Proceedings of the Third World Fisheries Congress: Feeding the World with Fish in the Next Millenium—The Balance between Production and Environment
Effects of the Rearing System Water Current on Growth and Swimming Ability of Masu Salmon Oncorhynchus masou masou
Teruo Azuma, S. Noda, T. Yada, T. Nakanishi, M. Ototake, H. Nagoya, S. Moriyama, H. Yamada, M. Iwata
The catch of domestic stocks of masu salmon Oncorhynchus masou masou, an important species in Japanese fisheries, has declined to very low levels (e.g., from 3,967 mt in 1984 to 1,800 mt in 1997; FAO 1999), despite efforts such as marine ranching programs. Demand for the culture and release of this species is high. Because improvement of growth and fitness are expected to assist or enhance the survival rates of fish for culture or release, manipulation of the water current during the rearing period is expected to bring advantages to the fish production. However, the effects of water current on the growth and fitness of masu salmon are unknown.
In this paper, we report on the effects of a water current introduced into the rearing system on biological characteristics such as growth, life-stage differentiation, endocrinological changes, maturation, biodefense power, and swimming ability, all of which are strongly related to survival and body condition.
Nine hundred 1-year-old (1+) and seven hundred fifty 2-year-old (2+) masu salmon were used in the present study. They were of the same strain, which had been successionally bred and kept in the National Research Institute of Aquaculture, Nikko Branch. Fish were fed to satiation twice a day, 5 d/week, and maintained in outdoor ponds with a running water system before starting the experiments. Three hundred 1+ individuals and two hundred fifty 2+ individuals were selected randomly from the ponds and introduced separately into three circular tanks (2 t; 1,250 mm in diameter; 1,640 mm high) set to an average water velocity of 2, 13, or 23 cm/s, with a supply of fresh spring water at a rate of 60 L/s. The different water velocities were created by differing the direction of inlet flow, introduced just below the water surface. The flow was directed straight down for minimum velocity, horizontally from the outer edge without a pump for medium velocity, and horizontally from the outer edge with a pump for maximum velocity. Flow rates were determined at nine points spread equally from the periphery to the center and from the top to the bottom of the tank using a flowmeter (UC-3, Tamaya Corp.), and average speed was calculated for each tank.