REPRODUCTIVE BIOLOGY OF INDIAN BACKWATER OYSTER (Crassostrea madrasensis) COLLECTED FROM THE SOUTH EAST COAST OF BANGLADESH

Abstract

Crassostrea madrasensis an oyster is a highly promising species for mariculture, exhibiting significant potential for cultivation due to its rapid growth rate. A thorough understanding of the reproductive biology of C. madrasensis is crucial for advancing oyster farming technology. The objective of this study was to examine the annual reproductive cycle with particular focus on the temporal changes in sex ratios, biometric relationships, and the condition index of C. madrasensis, collected from the Maheshkhali Channel, Cox's Bazar, over a 12-month period from April 2023 to May 2024. The analysis of allometric relationships between linear dimensions and weight variables revealed negative allometric growth, with b value less than 03. All morphometric relationships demonstrated a positive linear correlation, with a particularly strong positive correlation observed between the shell height and total weight (r = 0.8169), and the shell length and total weight (r = 0.6663). The sex ratio of males to females was determined to be 1:1.13 (P > 0.001), using the Chi-square (χ²) test. Additionally, 4.13% of the sampled oysters exhibited hermaphroditism. Gonadal histology exhibited five distinct stages and two reproductive cycles. While gametogenesis started from January to July, mature oysters were primarily observed from September to November and March to May. Two distinct spawning events were identified through histological analysis: one from November to December and another from April to June. The condition index (CI) fluctuated between 56.51 ± 25.64 and 108.29 ± 30.41, with the peak in May and December. A subsequent decline in CI was observed, aligning with histological evidence of spawning activity. Notably, the CI remained high in December, a month typically associated with spawning and post-spawning phases, indicating that CI values are influenced by factors beyond reproduction, such as water quality, food availability, and environmental conditions. In conclusion, this detailed study provides valuable insights into the morphological traits, reproductive patterns, and cycles of C. madrasensis, offering critical knowledge about its life cycle and optimal breeding periods for commercial aquaculture.