Comparison of condition indices and their seasonal variation in the freshwater clam,Egeria radiata(Lamarck) (Tellinacea: Donacidae), from the Cross River, Nigeria

摘要

Abstract.From February 1987 to September 1989, the monthly variations of eight indices of condition which are commonly used in bivalve aquaculture were determined forEgeria radiata(Lam. 1804) (Bivalvia: Tellinacea: Donacidae) from the Cross River, Nigeria. The indices were compared and their suitability for determining the spawning season ofEgeria radiatawas assessed. In general, a fall in condition index was observed during the rainy season (June‐October) and coincided exactly with minimum phytoplankton and pigment abundance. This decline in condition at the end of the wet season is as likely to be due to tissue depletion for maintenance under poor environmental condition as it is due to reproduction. The indices could be used as a quick and fast tool in assessing the spawning cycle of bivalves in the tropic