Reproductive biology of the saucer scallop Amusium japonicum balloti (Bernardi) in central Queensland waters

Abstract

Gonad development, spawning periodicity, relationships between shell height and gonad development, and fecundity were examined in two populations of A. japonicum balloti over periods of 12 months. In both populations animals possessing mature gonads were most abundant in winter months and spawning was completed by November. All gonads examined microscopically were gonochoristic with the exception of a single functional hermaphrodite. Most animals examined attained sexual maturity at a shell height of 90 mm or larger, but animals less than 70 mm were found to have developing gonads. Oocyte numbers varied with gonad weight, and a range of 3 .20 × 105-2. 65 x 106 mature oocytes were estimatedfor scallops having shell heights between 85 and 107 mm. Comparison of gonad development using macroscopic gonad indices and histological examinations indicates that the macroscopic gonad index used in this study was restricted in accuracy, particularly in describing the earlier stages of sexual development.