Abstract
Underyearling fall chinook salmon (Oncorhynchus tshawytscha) were reared at two temperatures (9 and 15°C) and three photoperiods simulating winter (WIN), spring-summer (SS), and natural (NAT) conditions. The two artificial photoperiods were adjusted according to fish size so that an equinoctial photoperiod was synchronized with a hypothesized optimum size range for smolting (8-14 cm fork length). Fish exposed to a winter (WIN) photoperiod had the slowest growth rate. Fish under the SS photoperiod at both temperatures and under the WIN photoperiod at 9°C displayed hypoosmoregulatory capability near the equinoctial daylength. Thyroxine concentrations in fish reared under a natural photoperiod remained at basal levels during the period of early saltwater adaptiveness and throughout the remainder of the experiment. Thyroxine titers showed significant increases under all experimental photoperiod-temperature combinations near the equinoctial daylength with the exception of the 15°C/SS treatment.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 185-192 |
| Number of pages | 8 |
| Journal | Aquaculture |
| Volume | 46 |
| Issue number | 3 |
| DOIs | |
| State | Published - Jun 1 1985 |
Bibliographical note
Funding Information:Sea Grant Research contribution No. 129 and University of Minnesota Agricultural Experiment Station Scientific Journal Series No. 14200. This work is the result of research sponsored by the Minnesota Sea Grant Program, supported by the NOAA Office of Sea Grant, Department of Commerce, under Grant No. NA80AA-D-00114. The U.S. Government is authorized to reproduce and distribute reprints for government purposes, notwithstanding any copyright notation that may appear hereon. We are indebted to Walton Dickhoff for conducting thyroxine radioimmunoassays, W. Craig Clarke for critical review of the manuscript, and Todd Harvey for assistancei n the laboratory.