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Channel catfish was used to investigate the enhancement of vaccine efficacy following dietary supplementation with arginine (ARG, 4% of diet), glutamine (GLN, 2% of diet), or a combination of both. After vaccination against Edwardsiella ictaluri, humoral and cellular immune responses, along with lymphoid organ responses were evaluated. E. ictaluri-specific antibody titers in plasma were higher (P < 0.05) in fish fed the supplemented diets compared to those fed the basal diet as early as 7 d post-vaccination (dpv). B-cell proportion in head-kidney was higher (P < 0.05) at 14 dpv in vaccinated fish fed the GLN diet. The responsiveness of spleen and head-kidney lymphocytes against E. ictaluri was enhanced (P < 0.05) by dietary supplementation of ARG or GLN at 14 dpv. Additionally, at 7 dpv, vaccinated fish fed the GLN diet had higher (P < 0.05) head kidney weights relative to the other dietary treatments, and vaccinated fish fed ARG-supplemented diets had higher (P < 0.05) protein content in this tissue. Results from this study suggest that dietary supplementation of ARG and GLN may improve specific cellular and humoral mechanisms, enhancing the acquired immunity in vaccinated channel catfish., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Specific components of both the innate and adaptive immune systems of channel catfish were evaluated after supplementation of culture media with arginine (ARG) and/or glutamine (GLN). Primary cell cultures of head-kidney macrophages (MØ) were used for phagocytic and bactericidal assays against Edwardsiella ictaluri. Additionally, proliferation assays were conducted with naïve peripheral blood lymphocytes (PBL) exposed to non-specific mitogens. To indirectly assess amino acid utilization of both MØ and PBL, amino acid levels, with emphasis on ARG and GLN, were evaluated in the basal medium before and after activation or mitogenic exposure. After bactericidal and proliferation assays, the sum of the media free amino acid pool significantly (P < 0.05) decreased 23% and 45%, respectively. Glutamine levels in medium decreased by 38% and ARG by 18% during the bactericidal assay. Also, decreases of 52 and 46% from initial values were found after the proliferation assay for GLN and ARG, respectively. Macrophage phagocytosis and killing ability was significantly (P < 0.05) enhanced by ARG supplementation to culture media regardless of GLN supplementation. Proliferation of naïve T- and B-lymphocytes upon mitogenic exposure was significantly (P < 0.05) enhanced by supplementing ARG and GLN to the media, but limited synergistic effects were observed. These results suggest that in vitro, ARG and GLN are important substrates and immunomodulators of both innate and adaptive responses in fish leukocytes, and further highlights the potential use of ARG and GLN as immunonutrients in aquafeeds., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Abstract: The present experiment was conducted to investigate the effects of graded amounts of dietary GLN on the intestinal morphology, plasma amino acids and growth performance of juvenile channel catfish. Six experimental diets (280gkg−1 crude protein, 80gkg−1 lipid) were composed of casein, gelatin and crystalline amino acids and supplemented with 0, 5, 10, 15, 20 or 30g free glutamine kg−1. These diets were fed to triplicate groups of fish (average initial weight of 6.1) for 10weeks after which blood and intestinal samples were collected. Intestinal microstructures were positively affected by dietary GLN at the highest levels of supplementation (20 and 30gkg−1), significantly (P <0.05) increasing enterocyte and microvilli height in anterior, mid and posterior intestinal sections. Moreover, a subsequent experiment revealed that GLN supplementation significantly (P <0.05) increased the enterocyte migration rate in all sampled intestinal segments. In contrast, immunohistochemical staining of proliferating cells with mouse anti-proliferating cell nuclear antigen (PCNA), revealed an increased number of proliferating cells only at the distal intestine. Plasma amino acid levels 15h postprandial showed significantly (P <0.05) higher levels of asparagine, serine, glycine and threonine in fish fed the diet supplemented with 20g GLN kg−1 diet. Despite the consistent trend of higher values seen in fish fed the diet supplemented with 20g GLN kg−1, there were no significant (P >0.05) differences in growth-related parameters among treatments. The present results demonstrate an efficient utilization of free GLN by intestinal mucosal cells of channel catfish, which resulted in enhancement of the enteric microstructure along with increased migration rates of enterocytes and modified plasma amino acid profiles. However, these results were not translated into improved growth at the end of the 10-week feeding trial. [Copyright &y& Elsevier]

Abstract: Both arginine and glutamine play important roles in tissue repair, cell replication and collagen synthesis which impact animal growth and survival. Thus, a 7-week feeding trial was conducted to determine the effects of dietary arginine and glutamine on growth performance, innate immune responses and intestinal structure of juvenile red drum, Sciaenops ocellatus (6.9±0.04g, initial average weight). Protein in all experimental diets was derived from menhaden fishmeal and dehulled, solvent-extracted soybean meal to provide isonitrogenous (44% crude protein) and isolipidic (10%) diets. The basal diet contained 0.14% glutamine and 1.72% arginine on a dry-matter basis, which exceeds the established dietary requirement of red drum. Experimental diets were prepared by supplementing the basal diet with either arginine at 1% of dry weight, glutamine at 1%, glutamine at 2%, or both arginine and glutamine at 1%, with adjustments in glycine to maintain equal nitrogen among all diets. Feed efficiency was significantly (P <0.05) improved by supplementation of glutamine at 2% and the combination of both arginine and glutamine at 1% of diet. Neutrophil oxidative radical production in fish fed the glutamine and/or arginine-supplemented diets was significantly (P =0.03) higher compared with that of fish fed the basal diet, with a synergistic effect observed in fish fed the combined arginine–glutamine diet. Significantly (P <0.05) higher serum lysozyme activity also was observed in fish fed the diet supplemented with 1% of both arginine and glutamine. Extracellular superoxide anion production by red drum macrophages was significantly (P <0.05) higher for fish fed diets with glutamine at either 1 or 2% and the 1% arginine–glutamine combination compared to fish fed the basal diet. Similarly, macrophages from fish fed the diet with glutamine at 2% and the arginine–glutamine combination at 1% produced significantly higher amounts of intracellular superoxide anion. Morphometric analyses – i.e., measurements of enterocyte, microvillus and fold heights – demonstrated positive effects of both dietary glutamine and arginine in different portions (proximal, mid and distal) of the gastrointestinal tract of red drum. In general, fish fed the diet supplemented with 2% glutamine had the greatest increases in magnitude of the chosen structures, although those fed the diet with arginine at 1% also yielded improved scores for some enteric portions. Therefore, results from the present study establish the importance of both dietary arginine and glutamine supplementation in improving feed efficiency, as well as eliciting positive changes to several components of the innate immune system and intestinal functionality of red drum. [Copyright &y& Elsevier]

Abstract: Various studies with fish species indicate that dietary arginine (Arg) and glutamine (Gln) supplementation may support an enhanced performance beyond simply improving weight gain. Therefore, a feeding trial was conducted to determine the effects of dietary Arg or Gln on growth performance, immune responses and intestinal morphology of juvenile hybrid striped bass, Morone chrysops × Morone saxatilis (4.1±0.02g, initial average weight). The basal diet was formulated from menhaden fishmeal and solvent-extracted soybean meal to contain 45% crude protein and 10% lipid. Arginine and Gln were singularly added to the basal diet at either 1% or 2% or both amino acids were added in combination at 1% to formulate experimental diets with adjustments in glycine to maintain all diets iso-nitrogenous. Fish were fed the experimental diets for a period of 8weeks, at the end of which final weight, specific growth rate and feed efficiency were significantly (P <0.05) higher in fish fed diets supplemented with Arg at either 1 or 2%, Gln at 1%, Arg and Gln both at 1%, but not in those fed the diet supplemented with Gln at 2%. Arginine and/or Gln supplementation tended to improve neutrophil oxidative radical production, but not significantly (P >0.05). However, significantly higher serum lysozyme activity was observed in fish fed the diet supplemented with Arg at either 1 or 2% and Gln at 1%. Intracellular superoxide anion production by hybrid striped bass macrophages also tended to increase, while extracellular superoxide anion production was significantly improved by supplementation of Arg at 1% and Gln at either 1 or 2% of diet. Morphometric analyses demonstrated positive effects of both dietary Arg and Gln on histo-morphological measurements in different portions of the gastrointestinal tract of hybrid striped bass. The 1% Arg diet resulted in the greatest increases in size of the chosen enteric structures, but the other four experimental diets also significantly improved the scores for various intestinal portions compared to fish fed the basal diet. Results from the present experiment demonstrate the importance of dietary supplementation of both Arg and Gln in improving growth performance, eliciting positive changes to several components of the innate immune system, and also benefiting the intestinal functionality of hybrid striped bass. [Copyright &y& Elsevier]