Journal of Fisheries

Apparent digestibility coefficients of selected feed ingredients for Asian seabass, Lates calcarifer reared in recirculatory aquaculture system

2026-05-01T07:52:30+00:00

Digestible nutrient-based feed formulations have become more prevalent in aquaculture, especially in intensive recirculatory aquaculture systems (RAS). In order to maximize growth performance and feed efficiency in Asian seabass (Lates calcarifer) raised in RAS while minimizing waste output, it is imperative to assess the apparent digestibility of nutrients from different feed ingredients used in the feed formulations. Accordingly, an eight-week study was conducted to analyse the apparent digestibility coefficients of nutrients in selected protein sources for Asian seabass, Lates calcarifer, reared in RAS. The reference diet consisted of commercial seabass feed with 47% crude protein. The test diets were formulated based on a 70:30 ratio approach for ingredient digestibility evaluation using fishmeal (FM), squid meal (SQM), soybean meal (SBM), corn gluten meal (CGM), wheat flour (WF), and broken rice (BR). The reference and test diets were finely ground for homogeneity, mixed with 0.5% commercial binder for stability, digestibility indicator (0.5% chromic oxide), and 2 mm pellets were produced. Growth of fish fed different diets was significantly affected owing to large variations in the inclusion levels of each ingredient. ADC of protein, lipid and energy varied from 81 to 93%, 62.8 to 90.1% and 81 to 90.3% respectively. FM and SQM exhibited significantly higher nutrient digestibility values, as fish are carnivorous. The higher nutrient digestibility of major plant-based protein ingredients suggests a higher quality of source materials. Overall, the present study provides information on the bioavailability of nutrients in animal and plant feedstuffs for Asian seabass reared in RAS.

Socio-economic assessment of dry fish processors in Cuddalore District, Tamil Nadu, India

2026-04-30T07:50:29+00:00

The present study focuses on the socio-economic characteristics and occupational structure of dry fish processors in the Cuddalore District of Tamil Nadu, India. The primary data was collected from 100 dry fish processors in Cuddalore (50%) and Parangipettai (50%) blocks of the district in 2025 using a structured interview schedule. It was found that the sector was mostly women-dominated (87%) and 66% of respondents were above 45 years. Dry fish processing was the main occupation for 82% of the respondents. Most of the respondents belonged to nuclear families (74%) with 3–5 members. Raw fish procurement was mostly dependent on landing centers (67%), and traditional cement floor drying (54%) was predominant. Credit dependence was reported by 61% of the respondents, mostly from non-institutional sources (62%). Garrett ranking revealed that raw fish scarcity (Garrett mean score: 71.69) and weather uncertainty (Garrett mean score: 67.80) were the key constraints. A statistically significant association was observed between village location and production quality preference (χ² = 15.458; p < 0.05). The study concluded that the dry fish processing sector was an economically important but structurally vulnerable component of the marine fisheries value chain, which requires better institutional support and technological assistance to improve livelihood stability.

Dietary tryptophan intervention on growth and stress of Asian seabass, Lates calcarifer reared in recirculating aquaculture system

2026-04-30T07:50:42+00:00

The rapid expansion of recirculating aquaculture system (RAS) aquaculture demands precise dietary strategies. Determining optimal tryptophan levels and understanding their combined effects on growth, blood responses, and stress regulation in Asian seabass remain limited. Addressing this knowledge gap, an experiment was conducted to evaluate the effects of L-tryptophan supplementation on growth, hematobiochemical responses and stress regulation of Asian seabass in RAS. Five isonitrogenous and isocaloric treatment diets were formulated to contain graded levels of L-tryptophan at 0.47 (T1), 0.53 (T2), 0.59 (T3), 0.66 (T4) and 0.72% (T4) of diet. At the end, an increase was observed in the growth of fish fed the T1 diet, after which no variation was observed. Dietary L-tryptophan had no effect on FCR across all the diet groups. Second order polynomial regression analysis of weight gain against dietary tryptophan levels indicated that the dietary tryptophan requirement for Asian seabass reared in RAS was 0.61% of the diet. No differences were observed in whole body composition and haematological responses among the treatment groups. Cholesterol and HDL-C levels followed trend similar to the growth performance. Cortisol level was significantly lowered in T1 than the control, whereas no variation was observed among other groups. Second order polynomial regression analysis of HDL-C and cortisol against dietary tryptophan levels showed that the dietary tryptophan requirement were 0.61% and 0.62% of the diet respectively. Overall, L-tryptophan at 0.61–0.62% maximizes growth, stress responses, and tryptophan–serotonin–cholesterol axis regulation in Asian seabass in RAS culture systems, optimizing performance.

Effects of temperature on somatic growth, gastric pepsin activity, and endocrine dynamics in orangefin labeo (Labeo calbasu)

2026-04-30T07:50:55+00:00

This study investigated the effects of varying water temperatures on somatic growth, digestive enzyme activity, and endocrine responses in orangefin labeo (Labeo calbasu), a commercially important freshwater fish species. The experiment was performed in triplicate using 100 L glass aquaria at four temperature levels: 22, 26, 30, and 34°C. Over a 60-day experimental period, growth performance, pepsin activity, and hormonal dynamics were analyzed to identify optimal thermal conditions for aquaculture. Results demonstrated that 30°C was the most favorable temperature, yielding the highest specific growth rate (SGR: 0.45±0.05% day^–1, n = 10), weight gain (3.07±0.70 g, n = 10), and length increase (1.29±0.57 cm, n = 10). In comparison, 22°C exhibited the lowest growth metrics (one-way ANOVA: p < 0.05). A thermal threshold for enzymatic efficiency was shown by significantly lower pepsin activity at both lower (22°C) and higher (34°C) temperatures, whereas digestive pepsin activity peaked at 30°C (8.34±0.71 U₃₇ mg protein^–1). Endocrine analysis revealed that the hormonal dynamics also temperature dependent. Reproductive hormones-follicle-stimulating hormone (FSH: 1.45±0.10 mIU mL⁻¹), luteinizing hormone (LH: 1.61±0.04 mIU mL⁻¹), testosterone (1.50±0.01 ng dL⁻¹), and estradiol-17β (E2) reached peak at 30°C which were higher than in other treatments (p < 0.05). Overall L. calbasu exhibited optimal growth, digestive efficiency, and reproductive performance within a narrow temperature range of 26–30°C (p < 0.05). These findings underscore the species’ sensitivity to temperature variation and highlight the importance of maintaining stable thermal conditions to ensure sustainable productivity and conservation in aquaculture.

Effects of fish waste silage and vitamin-C supplemented diet on growth and haematological parameters of common carp, Cyprinus carpio (Linnaeus, 1758) fingerlings

2026-04-30T07:51:08+00:00

A 60-day experiment was conducted to evaluate the growth performance, feed utilization and haematological parameters of common carp, Cyprinus carpio under four dietary treatments with three replicates for each. These were control (0%), T1 (15%), T2 (30%) and T3 (45%) fish waste silage containing diets. Nutritional profile of experimental feeds was: crude protein (25–25.75%), lipid (8.46–8.96%), moisture (10.64–11.16%), ash (14.05–14.87%), crude fiber (4.07–4.32%), and nitrogen-free extract (35.69–37%). The haematological parameters were observed of C. carpio, which improving White blood cells, Red blood cells, haemoglobin (Hb) and Hematocrit (HCT) within the healthy physiological range. Growth performance parameters were observed at the end of the experiment. The highest length gain (5.96±0.05 cm), weight gain (8.43±0.15 g), percentage weight gain (161.44±10.14%), specific growth rate (0.46±0.01%), protein efficiency ratio (3.03±0.18 g), hepatosomatic index (0.05±0.00%), and intestinal somatic index (0.33±0.00%) was observed compared to the control groups. The highest feed conversion ratio (1.91±0.47) was observed in control group compared to the treatment group. Carcass composition of the fish at the end of the trial was similarly analyzed for protein (58.87–60.29%), lipid (13.10–13.78%), moisture (10.25–10.96%), ash (9.21–9.32%), and NFE (6.45–0.73%) content. Water quality parameters remained within acceptable limits throughout the study period. The results suggest that specific dietary treatments significantly enhanced growth, haematological parameters, carcass composition, and feed utilization in common carp.