Condition Index (CI) was used to estimate the reproductive biology cycle of the hard clam Meretrix lyrata based on dry
body weight and shell weight. High CI value was observed due to the increase in the body weight of the hard clam that
corresponding to the maturity stage and early spawning. The CI value of M. lyrata from Buntal Village, Kuching, Sarawak
showed three highest peaks during the 12-month study on May and October 2013 and March 2014. The lowest CI values
were obtained in September and November 2013 and April 2014. Ammonia nitrogen was the only water parameter that
significantly correlated to the CI values. The CI application is important to estimate the maturity of hard clam gonad
to facilitate conservation activity through the hard clam harvesting out of the gonad maturation and spawning period.
Samples of Pinna bicolor Gmelin and Pinna deltodes Menke were collected from the seagrass bed of Sungai Pulai, covering Merambong shoal, Tanjung Adang shoal and Merambong Island off south western coast of Johor, Malaysia for morphological study from August 2005 to June 2006. It was observed that P. deltodes is associated with hard substratum and P. bicolor is associated with soft substratum in the study area. Physically there was no difference between P. bicolor and P. deltodes. The species were identified on the basis of nine internal and external characteristics of the valves. The two species were found to be morphologically different on the basis of width of sulcus, distance between posterior adductor muscle to posterior dorsal nacreous layer, dorsal posterior margin length and shell width.