LAUSR

Abstract American shad (Alosa sapidissima) is one of the most vulnerable and overreacting fish to disturbance. Any handling may cause serious lesion or death, and suspend gonad maturation and ovulation, eventually resulting in failure in hormone induced reproduction. In this study, we first reported a specially designed dual-drain recirculating aquaculture system (RAS), which leads to a successful integration of maturation and natural reproduction of anadromous American shad without any handling for hormone administration. The results illustrate the relationships among the change of seasonal temperature, gonadal maturation and spawning behavior of American shad in the freshwater environment. A total of 300 one-year-old fish were selected as brookstock (495.8 g for females and 441.1 g for males) with a sex ratio of 1:1. Fish grew, matured and naturally spawned in each of the RAS tank under two temperature manipulation regimes. The gonadosomatic indices increased significantly in two months before the start of spawning from 1.46% in females and 0.82% in males in January, to 5.19% in females and 2.73% in males in March. Fish at different temperature regimes started mating in early February and spawning in late March when the water temperature reached 19.3 °C. On average, females produced 65,930 eggs per kg body weight during the 2-month spawning period, resulting in 77.5% fertilization rate and 41.0% hatching rate. This study reports the first successful case of natural spawning on American shad in a specially designed RAS through temperature manipulation.