Maturity and spawning period of Thrissocles purava (Ham.) as determined by ova-diameter measurements

Abstract

The peak period of occurrence of Thrissocles purava (Ham.) in Bombay waters is in two seasons, namely February-April and August-October. The mature, spent and maturing fish are caught in inshore waters in these periods. The post-larval forms are also encountered in the plankton samples taken in these months. During the remaining months a few young, immature specimens are available in small numbers. The range of diameters of immature, maturing and mature ova is from 0.08 mm. to 0.44 mm.; 0.45 mm. to 0.76 mm. and 0.92 mm. to 1.26 mm. respectively. The mature ovaries of this species are found to contain only two groups of ova, namely mature and immature. The spawning season, as determined by the ova diameter measurements and the structure of the mature ovary, is found to be the same as the peak period of occurrence of this species in inshore waters. Relatively high percentages of mature and spent females during this period further supports the view that the species visits the Bombay shores mainly for spawning. The spawning period for individual fish is of a short duration and there is only one spawning a season. The minimum period required for the rematuration of the spent ovaries is about six months. The size at first maturity is found to be about 170 mm.