CORRELATION BETWEEN THE EDIBLE FRESHWATER BIVALVES AND SOME ECOLOGICAL FACTORS AT SELECTED SITES OF CAGAYAN RIVER

The edible freshwater bivalves identified in Cagayan River were: Batissa childreni, Corbicula manilensis and Psammotaea virescens. Corbicula manilensis was the most abundant species collected. High density and bigger sized bivalves were collected in the months of May, which was the peak season. A high density of Batissa childreni was noted as the temperature of water was low. Total hardness and organic content significantly influenced the density of Corbicula manilensis and Psammotaea virescens. Lesser density of Corbicula manilensis resulted as the total hardness decreased while high density of Psammotaea virescens was noted as the organic content of the substrate increased. Relative abundance was greatly affected by the total water hardness. A positive correlation existed between relative abundance of Corbicula manilensis and total hardness. Shell sized of Corbicula manilensiswas bigger as the total hardness increased and bigger sized Psammotaea virescens was noted as the organic content of the substrate increased. No predictor variables were significantly correlated with relative abundance of Psammotaea virescensand the shell sized of Batissachildreni.