Reproductive Ecology of the Java Rabbitfish, Siganus javus, in the Southern South China Sea

Abstract

Fish reproductive biology influences their life history and can impact their vulnerability to fisheries; therefore, for sustainable management and development, a proper understanding is crucial. Reproductive biology, including maturation, spawning season, fecundity, and sex ratio, was examined throughout the year in the Java Rabbitfish, Siganus javus, in the southern South China Sea. This study is the first to examine reproductive traits by collecting a total of 339 S. javus specimens monthly from September 2017 to August 2018 through detailed gonad histology. The spawning season of female S. javus was mainly restricted to July, August, October, and December, whereas male fish were found to spawn throughout the year. Inter-species variations in the spawning season were observed within the genus, which is influenced by interspecific spawning strategies and regional environmental factors. The sex ratio close to 1:1 suggests that the fish population is in equilibrium in the region. The fecundity of S. javus ranged from 1.8 × 10⁵ to 12 × 10⁵, which was similar to that of other species in Siganus, suggesting less inter- and intra-species variation in fecundity within the family. The middle maturation stage was absent throughout the year, probably due to the different habitat uses during their life history. Reproductive biology might influence other biological aspects, such as migration and behaviour in the fish.

1. Introduction

Coral reefs are found in tropical waters worldwide, where they are estimated to occupy approximately 284,300 km² of shallow water near the coastlines of more than 100 countries [1,2]. Coral reefs mainly occur in the South Pacific, followed by Southeast Asia, the Indian Ocean, the Middle East, the Caribbean, and finally, the Atlantic [3]. Among these reefs, Southeast Asia is recognised as a biodiversity hotspot with high species diversity and abundance [4]. It is estimated that 34% of the Earth’s coral cover is in the coastal areas of Southeast Asia [4,5]. Additionally, these coral reefs serve as important breeding and nursery grounds for many coral reef fishes [4]. Shallow-water coral reef fishes are vital sources of food and income across the Pacific region, supporting subsistence and small-scale commercial fishing [6]. The fisheries related to coral reefs provide resources for millions of people in tropical regions [7]. In tropical areas, particularly Southeast Asia, small-scale fisheries are crucial economic resources for local residents, especially in terms of food security [8,9].

Rabbitfish (genus Siganus) are coastal fisheries communities and essential components of coral reef fish populations. As herbivorous species that graze on and browse macroscopic algae, rabbitfish play vital roles in ecosystem functioning by helping control algal growth, maintaining coral reef community structure [10,11,12,13], and improving conditions for coral recruitment, recovery, and maintenance [14]. Siganus are also of considerable interest in aquaculture because of their advantageous life history traits, such as lower trophic needs, rapid growth and maturation, high fecundity, and recurrent spawning. These key life history characteristics of rabbitfish are believed to be resilient to overfishing, although overexploitation has occurred in some regions [15,16,17].

The Java Rabbitfish, Siganus javus, is distributed across the Indo-West Pacific from the Persian Gulf through the Malay Peninsula to Vanuatu in the east, to the Philippines in the north, and northern Australia in the south [18]. This species inhabits shallow coastal waters near coral reefs, rocks, and brackish lagoons [18]. Siganus javus is a significant fish species due to its importance in small-scale fisheries, and local communities in Southeast Asia generally consume it. However, despite its commercial and cultural significance, information on the species’ biology, ecology, and stock status is highly limited compared to other rabbitfish species, and fisheries are not explicitly managed.

Reproductive biology, such as maturation, spawning season, potential fecundity, and sex ratio, is vital for understanding changes in certain fish populations. It is crucial for analysing fish population dynamics, especially in exploited species [19]. Information on the reproductive biology of commercially important species is key for advancing the aquaculture industry [20]. Understanding key reproductive traits, such as spawning periodicity, can support management efforts to protect critical life stages. Details on spawning periodicity are also important for practical fisheries assessments, including estimating spawning potential ratios and annual reproductive output or spawning stock biomass per recruit [21]. Additionally, spawning periodicity aids in understanding and evaluating levels of overexploitation and overfishing.

In the present study, reproductive biology aspects such as maturation, spawning season, fecundity, and sex ratio are examined throughout the year in S. javas, in the fishing grounds of Brunei Darussalam off Borneo Island in the southern South China Sea. The information on reproductive biology and ecology helps improve our understanding of biology and ecology, fisheries management, and aquaculture in coral reef species.

2. Materials and Methods

2.1. Study Area

Siganus javus was collected from the waters of Brunei Darussalam in the southern South China Sea (Figure 1). In Brunei Darussalam, fishing activities were categorised into four zones based on distance from the coastline: Zone 1 [0–3 nautical miles (nm)], Zone 2 (3–20 nm), Zone 3 (20–45 nm), and Zone 4 (45–200 nm offshore) [22] (Figure 1). Siganus javus was caught along with other fish by local fishermen in Zone 1, where most reef areas are found within this zone [23]. Following the catch, all fish were landed immediately at a local fish market (Jerudong market), which is located adjacent to the fishing grounds [18].

The study area’s climate is influenced by a monsoon pattern characterised by winds and rainfall. The southwest monsoon, from April to September, brings the least rainfall. Conversely, the northeast monsoon, spanning December to March, is associated with the strongest winds.

2.2. Fish

The aim was to randomly collect 30 specimens each month, when possible, and a total of 339 S. javus specimens were gathered monthly from September 2017 to August 2018. The goal was to collect 30 specimens every month, with numbers ranging from 28 to 34, except for February 2018, which had only 5 specimens (

Table 1. Morphological and reproductive characteristics of Siganus javus in the southern South China Sea.

Sex	Maturation Stage	Number of Specimens	Total Length (cm)		Body Weight (g)		Gonadosomatic Index		Oocyte Diameter (µm)
			Mean ± SD	Range	Mean ± SD	Range	Mean ± SD	Range	Mean ± SD	Range
female	0	55	30.53 ± 4.79	19.00–42.00	380.36 ± 163.40	99.85–1001.93	0.46 ± 0.26	0.15–2.15	58.25 ± 10.49	40.96–98.57
	I	53	29.53 ± 4.70	21.00–40.00	363.27 ± 182.10	128.15–935.75	0.53 ± 0.21	0.25–1.62	72.08 ± 24.37	47.70–206.52
	II	0
	III	10	28.68 ± 4.96	22.50–37.00	350.90 ± 161.50	147.26–632.63	1.13 ± 0.58	0.08–1.92	193.03 ± 47.88	106.35–261.57
	IV	16	31.18 ± 3.22	26.00–37.50	421.14 ± 126.88	276.70–667.29	3.65 ± 1.69	1.30–6.74	268.48 ± 28.97	235.49–332.71
	V	6	32.05 ± 5.00	27.50–39.00	492.82 ± 210.39	259.57–696.73	1.22 ± 0.10	0.08–2.73	112.06 ± 66.76	41.20–189.35
	VI	18	30.76 ± 3.53	23.00–36.20	373.07 ± 108.47	172.48–579.31	0.64 ± 0.30	0.25–1.27	61.05 ± 27.59	41.34–168.89
male	0	3	25.83 ± 8.22	16.50–32.00	315.94 ± 221.97	71.16–504.16	0.06 ± 0.06	0.01–0.13
	I	2	20.85 ± 0.21	20.70–21.00	134.13 ± 12.08	125.59–142.67	0.08 ± 0.04	0.05–0.11
	II	13	31.54 ± 4.21	24.00–40.00	465.29 ± 185.22	192.26–898.48	0.22 ± 0.17	0.08–0.74
	III	25	28.16 ± 3.6	22.00–38.50	300.50 ± 123.34	165.59–740.59	0.80 ± 0.10	0.06–4.83
	IV	98	29.17 ± 4.02	21.50–41.50	336.90 ± 132.80	143.54–925.90	0.71 ± 0.77	0.06–3.96
	V	40	30.35 ± 4.97	19.80–38.50	366.55 ± 168.25	115.24–790.73	0.13 ± 0.09	0.03–0.39

).

The total length (TL) and body weight (BW) of each fish were measured to the nearest 0.01 cm and 0.01 g, respectively. The fish were dissected to remove and weigh the gonads of both females and males using an analytical balance accurate to 0.001 g. The sex and sexual stage of each fish were determined through macro-observation of the gonads and histology.

The ovaries of female individuals were halved vertically for fecundity analysis, and the other half was preserved in 10% neutral buffered formalin for histological study to determine the maturation stage [19].

The gonadosomatic index for females was calculated using the formula GSI = GW/BW × 100.

2.3. Histology

All specimens’ gonads were examined for histology. Routine histological techniques were employed following Slaoui and Fiette [24] and Arai and Abdul Kadir [25]. Gonads were embedded in paraffin blocks and sectioned to a thickness of 4 to 5 μm before being stained with haematoxylin–eosin and observed under a light microscope (Nikon Eclipse L200N; Nikon Metrology Inc., Brighton, MI, USA), where photographs were taken to provide a detailed illustration of the results.

In female S. javus, ovarian development is classified into seven stages: the immature stage (stage 0), early maturing stage (stage I), mid-maturing stage (stage II), late maturing stage (stage III), fully maturing stage (stage IV), spent stage (stage V), and regenerating stage (stage VI) [26,27,28,29].

The diameter of the oocyte at each maturation stage was measured to understand ovarian development during maturation (Table 1).

Testicular development was classified into six stages in male S. javus: the immature stage (stage 0), preparatory stage (stage I), early germinal epithelium development stage (stage II), mid-germinal epithelium development stage (stage III), late germinal epithelium development stage (stage IV), and spent stage (stage V) [27,30,31].

2.4. Fecundity

The matured gonads of females were examined for fecundity gravimetrically using the hydrated oocyte method [32]. After weighing the ovaries, three subsamples were collected from the anterior, middle, and posterior parts of each ovary [33]. Each subsample was weighed to the nearest 0.001 g and preserved in 4% neutrally buffered formalin. Each subsample slide was examined under the macroscopic staging system, where the eggs on the entire slide were counted individually. Before placing the subsample slide under the macroscopic staging system, a 1 cm × 1 cm grid was drawn on Petri dishes to aid in counting the eggs [33]. The number of oocytes in each subsample (F1, F2, and F3) was estimated using the following equation: F1, F2, or F3 = (number of oocytes in subsample) × (gonad weight/subsample weight). Each fish’s fecundity (F) was estimated using the equation F = (F1 + F2 + F3)/3.

2.5. Length at First Maturity

The total length (TL in cm) at first maturity, which is the TL at which 50% of individuals are sexually mature, for both females in stages IV, V, and VI and males in stages IV and V, was estimated using the logistic equation, as outlined by Karna and Panda [34].

The proportional frequencies were fitted to a two-parameter logistic curve.

P = 1/[1 + exp (−a(TL–L50))]

Here, P represents the proportion of mature individuals at TL, a is the constant parameter that determines the slope of the maturity curve, and L50 denotes the total length at which 50% are mature. The L50 was estimated using the Excel add-in tool “solver” [34].

2.6. Statistics

All statistical analyses were performed using SPSS version 22. A p-value less than 0.05 is considered “significant”; conversely, a p-value greater than 0.05 is regarded as “not significant.” The deviation of sex ratio from 1:1 was assessed using the Chi-square test. Variations in monthly gonad maturation stages and the significance between each month and stage were evaluated with a one-way ANOVA, followed by post hoc analyses using the Tukey test to determine the α level at a 95% confidence interval. The correlation between fecundity and body size was analysed using Pearson’s correlation. The mean oocyte diameter during the maturation stage (stage IV) was evaluated with a one-way ANOVA, and post hoc analyses using the Tukey test were performed to estimate the α level at a 95% confidence interval. The significance of the correlation between fecundity and body size was further analysed through Pearson’s correlation.

3. Results

3.1. Sex Ratio

Siganus javus was observed throughout the year in the southern South China Sea, although no females were noted in February. A total of 158 females and 181 males were recorded, resulting in a female–male sex ratio of 1:1.15, which did not significantly differ from the 1:1 ratio (Chi-square test, p > 0.05).

3.2. GSI and Histology in Female

The GSI for female Siganus javus ranged from 0.15 to 6.74 (Figure 2a).

The GSIs of S. javus in December were significantly higher than those in January, April, May, September, and November (ANOVA, −5.342 ≤ H3 ≤ 4.210, p < 0.05–0.001); however, there were no significant differences compared to March, June, July, August, and October (ANOVA, −0.376 ≤ H3 ≤ 3.050, p > 0.05). The maturation stage (stage IV) was observed in July, August, October, and December (Figure 3a), indicating spawning peaks for female S. javus.

The mean GSI values for stage 0, stage I, stage III, stage IV, stage V, and stage VI were 0.46 ± 0.26, 0.53 ± 0.21, 1.13 ± 0.58, 3.65 ± 1.69, 1.22 ± 0.99, and 0.64 ± 0.30, respectively. There was no stage II in the current study. The highest GSI was observed in the fully maturing stage (stage IV) (ANOVA, −7.235 ≤ H3 ≤ 4.140, p < 0.05–0.001), while no significant differences were noted in the GSI between stage IV and stages III and V (ANOVA, −1.992 ≤ H3 ≤ 2.112, p > 0.05). The lowest GSI was recorded in the immature stage (stage 0) (ANOVA, −7.235 ≤ H3 ≤ −3.641, p < 0.05–0.001), with no significant differences found between stage 0 and stages I, V, and VI (ANOVA, −2.428 ≤ H₃ ≤ −2.036, p > 0.05).

There was a significant positive correlation between the maturation stage and GSI (Pearson’s correlation analysis, p < 0.001).

The means ± SDs of TLs in stages 0, I, III, IV, V, and VI were 30.53 ± 4.79 cm, 29.53 ± 4.70 cm, 28.68 ± 4.96 cm, 31.18 ± 3.22 cm, 32.05 ± 5.00 cm, and 30.76 ± 3.53 cm, respectively (Table 1). The corresponding means for BWs were 380.36 ± 163.40 g, 363.27 ± 182.10 g, 350.90 ± 161.50 g, 421.14 ± 126.88 g, 492.82 ± 210.39 g, and 373.07 ± 108.47 g, respectively (Table 1). No significant differences in TL and BW were observed among the maturation stages (ANOVA, 5.122 ≤ H3 ≤ 6.208, p > 0.05). These results indicate that maturation is not affected by body size.

3.3. Oocyte Development and Fecundity

Oocyte diameters (mean ± SD) in S. javus at stages 0, I, III, IV, V, and VI were 58.25 ± 10.49 μm, 72.08 ± 24.37 μm, 193.03 ± 47.88 μm, 277.11 ± 30.86 μm, 112.06 ± 66.76 μm, and 61.05 ± 27.59 μm, respectively (Table 1). The oocyte diameter during the maturation stage (stage IV) was the highest (ANOVA, −7.353 ≤ H3 ≤ 6.550, p < 0.05–0.001); however, no significant difference was observed between stages IV and III (ANOVA, H3 = −0.730, p > 0.05). The oocyte diameter in the immature stage (stage 0) was significantly lower than that in stages I, III, and IV (ANOVA, −7.353 ≤ H3 ≤ −3.301, p < 0.05–0.001), while no significant differences were found between stage 0 and stages V and VI (ANOVA, −1.631 ≤ H3 ≤ 0.597, p > 0.05).

Significant positive correlations were observed between the maturation stage and oocyte diameter (Pearson’s correlation analysis, p < 0.001). This suggests that oocyte development corresponds with the maturation process.

The fecundity of S. javus was a mean ± SD of 3.52 × 10⁵ ± 2.94 × 10⁵ (range: 1.8 × 10⁵ to 12 × 10⁵). Significant positive correlations were found between fecundity and total length (TL) and body weight (BW) based on Pearson’s correlation analysis (p < 0.001).

3.4. GSI and Histology in Male

The GSI of male S. javus ranged from 0.01 to 4.82 (Figure 2b). In males, the GSIs in December and October were significantly higher than those in March and November (ANOVA, −3.666 ≤ H3 ≤ 4.574, p < 0.05–0.001); however, there was no significant difference compared to January, February, April, May, June, July, August, or September (Figure 2b). The late germinal epithelium stage (stage IV) was observed throughout the year, except in February (Figure 3b), when samples were scarce.

The mean GSIs in stages 0, I, II, III, IV, and V were 0.06 ± 0.06, 0.08 ± 0.04, 0.22 ± 0.17, 0.78 ± 0.99, 0.71 ± 0.77, and 0.13 ± 0.09, respectively. The GSI for the late maturation stage (stage IV) was significantly higher than that for the immature stage (stage 0) (ANOVA, H3 = −3.015, p < 0.05). The immature stage was significantly lower than stages IV and III (ANOVA, −3.015 ≤ H3 ≤ −2.987, p < 0.05). Stage V was significantly lower than stages IV and III (ANOVA, H3 = 5.286 to 6.874, p < 0.05). No significant differences in the GSI were found among other stage comparisons (ANOVA, −2.641 ≤ H3 ≤ 1.598, p > 0.05). A significant correlation between the maturation stage and GSI was observed (Pearson’s correlation analysis, p < 0.05).

The mean ± SD of TLs in stages 0, I, II, III, IV, and V were 25.83 ± 8.22 cm, 20.85 ± 0.21 cm, 31.54 ± 4.21 cm, 28.16 ± 3.66 cm, 29.17 ± 4.02 cm, and 30.35 ± 4.97 cm, respectively (Table 1). The means of BWs were 315.94 ± 221.97 g, 134.13 ± 12.08 g, 465.29 ± 185.22 g, 300.50 ± 123.34 g, 336.90 ± 132.80 g, and 366.55 ± 168.25 g, respectively (Table 1). The body size (TL and BW) in stage I was significantly lower than that in stage II (ANOVA, H3 = −3.185, p < 0.05). However, there was no significant difference in body size between stage I and stages 0, III, IV, and V (ANOVA, −2.464 ≤ H3 ≤ 1.882, p < 0.05). The body size in stage III was significantly lower than that in stage II (ANOVA, H₃ = 3.251, p < 0.05), but no significant difference was observed between stage III and stages 0, I, IV, and V (ANOVA, −1.872 ≤ H₃ ≤ 0.671, p > 0.05). Additionally, no significant differences were found between stage 0 and stages I, II, III, IV, and V, between stage II and stages IV and V, and between stages IV and V (ANOVA, −1.096 ≤ H₃ ≤ 2.671, p > 0.05). These results suggest that maturation is generally not influenced by body size, similar to females.

The body size (TL and BW) at full maturation (stage IV) in males was significantly smaller than (stage IV) in females (Pearson’s correlation analysis, p < 0.05).

3.5. Length at First Maturity

The estimated TL at first maturity for females and males was 30.9 cm and 29.2 cm, respectively (Figure 4).

4. Discussion

This is the first study into the life history, especially the reproductive biology, of S. javus. However, the fish is widely distributed throughout the Indo-West Pacific region and is a commercially important species. The spawning season of female S. javus is very limited to July and August, as well as October and December, whereas male fish spawn throughout the year. Although there is no information about the spawning seasons of S. javus for both females and males apart from this study, the year-round spawning of male S. javus is similar to that of the whitespotted rabbitfish Siganus sutor in Kenya [35], whereas a short spawning season in S. sutor has also been observed in Tanzania [36]. The spawning season for female S. javus partly overlaps (October to December) with that of the dusky spinefoot Siganus luridus in Lebanon [37], and various spawning seasons have been recorded within Siganus, including the white-spotted spinefoot Siganus canaliculatus in Japan [38] and Oman [39], the marbled spinefoot Siganus rivulatus in the Northern Mediterranean [40], and the scribbled rabbitfish Siganus spinus in Japan [26] (Table 2). The differences in reproductive seasons observed in Siganus may be caused by interspecific spawning strategies and regional variations in environmental conditions. Variations in habitat water temperature are considered a key factor influencing the timing and duration of the spawning season in Siganus [41]. Further research into the spatial and temporal variations in the timing and length of the spawning season in S. javus across its range is essential for a comprehensive understanding of its reproductive biology.

Many studies have reported that fish living in tropical waters and warm temperate regions spawn continuously throughout the year (e.g., [25,42,43,44,45]). Therefore, continuous reproduction was expected in female S. javus, although the study showed that the spawning seasons were limited to two to three months. Skip spawning events were also observed in other Lutjanidae, including S. canaliculatus, S. sutor, S. luridus, and S. argenteus (Table 2). Skip spawning may occur when female fish are in unfavourable environmental conditions [46]. Fifteen female S. javus were in resting stage (stage VI), which could indicate a skipped spawning event. This skipped spawning is an adaptive trait that increases lifetime reproductive output when environmental conditions are harsh, enabling them to spawn in subsequent reproductive seasons when conditions improve [46]. Only females were affected, as the energy cost of egg production exceeds that of sperm in males [46,47].

Table 2. Spawning season of female Siganus across various countries and regions.

Species	Country/Region	Spawning Period	Reference
S. canaliculatus	Singapore	January–April	[48]
	Palau	March–May	[49]
	Asian estuaries	January–April	[50]
	Hong Kong	March–June	[51]
	Japan	April–June	[52]
	Japan	March–August	[38]
	Arabian Gulf UAE	April–July, November	[16]
	Oman	June–July, November–February	[39]
S. sutor	Kenya	January–February, May–June	[35]
	Kenya	June–July, November–January	[35]
S. rivulatus	Northeastern Mediterranean	July–August	[40]
	Lebanon	June–July	[37]
S. spinus	Japan	June–August	[26]
S. luridus	Lebanon	June–July, October–January	[37]
S. argenteus	Guam	March–May, August–September	[29]
S. javus	Brunei Darussalam	July–August, October–December	This study

Table 2. Spawning season of female Siganus across various countries and regions.

Species	Country/Region	Spawning Period	Reference
S. canaliculatus	Singapore	January–April	[48]
	Palau	March–May	[49]
	Asian estuaries	January–April	[50]
	Hong Kong	March–June	[51]
	Japan	April–June	[52]
	Japan	March–August	[38]
	Arabian Gulf UAE	April–July, November	[16]
	Oman	June–July, November–February	[39]
S. sutor	Kenya	January–February, May–June	[35]
	Kenya	June–July, November–January	[35]
S. rivulatus	Northeastern Mediterranean	July–August	[40]
	Lebanon	June–July	[37]
S. spinus	Japan	June–August	[26]
S. luridus	Lebanon	June–July, October–January	[37]
S. argenteus	Guam	March–May, August–September	[29]
S. javus	Brunei Darussalam	July–August, October–December	This study

Although the study covered the entire year, the middle maturation stage (stage II) was absent in the analysed female S. javus. Coral reef fishes, such as snappers, live in mangroves and seagrass beds during the premature stage, migrating to coral reefs when they reach the pre-adult stage [38]. Therefore, the absence of the middle maturation stage in female S. javus could be attributed to different habitat uses during their life history. While the middle maturation stage was not observed, oocyte size can indicate the development stage, as oocytes in later development stages are generally larger.

There was no significant difference in the male–female sex ratio. The sex ratio close to 1:1 suggests that the fish population is in equilibrium, since the number of males and females is equal. The result was also consistent with other Siganus, S. rivulatus and S. luridus in Lebanon [37]. The equal sex ratio might allow males and females to find their mates easily before spawning. Subsequently, it could enhance reproductive success because an unequal sex ratio during the reproductive season leads to mating competition [53].

The TL and BW at the maturation stage (stage IV) of female S. javus were found to be larger than those of males. Size differences in maturity between the sexes may be attributed to reproductive tactics that enhance reproductive success [54]. Life history theory suggests that delayed maturation can be a disadvantage, as fish require additional time to grow larger [55,56]. To increase reproductive success, females tend to feed for longer and mature later, thereby achieving a larger size [54]. Larger females are also known to produce bigger and higher-quality eggs [57]. Siganus javus could similarly adopt this reproductive strategy to maximise reproductive success.

The TL at first maturity estimated in this study (approximately 30 cm) was higher than estimates from previous studies on Siganus: S. sutor in Kenya (22.8–28.2 cm for females and 21.7–24.0 cm for males) [34,36,58], in Tanzania (21.6 cm for females and 20.3 cm for males) [26], and S. canaliculatus in Oman (23.9 cm for females and 22.6 cm for males) [29]. These findings suggest that differences in length at first maturity may be species-specific, indicating that S. javus might take longer to reach maturity. Additionally, environmental factors such as temperature, population size, and food availability could cause variations in estimates from previous studies on Siganus: S. sutor in Kenya (22.8–28.2 cm for females and 21.7–24.0 cm for males) [24,26,44,45], in Tanzania (21.6 cm for females and 20.3 cm for males) [36], and S. canaliculatus in Oman (23.9 cm for females and 22.6 cm for males) [39]. These findings imply that the differences in length at first maturity may be species specific, suggesting that S. javus might require more time to reach maturity. Furthermore, environmental factors such as temperature, population size, and food availability could lead to variations in sexual maturation, as intra-species differences in TL at first maturity were observed in S. sutor in Kenya [35].

The fecundity of S. javus ranged from 1.8 × 10⁵ to 12 × 10⁵. Overlapped fecundity was observed in S. javus (6.8 × 10⁵–45 × 10⁵) in Sri Lanka [59]. In Siganus, the fecundity of S. canaliculatus varied from 1.1 × 10⁵ to 27 × 10⁵ in Sri Lanka [59] and from 2.4 × 10⁵ to 6.1 × 10⁵ in Oman [39]. The golden-lined spinefoot, Siganus lineatus, exhibited a fecundity range of 15 × 10⁵ to 27 × 10⁵ in Sri Lanka [59]. The fecundity of S. javus increased with body size (TL and BW). Fecundity is generally positively correlated with fish size (TL and BW) in Siganus [39,40]. These results suggest that there may be less inter- and intra-species variation in fecundity within Siganus.

5. Conclusions

In the present study, reproductive characteristics such as spawning season and period, gonad development, and fecundity were identified in S. javus in the southern China Sea. Reproductive biology significantly influences other biological features such as growth, migration, and predation risk. Therefore, understanding a species’ reproductive biology is crucial for comprehending its ecology, behaviour, and many other aspects of its life history. This knowledge can also assist in the management and conservation of commercial fish species.