Past seawater experience enhances subsequent growth and seawater acclimability in a later life stage in rainbow trout Oncorhynchus mykiss

Abstract

In the present study, we attempted to investigate the effects of temporal seawater experience on subsequent growth and later seawater acclimability in rainbow trout. To elucidate seawater acclimability of small juveniles (3–4 g), fish were transferred to seawater diluted to 25 ppt (25-ppt seawater) and the change in blood osmolality was examined. All the juveniles survived transfer to 25-ppt seawater for 7 days with blood osmolality remaining within a physiological range, indicating successful acclimation to 25-ppt seawater. For the preparation of seawater-experienced fish, young adults of rainbow trout (about 40 g) were exposed to 25-ppt seawater for 7 days without feeding, transferred back to fresh water, and reared with feeding for another 76 days. The daily growth rate was higher in seawater-experienced fish (1.86%/day) than in control fish (1.66%/day). The seawater-experienced and control fishes were then transferred directly to full-strength seawater. The blood osmolality stayed within a normal range with a transient increase just after transfer in seawater-experienced fish, but kept increasing without a declining trend in control fish. Our findings showed that temporal seawater exposure in the past enhances subsequent growth and seawater acclimability in the later life stage in rainbow trout.