Genetic and morphological characterization of invasive tilapia in Morocco confirm the presence of two feral species Oreochromis niloticus (Linnaeus, 1758) and Oreochromis aureus (Steindachner, 1864) and their hybrids

Abstract

Two tilapia species, Oreochromis aureus and Oreochromis niloticus, were introduced into Morocco in 2004 for fish farming. O. niloticus was subsequently introduced into the wild in several watersheds. During a fish survey at six locations, we observed other specimens of tilapia that appear to be more related to O. aureus. Partial sequences of COI and S7 genes and geometric morphometrics were used to assess the specific status of all the specimens. Out of 1691 specimens sampled, 159 COI and 153 S7 partial sequences were obtained and confirmed the presence of both species. O. aureus was present in part of Rabat-Salé-Kenitra region (the Nador Channel (NC), Al Kansra dam (AK) and Oued Sebou (OS)) while O. niloticus was found in the fish farm (AS), in the province of Rabat (Sidi Mohamed Ben Abdellah dam (BA)) and the region of Casablanca-Settat (Al Massira dam (AM)). A few hybrids were identified at AS and OS. Body shapes and sizes were assessed using geometric morphometrics with 18 landmarks and were found to differ significantly between O. aureus and O. niloticus. Both species exhibited significantly different allometric changes during their growth, but kept their morphological signature independently of their specific allometric changes during growth. Specimens from riverine environments (OS, NC) had a similar shape with an elongated body with a large head and eye, while individuals found in lacustrine environments (AK, AM and BM) had a larger body depth, small head and eye. Morphometrics also suggested that hybrids or sympatry could occur to a small extent in AS, OS and NC.