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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.

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Two trials were conducted to determine the e⁄cacy of ¢sh fed live yeast Debaryomyces hansenii strain CBS 8339 on immune and antioxidant systems in leopard grouper Mycteroperca rosacea infected with Aeromonas hydrophila. Juveniles (12 AE 0.5 g) were fed with a control diet or a D. hansenii-supplemented diet (10 6 colony-forming units per gram) for 5 weeks. The live weight of ¢sh was registered on a weekly basis. After 4 weeks, ¢sh from each treatment were immunocompromised with pathogenic A. hydrophila and further fed for1week in order to evaluate the e¡ect on immunological and antioxidant parameters. Generally, the results showed enhanced growth performance in ¢sh fed the diet containing yeast compared with the control. Addition of live yeast had no signi¢cant e¡ect on the immunological parameters after 4 weeks of feeding. However, post infection with A. hydrophila ¢sh fed the yeast-supplemented diet resulted in a sig-ni¢cant increase in the levels of plasmatic immunoglobulin M. Superoxide dismutase and catalase (CAT) activities were signi¢cantly higher in the yeast group. In this ¢sh, CAT and heat shock protein 70 genes were up-regulated before and after infection of A. hydrophila. The present study is the ¢rst one reporting that yeast (D. hansenii) can enhance immunity and resistance against A. hydrophila.

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