Evaluation of different dietary additives based on growth performance,innate immunity and disease resistance in juvenile Amur catfish,Silurus asotus

Three different dietary additives were evaluated based on growth performance, innate immune responses and disease resistance in juvenile Amur catfish Silurus asotus. Four diets were prepared by supplementing 0.4% Song-gang® stone (SG), 0.05% Yucca meal (YM), 0.05% β-glucan (BG) in combination with 0.04% SG and 0.05% BG (SG + BG) to a basal commercial diet (control; CONT). Triplicate groups of fish averaging 4.95 ± 0.05 g were fed one of the test diets between 3 and 5% body weight for 8 weeks. At the end of the feeding trial, weight gain, specific growth rate, feed efficiency and protein efficiency ratio of fish fed SG and SG + BG were significantly higher than those of fish fed the BG and CONT diets (P < 0.05). Lysozyme activity in fish fed the SG, YM, and SG + BG diets was significantly higher than those of fish fed the CONT diet. Super oxide dismutase (SOD) activity was significantly higher among fish fed the SG, YM, BG and SG + BG diets than fish fed the CONT diet. After 14 days challenge test with Edwardsiella tarda, cumulative survival rates of fish fed the SG and SG + BG diets were significantly higher than those of fish fed the BG and CONT diets. Results revealed that dietary SG or SG + BG diets had positive responses over other additives in juvenile Amur catfish. However, Song-gang® stone is proposed to be a cheaper dietary additive contributing 0.04 cents/kg of feed based on economic point of view.     

Evaluation of dietary natural mineral materials as an antibiotic replacer on growth performance,non‐specific immune responses and disease resistance in rainbow trout,Oncorhynchus mykiss

We evaluated the effects of some dietary natural mineral materials as an antibiotic replacer based on growth performance, non‐specific immune responses and disease resistance in juvenile and subadult rainbow trout, Oncorhynchus mykiss. First experiment, juvenile rainbow trout averaging 2.7 ± 0.02 g (mean ± SD) were fed one of the six experimental diets; a basal commercial diet as a control (CON), CON with oxytetracycline (OTC), with yellow loess (YL), with Macsumsuk^® (MS), with Song‐Gang^® stone (SG) and with barley stone (BS) at 0.4% of each diet. At the end of 8‐week feeding trial, weight gain (WG), specific growth rate (SGR), feed efficiency (FE) and protein efficiency ratio (PER) of fish fed YL diet were significantly higher than those of fish fed CON diet. Non‐specific immune responses such as superoxide dismutase (SOD), myeloperoxidase (MPO), lysozyme (LYS) activity and oxidative radical production of fish fed YL diet were higher than those of fish fed CON diet. At the end of 15 days of challenge test with Aeromonas salmonicida, average cumulative survival rate of fish fed YL diet was significantly higher than that of fish fed BS and CON diets. However, there were no significant differences among fish fed YL, SG and OTC diets. Second experiment, subadult rainbow trout averaging 261.5 ± 3.5 g (mean ± SD) were fed one of the four experimental diets for 22 weeks: CON, and CON with OTC, YL or SG at 0.4% of each diet. At the end of feeding, growth performance of fish fed SG and YL diets was significantly higher than that of fish fed CON diet. Non‐specific immune responses in terms of SOD, MPO, LYS and NBT of fish fed SG and YL diets were significantly higher than those of fish fed CON diet. However, there were no significant differences among the fish fed YL, SG and OTC diets. The results indicate that dietary yellow loess or Song‐gang^® stone at 0.4% of diet could replace oxytetracycline in juvenile and subadult rainbow trout.     

Dietary choline requirement of juvenile olive flounder (Paralichthys olivaceus)

An eight‐week study was conducted to determine the optimum dietary choline level in juvenile olive flounder, Paralichthys olivaceus. Seven diets were prepared to contain 0, 250, 500, 750, 1,000, 2,000 and 3,000 mg/kg diet. Juveniles (5.9 ± 0.03 g; 5.5 ± 0.4 cm; mean ± SD) were randomly distributed into 21 tanks (25 fish/tank) and fed one of the diets in triplicates. Survival rate of fish fed the diet containing the lowest choline level was significantly lower than those of fish fed the other diets (p < 0.05). Final body weight, weight gain, specific growth rate, feed efficiency and protein efficiency ratio significantly increased with increasing choline levels up to 1,000 mg/kg diet. Whole‐body protein and lipid contents increased in accordance with choline levels up to 750 mg/kg diet, beyond which they plateaued. Liver and muscle lipid contents elevated with increasing choline levels up to 2,000 mg/kg diet. Plasma cholesterol esters, triglycerides, cholesterol and total lipids were significantly influenced by the graded choline levels; however, responses of those indices were not identical. Broken‐line analyses of weight gain and liver choline concentrations responding to the graded choline levels revealed that choline requirements of the juvenile flounder could be between 847 and 1,047 mg/kg diet.     

Optimum dietary protein‐to‐energy ratio for juvenile whiteleg shrimp,Litopenaeus vannamei,reared in a biofloc system

An 8‐week feeding trial was conducted to evaluate the optimum dietary protein‐to‐energy (P/E) ratio in juvenile whiteleg shrimp, Litopenaeus vannamei. Six diets were formulated with two protein levels (30% and 35%) and three digestible energy levels (16, 17.5 and 19 kJ/g diet) at each protein level (₃₀P₁₆, ₃₀P_17.5, ₃₀P₁₉, ₃₅P₁₆, ₃₅P_17.5 and ₃₅P₁₉). Fifty shrimp averaging 0.97 ± 0.03g (Mean ± SD) were randomly distributed in biofloc tanks and fed one of the experimental diets. Weight gain (WG), specific growth rate (SGR) and feed efficiency (FE) of shrimp fed the ₃₅P_17.5 diet were significantly higher than those of shrimp fed ₃₀P₁₆, ₃₀P_17.5 and ₃₀P₁₉ diets (p < .05). Results for non‐specific immune responses showed that diet ₃₅P_17.5 caused higher lysozyme activity in shrimp comparing to lower protein diets. Thiobarbituric acid reactive substances (TBARS) of plasma were lower for shrimp fed on diets consisting of higher protein and energy levels than shrimp fed on the ₃₀P₁₉ diet. Analyses of digestive enzyme activities showed higher trypsin activities for shrimp fed on ₃₅P_17.5 and ₃₅P₁₉ diets comparing to ₃₀P₁₆ and ₃₀P_17.5 diets. Also, hepatopancreatic lipase activity of shrimp fed ₃₅P₁₆, ₃₅P_17.5 and ₃₅P₁₉ diets were significantly higher than those of shrimp fed the other diets. In conclusion, based on the results for growth performance, biochemical parameters, immune responses, oxidative stress and enzyme activities, 35% protein and 17.5 kJ/g digestible energy (₃₅P_17.5) could be considered as the optimum protein‐to‐energy ratio in the diet of juvenile whiteleg shrimp reared in a biofloc system.     

Fishing performance of environmentally friendly tubular pots made of biodegradable resin (PBS/PBAT) for catching the conger eel Conger myriaster

Lost or abandoned fishing gear made of synthetic fibers or plastics that do not decompose in the sea. These gear result in “ghost fishing”, that retain their function as fishing gear. To solve this problem, we developed fishing gear made of aliphatic polyester (PBS/PBAT), which is biodegraded by microorganisms after a certain period. The marine fishing performance of the biodegradable material of tubular pots for conger eel was compared with that of commercial pots in the southern coastal sea of Korea, where fishing gear loss rates are high. A comparative analysis of the elastic recovery of different types of funnel material was conducted. Two types of fishing gear were tested: (1) a pot with a body and funnel made of biodegradable materials and (2) a commercial pot made of recycled polyethylene (PE). Then, field experiments were conducted on the two pot types, which were arranged alternately. The funnel rips made of biodegradable material showed better elastic recovery than that of the commercial pot. Marine fishing performance of the biodegradable pots was similar to that of the commercial pots (Mann–Whitney test, p > 0.05). There was also no significant difference in the catch per unit effort (CPUE) by the Mann–Whitney test, p > 0.05. Thus, biodegradable materials represent an environmentally friendly alternative to recycled PE for fabricating tubular pots to catch conger eel.     

Evaluation of dietary soybean meal as fish meal replacer for juvenile whiteleg shrimp,Litopenaeus vannamei reared in biofloc system

Different levels of dietary soybean meal (SBM) as a fish meal (FM) replacer, with and without amino acid supplementation, for whiteleg shrimp, Litopenaeus vannamei reared in the biofloc system was examined in eight weeks of feeding trial. Eight experimental diets consisted of a basal diet with 0% FM replacement by SBM provided in clear sea water without biofloc system (S₀SW), four diets replacing FM at 0% (S₀), 33% (S₃₃), 67% (S₆₇) and 100% (S₁₀₀) by SBM, and three diets replacing FM at 33% (S₃₃A), 67% (S₆₇A) and 100% (S₁₀₀A) by SBM supplemented with amino acids (methionine and lysine) in the seawater biofloc system. Results of water quality analyses showed significantly lower total suspended solids and nitrate for S₀SW group than all other treatments. Diets S₀ and S₃₃A resulted in higher weight gain and specific growth rate among all groups, with no significant differences with S₃₃ group. In addition, whole-body protein and amino acid compositions of shrimp fed S₀SW were lower than most biofloc groups. Haemolymph parameters showed significant differences in total protein, cholesterol and triglyceride between groups S₀ and S₀SW. Also, superoxide dismutase activity showed a decreasing trend with increasing replacement level. In conclusion, based on these results, SBM could replace up to 33% of FM with or without amino acid supplementation in juvenile whiteleg shrimp diets reared in the biofloc system.

     

Effects of the Dietary Fermented Tuna By‐product Meal on Growth,Blood Parameters,Nonspecific Immune Response,and Disease Resistance in Juvenile Olive Flounder,Paralichthys olivaceus

This study evaluated the effects of dietary fermented tuna by‐product meal (FTBM) in juvenile olive flounder, Paralichthys olivaceus. Five diets were formulated to replace fishmeal (FM) with FTBM at 0% (FTBM₀), 12.5% (FTBM_12.5), 25.0% (FTBM₂₅), 37.5% (FTBM_37.5), or 50% (FTBM₅₀). After 8 wk, weight gain, specific growth rate, and feed efficiency of fish fed FTBM₀ and FTBM_12.5 diets were significantly higher than fish fed the other diets (P < 0.05). Also, mean cumulative survival rates (%) of fish fed the FTBM₀ and FTBM_12.5 diets were significantly higher than those fed FTBM₅₀ diet at Day 9 postchallenge with Edwardsiella tarda (P < 0.05). Protein efficiency ratio of fish fed FTBM₀ and FTBM_12.5 diets was significantly higher (P < 0.05) than fish fed diets FTBM_37.5 and FTBM₅₀. Broken‐line regression analysis of weight gain showed an optimal FM replacement level of 10.65% with FTBM. Therefore, the optimal dietary inclusion of FTBM in juvenile olive flounder diets could be greater than 10.65% but less than 12.5% without any adverse physiological effects on fish health.     

Effects of dietary Yucca meal on growth,haematology, non‐specific immune responses and disease resistance of juvenile Nile tilapia,Oreochromis niloticus (Linnaeus, 1758)

A 10‐week feeding trial was conducted to determine the effects of dietary yucca meal supplementation on growth, haematology, non‐specific immune responses and disease resistance in juvenile Nile tilapia, Oreochromis niloticus. Six isonitrogenous and isoenergetic experimental diets were formulated to contain 0% (YMS₀), 0.1% (YMS_0.1), 0.3% (YMS_0.3), 0.5% (YMS_0.5), 1% (YMS_1.0) and 2% (YMS_2.0) dietary yucca meal on the dry weight basis. Results of this study showed a higher growth performance for YMS_0.1 group with significant differences with YMS_0.5, YMS_1.0 and YMS_2.0 groups. In addition, whole‐body protein content of fish fed the YMS_0.1 diet was significantly higher as compared to YMS₀. Plasma lysozyme activity significantly increased in YMS_0.1 group comparing to YMS₀ and YMS_0.5 groups. Respiratory burst activity of phagocytic blood cells was significantly enhanced when fish were fed the YMS_0.1 diet. Results also showed that yucca meal supplementation had moderate effects on glutamic oxaloacetic transaminase and cholesterol levels. After the 14‐day challenge test with Aeromonas hydrophila, cumulative survival of fish fed YMS_0.1 diet was significantly higher than that of fish fed diet YMS₀, YMS_1.0 and YMS_2.0. These results suggest that the optimum dietary yucca meal inclusion level in the diet of juvenile Nile tilapia could be between 0.1% and 0.14% (23.9~33.4 mg kg^?1 saponin) as a feed additive to promote growth, enhance the non‐specific immune responses and increase disease resistance.     

Effects of two dietary probiotics (Bacillus subtilis or licheniformis) with two prebiotics (mannan or fructo oligosaccharide) in Japanese eel,Anguilla japonica

A 12‐week feeding trial was conducted to investigate the effects of two dietary probiotics; Bacillus subtilis KCTC 2217 or Bacillus licheniformis KCCM 11775 with two prebiotics; mannan oligosaccharide (MOS) or fructooligosaccharide (FOS) in Japanese eel. Fish averaging 12.8 ± 0.47 g (mean ± SD) were randomly distributed into five treatments with triplicate tanks. A basal control diet (CON) and four synbiotic diets supplementing B. subtilis + MOS (BSM), B. subtilis + FOS (BSF), B. licheniformis + MOS (BLM), and B. licheniformis + FOS (BLF). Weight gain and specific growth rate of fish fed all synbiotic diets were higher than those of fish fed CON. Immune‐related gene expression of heat shock protein 70 and immunoglobulin M of fish fed BSF and BLM were significantly higher than those of fish fed CON. Fish fed BSF and BLM had significantly higher intestinal villi length than those of fish fed BLF and CON (p < .05). Disease resistance against Aeromonas hydrophila of fish fed all synbiotic diets were significantly higher than those of fish fed CON (p < .05). Therefore, these results indicated that dietary B. subtilis with FOS (BSF) and B. licheniformis with MOS (BLM) could have beneficial effects on intestinal morphology, and immune‐related gene expression in Japanese eel.