Relationship between Seawater Adaptability and Body Weight in 0+ Landlocked Rainbow Trout.

Abstract

A seawater challenge test was conducted on 0+ age-group landlocked rainbow trout Oncorhynchus mykiss to estimate the sufficient size for seawater culture. The seawater adaptability of fish of different body weights (averages respectively 50, 100, 150, and 200g) was assessed accoring to mortality, muscle moisture content, gill Na+-K+ATPase activity, and serum Na concentration, at intervals of 0, 6, 12, 24, 48, and 96h after direct transfer into seawater (31.6‰). A high mortality occurred among fish in the 50g weight class. Muscle moisture content in the 200g weight class showed less change than in other classes. The serum Na concentration in the 50 and 100g weight classes was higher than in the 150 and 200g weight classes after seawater transfer. These results indicate that the seawater adaptability of fish is size dependent, and that fish over 150g may acquire complete seawater adaptability. Therefore, fish over 150g are of sufficient size to develop in seawater culture and these fish can be transferred directly into seawater without any acclimation.