Abstract
The relationship between morphological traits and feeding ecology of the only two tilapiine cichlids (Sarotherodon galilaeus and Oreochromis niloticus) in Lake Geriyo, northeastern Nigeria, was examined. Stomach contents of 504 individuals were examined and analyzed to relate morphological differences of each species to its dietary preferences. Eleven ecological relevant morphological variables, including total length, standard length, head length, body depth, eye diameter, pectoral spine length, pelvic spine length, dorsal fin ray count, dorsal spine count and anal fin ray count, were also measured and subjected to Principal coordinate analysis (PCoA) to relate morphological differences of each species to its dietary preferences. The PCoA (using Euclidean distance) revealed a large morphological distance between species indicating adaptation for different spatial and vertical distributions within the lake. Furthermore, the correlation of these morphological differences with particular diet categories suggests a potential for specialized trophic tendencies, however, the high occurrence of two major food types (macrophytes and plankton) in stomach contents of both species indicate generalist trophic tendencies. While a high trophic overlap index (0.98) was recorded for both species, the trophic niche breadth was higher for S. galilaeus (4.18±0.32), compared to O. niloticus (3.33±0.24). Despite the large morphological differences of both tilapias, the high trophic overlaps indicate limited food options within Lake Geriyo. In addition, the successful coexistence of the tilapias in the face of limited food resources indicates suitable partitioning of food resources in the lake.