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The photobiological responses of fish are strongly influenced by the surrounding photoperiod conditions. This study aimed to evaluate the effects of photoperiod on the growth performance, gonadal development, major haematological parameters, skin coloration, and proximate composition of Nile tilapia (Oreochromis niloticus). Four photoperiod treatments were employed: 2h of light and 22h of dark (02L:22D), 12h of light and 12h of dark (12L:12D), 17h of light and 7h of dark (17L:07D), and 22h of light and 2h of dark (22L:02D), denoted as Treatment one (T1), Treatment two (T2), Treatment three (T3), and Treatment four (T4), respectively. Fingerlings (3.21±0.51g) were reared for 90 days and provided a commercial diet (35% crude protein) twice daily at 5% of their body weight. The light intensity was maintained at 1350lux throughout the study period. Compared with those under the other treatments, significantly greater weight gain (WG) (47.09±13.89), percentage WG (%WG)(1465.05±394.29), and specific growth rate (SGR) (3.05±0.25), along with a lower feed conversion ratio (FCR) (1.79±0.44), were observed under the 17L:07D photoperiod. The gonadosomatic index (GSI) was highest in T4 for both males (1.11%±0.41%) and females (7.18%±1.10%). Skin brightness was also greater in T4 (L∗=85.63±0.31) than in T1 (L∗=71.02±0.51). Red blood cell (RBC) counts were significantly higher in T3 (1.56±0.06×10[sup.6]/µL), whereas white blood cell (WBC) counts were highest in T4 (31.72±0.16×10[sup.3]/µL). Hemoglobin (Hb), hematocrit (Hct), mean corpuscular volume (MCV), mean corpuscular Hb (MCH), MCH concentration (MCHC), and monocyte levels showed no significant differences among treatments. Proximate composition showed the highest protein content in T3 (14.47±0.19) and the greatest lipid content in T4 (1.82±0.06). Overall, 17L:07D (T3) optimizes growth and protein deposition, whereas 22L:02D (T4) enhances reproduction, lipid accumulation, and skin pigmentation in Nile tilapia.

Fishes are an important component of human nutrition, mainly acting as source of essential fatty acids in the prevention of cardiovascular disorders. The increase in their consumption has led to a growth of fishes waste; therefore, the disposal and recycling of waste has become a key issue to address, in accordance with circular economy principles. The Moroccan Hypophthalmichthys molitrix and Cyprinus carpio fishes, living in freshwater and marine environments, were collected at mature and immature stages. The fatty acid (FA) profiles of liver and ovary tissues were investigated by GC–MS and compared with edible fillet tissues. The gonadosomatic index, the hypocholesterolemic/hypercholesterolemic ratio, and the atherogenicity and thrombogenicity indexes were measured. Polyunsaturated fatty acids were found to be abundant in the mature ovary and fillet of both species, with a polyunsaturated fatty acids/saturated fatty acids ratio ranging from 0.40 to 1.06 and a monounsaturated fatty acids/polyunsaturated fatty acids ratio between 0.64 and 1.84. Saturated fatty acids were found to be highly abundant in the liver and gonads of both species (range 30–54%), as well as monounsaturated fatty acids (range 35–58%). The results suggested that the exploitation of fish wastes, such as the liver and ovary, may represent a sustainable strategy for the achievement of high value-added molecules with nutraceutical potential.

The stage of sexual maturity, fecundity, and relationship of gonadosomatic (GSI), hepatosomatic (HSI), and hepatogonadal (HGI) indices in mullet Mugil cephalus, captured in Bahía de Buenaventura, was examined in the present study. With the help of artisanal fishermen, 21 specimens (all females) were collected in February 2024. The mullets measured in total length between 28.0 and 35.5 cm (30.8 ± 2.3 cm standard deviation) and weighed between 200.0 and 364.5 g (246.6 ± 43.6 g). The fecundity of females weighing 257.8 ± 48.9 g was estimated at 423,659 ± 103,208 oocytes. The GSI and HSI increased from 1.0 ± 0.4 to 6.4 ± 1.5% and from 0.8 ± 0.2 to 1.0 ± 0.1% in immature to mature females, respectively. Also, significantly different from each other, the values of the HGI in immature females were 72.2 16.3%, compared to that of mature females of 17.2 ± 4.6%. Since the liver is responsible for the synthesis and production of vitellogenin, which is then taken up by the oocytes in the gonad (ovary), the HGI may also be a very useful indicator of sexual maturity in mullet, as well as for other fishes.

The Garua bacha, Clupisoma garua , holds considerable commercial and nutritional significance as a fish species. This study investigates the relationships between GSI (gonadosomatic index) and eco-climatic conditions, and provides comprehensive insights into several facets of reproduction, such as size at first sexual maturity ( L m ), spawning season, peak spawning period, and proposes sustainable management strategies for C. garua in the Ganges River, northwestern, Bangladesh. Since January to December 2017, 570 female individuals have been gathered from the Ganges River using cast nets, gill nets, and square lift nets on a monthly basis. The total length (TL) of the specimens varied from 3.90 to 26.30 cm. L m was estimated as 14.30 cm based on the results of the TL vs . GSI, MGSI (modified gonadosomatic index), DI (Dobriyal index), 14.00 cm through TL-FL regressions, and 15.18 cm depending on L max for this species. Furthermore, the spawning period was observed from May to August, peaking in June and July, based on greater GSI, MGSI, and DI values. Throughout the peak spawning season, there was not a significant differ from a value of 100 in the relative weight ( W R ) of the female species. During the spawning season, a substantial association between temperature and GSI ( p  = 0.0038); rainfall and GSI ( p  = 0.0043); DO and GSI ( p  = 0.0043); pH and GSI ( p  = 0.0002); and alkalinity and GSI ( p  = 0.0001) was detected. Analyzing a 55-year data series (1964–2018), it became clear that an increase in average air temperature of 0.0289 °C and a decrease in rainfall of 2.988 mm per year might possibly delay the spawning season of this species. As a consequence, the results of this study provide crucial information for developing management strategies to safeguard C. garua populations in the Ganges River and its adjacent ecosystems.

The bogue, Boops boops (Linnaeus, 1758), is an omnivorous fish species that often aggregates near fish farms. In addition to being attracted to food, bogues also hide from predators near floating cages. Some specimens can also be found in the cages, where they coexist for a time with farmed fish. In general, there is a relationship between food availability and gonadosomatic index (GSI) of the fish. Therefore, the aim of this work was to investigate the relationship between body condition and gonadosomatic index (GSI) of bogues. The research was carried out in May 2023, during the spawning period of bogue. Samples were collected from three locations in the middle part of the Eastern Adriatic: in the immediate vicinity of the cages (A), at the floating cage (C) and at a location far away from the cages (W). The females from all three locations were heavier (315.41±119.53g) than the males (281.47±79.20g), while the difference in length between the sexes was not statistically significant. The condition index (CI) and viscerosomatic index (VSI) were significantly higher in bogues from floating cage. The decomposition of the condition index was used to evaluate the influence of body condition on the gonadosomatic index. Fish with a higher condition index also had a higher gonadal condition index (CIg), which was 0.03±0.01 at location A, 0.05±0.01 at location W, with the highest value found in the bogues from location C (CIg=0.06±0.04). Bogues sampled in floating cages differed in most studied parameters from wild population samples, but also from specimens caught in the immediate vicinity of the cages indicating the direction for further research of interactions between wild fish populations and aquaculture.

The reproductive contribution of river-resident (freshwater) Japanese eels (Anguilla japonica) remains poorly understood, particularly following recent paradigm shifts that emphasise the predominance of ocean-resident “sea eels.” To elucidate the riverine life history and maturation strategies of freshwater residents, we investigated the age structure, morphological traits, and gonadal development of 100 river-resident Japanese eels captured over a three-year period (2007–2009: n = 33, 40, and 27, respectively) in the middle reaches (25–50 km upstream) of the Oi River, Shizuoka Prefecture, Japan. Age determination using sagittal otoliths revealed a broad age distribution from 4 to 15 years. Among the female population (n = 85), highly significant positive correlations were observed between age and growth parameters (Total Length, R2 = 0.771; Body Weight, R2 = 0.709; p < 0.001). Highly mature silver eels with markedly elevated gonadosomatic indices (GSI) were captured at the uppermost sampling site, immediately downstream of an impassable dam barrier. This spatial concentration of mature females suggests an energetic and temporal life-history strategy in which river-resident eels initiate precocious maturation in the upper reaches to compensate for the prolonged downstream migration to the river mouth. Notably, the calculated female growth rate of approximately 3.6 cm/year was significantly slower than that reported for coastal and estuarine conspecifics in Japan, indicating a distinct slow-growth history unique to river-resident cohorts. Although historical baselines exhibit significant annual variation (ANOVA, p < 0.05), they provide an invaluable benchmark for river-resident cohorts prior to the severe depletion of wild stocks. Our findings underscore that large freshwater-resident females may serve as vital somatic and reproductive reserves, and provide key recommendations for rigorous habitat conservation within river systems to sustain the species.

We used a 298-day (July to April) laboratory mesocosm experiment with Newfoundland green sea urchins (Strongylocentrotus droebachiensis) to test the prediction that growth and feeding are largely unaffected by light quantity and quality within the visible-light spectrum. Sea urchins experienced either of three light environments simulating differences in illuminance and red/blue light ratios among common habitats for the species: tide pool, shallow subtidal, and deeper subtidal habitats. Sea urchins were fed exclusively kelp (Alaria esculenta) and exposed to natural photoperiod. Light had no effect on body diameter and weight. Diameter, but not weight, changed over time with a low, yet statistically significant, 3% increase from August to February. Gonadosomatic index (GSI) of sea urchins in the mesocosms doubled from ~ 10% in Aug to ~ 20% in February, with no further change in April, independently of light. GSI of sea urchins in the field was comparatively lower throughout the experiment, being similarly low, ~ 5%, in August, December, and April, and peaking significantly higher at ~ 9% in February. Light also did not affect feeding on kelp, which, however, differed significantly among the three sampling months, peaking in November. Seasonal patterns of feeding in the mesocosms followed that in natural habitats. Our findings speak highly to the relative insensitivity of the species to its visible-light environment within the range tested. They also reinforce the paradigm that in green sea urchin, visible-light quantity and quality have a much lesser impact on somatic and gonadic growth and feeding than food quality and availability.

This study was carried out to estimate the sex ratio, maturity size, gonadosomatic index (GSI), and peak breeding season of mud crabs. Samples were collected randomly from the estuary and river of the study area. Sampling was carried out monthly from April to September at every full moon during one high tide. A total number of 240 specimens were sampled, where 53 individuals were hermaphrodite. The crabs were shifted alive to the biology and histology lab for detailed biological study. Sex was determined. Male and female sex ratio and breeding season were also investigated. The male:female ratio was 1:0.96 and the ovarian development was categorized into five stages based on internal observations, viz. immature (stage I), underdeveloped (stage II), early developed (stage III), late developed (stage IV), and mature (stage V). The maturity percentages were 37%, 19%, 13%, 11%, and 20%, respectively. 50% maturation was estimated at 82.36 mm internal carapace width (ICW). The highest mean GSI value was 7.97 ± 3.03. The mature stage was found in all the working periods. This shows that females have activated ovaries in all the working months, and the species are continuous breeders. A higher frequency of vitellogenic ovary and higher GSI value were found in September. The maximum GSI value was found in the size group 70-79 mm. The study shows that the capture from the wild sources of mud crabs without any regulation can threaten the population structure. The capture of female mud crabs should be more than 82.36 mm ICW, which will help conserve and protect young crabs.

Fish reproductive biology plays an important role for fishery management, especially in developing countries. The aim of this study was to compile all available information and analyze reproduction patterns of marine fishes in three Large Marine Ecosystems (LMEs): North, East, and South Brazil Shelves. We tested the hypothesis that the onset and duration of spawning season differ among these three LMEs; compared the ratio between length at first maturity and asymptotic length with the global trend observed; analyzed sex ratios; and tested whether females allocate more energy into reproduction than males. The following data were compiled from published sources and ‘grey’ literature: sex ratio, spawning season, gonadosomatic indices (GSI), and length at first maturity (Lm). The reproductive load was estimated as Lm/L∞. The median extension of the spawning season in the North, East, and South Brazil Shelves were 6.5, 6.0 and 5.0 months, respectively, with higher frequency during austral summer in South Brazil. Marine fishes from these three LMEs can be grouped in summer and non-summer spawners. About ninety six percent of the cases the reproductive load was between 0.3 and 0.8, which is slightly shifted toward smaller values, compared with the global range of 0.4-0.9. Gonadosomatic indices for females were higher. Contrary to some expectations, there is seasonality in the reproduction of tropical fishes. However, seasonality is stronger in southern populations. Size at first maturity is not efficiently used as a tool for fisheries management in the ecosystems analyzed.

The present study aimed to evaluate the length-weight and length-length relationships as well as the condition factor and gonadosomatic index of the Blackspot snapper, Lutjanus fulviflamma in the northern Persian Gulf, Hormozgan Province, Iran. The specimens were collected monthly from April 2016 to March 2017. The size (TL, total length; FL, fork length; SL, standard length) were measured and weighted (BW, total body wet weight). A total of 446 individuals were analyzed. The TL-BW relationship indicated isometric growth pattern in both sexes. In females, the means for condition factor was higher than males. In both sexes, the lowest value of both condition factor and gonadosomatic index were detected in autumn with ascending trend in the next seasons reaching the peak in spring. The oscillation in condition factor, as well as gonadosomatic throughout the sampling period, was most prominent in females which may be related to the reproductive cycle. The information reinforces data to define fishing closed seasons in this important fish that is used in many places in the world.