Growth and reproductive activities in a bivalve anadara antiquata (linnaeus 1758) on the Dar es Salaam coast

Growth and the reproductive biology of Anadara antiquata (Linnaeus 175$) have been studied by allometry, examination of the size frequencies of random samples, macroscopic observations of the visceratmass, microscopic observations of gonadal smears and by detailed histological sections of the gonads. Examination of the overall size frequency distribution revealed a bimodal distribution with modes at 32.5 mm and 42.5 mm. The length of one-year-old Anadara antiquata is estimated to be 24.4 mm. Strong correlation coefficient (P<0.001) exists between shell length and whole live weight, also between shell weight and wet meat weight. A non-linear relationship has been established between shell length and whole live weight. Shell weight has been shown to increase linearly with increasing wet meat weight. Regression equations describing the studied growth parameters have been worked out. Meat yield has been shown to increase with increasing size. Cockles in the size class 31-40 mm had the highest Condition Index (CI). However, above 40 mm, the CI decreased with increase in size. Studies on seasonal changes in CI revealed the occurrance of two peaks, one in October and the other in January. The possible attributes for the observed CI peaks are discussed. Anadara antiquata has been shown to have a prolonged spawning period with two spawning peaks, one which occurred in October-November and the other in April. Cockles reach maturity at 26-28 mm of shell length for males and 31-33 mm for females. The ratio of males to females in the adult population was 1:1.13. The possible occurrance of sex change during the life span of this bivalve species is discussed. The harvesting of cockles less than 45 mm of shell length is to be discouraged because it might reduce the reproductive capacity of the species.