
L310 lx24L:0DConstant illumination
L4100 lx8L:16D08:00 ON/16:00 OFF
L5100 lx16L:8D08:00 ON/00:00 OFF
L6100 lx24L:0DConstant illumination
L71000 lx8L:16D08:00 ON/16:00 OFF
L81000 lx16L:8D08:00 ON/00:00 OFF
L91000 lx24L:0DConstant illumination
Table 2. The light intensity of illuminance measurement points.
Table 2. The light intensity of illuminance measurement points.
Red Point (2, 2) Illuminance (lx)Blue Points (0, 0), (0, 4), (4, 4), (4, 0) Illuminance (lx)Blue Points (1, 1), (1, 3), (3, 3), (3, 1) Illuminance (lx)
102.485.03
10045.5255.03
1000153.74332.39
Table 3. The definition of swimming behavior parameters.
Table 3. The definition of swimming behavior parameters.
ParameterDefinition
Average Swimming Speed (AS)The distance moved per unit time, calculated as AS (m/s) = X/t, where X is the total movement distance (m) and t is the total movement time (s).
Average Angular Change (AC)The angular deviation of the movement direction at time t2 relative to the direction at time t1, with the initial movement at time t0 serving as the reference.
Total Movement (TM)The total distance moved by the experimental fish within time t, using the tip of the fish’s snout as the positional marker.
Average Distance from the Center (DC)The average distance of the fish’s positional marker (tip of the snout) from the coordinate origin over the time period t.
Fastest Movement (FM)The maximum distance covered by the experimental fish within a 1 s interval that exceeds twice its average swimming speed.
Note: The selection and quantification methods for swimming behavior indicators were based on the studies by Kane et al. [43] and Yalsuyi et al. [44], and were optimized for implementation according to the requirements for this experiment.
Table 4. Effects of light intensity and photoperiod on AS (D1), AC (D1), AC (D50), TM (D1), DC (D1), DC (D50), and FM (D1) by two-way ANOVA.
Table 4. Effects of light intensity and photoperiod on AS (D1), AC (D1), AC (D50), TM (D1), DC (D1), DC (D50), and FM (D1) by two-way ANOVA.
ParameterVariation SourcesSSdfFp
AS (D1)Light intensity0.06028.200.002
Photoperiod0.144313.04<0.001
Light intensity × Photoperiod0.11565.230.001
Residual0.08824
AC (D1)Light intensity0.01725.570.010
Photoperiod0.03938.230.001
Light intensity × Photoperiod0.134614.32<0.001
Residual0.03724
AC (D50)Light intensity246.405213.80<0.001
Photoperiod342.275312.78<0.001
Light intensity × Photoperiod184.20963.440.014
Residual214.22624
TM (D1)Light intensity120.392215.74<0.001
Photoperiod155.127313.52<0.001
Light intensity × Photoperiod113.22864.930.002
Residual91.79524
DC (D1)Light intensity0.00020.010.986
Photoperiod0.216319.14<0.001
Light intensity × Photoperiod0.11465.070.002
Residual0.09024
DC (D50)Light intensity0.02829.730.001
Photoperiod0.163338.44<0.001
Light intensity × Photoperiod0.03163.610.011
Residual0.03424
FM (D1)Light intensity0.36828.720.001
Photoperiod1.250319.71<0.001
Light intensity × Photoperiod0.88166.95<0.001
Residual0.50724
Table 5. Effects of light intensity and photoperiod on AS (D50), TM (D50), and FM (D50) by Kruskal–Wallis test.
Table 5. Effects of light intensity and photoperiod on AS (D50), TM (D50), and FM (D50) by Kruskal–Wallis test.
ParameterVariation SourcesdfHp
AS (D50)Light intensity21.360.507
Photoperiod322.55<0.001
TM (D50)Light intensity22.420.298
Photoperiod320.70<0.001
FM (D50)Light intensity21.050.593
Photoperiod321.03<0.001
Table 6. Effects of light treatment groups and treatment duration on the AS, AC, TM, DC, and FM of rainbow trout.
Table 6. Effects of light treatment groups and treatment duration on the AS, AC, TM, DC, and FM of rainbow trout.
ParameterGroupD1D50
ASL00.42 ± 0.04 Abcd0.33 ± 0.01 Bb
L10.58 ± 0.08 Bab0.65 ± 0.01 Aa
L20.42 ± 0.06 Bbcd0.65 ± 0.03 Aa
L30.61 ± 0.04 Ba0.68 ± 0.03 Aa
L40.58 ± 0.09 Bab0.68 ± 0.03 Aa
L50.31 ± 0.12 Bd0.52 ± 0.03 Aa
L60.35 ± 0.02 Bcd0.68 ± 0.03 Aa
L70.50 ± 0.04 Babc0.60 ± 0.11 Aa
L80.47 ± 0.01 Babcd0.68 ± 0.03 Aa
L90.57 ± 0.04 Bab0.70 ± 0.02 Aa
ACL038.41 ± 1.56 Bc44.35 ± 3.18 Aabc
L135.21 ± 4.44 Bc39.86 ± 1.37 Aabc
L254.57 ± 9.88 Aab33.85 ± 4.11 Bcd
L341.79 ± 4.56 Bbc48.97 ± 1.93 Ad
L437.48 ± 1.20 Bc48.97 ± 1.93 Aab
L548.11 ± 4.39 Aabc45.35 ± 3.37 Babc
L659.87 ± 5.96 Aa45.21 ± 2.86 Babc
L748.55 ± 2.28 Babc51.44 ± 0.44 Aa
L834.89 ± 2.95 Bc51.09 ± 2.91 Aa
L938.94 ± 0.76 Bc41.86 ± 0.12 Abcd
TML012.64 ± 1.39 Acde9.98 ± 0.12 Bb
L121.36 ± 0.12 Ba16.80 ± 0.15 Ab
L212.77 ± 1.58 Bcde18.76 ± 0.94 Aab
L318.56 ± 1.14 Aab19.42 ± 0.82 Aab
L415.48 ± 2.23 Bbcd20.83 ± 0.82 Aa
L59.43 ± 3.89 Be15.94 ± 0.84 Ab
L610.35 ± 0.43 Bde20.50 ± 0.79 Aab
L715.35 ± 1.22 Bbcd20.22 ± 1.70 Aab
L814.90 ± 1.07 Bbcde20.87 ± 0.67 Aa
L917.29 ± 1.13 Aabc18.76 ± 5.08 Ab
DCL00.57 ± 0.08 Ac0.62 ± 0.03 Ad
L10.65 ± 0.02 Bbc0.75 ± 0.00 Abcd
L20.73 ± 0.04 Bab0.75 ± 0.04 Aabc
L30.86 ± 0.07 Aa0.70 ± 0.17 Bcd
L40.84 ± 0.04 Aa0.85 ± 0.04 Aa
L50.66 ± 0.01 Bbc0.73 ± 0.01 Abcd
L60.73 ± 0.04 Bab0.78 ± 0.05 Aabc
L70.72 ± 0.04 Babc0.84 ± 0.03 Aa
L80.79 ± 0.01 Bab0.82 ± 0.03 Aab
L90.74 ± 0.06 Bab0.77 ± 0.04 Aabc
FML01.08 ± 0.07 Acde0.81 ± 0.02 Bc
L11.58 ± 0.22 Aab1.47 ± 0.06 Bab
L21.05 ± 0.12 Bcde1.55 ± 0.14 Aab
L31.70 ± 0.01 Aa1.64 ± 0.08 Aab
L41.56 ± 0.15 Aab1.64 ± 0.08 Aa
L50.82 ± 0.34 Be1.23 ± 0.09 Ab
L60.95 ± 0.08 Bde1.61 ± 0.10 Aa
L71.27 ± 0.08 Babcd1.47 ± 0.24 Aab
L81.19 ± 0.04 Bbcde1.65 ± 0.13 Aa
L91.41 ± 0.02 Babc1.56 ± 0.07 Aa
Note: Data are presented as mean ± standard deviation (SD). Different lowercase letters within the same column indicate significant differences among light treatment groups at the same time (p < 0.05). Different uppercase letters within the same row indicate significant differences between day 1 and day 50 within the same light treatment (p < 0.05).
Table 7. Correlations between feeding behaviors of rainbow trout (D1).
Table 7. Correlations between feeding behaviors of rainbow trout (D1).
ParameterASACTMDCFM
AS--−0.47 **0.85 **0.41 **0.89 **
AC --−0.50 **−0.11−0.51 **
TM --0.280.79 **
DC --0.40 *
FM --
Note: ** Correlation is significant at the 0.01 level (2-tailed), and * correlation is significant at the 0.05 level (2-tailed).
Table 8. Correlations between feeding behaviors of rainbow trout (D50).
Table 8. Correlations between feeding behaviors of rainbow trout (D50).
ParameterASACTMDCFM
AS--0.040.81 **0.54 **0.82 **
AC --0.270.60 **0.11
TM --0.63 **0.81 **
DC --0.52 **
FM --
Note: ** Correlation is significant at the 0.01 level (2-tailed).
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MDPI and ACS Style

Liu, X.; Huang, L.; Liu, Q.; Wang, R.; Liu, B.; Li, Z.; Song, Y.; Huang, Z. Effects of Light Intensity and Photoperiod on the Feeding Behavior of Rainbow Trout Oncorhynchus mykiss (Walbaum, 1792). Fishes 2026, 11, 183. https://doi.org/10.3390/fishes11030183

AMA Style

Liu X, Huang L, Liu Q, Wang R, Liu B, Li Z, Song Y, Huang Z. Effects of Light Intensity and Photoperiod on the Feeding Behavior of Rainbow Trout Oncorhynchus mykiss (Walbaum, 1792). Fishes. 2026; 11(3):183. https://doi.org/10.3390/fishes11030183

Chicago/Turabian Style

Liu, Xiao, Liuyi Huang, Qiqing Liu, Run Wang, Bo Liu, Zhaomin Li, Yacai Song, and Ziyi Huang. 2026. "Effects of Light Intensity and Photoperiod on the Feeding Behavior of Rainbow Trout Oncorhynchus mykiss (Walbaum, 1792)" Fishes 11, no. 3: 183. https://doi.org/10.3390/fishes11030183

APA Style

Liu, X., Huang, L., Liu, Q., Wang, R., Liu, B., Li, Z., Song, Y., & Huang, Z. (2026). Effects of Light Intensity and Photoperiod on the Feeding Behavior of Rainbow Trout Oncorhynchus mykiss (Walbaum, 1792). Fishes, 11(3), 183. https://doi.org/10.3390/fishes11030183

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