Allometry and condition index in the freshwater bivalve Parreysia corrugata (Muller) from river Kempuhole, India

Allometry and condition index of freshwater bivalve Parreysia corrugata (Muller) inhabiting the river Kempuhole, tributary of river Nethravathi, in the Western Ghats were examined from April 2005 to May 2006. The length-breadth and length-width relationships for the entire study period were L = 2.314 + 0.585B and L = 1.907 + 0.333W respectively. The b values of length-breadth and length-width relationships varied from 0.5518 (March 2006) to 0.6519 (August 2005) and 0.2986 (July 2005) to 0.3735 (August 2005) respectively. The relationships between length-total weight, length-wet weight, length-shell weight and length-dry weight were W = 0.0003428L^2.777 , W = 0.00004197L^2.885 , W = 0.0001738L^2.802 and W = 0.00001127L^2.832 respectively. The monthly equilibrium constant values of length-total weight relationship ranged from 2.606 (July 2005) to 2.945 (August 2005), where as for length-shell weight relationship, the values ranged from 2.691 (May 2006) to 3.1 (August 2005). The best values fluctuated between 2.781 (June 2005) and 3.58 (July 2005) for length-wet weight, while the values for length-dry weight fluctuated between 2.665 (April 2006) and 3.668 (October 2005). The monthly values of equilibrium constant indicated the relative growth in body weight of P. corrugata. The values of condition indices showed significant fluctuations. The highest condition index (15.1) was recorded during April 2005 where as the lowest (4.4) was in January 2006. The data indicated that the condition of mussel was fairly good from April to August 2005. The best time for commercial exploitation appears to be during this period. The condition index showed decreasing trend from September onwards and reached the lowest value during January. Thereafter, the condition gradually increased. Seasonal fluctuation of condition in P. corrugata was probably, related to reproductive activity. The ambient environmental variables and biological variables of P. corrugata revealed that a total of 5 component which accounted for 94.24% of total variance.