The present study examined the efficacy of dietary selenium-enriched spirulina (SeE-SP) on growth performance, antioxidant response, liver and intestinal health, immunity and disease resistance of Asian seabass, Lates calcarifer. A total of 480 seabass juveniles with an initial weight of 9.22 ± 0.09 g/fish were randomly assigned to four dietary groups. The fish were fed a fishmeal protein replacement diets with SeE-SP at 5%, 10%, and 20%, namely SeE-SP5, SeE-SP10, and SeE-SP20, and a fishmeal-based diet as control for 8 weeks. The results indicated that seabass juveniles fed SeE-SP5 and SeE-SP10 diets grew at the same rate as the fish fed a fishmeal-based control diet after 8 weeks of feeding, while SeE-SP20 grew at a significantly lower rate than the control (p < 0.05). Although most of the measured biochemical parameters were not influenced by the Se-SP diets, serum antioxidant-enzyme glutathione peroxidase (GPx) and immunological indices, such as lysozyme activity and immunoglobulin-M, were found significantly higher in the SeE-SP5 and SeE-SP10 diets compared to control. In addition, the fish fed the SeE-SP5 diet showed significantly lower mortalities after the 14-day of bacterial challenge with V. harveyi. These outcomes indicated that up to 10% inclusion of SeE-SP in the diet of juvenile Asian seabass does not compromise growth, while SeE-SP5 enhanced disease resistance in juvenile seabass.

The effects of tuna viscera hydrolysate (TVH) on juvenile pompano Trachinotus blochii, growth performance, nutritional response, intestinal and liver health, and resistance to Streptococcus iniae were investigated in this study. Five isonitrogenous and isocaloric diets (protein 46.0%, lipid 10.0%) were formulated in which TVH was added to replace fishmeal protein at levels of 0 (control), 30, 60, 90, and 120 g kg^-1, labelled as TVH0, TVH05, TVH10, TVH15, and TVH20, respectively. Triplicate groups of pompano were fed the respective diets for ten weeks. The results showed that fish fed diets containing TVH10 produced significantly higher final body weight and specific growth rate in comparison to the fishmeal control ( ). Dietary TVH did not produce any effect on feed utilisation, somatic indices, and proximate composition of juvenile pompano ( ). While most amino acids were unchanged by the dietary inclusion of TVH, phenylalanine and valine levels were significantly lower in the fish fed TVH20 diet compared to the control. Fish fed the TVH20 diet had significantly lowered total serum protein compared to the TVH10 treatment, whereas other biochemical parameters in the blood did not show any difference among treatments. The intestinal histology indicated a significant increase in goblet cell numbers in fish fed TVH10 diet. Fish fed diet supplemented with TVH showed the highest disease resistance against Streptococcus iniae after 14 days of challenge. Based on a quadratic regression between final body weight and dietary TVH levels, the optimum TVH was calculated to be 10% or 60.0 g kg^-1 for maximum growth performance when fed to pompano.

A six-treatment study in a 3 × 2 factorial design was conducted to investigate whether dietary supplementation of shrimp hydrolysate (SH) improves the efficacy of meat and bone meal (MBM) replacing fishmeal protein in juvenile giant trevally Caranx ignobilis. A fishmeal-based diet (MBM0) was used as a control; two low fishmeal diets were prepared by replacing 25% (MBM25) and 50% (MBM50) of fishmeal protein with MBM; and another three treatments by supplementing MBM0, MBM25, and MBM50 with 45-g/kg SH supplementation (MBM0SH, MBM25SH, MBM50SH) were produced. The results showed that fish fed MBM25 and MBM50 caused lower growth and feed utilization than MBM0, whereas no differences were observed among fish fed MBM25SH, MBM50SH, and MBM0. Increasing dietary MBM levels resulted in decreased lipids in fish muscles and increased ash contents, while SH supplementation improved the muscle lipid levels. Substituting fishmeal with MBM increased monounsaturated fatty acids (MUFA) and decreased polyunsaturated fatty acids (PUFA), n-3 polyunsaturated fatty acid (n-3 PUFA), n-3 highly unsaturated fatty acids (n-3 HUFA), and n-3/n-6 HUFA, whereas SH supplementation enhanced n-3 PUFA, n-3 HUFA, and n-3/n-6 HUFA. The goblet cell density in the intestine increased in fish fed diets supplemented with SH. The study suggested that dietary supplementation of 45-g/kg SH increased the efficacy of substituting MBM protein for 50% of fishmeal protein without compromising the growth of juvenile giant trevally.

The dietary selenium (Se) requirement has been determined for cobia Rachycentron canadum using purified diet; however, its role in the utilisation of plant-derived ingredients has not been evaluated in the species. Therefore, a 3 x 2 factorial experimental design involving three inclusion levels (0, 210 and 315 g/kg) of lupin Lupinus angustifolius kernel meal (LKM) and two concentrations (0 and 0.8 mg/kg) of Se was used to evaluate the effects of Se supplementation in conjunction with LKM on the growth, feed utilisation and physiological responses in the cobia. Six isonitrogenous (46.5 % crude protein) and isoenergetic (21 MJ/kg gross energy) diets were formulated and fed to cobia for 7 weeks in a flow-through seawater system. The results showed significant effects of Se supplementation and its interaction with dietary lupin on the growth and feed efficiency of cobia. Se supplementation significantly improved the growth and feed utilisation efficiency in cobia fed lupin-based diets. The nutrient digestibility of fish fed supplemental Se lupin-based diets was significantly higher than that of fish fed diets without Se supplementation at each inclusion level of LKM. There were no significant effects of dietary Se supplementation on the survival, muscle composition or muscle amino acids, whereas regression analysis indicated a positive linear relationship between tissue Se accumulation and dietary Se levels. An enhancement of haematological responses was also observed in cobia fed Se-supplemented diets. In summary, cobia fed lupin-based diets required higher dietary Se supplementation for higher feed utilisation efficiency than previously quantified for the casein-based diet.

The application of fish protein hydrolysates (FPHs) in aquaculture has achieved encouraging outcomes due to its growth and health promoting properties. This trial was carried out to detemine the effects of various alcalase‐derived fish protein hydrolysate (FPH) supplementation on growth, feed utilization, proximate composition, liver and gut histology of juvenile giant trevally fed low fishmeal diets. Four tested diets (52% protein and 10% lipid) were produced, in which fishmeal and poultry meal (PM) were the main protein sources in the basal diet. 50 g/kg of each shrimp hydrolysate (SH), squid hydrolysate (SHH), and tuna hydrolysates (THs) were supplemented into the basal diet, namely SH, SHH, and TH, respectively. Fish were fed experimental diets in 56 days with four replicates per dietary group. The results reported that giant trevally fed SH, SHH and TH achieved higher growth than those fed the control. Feed intake (FI) didn’t alter, but lower feed conversion ratio (FCR) was seen in fish fed SH compared to the control, demonstrating that SH improved feed utilization. Protein and ash contents were increased in fish fed SH, SHH, and TH supplemented diets, whereas increased whole‐body lipid was obtained in those fed TH. Dietary SH, SHH, and TH supplementations contributed to higher whole‐body isoleucine, and higher lysine was seen in fish fed SH and TH. Total intestinal aerobic microbiota increased in fish fed SH, whereas Vibrio spp . density was relatively low among treatments. The goblet cells also increased in the intestine of the fish fed SH, indicating that SH could enhance intestinal health. The results indicated that all fish hydrolysates had beneficial effects of growth performance of juvenile giant trevally, in which SH showed more bioavailable than others, by improving feed efficiency and intestinal health.