Comparative study of tilapiine populations from two contrasting habitats in Ghana

Abstract

The study investigates heavy metal (Arsenic, Cadmium, Lead and Mercury) concentrations in the black chinned tilapia (Sarotherodon melanotheron) inhabiting Benya (an open lagoon) and Fosu (closed lagoon) in the Central Region of Ghana, as well as an analysis of the size –gill relations of the cichlids. The determination of heavy metal concentrations involved the use of CHRIST BETA 1 – 16 freeze drying machine to digest the fish samples which were then asprated using AAS 240fs process. The weight, standard and total lengths as well as gill length and volume of the remaining sample were determined. The results indicated that fish samples from the Fosu lagoon recorded relatively higher Cd (0.28 mg/kg) and As (0.144 mg/kg) concentrations. However, fish samples from Benya had higher concentration of Pb (0.88 mg/kg). The levels of mercury concentration in the fish from both lagoons were below detection limits (µ0.001 mg/kg). Concentrations of Cd in the fish samples from the two populations was statistically significant (p<0.000). However, the differences in the concentrations of Pb and As were not statistically significant (p>0.05). The S. melanotheron specimens from Benya lagoon were much longer than those from Fosu lagoon. There was a positive curvilinear relationship between the standard length and body weight of both populations, with the correlation coefficient being slightly higher for the Benya (r = 0.96) than the Fosu (r = 0.92). Growth was isometric in both cases (b= 2.54, t= 1.2, P> 0.05 for Benya; b= 2.51, t = 0.92, P> 0.05 for Fosu). In both populations, gill length correlated weakly with standard length in a positive linear function (r < 0.45) while gill volume showed a considerably strong linear relationship with body weight in the Benya population (r = 0.70) although this correlation was moderate for the Fosu population (r = 0.54).