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Article

Optimizing Pellet Size and Feeding Strategy Using an Automatic Feeder in Juvenile Olive Flounder (Paralichthys olivaceus)

by
Seong-Mok Jeong
,
Sang-Woo Hur
,
Jinho Bae
and
Byung Hwa Min
*
Aquafeed Research Center, National Institute of Fisheries Science, Pohang 37517, Republic of Korea
*
Author to whom correspondence should be addressed.
Fishes 2025, 10(9), 458; https://doi.org/10.3390/fishes10090458
Submission received: 24 June 2025 / Revised: 23 August 2025 / Accepted: 27 August 2025 / Published: 11 September 2025
(This article belongs to the Special Issue Application of Artificial Intelligence in Aquaculture)
Versions Notes

Abstract

Feeding is among the most labor-intensive tasks in aquaculture, yet it is critical for productivity and operational efficiency. Although automated feeding systems reduce labor, the absence of data on optimal pellet size, feeding rate, and frequency has led to inconsistent practices and productivity. We evaluated the applicability of a low-cost automatic feeder and determined optimal pellet size and feeding frequency for juvenile olive flounder (Paralichthys olivaceus) in an experiment where 600 fish (83.4 ± 0.7 g (mean ± SD)) were randomly assigned to 12 flow-through tanks (60 fish/tank) in triplicate. In Experiment 1, fish fed 5-mm pellets presented greater weight gain and protein efficiency ratio (PER) than those fed 3-mm pellets (p < 0.05). In Experiment 2, manual feeding was compared to automatic feeding. Fish fed three times per day at a 1.3% daily feed intake (DFI) achieved similar growth but an improved feed conversion ratio and PER compared to manually fed fish (p < 0.05). Our findings support the use of 5-mm pellets at 1.3% DFI with a low-cost automatic feeder for maintaining productive juvenile flounder. These results present a practical automation strategy that enables small and medium-sized aqua-farms to reduce labor while maintaining productivity equivalent to manual feeding.
Keywords:
automatic feeder; feeding frequency; olive flounder; pellet size
Key Contribution: This study evaluated the practicality of an automatic feeder in juvenile olive flounder aquaculture and identified optimal pellet size and feeding frequency for improving growth performance and feed efficiency.

1. Introduction

Traditional aquaculture often has several limitations, including high labor requirements, which limit the sustainability of the aquaculture industry [1]. Although feeding is one of the most critical factors affecting productivity and operational efficiency in aquaculture systems, it remains the most labor-intensive task, highlighting the need for alternative technologies to replace manual feeding. Recent technologies incorporating artificial intelligence and the Internet of Things have been developed to address the limitations of traditional aquaculture practices and ultimately reduce the labor input through automation [1,2,3,4]. However, the implementation of automated feeding systems often requires substantial structural modifications and financial investment in existing aquaculture facilities, posing practical limitations. Automatically supplying feed based on observations of fish feeding behavior is a difficult and complex task. Therefore, externally attachable low-cost automatic feeders that can be installed without altering existing infrastructure represent a realistic alternative.
Feeding frequency regulates growth performance, feed intake, and operational costs in aquaculture [5,6,7]. Overfeeding can promote economic losses due to wastage and environmental degradation, such as water pollution. Conversely, underfeeding may fail to meet the nutritional requirements of fish, potentially impairing growth and overall yield [8,9,10]. In practice, feeding decisions often rely heavily on the subjective judgment of farm operators, based on the visual assessment of fish appetite and behavior [11,12]. Indeed, determining the appropriate feeding rate and frequency remains a highly intuitive and challenging task, which is “more of an art than a science” [13]. The feeding frequency of various fish species, including pikeperch, Gibel carp, rainbow trout, and Atlantic halibut, has been investigated. The optimal feeding frequency may range widely, from 2 to 24 times per day, depending on species-specific physiological characteristics and fish size [14,15,16,17]. Numerous studies have examined the optimal feeding frequency in various flounder species [18,19,20]. However, this is predominantly based on manual feeding methods, limiting its relevance to commercial aqua-farms that employ automatic feeders. Consequently, owing to the uncertainty of not knowing the optimal feeding rates for their automated systems, farmers sometimes resort to overfeeding, despite the risk of feed waste. Therefore, to maximize the growth efficiency of flounder and minimize such waste, it is essential to determine the optimal feeding frequency for each growth stage when using automatic feeders.
Pellet size greatly influences digestive efficiency and feed intake; thus, providing size-appropriate diets at each developmental stage is crucial for optimizing energy utilization and growth [21,22,23]. It is generally assumed that smaller feed particles have superior digestibility due to their high surface-to-volume ratio [23,24,25]. Nonetheless, the performance of smaller-sized feed in terms of feeding efficiency and growth performance in aquaculture remains a topic of debate. This uncertainty becomes even more critical when using automatic feeders, as machine-delivered feed differs from manual feed, affecting feed loss and intake efficiency based on pellet size. Therefore, determining the optimal pellet size for these systems is essential to establish clear and effective guidelines for aquaculture.
The olive flounder (Paralichthys olivaceus), a demersal fish species, is a key aquaculture resource in East Asian countries, including the Republic of Korea, Japan, and China [26]. Several studies have been conducted to optimize feeding strategies for enhancing the growth and efficiency of olive flounder [9,27,28]. In practice, however, aqua-farms face a dual economic pressure. The high cost of precision equipment makes installation unfeasible, while rising labor costs make automation a necessity. Consequently, low-cost automatic feeders that deliver a set quantity of feed at preset times have become a practical alternative. However, the lack of scientific data on optimal pellet size, feeding frequency, and quantity leads to inefficient, experience-based operations on most farms. This study, therefore, aimed to determine the optimal pellet size and feeding frequency to maximize the performance of juvenile olive flounder under an automated feeding system, using manual feeding as a control.

2. Materials and Methods

2.1. Experimental Fish and Feeding Conditions

This study comprised two separate experiments, with their specific designs summarized in Table 1. The proximate composition of the commercial feed (Suhyup Feed, Uiryeong-gun, Republic of Korea) used during both the acclimation and experimental periods is presented in Table 2. Juvenile olive flounder were obtained from a stock reared at the Aquafeed Research Center in Pohang, Republic of Korea. Prior to the start of the trial, all fish were acclimated for 2 wk to the experimental tank environment and feeding methods (manual or automatic). During this period, they were fed a commercial diet of the specific pellet size designated for their respective experimental group. After acclimation, the experiment was conducted in 1.231-ton (1231 L) circular tanks maintained with a flow-through system. Fish were randomly assigned to these tanks at a density of 60 fish per tank.
Experiment 1 evaluated the effects of pellet size on growth performance and feed utilization using an automatic feeder (AT-310, Dicle Petree, Incheon, Republic of Korea). Experiment 2 assessed the effects of the feeding method (automatic vs. manual) and frequency. A commercially available automatic feeder was pre-calibrated to ensure consistent feed delivery at specified time intervals. Feed amounts were assessed daily by weighing uneaten feed collected from feeding trays. The feeding trial lasted 8 wk. During the experimental period, we promptly removed any dead fish and maintained daily records of the feed intake and body weight of mortalities. Throughout the trial, water temperature and dissolved oxygen (DO) were measured daily using a YSI multiparameter meter (YSI Pro DSS, YSI Inc., Yellow Springs, OH, USA). The average water temperature was 23.2 ± 0.4 °C, and DO levels were maintained at 7.6 ± 0.2 mg/L via continuous aeration with air stones in each tank.

2.2. Sample Collection and Analytical Methods

At the end of the 8-wk feeding trial, all fish were again fasted for 24 h and then anesthetized with a 2-phenoxyethanol solution (100 ppm). The final number of fish in each tank was then counted to determine the survival rate, and the final total biomass was weighed for growth performance analysis. Following the biomass measurement, five fish were randomly sampled from each tank for the measurement of biometric parameters, including total length, liver weight, and intestinal weight. Growth, feed utilization, and biological indices of fish were calculated using the following formulas:
weight gain (WG, %) = (final body weight − initial body weight) × 100/initial body weight
specific growth rate (SGR, %/day) = [(ln final weight − ln initial weight)] × 100/d reared]
feed conversion ratio (FCR) = feed intake/wet weight gain
daily feed intake (%, DFI) = (feed intake × 100)/[(initial body weight + final body weight + dead weight) × d/2]
protein efficiency ratio (PER) = wet weight gain/protein intake
condition factor (CF, g/cm3) = total body weight of fish (g) × 100/total length of fish (cm)3
viscerosomatic index (VSI) = viscera weight of fish × 100/total body weight of fish, and
hepatosomatic index (HSI) = liver weight of fish × 100/total body weight of fish
Dorsal muscle samples were then collected from these same fish and stored at −25 °C for subsequent analysis.
The proximate composition of the experimental diets and dorsal muscle was analyzed following the standard methods of the Association of Official Analytical Chemists [29]. Crude protein (N × 6.25) was measured using a FOSS 8400 Automatic Kjeldahl Nitrogen Determinator (FOSS, Hillerød, Denmark), and crude lipid was analyzed using a Soxtec System 2043 (FOSS, Hillerød, Denmark). The moisture content was determined after drying at 135 °C for 2 h in a convection oven. The ash content was quantified by incinerating samples in a muffle furnace at 600 °C for 6 h.
For bound amino acid composition analysis, 20 mL of 6N HCl was added to the sample, which was then vacuum-sealed and subjected to acid hydrolysis in a dry oven at 110 °C for 24 h. The hydrolysate was filtered through a glass filter, and the filtrate was vacuum-concentrated at 55 °C to completely evaporate hydrochloric acid and water. The concentrated sample was adjusted to 25 mL in a volumetric flask with sodium citrate buffer (pH 2.20), filtered through a 0.45-µm membrane filter, and analyzed using an automatic amino acid analyzer (Biochrom 30+; Biochrom Ltd., Cambridge, UK).
At the end of the trial, blood was drawn from the caudal vasculature of three anesthetized fish per tank (a total of nine fish per dietary treatment) using heparinized syringes fitted with 23-gauge (23G) needles (KOVAX-Syringe; Korean Vaccine, Seoul, Republic of Korea). The collected blood samples were immediately centrifuged at 2795× g for 10 min to isolate the plasma using a refrigerated centrifuge (VS-24SMTi; Vision S & Tech., Daejeon-Si, Republic of Korea). The isolated plasma was then stored at −80 °C until analysis. Plasma concentrations of glucose (product code: 981780, Thermo Fisher Scientific Oy, Vantaa, Finland), total protein (product code: 981827, Thermo Fisher Scientific Oy, Vantaa, Finland), triglycerides (product code: 981786, Thermo Fisher Scientific Oy, Vantaa, Finland), alanine aminotransferase (ALT, product code: 981759, Thermo Fisher Scientific Oy, Vantaa, Finland) and aspartate aminotransferase (AST, product code: 981771, Thermo Fisher Scientific Oy, Vantaa, Finland) were subsequently analyzed using a fully automatic wet chemistry analyzer (Indiko, Waltham, MA, USA), following the manufacturer’s instructions.

2.3. Statistical Analysis

All statistical analyses were performed using SPSS version 23 (IBM Corp., Armonk, NY, USA). Prior to analysis, all data were checked for normality and homogeneity of variances using Levene’s tests. In Experiment 1, differences between the two treatment groups were analyzed by an independent t-test. For Experiment 2, the data were subjected to a one-way analysis of variance, and significant differences among group means were determined using Tukey’s multiple range test. For all analyses, statistical significance was set at p < 0.05. The results are presented as the mean ± standard error (SE).

3. Results

3.1. Growth Performance and Biometry

When using an automatic feeder under a restricted DFI rate (~1.3%), fish-fed 5-mm pellets exhibited higher weight gain, specific growth rate (SGR), and protein efficiency ratio (PER) than those fed 3-mm pellets (p < 0.05). However, their survival rate was not affected by pellet size (p > 0.05).
Table 3 and Table 4 present the growth performance and biometric parameters under different feeding methods and frequencies. Weight gain and SGR were significantly higher in the group fed manually to satiation three times per day (H-3S) compared with the group fed five times per day using the automatic feeder (A-5R) (p < 0.05), but did not differ from the restricted group fed three times per day via the automatic feeder (A3-R) (p > 0.05). In contrast, the feed conversion ratio (FCR) was higher in the A-3R group than in the H3-S group (p < 0.05), indicating reduced feed efficiency under restricted automatic feeding conditions.
The condition factor, hepatosomatic index, and viscerosomatic index were not affected by pellet size or feeding frequency (p > 0.05).

3.2. Plasma Parameters

In both experiments, no differences (p > 0.05) were observed in plasma glucose, total protein, and triglyceride concentrations among treatments, indicating that neither pellet size nor feeding frequency had a measurable impact (Table 5 and Table 6). However, both feed size and feeding frequency affected ALT levels. Regarding feed size, the 3-mm diet resulted in significantly lower ALT levels than the 5-mm diet. Furthermore, a comparison among experimental groups revealed that the A-5R group had significantly lower ALT values than both the H-3S and A-3R groups (p > 0.05).

3.3. Proximate and Bound Amino Acid Composition of Dorsal Muscle

The proximate and bound amino acid compositions of the dorsal muscle are presented in Table 7 and Table 8, respectively. Moisture, crude protein, crude lipid, and ash contents in the dorsal muscle were not affected by pellet size (p > 0.05). However, the feeding frequency influenced crude lipid content. The H-3S group exhibited significantly lower crude lipid content than the A-3R and A-5R groups (p < 0.05). No differences were observed in the other parameters based on feeding frequency or level (p > 0.05). For the bound amino acid composition, pellet size had no significant effect (p > 0.05). In contrast, feeding frequency significantly affected valine levels, which were higher in the H-3S group compared to the A-3R and A-5R groups (p < 0.05). No other amino acids were affected by feeding frequency.

4. Discussion

With automatic feeders, the system must be able to closely monitor the behavioral characteristics and rearing environment of the target species and respond in real time. However, no automatic feeder has been developed based on the behavioral characteristics of olive flounder, and research remains insufficient for designing optimized systems. Therefore, this study assessed the performance of a commercially available automatic feeder that dispenses a predetermined amount of feed at preset intervals in terms of feed utilization and fish condition.
The results of this study challenge the common hypothesis that smaller feed particles are superior due to their higher surface-to-volume ratio [23,24,25]. In our trial, juvenile olive flounder tended to exhibit improved growth when fed pellets larger than 3-mm. This outcome may be due to smaller feed particles having a shorter gastric retention time, potentially leaving the stomach before sufficient digestion occurs and thereby reducing nutrient absorption efficiency [22,30,31,32,33]. Furthermore, from an energetic perspective, the net energy gain can be substantially reduced when smaller particles are consumed, as the energy required for capture does not decrease proportionally with particle size [32,33,34,35]. These findings are highly consistent with a previous study on olive flounder (body weight: 62–160 g), which also demonstrated that pellets of ≥5-mm yielded the greatest growth performance and PER compared to 3- and 4-mm pellets [28]. Therefore, we recommend that when rearing olive flounder >100 g using automated feeding systems, feed particles with a diameter of at least 5-mm should be used to enhance growth performance.
In the present study, restricting the DFI to 1.3% of body weight resulted in growth performance and feed utilization comparable to that of the satiation-fed group. This finding, however, contrasts with the results of Seo et al. [36], who reported that olive flounder (~55 g) fed to satiation two or three times daily exhibited superior growth and feed efficiency compared to a restricted-fed group. This discrepancy may likely be attributed to the different dietary protein levels used in the two studies; the diet in Seo et al. [36] contained 45–47% crude protein, whereas the diet in the present study contained a substantially higher level of 56%. Given that the growth of olive flounder is highly responsive to dietary protein levels [9,27,28], it is plausible that the high-protein diet in our study supplied sufficient nutrients to support maximal growth even under the restricted feeding regime, thus eliminating any significant difference from the satiation group.
Optimizing feeding frequency is a critical, species-specific challenge in aquaculture, as demonstrated by various species like pike perch and Korean rockfish, where moderate frequencies (e.g., 2–6 times daily) are optimal [14,37,38,39]. According to Sousa et al. [40], high feeding frequencies, including nocturnal feeding, can significantly enhance productivity, as demonstrated by the case of groupers fed every 2 h. Although high-frequency and nighttime feeding strategies may offer growth benefits, their implementation via manual feeding is often impractical due to prohibitive labor demands. Low-cost automatic feeders present a practical solution, enabling scheduled feed delivery around the clock. However, when operated without clear, science-based protocols, these automated systems can easily lead to overfeeding, resulting in substantial feed waste, deterioration of water quality, and, consequently, reduced farm profitability [41]. Therefore, to fully leverage the benefits of automation while ensuring economic and environmental sustainability, it is essential to establish strategic feeding protocols that include the optimal feeding rates, quantities, and pellet dimensions for each developmental stage of olive flounder. Furthermore, future research must move beyond simply delivering precise quantities on a fixed schedule (including nighttime feeding) and focus on integrating information and communications technology (ICT). This will enable the development of true ‘smart feeding’ systems that dynamically adjust feed supply based on real-time data, such as water quality and the behavioral feeding responses of the fish.
A key finding of this study was that plasma glucose, triglyceride, and total protein concentrations did not differ significantly among the various feeding frequency groups. Increased frequency has been shown to elevate plasma metabolites [20,42,43], while severe restriction can decrease total protein due to catabolism [44]. We propose that the lack of a response in our study was due to the feeding level across all treatments (~85% of satiation) being sufficient to meet the basal nutritional requirements of the fish. Once an appropriate level of nutrition is supplied and physiological equilibrium is reached, the influence of meal timing (i.e., feeding frequency) on biochemical responses is likely diminished. Alanine aminotransferase (ALT) in the blood is a key biochemical marker used to evaluate hepatic health in vertebrates, with elevated levels typically indicating liver damage [45,46,47]. In the present study, flounder that were fed either smaller-sized pellets or more frequently (five times daily) exhibited significantly lower ALT levels than other experimental groups. This suggests that these feeding regimens positively influence liver health, likely by reducing the metabolic load and associated stress on the organ. However, the biological significance of these ALT values warrants careful interpretation. For instance, a previous study on flounder by Okorie et al. [48] reported an ALT level of 3.3 U/L in a group subjected to long-term fasting. In contrast, all experimental groups in our study, including the control, displayed substantially lower ALT levels. This indicates that, while the inter-group differences were statistically significant, all fish were likely in a healthy, non-pathological state. Therefore, our findings should not be interpreted as evidence that certain feeding conditions prevent liver damage, but rather that an optimized feeding strategy—such as using smaller pellets or increasing feeding frequency—more effectively alleviates metabolic stress, thereby maintaining liver function in an optimal state.
A notable finding of this study was the relatively higher lipid content observed in the dorsal muscle of juvenile flounder under a restricted feeding regime. This is contrary to the general phenomenon where insufficient nutrient intake reduces body fat, as stored lipids are mobilized for energy, a process observed in various species. Typically, body fat accumulation is reported when feeding frequency or quantity is increased, unlike in the present study [49,50,51,52,53,54]. Therefore, the results of this study suggest a potential compensatory adaptation mechanism under nutrient-limited conditions, wherein lipids are preferentially stored or retained in the dorsal muscle—essential for maintaining locomotor capacity—instead of in metabolically active organs like the liver or viscera. This may be interpreted as a crucial survival strategy to optimize energy storage efficiency in a nutrient-scarce environment.
In this study, the valine content in the dorsal muscle of olive flounder from the full-fed group was significantly higher than that of the restricted-fed group (p < 0.05), whereas no significant differences were observed in other amino acids. This result is likely attributed to the higher feed intake in the full-fed group, which led to a greater accumulation of valine, an essential amino acid that must be obtained from the diet. Lacking the ability for endogenous synthesis of valine, fish must obtain the necessary quantities for survival and growth entirely from external dietary sources [55]. It is well-documented that dietary amino acid composition directly influences the amino acid profile of fish muscle tissue [56,57], a principle that aligns with our findings. Valine, a branched-chain amino acid (BCAA), is indispensable for fish growth, playing a vital role in protein synthesis and gene expression [58]. The valine requirement for olive flounder is known to vary by growth stage, with previous reports suggesting 2.5% of dietary protein [59,60], and a more recent study indicating 17.7–18.9 g/kg for juveniles of approximately 25 g [61]. Although the dietary percentage of valine was not a variable in our experiment, the restriction of feed intake caused a divergence in muscle valine levels. This suggests that the restricted-fed flounder did not receive sufficient valine to meet their metabolic demands for growth. Therefore, we conclude that, for olive flounder weighing approximately 80 g, a minimum dietary valine content of 2.7% is necessary to support normal growth and maintain muscle quality under a restricted feeding regime. It should be noted, however, that this study was conducted on a specific size class of fish. Further research is needed to determine the optimal valine requirement for other sizes of olive flounder and under different culture conditions, such as varying water temperatures or feeding-to-satiation regimes.

5. Conclusions

This study confirmed that, for juvenile olive flounder (averaging over 80 g), an automated feeding strategy using a low-cost feeder—supplying 5-mm pellets at a daily feed intake (DFI) of 1.3% three times daily—effectively maintained growth performance, feed utilization, physiological health, and dorsal muscle composition at levels comparable to a conventional hand-feeding method using the same protein (56%) and lipid (8%) feed. While this study provides a foundational framework for applying automatic feeders in flounder aquaculture and can contribute to the development of standardized feeding protocols, further research is required on the application of low-cost automatic feeders for various size classes of flounder.

Author Contributions

Conceptualization, S.-M.J.; Validation, S.-M.J. and J.B.; Investigation, S.-M.J.; Data Curation, S.-M.J.; Writing—Original Draft Preparation, S.-M.J.; Funding Acquisition, S.-W.H.; Writing—Review and Editing, B.H.M.; Supervision, B.H.M. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by a grant from the National Institute of Fisheries Science, Republic of Korea (R2025036).

Institutional Review Board Statement

The animal study protocol was approved by the Institutional Animal Care and Use Committee of the National Institute of Fisheries Science (Protocol No. 2024-NIFS-IACUC-22; approved on 29 March 2024).

Informed Consent Statement

Not applicable.

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors on request.

Acknowledgments

We would like to thank E.S. Son at the National Institute of Fisheries Science for their assistance in the feeding trial.

Conflicts of Interest

The authors declare no conflict of interest.

Abbreviations

The following abbreviations are used in this manuscript:
PERProtein efficiency ratio
DFIDaily feed intake
FCRFeed conversion ratio
H-3SHand feeding, three times per day, to satiation
A-3 mmAutomatic feeding, 3-mm pellet size
A-5 mmAutomatic feeding, 5-mm pellet size
A-3RAutomatic feeding, 3 times per day, restricted level
A-5RAutomatic feeding, 5 times per day, restricted level
SGRSpecific growth rate

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Table 1. Feeding regimes in Experiments 1 and 2.
Table 1. Feeding regimes in Experiments 1 and 2.
ExperimentTreatment CodeFeeding MethodPellet SizeFeeding Frequency (Time)Feeding Level
Experiment 1A-3 mmAutomatic3-mm3 times/d (09:00, 13:00, 17:00)Restricted (85–90% of satiation)
A-5 mmAutomatic5-mm3 times/d (09:00, 13:00, 17:00)Restricted
Experiment 2H-3SManual5-mm3 times/d (09:00, 13:00, 17:00)Satiation
A-3RAutomatic5-mm3 times/d (09:00, 13:00, 17:00)Restricted
A-5RAutomatic5-mm5 times/d (09:00, 11:00, 13:00, 15:00, 17:00)Restricted
Table 2. Nutrient composition (%) of experimental feeds.
Table 2. Nutrient composition (%) of experimental feeds.
ContentExperimental Diets
3-mm5-mm
Proximate composition (%, dry matter)
Dry matter91.8 ± 0.192.9 ± 0.0
Crude protein57.4 ± 0.056.5 ± 0.1
Crude lipids8.14 ± 0.128.55 ± 0.12
Ash13.9 ± 0.014.0 ± 0.1
Essential amino acid composition (% of experimental diets, dry matter)
Arginine2.94 ± 0.012.91 ± 6.89
Histidine1.58 ± 0.021.51 ± 0.02
Isoleucine2.13 ± 0.002.12 ± 0.00
Leucine3.69 ± 0.023.67 ± 0.02
Lysine3.61 ± 0.003.62 ± 0.01
Methionine0.84 ± 0.000.89 ± 0.01
Phenylalanine2.00 ± 0.002.01 ± 0.01
Threonine2.09 ± 0.002.08 ± 0.00
Valine2.50 ± 0.012.53 ± 0.00
Values are presented as mean ± standard error (SE) of quadruplicate (n = 4) measurements, while bound amino acids are presented as the mean of duplicate (n = 2) measurements.
Table 3. Growth performance, feed utilization, and biometric parameters of olive flounder fed different pellet sizes for eight weeks.
Table 3. Growth performance, feed utilization, and biometric parameters of olive flounder fed different pellet sizes for eight weeks.
ParameterExperimental Group
A-3 mmA-5 mm
Growth performance
Initial body weight (g/fish)83.6 ± 0.383.4 ± 0.5
Final body weight (g/fish)238.6 ± 0.6254.3 ± 4.2
Weight gain (%) 185.3 ± 0.4205.0 ± 3.2 *
Specific growth rate (%/day) 1.87 ± 0.001.99 ± 0.02 *
Feed conversion ratio 0.77 ± 0.010.73 ± 0.01
Daily feed intake (%) 1.28 ± 0.011.30 ± 0.01
Protein efficiency ratio 2.27 ± 0.032.43 ± 0.04 *
Survival (%) 94.4 ± 1.595.6 ± 3.6
Biometric parameters
Condition factor 1.00 ± 0.011.01 ± 0.02
Hepatosomatic index 1.72 ± 0.081.79 ± 0.07
Viscerosomatic index 3.30 ± 0.093.25 ± 0.03
Values are the mean of triplicate groups (n = 3) and presented as mean ± SE. Asterisks (*) within the same column indicate significant differences between experimental groups (p < 0.05). The lack of a superscript letter indicates no significant differences among treatments.
Table 4. Growth performance, feed utilization, and biometric parameters of olive flounder fed at different frequencies for eight weeks.
Table 4. Growth performance, feed utilization, and biometric parameters of olive flounder fed at different frequencies for eight weeks.
ParameterExperimental Group
H-3SA-3RA-5R
Growth performance
Initial body weight (g/fish)83.1 ± 0.483.4 ± 0.583.5 ± 0.6
Final body weight (g/fish)261.7 ± 2.2254.3 ± 4.2250.6 ± 1.9
Weight gain (%) 215.0 ± 2.3 a205.0 ± 3.2 ab200.1 ± 3.9 b
Specific growth rate (%/d) 2.05 ± 0.01 a1.99 ± 0.02 ab1.96 ± 0.02 b
Feed conversion ratio 0.77 ± 0.01 a0.73 ± 0.01 b0.74 ± 0.01 ab
Daily feed intake (%) 1.42 ± 0.02 a1.30 ± 0.01 b1.30 ± 0.00 b
Protein efficiency ratio 2.28 ± 0.02 b2.43 ± 0.04 a2.39 ± 0.02 ab
Survival (%) 97.2 ±1.595.6 ± 3.696.7 ± 1.0
Biometric parameters
Condition factor 1.08 ± 0.031.01 ± 0.021.01 ± 0.01
Hepatosomatic index 1.79 ± 0.121.79 ± 0.071.72 ± 0.06
Viscerosomatic index 3.23 ± 0.063.25 ± 0.033.34 ± 0.07
Values are the mean of triplicate groups (n = 3) and presented as mean ± SE. Different superscript letters (a, b) indicate significant differences among treatments (p < 0.05). The lack of a superscript letter indicates no significant differences among treatments.
Table 5. Plasma biochemical parameters of olive flounder fed different pellet sizes for eight weeks.
Table 5. Plasma biochemical parameters of olive flounder fed different pellet sizes for eight weeks.
ParameterExperimental Group
A-3 mmA-5 mm
Plasma parameters
Glucose (mg/dL)24.4 ± 2.3327.8 ± 2.90
Total protein (g/dL)4.73 ± 0.174.90 ± 0.24
Triglyceride (mg/dL)193 ± 21.7191 ± 1.3
ALT 1 (U/L)0.39 ± 0.020.84 ± 0.06 *
AST 2 (U/L)10.6 ± 1.815.0 ± 0.7
Values are the mean of triplicate groups (n = 3) and presented as mean ± SE. Asterisks (*) within the same column indicate significant differences between experimental groups (p < 0.05). The lack of a superscript letter indicates no significant differences among treatments; 1 ALT = alanine aminotransferase; 2 AST = aspartate aminotransferase.
Table 6. Plasma biochemical parameters of olive flounder fed at different frequencies for eight weeks.
Table 6. Plasma biochemical parameters of olive flounder fed at different frequencies for eight weeks.
ParameterExperimental Group
H-3SA-3RA-5R
Glucose (mg/dL)39.1 ± 5.1427.8 ± 2.9025.8 ± 1.09
Total protein (g/dL)5.15 ± 0.184.90 ± 0.244.92 ± 0.10
Triglyceride (mg/dL)194 ± 13.1191 ± 1.3178 ± 6.8
ALT 1 (U/L)1.10 ± 0.08 a0.84 ± 0.06 a0.40 ± 0.09 b
AST 2 (U/L)14.1 ± 0.2915.0 ± 0.7114.4 ± 3.57
Values are the mean of triplicate groups and presented as mean ± SE (n = 3). Different superscript letters (a, b) indicate significant differences among treatments (p < 0.05). The lack of a superscript letter indicates no significant differences among treatments; 1 ALT = alanine aminotransferase; 2 AST = aspartate aminotransferase.
Table 7. Proximate composition of the dorsal muscle of olive flounder fed different pellet sizes for eight weeks.
Table 7. Proximate composition of the dorsal muscle of olive flounder fed different pellet sizes for eight weeks.
ParameterExperimental Group
A-3 mmA-5 mm
Proximate composition (% dry matter)
Dry matter76.3 ± 0.176.2 ± 0.3
Crude protein89.9 ± 0.491.2 ± 0.2
Crude lipids1.69 ± 0.031.81 ± 0.35
Crude ash1.52 ± 0.011.58 ± 0.03
Essential amino acid composition (% in protein)
Arginine6.17 ± 0.076.16 ± 0.02
Histidine2.57 ± 0.012.61 ± 0.02
Isoleucine4.87 ± 0.014.83 ± 0.03
Leucine8.05 ± 0.017.99 ± 0.02
Lysine9.46 ± 0.039.26 ± 0.07
Methionine2.89 ± 0.052.90 ± 0.00
Phenylalanine4.06 ± 0.024.04 ± 0.00
Threonine4.75 ± 0.004.74 ± 0.02
Valine5.58 ± 0.025.57 ± 0.05
Values are the mean of triplicate groups (n = 3) and presented as mean ± SE.
Table 8. Proximate composition of the dorsal muscle of olive flounder fed at different frequencies for eight weeks.
Table 8. Proximate composition of the dorsal muscle of olive flounder fed at different frequencies for eight weeks.
ParameterExperimental Group
H-3SA-3RA-5R
Proximate composition (% dry matter)
Dry matter76.3 ± 0.276.2 ± 0.376.3 ± 0.1
Crude protein91.0 ± 0.791.2 ± 0.290.3 ± 1.0
Crude lipids1.03 ± 0.06 b1.81 ± 0.35 a1.63 ± 0.08 a
Ash1.59 ± 0.051.58 ± 0.031.62 ± 0.02
Essential amino acid composition (% in protein)
Arginine6.17 ± 0.066.17 ± 0.076.08 ± 0.04
Histidine2.63 ± 0.052.57 ± 0.012.57 ± 0.01
Isoleucine4.88 ± 0.034.87 ± 0.014.82 ± 0.02
Leucine8.11 ± 0.038.05 ± 0.018.06 ± 0.03
Lysine9.56 ± 0.069.46 ± 0.039.44 ± 0.06
Methionine2.88 ± 0.052.89 ± 0.053.02 ± 0.04
Phenylalanine4.12 ± 0.074.06 ± 0.024.17 ± 0.07
Threonine4.75 ± 0.024.75 ± 0.004.77 ± 0.05
Valine5.82 ± 0.03 a5.58 ± 0.02 b5.53 ± 0.02 b
Values are the mean of triplicate groups (n = 3) and presented as mean ± SE. Different superscript letters (a, b) indicate significant differences among treatments (p < 0.05). The lack of a superscript letter indicates no significant differences among treatments.
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Jeong, S.-M.; Hur, S.-W.; Bae, J.; Min, B.H. Optimizing Pellet Size and Feeding Strategy Using an Automatic Feeder in Juvenile Olive Flounder (Paralichthys olivaceus). Fishes 2025, 10, 458. https://doi.org/10.3390/fishes10090458

AMA Style

Jeong S-M, Hur S-W, Bae J, Min BH. Optimizing Pellet Size and Feeding Strategy Using an Automatic Feeder in Juvenile Olive Flounder (Paralichthys olivaceus). Fishes. 2025; 10(9):458. https://doi.org/10.3390/fishes10090458

Chicago/Turabian Style

Jeong, Seong-Mok, Sang-Woo Hur, Jinho Bae, and Byung Hwa Min. 2025. "Optimizing Pellet Size and Feeding Strategy Using an Automatic Feeder in Juvenile Olive Flounder (Paralichthys olivaceus)" Fishes 10, no. 9: 458. https://doi.org/10.3390/fishes10090458

APA Style

Jeong, S.-M., Hur, S.-W., Bae, J., & Min, B. H. (2025). Optimizing Pellet Size and Feeding Strategy Using an Automatic Feeder in Juvenile Olive Flounder (Paralichthys olivaceus). Fishes, 10(9), 458. https://doi.org/10.3390/fishes10090458

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