The reproductive cycle of the Tuatua-Paphies subtriangulata (Wood, 1828), in New Zealand

The reproductive cycle of the tuatua, Paphies subtriangulata (Wood, 1828), a shallow-water surf clam, was studied from January to November 1993 in Little Omaha Bay, north-eastern New Zealand. Monthly samples were obtained from a shallow sub-tidal population, and analyses by microscopic examination of histological section of gonad. Four gametogenic stages best described the annual reproductive cycle. Three distinct phases of the reproductive cycle were identified: spawning from February to April, regeneration of gonad from may to late August as resumption of spawning activity from September to November. Gonads routinely exhibited several stages simultaneously and showed a slow progression in the dominance of these stages. Observations of natural spawning events in the field were made on eight occasions and verified the spawning times deduced from histological sections. These observations indicated that only a small proportion of the population spawned at one time, that there were large variations in spawning activity on a daily basis, and that the co-occurring related species Paphies australis spawned synchronously with Paphies subtriangulata. A 1:1 sex ratio was determined for adult tuatua and no hermaphrodites were encountered.