Effects of sperm to egg ratio, stocking density, delay of gamete contact, temperature and salinity on fertilisation success and D-larvae production of green mussel, Perna viridis

Mariculture of green mussel (Perna viridis) is being hindered by reliance on seed from the wild. Hatchery production helps increase seed stock, but little is known about the factors that may affect hatchery practices. Development of hatchery protocols to optimise production is therefore needed. This study determined factors affecting fertilisation and survival at the D-hinged stage namely: sperm to egg ratio; delay in gamete contact; egg stocking density; temperature; and salinity. Results indicated that maximum fertilisation and survival at the hinged stage was achieved at 50:1 sperm to egg ratio. Stocking density variation between 20 and 50 eggs mL(-1) had no significant effect on fertilisation, however, there was significantly higher survival from fertilised egg to the D-hinged stage at 20 eggs mL(-1) than at 50 eggs mL(-1) with non-significant reductions at 30-40 eggs mL(-1). Delay in gamete contact significantly affects fertilisation but not D-hinged survival. Fertilisation was significantly higher one hour after gamete liberation, but declined thereafter. Mussel eggs were successfully fertilised at varying temperatures from 25 degrees C to 35 degrees C, while a higher fertilisation rate was observed at a salinity of 28-31 ppt. For survival to the D-hinged stage, optimum temperature and salinity ranged from 28 degrees C to 30 degrees C and 28-31 ppt, respectively.