Plasma levels of insulin and liver glycogen contents in one- and two-year old Atlantic salmon (Salmo salar L.) during the period of parr-smolt transformation |
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| Authors: | Ian Mayer Bertil Borg Erika M Plisetskaya |
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| Institution: | (1) Department of Zoology, University of Stockholm, S-106 91 Stockholm, Sweden;(2) School of Fisheries, HF-15, University of Washington, Seattle, WA, 98195, U.S.A.;(3) Department of Zoology, University of Stockholm, S-106 91 Stockholm, Sweden |
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| Abstract: | Plasma levels of insulin were measured by specific radioimmunoassay in 1-year and 2-year old Atlantic salmon (Salmo salar) parr during the period of parr-smolt transformation. The two-year old fish were of two different categories; silvering pre-smolts
and previously mature male parr. If insulin plays an important role in parr-smolt transformation and/or subsequent osmoregulatory
changes it was expected that the pre-smolts would show a different insulin profile compared to the mature male parr and one-year
old parr, both of which show impaired hypoosmoregulatory ability compared to smolts. Measurements were taken during two separate
years. Between January and April both categories of two-year old fish had generally higher plasma levels of insulin compared
to the non-smolting one-year old parr. In the pre-smolts insulin levels ranged from 4.0 to 7.9 ng ml−1, and from 7.8 to 16.7 ng ml−1 in 1990 and 1992 respectively, while in the previously mature males the same respective values were from 4.3 to 10.0 ng ml−1, and from 6.6 to 24.1 ng ml−1. In the two-year old fish, whether pre-smolts or mature males, plasma insulin levels peaked between 1–2 months before final
smoltification, after which insulin titers declined sharply. In 1990, the 1-year old parr showed a dual peak in plasma insulin.
Insulin first peaked in February (7.8 ng ml−1), and then again in April–May (7.7 ng ml−1), while in 1992 the 1-year old parr showed a number of smaller transient peaks (5–7 ng ml−1) between March–May, followed by sharp elevation of insulin levels in June. Liver glycogen contents were at their highest
(3.5–5.0 g 100 g−1 I liver wet weight) in March in both 1-year and 2-year old fish. Glycogen levels were low during the later stages of parr-smolt
transformation, before rising again in June in both the 1-year old and precociously mature parr, but not in the smolts. |
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| Keywords: | insulin glycogen Atlantic salmon smoltification |
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