Changes in serum hormones of rainbow trout(Oncorhynchus mykiss) during progressive seawater adaptationα

Changes in serum hormones of rainbow trout(Oncorhynchus mykiss) during progressive seawater adaptationα

A variety of hormones, including estradiol-17β, thyroxine(T₄), triiodothyronine (T₃) and prolactin have been found to modulate various aspects of osmoregulation, growth, development and metabolism of vertebrates. This study was taken to examine external, behavioral, and endocrine changes of female rainbow trout (Oncorhynchus mykiss) living in 0‰, 5‰, 10‰, and 15‰ salt concentrations, respectively. All fishes survived at 5 ‰, and 10‰, whereas some fishes died at 15‰ up to 8 weeks during the seawater challenge test. When fish were adapted from 0‰ to 10‰, feed intake of fish started from the fifth day. When fish were progressively adapted from 0‰ to 5‰, 10‰ and IS%', external body color of fish changed from rainbow to light-grey color. At the same time, thyroxine and triiodothyronine concentrations significantly (P<0.05) increased, and then were at the highest level in 15‰ salinity. The levels of triiodothyronine significantly changed in all salinities and its level was at the highest peak in 15‰, salinity. Changes in serum prolactin levels correlated with changes in triiodothyronine in 10‰ (+0.923). The levels of serum hormones such as estradiol-17β, triiodothyronine and prolactin were significantly higher in seawater-adapted group than those in freshwater group. These results showed the levels of progressively increased hormones in rainbow trout adapted in seawater. Especially triiodothyronine and prolactin seemed to be attributed to the seawater adaptation of rainbow trout. The serum estradiol-17β did not closely correlate with the sexual maturation of rainbow trout adapted in seawater.