Morphological Changes in Corbicula fluminea (Muller 1774) Shells from Laguna de Bay, Philippines Due to Elevated Nitrate and Hexavalent Chromium

Developmental instability using fluctuating asymmetry is a tool for morphological assessment to reflect the state of species adaptation and individual fitness. This research focused on the conchological analysis of Corbicula fluminea (Muller, 1774) shells relative to key water parameters in Laguna de Bay, Philippines. Results from the western and eastern regions of the lake, characterized by marked differences in water qualities, indicate that linear shell characteristics are not significantly affected by water quality, in contrast to other geometric parameters. Geometric morphometrics of Malahanobis and Procrustes distances exhibit horizontal elongation in shells from the west, and vertical elongation in those from the east. Generalized linear mixed modelling of shell morphometry with water quality revealed an inverse relationship between NO3- and shell size, and a direct association between shell shape changes and elevated Cr (VI). The combination of NO3-, water pH and total suspended solids were the factors identified to have the most effect on shell size, with Cr (VI), NH4+, and water pressure playing significant roles in affecting shape. Results of this work demonstrate the utility of C. fluminea’s fluctuating asymmetry as influenced by water quality to constitute important baselines for the management of a lake and its biological resources.