Some aspects of the reproductive biology of Spratelloides gracilis (Schlegel) in the Ysabel Passage, Papua New Guinea

Abstract

Fecundity, length at first spawning, spawning seasonality and ovarian development of Spratelloides gracilis were determined by examining preserved ovaries from fish captured over a 5‐year period. Fecundity (F) was estimated from the number of eggs in the most advanced ovarian mode and was related to fish length (L) by the function: logeF=3.764 logeL‐7.308, and to weight (W) by: logeW= 1.210 logeW+7.337. Spawning was observed in most months of the year without any recognizable pattern between the years. Ova diameter frequencies were bimodal but the smaller mode remained stationary regardless of the position of the larger mode. This was interpreted as evidence that individual fish may spawn only once. From data on egg length versus fish length and gonad index versus fish length it was estimated that fish were first capable of spawning at 45 mm (fork length).