Reproductive Biology of Metapenaeus dobsoni (Miers, 1878) from the Western Coastal Waters of Sri Lanka

摘要

The reproductive biology of Metapenaeus dobsoni (Miers, 1878) from the western coastal waters of Sri Lanka has been studied during the period September 1998 to December 1999. The ratios of males to females in monthly catches from lagoon and offshore areas were found to be significantly different in certain months. There is a significant deviation of sex ratio from unity for the size range studied except for the smaller and larger length groups. Sizes at 50% maturity for males and females were estimated as 6.36 and 7.31 cm (total length) respectively. The estimated values for reproductive load were 0.55 and 0.54 for males and females respectively M. dobsoni spawns in the west coast of Sri Lanka throughout the year with peaks in March, September October and November. An offshore migration of females for spawning was also evident. The estimated Type-I fecundity (total number of eggs that have been initially separated from the ovary in the reproductive stage I) of M. dobsoni varied between 178,098 to 404,564 eggs for the size range 7.91 to 11.15 cm. The estimated Type-II fecundity (totai number of eggs, which are ready to be shed in the reproductive stage IV) varied between 91,652 to 225,679 eggs for the size range 6.96 to 11.72 cm. The estimated probability of an egg developing into recruit varied from 3.3 X 10~(-4) to 8.1 X 10~(-4).