Numbers of parental fish and artificial spawning beds that result for maximum seed production for Lefua echigonia

Lefua echigonia is a freshwater fish traditionally found in satoyama (countryside worked by human activity) areas of Japan. Its numbers are declining, however, owing to a deterioration of its habitat environment. At the Kanagawa Prefecture Fisheries Research Institute, scientists have successfully developed seed production technology by inducing natural spawning, then raising larvae under circulating filtration. The present study was conducted to determine how many parental fishes and spawning bed should be used to maximize seed production. The study vial conducted using 36-litre glass tanks and 2-ton fiberglass reinforced polyester (FRP) tanks. In the glass tanks, I varied the number of parental fish released in each tank and induced natural spawning to determine the ideal number of parental fishes. Eggs were most numerous in test sections containing one male and one female. I also found that this species is a multiple spawner, the spawning season lasts two months, and a single female can spawn more than 1,500 eggs during spawning season. To determine how many parental fishes should be used to maximize seed production in 2 t FRP tanks, I placed 20, 40 and 60 fish (half males and half females) into different tanks, and induced natural spawning. The highest number of hatched larvae produced per parental fish, occurred in the tank with 40 fish. Next, I placed 40 fish (20 males and 20 females) into three FRP tanks containing different numbers of artificial spawning beds (2, 3 and 4). I varied the strains of parental fishes, testing three times in each case, and compared the number of hatched larvae. The highest number of larvae was obtained in the tank with 4 spawning beds. This tank also had the highest number of hatched larvae per spawning bed. These results show that the increasing the number of artificial spawning beds can increase the number of eggs spawned.