Hybridization between non-indigenous Oreochromis niloticus and native Oreochromis species in the lower Kafue River and its potential impacts on fishery.
In the Kafue floodplains, Zambia, a study was done to determine whether meristic and/or other morphological metrics could distinguish putative hybrids (based on color patterns) between non-indigenous Oreochromis niloticus (Nile tilapia) and two native species of Oreochromis andersonii (three spot tilapia) and Oreochromis macrochir (green head tilapia) from the pure parental strains. We also surveyed local fishermen to document their knowledge and beliefs on the spread of O. niloticus in the last decade, the occurrence of hybridization, and any changes in catch per unit effort of these and other species. A sample of fifty fish specimens were collected for morphometric and meristic data using gill nets and seine nets, and augments by specimens purchased from the catches of local fishermen. A full standard multi-filament net with mesh sizes ranging from 25 to 150 mm in increments of 12.5 mm mounted in a fleet was used. The seine net used was of 25 mm mesh size, approximately 100 m long and 2 m high at the pocket. We analyzed the morphological and meristic data using the program STATISTICA. Our results confirm that: in the last decade, O. niloticus has spread throughout the Kafue floodplains from its initial site of introduction near the eastern end of the Kafue floodplain; putative hybrids between O. niloticus and O. andersonii cannot be distinguished from parental species based on morphometric or meristic traits; and survey results of local fishermen indicate that they have experienced increases in catch per-unit-effort of O. niloticus while simultaneously experiencing decreases in catch per-unit-effort of native tilapia.