Survival of salmonids in seawater and the time-frame of growth hormone action |
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| Authors: | Nathan L Collie Jonathan P Bolton Hiroshi Kawauchi Tetsuya Hirano |
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| Institution: | (1) Laboratory of Physiology, Ocean Research Institute, University of Tokyo, Nakano, Tokyo 164, Japan;(2) Department of Physiology, University of California at Los Angeles, School of Medicine, Los Angeles, CA, 90024, U.S.A.;(3) Laboratory of Molecular Endocrinology, School of Fisheries Sciences, Kitasato University, Sanriku, Iwate 022-01, Japan;(4) Laboratory of Physiology, Ocean Research Institute, University of Tokyo, Nakano, Tokyo 164, Japan |
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| Abstract: | In salmonids, growth hormone (GH) effectively promotes adaptation of freshwater (FW) fish to seawater (SW), but it has been
unclear whether GH has osmoregulatory actions apart from those consequent to an increase in body size. Our objectives were
first, to examine the minimum time and dose required for GH to enhance SW adaptation; and second, to optimize the conditions
for the acute GH response in developing a convenient GH bioassay based on its plasma ion lowering effect. Trout showed markedly
improved SW survival when transferred from fresh water 6, 24, or 48h after a single chum salmon GH injection (0.25 μg/g).
Preadapting trout to 1/3 SW enhanced the plasma ion lowering effect of ovine GH (oGH) injected 48h before transfer of the
fish to 80% SW. Endogenous plasma GH levels were elevated in control trout switched from low salinities to 80% SW but were
depressed in oGH-injected fish after transfer. Under optimal test conditions (1/3 SW preadaptation, 48h pre-transfer injection,
and 100% SW final challenge), the reduction in plasma Na+, Ca++, and Mg++ levels of oGH-injected fish was dose-dependent. The oGH doses giving minimum and maximum responses were 50 and 200 ng/g,
respectively. In short, GH exerts acute osmoregulatory actions that promote SW adaptation in the absence of changes in body
size. Compared with growth GH bioassays, the osmoregulatory assay is superior in economy of time, animal costs, and hormone
quantity required and potentially in specificity. |
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| Keywords: | growth hormone seawater adaptation rainbow trout osmoregulation plasma ions GH bioassay |
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