| Abstract: | Penaeus japonicus Bate is absent on the Italian coasts, but it is considered a very promising species for national aquaculture. To develop the shrimp-culture on a commercial basis, a convenient method for producing eggs and larvae of Penaeus japonicus was studied. A stock of 156 females, age class 1+ and F3, underwent unilateral eyestalk ablation and they were stocked with males in three plastic tanks (bottom area 14 m2) at a density of 25 individuals/m2 and a sex ratio of 1:1. Conditions of environment and management consisted of: temperature 21±3°C; natural light and photoperiod; total exchange of sea water every day; feeding on mussels. A month after eyestalk ablation the females were inspected every 7–10 days; mature females were transferred to the spawning tanks. Females with well developed gonads averaged 25.0% of the population of females at every inspection; 51.3% of spawners were impregnated with spermatophores; others were inseminated artificially by the method of introducing spermatophores into the thelycum. In six inspections (carried out during a period of 89 days), 3,028,525 eggs were released; a female released 17,500 eggs on the average (maximum was 123,000 eggs, minimum 4,340). The mean rate of fertilized eggs was 52.7%—67.7% from naturally inseminated females and 7.5% from the artificially inseminated ones. The mean hatching rate was 30.9%—40.1% from natural insemination and 3.3% from artificial insemination. Total amount of viable nauplii was 820,550. |
