Temporal Variation in Shell Growth Rate of CockleAnadara granosain Relation with its Reproductive Cycle

Abstract

A study was conducted on the relationship between the reproductive cycle and shell growth rate of Anadara granosa (Linnaeus, 1758). Gonadal maturity stages, increment width, and environmental factors were examined by means of a field enclosure experiment in Balik Pulau, Penang Island, Malaysia, from December 2011 to November 2012. Histological analysis of gonads showed that gametogenic activity of A. granosa occurred throughout the year, with maximum spawning activity observed from April 2012 to late June 2012 (15%–28%) in males and from March 2012 to late June 2012 (19%–44%) in females. Shell cross-section analysis showed that the increment widths of both sexes in the growing group (indeterminate and developing stages) and the spawning group (ripe and spawning stages) ranged from 35–57 to 8–17 µm, respectively. Seawater temperature and salinity recorded on a daily basis throughout the study period ranged from 22–33°C and 29–31, respectively. A comparison of increment width and gonad development stages in different environmental conditions showed that shell growth in the growing group decreased when seawater temperature and salinity decreased slightly. In contrast, increment widths in the spawning group were much narrower and were influenced by energy consumption during ripe and spawning stages. This study shows spawning breaks in shell structure are considered markers for identifying the period of sexual maturity. Therefore, spawning breaks are suitable proxies for interpretation of the temporal changes in shell microgrowth lines in terms of reproductive cycle of cockle and understanding the number of spawning periods throughout the year.