Landmark-based geometric morphometric analysis of body shape variation within population of Ibis fish, Ambassis interrupta, collected from Masao River, Butuan City, Philippines

Abstract

Abstract-Masao River Butuan City, Mindanao, Philippines is home to many organisms especially those associated with the freshwater communities.Fishes were abundantly present including one of the commercially important fishes, the Ambassis interrupta, locally known as "ibis". This study describes the variation in body shapes of A. interrupta using landmark-based geometric morphometric analysis. A total of 100 fish samples, collected from Masao River, Butuan City were digitized using sixteen landmark points. This study also determines the variations in the patterns of fluctuating asymmetry (FA) in a total of sixteen bilateral traits of A .interrupta. FA can be a helpful tool in measuring stress because an organism's ability to cope with genetic and environmental stress during development is manifested through FA measures. The Procrustes ANOVA showed differences in the patterns of asymmetry between sexes of the fishes. Three factors were analyzed for FA and these were: individuals, sides, and interaction of individuals and sides. The individual symmetry among the fish samples showed no significant differences, while the sides and interaction of individuals and sides showed a highly significant difference (P<0.0001). This could be due to the presence of fish ponds, application of feeds and communities dwelling along Masao River which may affect the physical and chemical condition of the river. This may also affect the overall phenotype of the fish. The results implied asymmetry in the left and right side of each sample, also in the interaction of individuals and sides. However, the individuals were symmetrical with each other. Principal Component Analysis revealed that the five significant principal components (PC1-PC5) contribute most to the variation that exist among individuals. A total of 71.46% of the variation exist in the FA interaction in female fish and a total of 62.04% is observed in the FA interaction in male fish. The results however indicate that fluctuating asymmetry are higher compared to individual variation in females, but individual variation is higher compared to fluctuating asymmetry in males.