Geometric Morphometric Analysis of Body Shape Variation in Glossogobius giuris from Lake Mainit, Agusan del Norte, Philippines

Most fish exhibit remarkable morphological diversity, which is often influenced by genetic variation and ecological pressures. Consequently, these are the outcomes of organisms' responses to their environment. Meanwhile, modern morphometrics can quantify shape variation within species of the same group. This study aims to determine the body shape variation of Glossogobius giuris from Lake Mainit, Agusan Del Norte, Philippines. 60 adult, uniform-sized fish samples were collected and subjected to standardized laboratory procedures. Further, the samples were digitized for 16 homologous landmark points and loaded into Symmetry Asymmetry Geometric Data (SAGE) Software. Across the tested factors—individuals, sides, and individual x sides—result shows that shape variations among individuals were highly significant (F = 2.1045, p < 0.0001), along with among males (F = 3.2711, p < 0.0001). Females exhibited higher Fluctuating Asymmetry (FA) (F = 18.99, p < 0.0001) compared to males (F = 7.0964, p < 0.0001). It suggests morphological shape differences across the sexes, and the shape variation observed could be a response to environmental perturbations. Shape variations were associated with swimming, food hunting, and predator defense. Moreover, Principal Component Analysis (PCA) demonstrates higher scores of FA in females (81.96%) than in males (74.76%). It was noticed that females had a high fluctuating asymmetry. It might be due to various physiological and ecological pressures compared to males. The observed levels of directional and fluctuating asymmetry in males and females, respectively, may indicate sex-linked morphological and developmental processes, which are important to consider in ecological or evolutionary contexts. Thus, utilizing geometric morphometrics can depict subtle differences across the same populations.