Effects of fertilization and incubation factors on the quality and yield of scallop, Pecten fumatus reeve, larvae

Variable quality and yield (percentage development from eggs) D-veligers of the scallop. Pecten fumatus Reeve, prompted assessment of fertilization and incubation protocols. Various sperm to egg ratios were tested on eggs suspended in sea water at different densities. Ratios of 1000:1 led to the highest D-veliger yield when eggs were incubated in suspension at one per millilitre. With increasing egg densities, the addition of 1000 sperm per egg led to increasing average numbers of sperm visible at the periphery of each egg, indicating that fewer sperm were necessary for fertilization at higher egg densities. The time period and temperature over which released gametes were stored before fertilization were also found to significantly affect D- veliger yield. Decreasing gamete storage temperature from 26 to 14°C increased D-veliger yield, as did a reduction in the gamete storage period from 6 to 1 h. The incubation of embryos at densities in the 5-50 ml^-1 range did not affect D-veliger yield. A significant increase in total bacterial counts in the culture water occurred with increasing embryo stocking densities. However, presumptive Vibrionaceae counts did not increase significantly with increasing embryo stocking densities. In a comparison of the viability of self- and cross-fertilized embryos and larvae, fewer self- fertilized embryos developed to D-veliger stage; however, percentage survival, although highly variable, did not differ significantly in subsequent larval rearing. Cross-fertilized larvae had attained a significantly larger size by day 7.