عنوان مقاله [English]
Anodonta cygnea (linea, 1876)is one of the most important benthic invertebrate of streams, ponds and wetlands of Pasikhan river catchment area. This study was conducted on 89 specimens of A. cygnea from 3 streams of pasikhan river watershed during July to September 2004 in order to study growth and age structure. The population comprised four age groups. The 3+ age group was dominant in the studied population. The lowest and greatest values for the length, width, height, total weight, wet soft tissue weight, dry soft tissue weight and shell weight of A. cygnea were 53.5-115.5mm, 15.6-46.2mm, 27.2-59.1mm, 11.23-127.02g, 8.74-71.73g, 0.47-5g, 2.49-36.73g, respectively, and their values increased with age. The frequency of two length classes 83-93 and 93-103mm were the highest. Instantaneous growth rates increased with age. The mean value of condition factor was 8.99±2.57 which increased to 3+age group and then decreased in 4+ age group. Shell weight was 27.15±9.7% total weight and its value increased with age. Shell dimensions were a suitable criteria for the biomass A. cygnea when applied to total weight and wet soft tissue weight (r2 values of 89-96 percent), but not to dry soft tissue weight (r2 values of 59-60 percent). The slope (b) (3.0923±0.089) of the shell length-total weight regression indicated isometric growth. A highly significant linear regression of height and width over length and of height over width as well as a highly significant nonlinear regression between shell length and mussel age were found.