Morphometric Characterization of Oreochromis Species Habitating in Jipe Lake, Kenya

Abstract

Lake Jipe, a shared resource at the Kenya-Tanzania border, has experienced significant fish introductions impacting its fish diversity. Despite these changes, the variations in morphometric characters of fish in the lake have not been documented following the establishment of non-native Oreochromis species. To address this, the present study assessed the morphological differences in Oreochromis niloticus, Oreochromis jipe and Oreochromis esculentus in Lake Jipe using morphometric traits to improve species identification for ease of fisheries management and conservation of the lake. These three species are known to share overlapping traits which makes their differentiation challenging. Using Image Analysis in ImageJ software version 1.54i and statistical analysis using R Version 4.3, the study hypothesized there were no significant differences in the morphometric characteristics of Oreochromis species in the lake. Welch's ANOVA revealed statistically significant correlations (p < 0.05) consistent in all species, with standard length and dorsal having the highest degree of significant positive association with total length, r > 0.8 across species. Correlations were weaker between total length and traits like caudal length (CL) and head length (HL), r < 0.5. All species exhibited negative allometric growth pattern (b < 3) suggesting faster growth in length than weight. This has important implications for fisheries management by guiding size-based harvesting strategies for sustainability. PCA revealed two principal components, (PC1 = 75.8%, PC2 = 10.4%) which contributed significantly to the observed variance in TL with TW. This study discriminated the species with total body weight and total length being the most distinctive morphometric measurements. Cluster dendrograms displayed site-specific species grouping with mixed groupings in the dendrograms indicative of potential hybridization events, especially where species distribution overlaps. This underscores the importance of further research to confirm species identity and potential admixture using genetic analyses. By refining the distinguishing traits, this study contributes to improved monitoring and management of Oreochromis fish populations in Lake Jipe.