The reproductive biology of pipi, Paphies australis (Gmelin, 1790) (Bivalvia: Mesodesmatidae). I. Temporal patterns of the reproductive cycle

The reproductive cycle of the New Zealand pipi (Paphies australis) was investigated over two years (May 1991 to April 1993) in a small harbour, in northeastern New Zealand. Samples of pipi gonads were processed using standard histological techniques, and the resultant sections placed into five developmental categories (early active, late active, mature, partially spawned and indeterminate). Gametogenesis was similar in bith years, beginning in autumn with most pipi in early active stages of development. By late winter many pipi were mature. Spawning commenced in early spring and continued through spring and summer. From a sample of 104 pipi collected in spring 1992 for investigation into the length at sexual maturity, all pipi were found to be sexually mature above 40mm shell length, but some individuals between 30-40 mm also had gonads with sex cells present. This sample had a sex ratio significantly biased towards females. Further analysis revealed that juveniles (below 40mm shell length) had a significantly higher proportion of females than males, but adults (above 40mm shell length) had a sex ratio of approximately 1:1. no evidence of hermaphroditism was observed.