Population genetic structure and condition factor of the wild redbreast tilapia coptodon rendalli (Boulenger, 1897) in Malawi

Abstract

Variation in performance of Redbreast tilapia from different groups remain the biggest challenge for aquaculturist to obtain the fast-growing parent stock in Malawi. This suggests that C. rendalli may have been speciated into different populations. Despite the evident variations in performance of different stock from different sources, there is lack of simple identification criteria of stocks from different aquatic systems to delineate the populations. Therefore, the study examined the morphological features; relative position of landmark points and linear distances between landmark points to identify key features that can be utilized in differentiating populations of C. rendalli. The study also evaluated the growth patterns using length-weight relationship to determine the relative condition of the parent stock from different sources. A total of 273 specimens of redbreast tilapia from eight different locations; Karonga, Nkhatabay, Nkhotakota, Salima, Mangochi, Lake Malombe, Lake Chiuta and River Shire were utilized in the study. Both univariate and multivariate analyses conducted on the 15 landmark points and 23 inter-landmark distances reported highly significant (p < 0.05) variations. Results obtained from relative landmark points and linear measurements generated from inter-landmark distances revealed three distinct populations. Positive allometric growth pattern was observed on the two groups of Lake Malombe and River Shire while the rest reported a negative allometric growth pattern. All length-weight relationships were significant (P<0.05), with r2 greater than 0.757. Relative condition factor (Kn) for all groups showed significant (p<0.01) correlation with body weight of C. rendalli. Fish health and wellbeing measured using relative condition factor (Kn) was best in Karonga individuals (1.0413) but relatively poor in Lake Malombe (1.0032). The current study suggests that C. rendalli shows morphological differences across different groups and that the differences are linked to the condition of the fish in terms of health and wellbeing.