Profiles in growth, smoltification, immune function and swimming performance of 1-year-old masu salmon Oncorhynchus masou masou reared in water flow

Abstract

Effects of water flow on the growth, smoltification, immune function and swimming performance were studied in cultured 1-year-old masu salmon Oncorhynchus masou masou. The experimental fish were exposed to 2, 13 or 23cm/s flow for 11 months. Fish exposed to 13 and 23 cm/s flows had larger body size after 11 months and higher condition factor after 2 months than those exposed to 2 cm/s flow. Blood levels of growth hormone and insulin-like growth factor-I were unaffected by flow conditions. The higher flow delayed progress of smoltification, whereas there was no clear difference in blood levels of thyroxine between the three flow groups. Superoxide anion produced by leukocytes was the highest in fish receiving 23 cm/s flow, whereas no difference was detected in the plasma immunoglobulin M concentration between the three flow groups after 11 months. Increased flow resulted in higher swimming performance during the rearing period. Correlations between the relative swimming speed and the specific growth rate (SGR) were observed. The swimming speed with the maximum SGR was estimated to be 1.04-fold the fork length per second. These results indicate that water-flow conditions can affect growth and fitness of juvenile masu salmon, which are desirable for both release programs and aquaculture of this species.