Changes in plasma somatostatin associated with seawater adaptation and stunting of coho salmon, Oncorhynchus kisutch

Somatostatins (SSs) are a family of peptide hormones made up of different m olecular forms that have been found to modulate various aspects of growth, development, and metabolism of vertebrates. In this study, coho salmon (Onc orhynchus kisutch) were used to evaluate the role of SSs in seawater (SW) a daptation. In experiment 1, pre-smelt and smelt coho salmon (age = 1-1.5 ye ars) were transferred to SW and sampled at zero, one, two, and seven days l ater. For both pre-smelts and smelts, plasma SS-25 concentrations rose foll owing SW exposure and reached peak levels two days after transfer; thereaft er, levels gradually declined. Interestingly, SS-25 levels were higher in p re-smelts lan those in smelts, a difference that was similar to that noted for rectal [Na+] and indicating a greater state of SW readiness for the sme lt group. In experiment 2, pre-smelt coho salmon were transferred to SW and sampled eight weeks later. Pre-smelt SW exposure resulted in significant g rowth retardation (stunting). Plasma levels of both SS-25 and SS-14 were si gnificantly higher in stunts than those in their normal (SW smelt) counterp arts. These results indicate that changes in SSs accompany SW adaptation an d that SSs may be involved with stunting associated with premature SW trans fer. (C) 1998 Elsevier Science B.V. All rights reserved.