Intra-specific morphological plasticity in three <i>Puntius</i> species in Sri Lanka

Phenotype of an organism is a result of interaction of genotype and environment. Individuals of a same species living in variety of habitats may subject to different environmental conditions. As a result, they may adapt to local conditions in those habitats which include the changes in morphology from the common phenotype. Different morphologies in individuals of same genotype is called phenotypic plasticity. This is considered as an important event in evolutionary ecology because these individuals are the first to subject to natural selection. Present study focused on phenotypic plasticity in three freshwater fish species namely Puntius dorsalis, P. vitatus and P. bimaculatus. Fish were sampled from different locations in four different altitude ranges of five major rivers of Sri Lanka. Twenty three length measurements and fifteen meristic characters were recorded from each individual and fourteen physicochemical parameters of each location were also measured. Relationship between altitude range and the species morphology was analysed by discriminant analysis and hierachical cluster analysis. Correlation of physicochemical parameters with the altitude range was also studied. Results showed that individuals living in different altitude ranges in different rivers and also in the same river were morphologically different. Results indicated that length characters which determine the shape of the individual mainly con- tribute to the discrimination of individuals according to their respective altitude range. Ratios of maximum body width to standard length, pre ventral length to post ventral length and fork length to standard length in P. dorsalis, P. vitatus and P. bimaculatus respectively were the main discrimination characters that grouped the individuals according to the respective altitudes. Variations in length characters were found to be adaptations to their habitat. Most physicochemical parameters were significantly correlated (negatively or positively) according to the altitude ranges where three species were collected. Phenotypic plasticity in the three Puntius species inhabiting different altitudes may have resulted as an adaptation to these variable physicochemical parameters.