An 11-wk feeding trial was conducted to evaluate three different protein hydrolysates as feed ingredients in high-plant-protein diets for juvenile olive flounder. Five experimental diets were fed to juvenile olive flounder to examine the effect of three different protein hydrolysates on growth performance, innate immunity, and disease resistance against bacterial infection. A basal fishmeal (FM)-based diet was regarded as a high-FM diet (HFM) and a diet containing soy protein concentrate (SPC) as a substitute for 50% FM protein was considered as a low-FM diet (LFM). Three other diets contained three different sources of protein hydrolysates, including shrimp, tilapia, and krill hydrolysates (designated as SH, TH, and KH), replacing 12% of FM protein. All diets were formulated to be isonitrogenous and isocaloric. Triplicate groups of fish (15.1 ± 0.1 g) were handfed one of the diets to apparent satiation twice daily for 11 wk and subsequently challenged against Edwardsiella tarda. Growth performance and feed utilization of fish fed hydrolysate-supplemented diets were significantly improved compared to those of fish fed the LFM diet. Dietary inclusion of the protein hydrolysates significantly enhanced apparent digestibility of dry matter and protein of the diets. In the proximal intestine, histological alterations were observed in the fish fed the LFM diet. The fish fed the hydrolysate diets showed significantly longer mucosal fold and enterocytes and greater number of goblet cells compared to fish fed the LFM diet. Respiratory burst activity was significantly higher in fish fed the TH and KH diets than fish fed the LFM diet. Significantly higher immunoglobulin levels were found in fish fed SH and KH diets compared to those of fish fed the LFM diet. Dietary inclusion of the protein hydrolysates in SPC-based diets exhibited the highest lysozyme activity. Significantly higher superoxide activity was observed in groups of fish fed the KH diet. Fish offered the protein hydrolysates were more resistant to bacterial infection caused by E. tarda. The results of this study suggest that the tested protein hydrolysates can be used as potential dietary supplements to improve growth performance and health status of juvenile olive flounder when they were fed a LFM diet. KEYWORDSEdwardsiella tarda, growth performance, intestinal morphology, olive flounder, protein hydrolysate, soy protein concentrate 1 Correspondence to: kjlee@jejunu.ac.kr

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Black soldier fly (Hermetia illucens) larvae (BSFL) are rich in protein and have the potential to be used in animal feed. The aim of the present study was to determine the immunoprophylactic effect of BSFL against Salmonella Gallinarum in broiler chicks as an alternative feed additive. Results showed that BSFL improved body weight gain and increased frequency of CD4+ T lymphocyte, serum lysozyme activity, and spleen lymphocyte proliferation. Moreover, BSFL reinforced bacterial clearance and increased survivability of broiler chicks against S. Gallinarum. These data suggested that BSFL has prophylactic properties with stimulating non-specific immune responses, as well as reduced bacterial burden against S. Gallinarum.

This study was aimed at examining the essentiality and requirement of inositol for Olive £ounder, Paralichthys olivaceus. Six casein^gelatin-based semi-puri¢ed diets were formulated to contain ¢ve di¡erent levels of myo-inositol (MI) (designated as M0, M01, M200, M400, M800 and M1600 for 0, 01antibiotic, 200, 400, 800 and 1600 mg kg À 1 respectively). After 20 weeks of a long-term feeding trial, ¢sh (initial body weight, 10 g) fed the M800 diet showed signi¢-cantly increased growth performances and survival. Liver lipid concentration tended to decrease as the dietary MI increased, although there was no signi¢-cant di¡erence among all treatments. Polyunsaturated fatty acid in the liver of the ¢sh fed the diets containing high levels (M1600) of MI was signi¢cantly increased. Hepatic inositol concentration of the ¢sh was signi¢cantly increased by dietary MI supplementation. The intestinal biosynthesis of inositol by micro£ora seemed to be insu⁄cient to prevent growth retardation in juvenile Olive £ounder. The optimum level of dietary MI for juvenile Olive £ounder was found to be 617 mg kg À 1 based on weight gain in a brokenline regression model. This ¢nding indicates that MI supplementation is required at a concentration of at least 617 mg kg À 1 to maximize the growth performances and to prevent abnormal lipid metabolism.