Flow Intermittence and Salinization Affect Life-History Traits in the Relict Sahara Desert Blue Tilapia (Oreochromis aureus) (Teleostei: Cichliformes: Cichlidae) in Morocco

The blue tilapia Oreochromis aureus is a native afro-tropical cichlid that occurs in Morocco. In the intermittent rivers and ephemeral streams (IRES), this species has been facing multiple environmental stressors, particularly flow intermittence and salinization that may affect their life-history traits. The current study addressed two relict sub-Saharan populations of O. aureus in the Draa basin, SE Morocco, from the permanent saline Tissint River and an intermittent highly salinized reach of the Draa River at Sidi El Mokhtar. Captured tilapias were weighed and measured for body length. Scaled-mass index (SMi) was calculated to assess body condition. Based on body length and scalimetry-determined age, von Bertalanffy growth parameters were estimated in addition to length and age at maturity, mortality rate and longevity using empirical relations. Fish were much smaller, lighter and in poorer condition in the intermittent salinized stream than in the permanent saline Tissint River. The asymptotic length was half, but the growth constant rate was double, with rather a lower growth performance compared to Tissint. Sexual maturation occurred earlier at a much smaller body length. The mortality rate was twice that observed in Tissint, and the estimated longevity was three times shorter. Overall, O. aureus adapts to the extreme conditions of flow intermittence and salinization in the Draa basin by exhibiting fast growth and earlier maturation, which likely contribute to higher fecundity and recruitment. These traits help compensate for the increased mortality rate and shorter longevity associated with these challenging conditions. Such information would be useful for conservation and management of these relict tilapias and their habitat. Moreover, fish farming can be potentially developed in the permanent flowing brackish waters.