Stimulation of non-specific immune functions in seawater-acclimated rainbow trout, Oncorhynchus mykiss, with reference to the role of growth hormone

The influence of acclimation to seawater (SW) and growth hormone (GK) admin istration on immune functions was examined in the rainbow trout (Oncorhynch us mykiss). After 3 days acclimation to dilute SW (12 parts per thousand, p pt), an increase in plasma lysozyme activity was observed compared to the f ish kept in fresh water (FW). No change was seen in plasma immunoglobulin M (IgM) levels. When they were transferred from dilute SW to full-strength S W (29 ppt) after a single intra-peritoneal injection of ovine or salmon GH, plasma sodium levels of GH-treated fish were significantly lower than thos e of the control fish injected with Ringer's solution 24h after the transfe r. The plasma level of IgM was not influenced by GH injection in the fish k ept in FW nor in those transferred to SW. The administration of GH increase d plasma lysozyme activity in the fish in FW, but no further increase was s een after SW transfer. The production of superoxide anions in peripheral bl ood leucocytes was stimulated by GH in both FW and SW. These results sugges t that GH is involved in the stimulation of the non-specific immune functio ns in SW-acclimated salmonids. (C) 2001 Elsevier Science Inc. All rights re served.