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a b s t r a c tThe nutritional potential of protein isolate from rubber seed (RPI) in the diets of Labeo rohita (initial average weight 4.45 ± 0.01 g) was assessed in a 60 days feeding trial. Five isonitrogenous (32.62 ± 0.13 CP Kg −1 ) and isocaloric (18.47 ± 0.08 MJ kg −1 ) experimental diets were formulated with graded level of RPI like 0%, 25%, 50%, 75%, or 100% in replacement for soybean protein isolate (SPI), and designated as Control, RPI25, RPI50, RPI75, RPI100, respectively. The RPI contributed 0%, 13%, 26%, 39% or 52% of the total dietary protein in the diets. Each diets were randomly assigned to 15 experimental tanks containing 12 fish in triplicates and fed to satiation twice daily at 10:00 h and 18:00 h. At the end of the feeding trial, the growth performance and nutrient utilization indices such as percent weight gain (WG%), specific growth rate (SGR), daily growth coefficient (DGC), feed intake (FI), protein efficiency ratio (PER), feed conversion ratio (FCR) and protein retention (PR) values were not significantly (p > 0.05) affected by the dietary treatments irrespective of inclusion levels of RPI. A significantly higher (p < 0.05) hepatosomatic index (HSI) was recorded in the control and RPI 50 group compared to other treatment groups (p < 0.05). The intestinal somatic index (ISI) and Survival rate were similar (p > 0.05) in all the groups. The apparent digestibility coefficients (ADCs) of dry matter and protein for fish fed the control and RPI 100 diets were found to be similar, while RPI 50 and RPI 75 groups exhibited a significantly lower value corresponding to the protease enzyme activity. The whole body compositions and digestive/metabolic enzymes activities among the various groups did not differ significantly (p > 0.05). The serum cholesterol and triglyceride levels were found to be significantly higher (p < 0.05) in the control compared to the RPI fed groups. Significantly higher serum glucose level was recorded in RPI 50, while a reverse was seen in the liver glycogen contents. Overall, this study clearly showed that RPI from rubber seed can serve as alternative protein source in the diets of L. rohita fingerlings without any adverse effects on growth, nutrient utilization and physio-metabolic responses.

Alternative sources of fish oil (FO) are one of the major problems in aquaculture; therefore, the goal of the present study was to examine insect (black soldier fly larvae) oil (BSLO) as a potential replacer of fish/soy oil in juvenile rainbow trout (initial average weight of 32 ± 0.15 g) feed. Four diets were formulated wherein FO (control diet) was completely replaced with either soybean oil (SO) or BSLO, and an additional BSLO-based diet supplemented with 1.5% bile acid (BSLO + BA) were fed to the fish for 10 weeks. Growth performance of the BSLO fed group was similar ( P > 0.05) to that of the FO and SO fed groups, however, the fish fed BSLO + BA diet registered the lowest growth ( P < 0.05). Oil sources did not ( P > 0.05) affect the major nutrient content of whole-body, however, the fatty acid composition of the muscle and liver was influenced ( P < 0.05), with the highest 14:0, 16:0, and total saturated fatty acid detected in BSLO or BSLO + BA fed trout compared to the others ( P < 0.001). No significant differences were observed in eicosapentaenoic acid + docosahexaenoic acid (EPA + DHA) or total n-3 polyunsaturated fatty acid (PUFA) content in muscle among the groups, whereas, the highest EPA:DHA and n-3:n-6 ratios were detected in the FO group. Gene expression for fatty acid binding protein ( fabp ) , fatty acid synthase ( fas ), and Δ5 desaturase in the liver was lower in FO ( P < 0.05), while BSLO + BA registered the highest Δ6 expression ( P = 0.006). Supplementation of BA in the BSLO diet increased superoxide dismutase (SOD) and catalase (CAT) activities compared to the other groups ( P < 0.05). In conclusion, BSLO could serve as a substitute for FO and SO in rainbow trout diet without negatively impacting growth performance, whole-body composition and nutrient retention, and modulate the expression of fatty acid metabolism-related genes in rainbow trout.

A 60-day feeding trial was conducted to evaluate the haemato-biochemical, innate immune response, antioxidant capacity and histopathological changes in Labeo rohita fingerlings fed rubber protein isolates (RPI). One hundred and eighty fingerlings (average weight 4.45 ± 0.01 g) were distributed into five experimental groups in triplicate and fed with isonitrogenous and isocaloric diets. Soybean protein isolate (SPI) served as the reference diet (Control), and the treatment diets were formulated as RPI, RPI, RPI and RPI replacing 25, 50, 75 and 100% of SPI protein, respectively. The growth performance indices like final body weight (9.54-10.27 g), net weight gain (5.09-5.84 g), metabolic growth rate (4.54-5.02) and feed efficiency ratio (0.60-0.65) among the various groups were not significantly different (P > 0.05). All the haematological parameters, except red blood cells, showed no significant differences compared with the control group (P > 0.05). The immuno-biochemical parameters like albumin, globulin, total immunoglobulin, respiratory burst and lysozyme activities among the various groups did not differ significantly (P > 0.05). The stress enzyme such as superoxide dismutase (SOD), catalase (CAT) and oxidative stress marker malondialdehyde (MDA) showed no significant difference (P > 0.05). Histopathological examination of the liver revealed no marked changes. In summary, the results showed that RPI was well utilised by the fish and its inclusion did not generate any oxidative-induced stress, thus, RPI may be suggested as a potential replacement for SPI in fish diets without any detrimental effects. Hence, protein isolation offers a unique opportunity for the utilisation of rubber seed meal.

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A 60‐day feeding trial was conducted to evaluate the effects of feeding Houttuynia cordata leaf meal and extract on the growth performance, nutrient utilization and expression of insulin‐like growth factor‐I (IGF‐I) in Labeo rohita fingerlings. Two hundred seventy fingerlings were randomly distributed in six experimental groups in triplicates. Six isonitrogenous (350 g/kg CP) and isocaloric (17 MJ/kg DE) diets were prepared with graded levels of leaf meal (LM) and leaf extract (LE), namely C (control, without LE and LM), LE‐0.25 (2.5 g/kg LE), LE‐0.5 (5 g/kg LE), LE‐1.0 (10 g/kg LE), LM‐1.0 (10 g/kg LM) and LM‐2.0 (20 g/kg LM). Significantly (p < 0.05) higher IGF‐I expression, weight gain %, specific growth rate and lower feed conversion ratio were observed in LM‐1.0 followed by LE‐1.0 group compared to control group. Higher protease activity was observed in LE‐1.0 compared to other experimental groups, while no significant changes were found for amylase and lipase activities. Compared to control, muscle alanine aminotransferase and aspartate aminotransferase activities were significantly higher in treatment groups except for LM‐2.0. These results suggest that either LE‐1.0 or LM‐1.0 can be supplemented in the diet to improve the growth of L. rohita. However, the supplementation of 10 g H. cordata leaf meal/kg feed can be the better option considering the cost of extraction.

Jatropha kernel meal was detoxified through the process of solid‐state fermentation using Aspergillus niger fungus. A 60‐d feeding trial was conducted to evaluate the effects of replacing soybean meal (SBM) with fermented Jatropha kernel meal (FJKM) on the hemato‐biochemical and histopathological parameters in Labeo rohita fingerlings (average weight 6.05 ± 0.04 g). A total of 180 fish were randomly distributed in 12 experimental tanks in four dietary groups, namely control (SBM‐based diet), T1 (10% FJKM replacing 33.3% SBM), T2 (20% FJKM replacing 66.7% SBM), and T3 (30% FJKM replacing 100% SBM). There was no significant difference in the red blood cell, white blood cell, hemoglobin, total protein, albumin, globulin, and respiratory burst activity among the various groups, but significantly higher hematocrit value and albumin/globulin ratio were observed in the T2‐fed group compared with the control. No statistical difference was found in serum glucose level of the control and FJKM‐fed groups. Histopathological examination of the intestine and liver indicated no adverse effects in the control and FJKM‐fed groups. Our findings revealed that FJKM can replace 100% SBM protein in the diets of L. rohita fingerlings, without any adverse effects on fish health.