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An 8-week feeding trial was conducted to evaluate the effects of dietary probiotics on growth, nonspecific immune responses and disease resistance in juvenile rainbow trout, Oncorhynchus mykiss. Fish averaging 5.8 AE 0.8 g (mean AE SD) were fed one of the five experimental diets; one control (Cont), and four other diets were prepared by supplementing single probiotics 1 (Bacillus subtilis; SP 1 , 0.5%), single probiotics 2 (Bacillus licheniformis; SP 2 , 0.5%), multi-probiotics (B. subtilis + B. licheniformis; MP, 0.5%) and oxytetracycline (OTC) at 5 g OTC kg À1 diet. After 8 weeks of the feeding trial, weight gain and specific growth rate of fish fed SP 1 , SP 2 and OTC diets were significantly higher than those of fish fed Cont diet (P < 0.05). Superoxide dismutase (SOD) and lysozyme activities of fish fed SP 1 , SP 2 and MP diets were significantly higher than those of fish fed Cont diet (P < 0.05). There were no significant differences in SOD and lysozyme activities among fish fed SP 1 , SP 2 , MP and OTC diets. In challenge test with Aeromonas salmonicida for 15 days, fish fed SP 1 , SP 2 and MP diets showed significantly higher cumulative survival rate than those of fish fed Cont diet (P < 0.05). However, there were no significant differences in cumulative survival rate among fish fed SP 1 , SP 2 , MP and OTC diets. Although there was a little advantage in fish fed MP diet in terms of non-specific immune responses, single or multi-probiotics are equally effective statistically. These results indicate that single or multi-probiotics had equal beneficial effects as an antibiotic replacer on growth performance, non-specific immune responses and disease resistance in juvenile rainbow trout.

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 AE 0.02 g (mean AE 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 â (MS), with Song-Gang â 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 AE 3.5 g (mean AE 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 â stone at 0.4% of diet could replace oxytetracycline in juvenile and subadult rainbow trout.

A 12‐wk feeding trial was conducted to evaluate the effects of the dietary fishmeal analogue (FMA) adding 2% shrimp soluble extract (SSE) on growing rainbow trout, Oncorhynchus mykiss. Fish averaging 146 ± 3.8 g (mean ± SD) were randomly distributed into 500‐L aquaria as groups of 20 fish per tank. Fish were fed the experimental diets in triplicate groups to apparent satiation twice a day on a dry matter basis. Each group was fed one of the four experimental diets: control (FM100% + FMA0%), FMA0 (FM100% + FMA0% + SSE2%), FMA12 (FM88% + FMA12% + SSE2%), and FMA24 (FM76% + FMA24% + SSE2%). After the feeding trial, weight gain and specific growth rate of fish fed the FMA0 and FMA12 diets were significantly higher than those of fish fed the FMA24 diet (P < 0.05). Feed efficiency and protein efficiency ratio values of fish fed the control, FMA0, and FMA12 diets were significantly higher than those of fish fed the FMA24 diet (P < 0.05). The values of superoxide dismutase activity showed significantly higher amounts for the FMA0, FMA12, and FMA24 groups than the control group (P < 0.05). Lysozyme activity in the FMA12 group was significantly higher than in the control group (P < 0.05). Therefore, according to our results, FMA with additive SSE can be used up to 12% as a substitute of fishmeal for growing rainbow trout.