Quantitative analysis of the seasonality of male reproduction in the spinylobster Panulirus japonicus (Decapoda : Palinuridae)

The gonadosomatic index (GST), ratio of area of the lumen to that of the se miniferous tubules, and sperm density were analyzed against body size and s eason in male spiny lobsters,Panulirus japonicus. sampled off Oshima Island . Tokyo, Japan. For functionally mature individuals (greater than or equal to 54 mm carapace length), regressions of GSI and area of the lumen against body size were significant only before the spawning season. GSI showed no clear seasonal changes. Germinal cells at all stages of spermatogenesis wer e found in the testis, and sperm were present in the vas deferens throughou t the year. However, seasonal changes in the 3 reproductive indices indicat e that P. japonicus has a distinct seasonal pattern for spermatogenesis and storage of sperm. The ratio of the area of the lumen to that of the semini ferous tubules was highest before the spawning season. Sperm density during and 1 month after the spawning season (from June to September). however, w as significantly lower than in other months.