Life-history traits in two invasive species of tilapias in Morocco

Abstract

Life-history traits (LHT) of Oreochromis niloticus in the Sidi Mohamed Ben Abdellah reservoir (BA reservoir) and Oreochromis aureus in the Nador Channel were studied and compared with those of other populations in the world. Specimens were collected between June 2018 and June 2020. Females of both species were smaller at first sexual maturity than males (O. niloticus: 204 vs. 255 mm, O. aureus: 147 vs. 158 mm). The age of maturity for each species was estimated from seasonal otolith growth marks, based on the von Bertalanffy growth function. The asymptotic length was higher in O. niloticus (males 296 mm and females 339 mm) than in O. aureus (males 171 mm and females 169 mm). Based on a literature survey and the results of this study, the type of ecosystem (reservoir vs. river) influenced growth performance indices (φ and φ′) in both species, with reservoirs leading to a higher asymptotic length in both O. niloticus and O. aureus than rivers. Moroccan populations presented the lowest growth index in the populations assessed. These observations suggest that while both invasive species were able to colonise and adapt to their new environments, this was at the expense of limiting their growth and reducing their size at first sexual maturity.