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Previous work has demonstrated several bene¢ts of dietary prebiotics for ¢sh. Here, we report the e¡ects of added dietary fructooligosaccharide (FOS), mannanoligosaccharide (MOS), transgalactooligosaccharide (TOS) and GroBiotic s -A (GBA) on the weight gain, feed e⁄ciency and non-speci¢c immunity of juvenile red drum fed soybean meal (SBM)-based diets, in brackish water at 25 AE 1 1C. Test diets incorporated FOS, MOS, TOS or GBA at 10 g kg À 1 in place of cellulose in a basal diet with 40% crude protein, half from SBM and half from ¢shmeal. After a 4-week feeding period, experimental ¢sh were challenged by exposure to Amyloodinium ocellatum, after which growth and survival were monitored for 2 more weeks. Feed e⁄ciency, serum lysozyme and intracellular superoxide anion production were signi¢cantly (Po0.05) enhanced by prebiotic supplementation. Likewise, survival after A. ocellatum exposure was signi¢cantly higher for ¢sh fed GBA, MOS and TOS (87%, 84% and 78%) versus 58% for ¢sh fed either the FOS or the basal diet. Taken together, these results indicate that inclusion of several prebiotics at 10 g kg À 1 of the diet is adequate to improve the feed e⁄ciency of red drum as well as to enhance disease protection.

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The effects of elevated dietary arginine on the hematology and immune function of juvenile channel catfish Ictalurus punctatus were evaluated by means of in vivo and in vitro experiments. Healthy juvenile channel catfish (average weight, 34.8 g) were fed casein-gelatin-based diets containing 28% crude protein and supplemented with crystalline L-arginine (ARG) at 0.5, 1, 2, or 4% of diet. An intact-protein diet containing 1.3% arginine also was included to investigate the effects of amino acid form (crystalline-free amino acids versus intact protein). Each purified diet was fed to apparent satiation to triplicate groups of fish for 6 weeks. At the end of the experimental feeding period, the fish were injected intraperitoneally with two doses (3 d apart) of 2 mg lipopolysaccharide/kg body weight. Six days after the initial injection, the fish were anesthetized and tissue samples were obtained to evaluate hematological and humoral and cellular immune parameters, including phagocytic activity of peritoneal macrophages, hemoglobin, hematocrit, mean corpuscular volume (MCV), blood cell counts, plasma protein, and hepatic superoxide dismutase activity. High dietary levels (4% ARG) resulted in significantly higher levels of hemoglobin, hematocrit, and circulating erythrocytes. Dietary ARG did not significantly affect MCV and the number of circulating leukocytes, lymphocytes, eosinophils, and monocytes. In vitro, a moderate level (2 mM) of ARG in the culture media was found to be ideal in significantly enhancing phagocytosis. This study demonstrates that some aspects of the immune system of channel catfish are sensitive to changes in dietary ARG.