Tilapia Zilli Lab Report

The correlation between mercury concentrations, weight and length in various fish species are indicated in figures 4.20-21. Total mercury concentrations were determined in some fish species in both the dry and the wet season from the Weija dam. About 42 samples of fish which consisted of three (3) species were sampled in all. Among the species were tilapia zilli (n = 7). Tilapia mariae (n = 7) and Chrysichthys nigrodigitatus (n=7) all of which are consumable (edible) by human. The mean T-Hg concentration in the fish species ranged from 0.00 to 0.04 mg/kg in the tilpia zilli, 0.00 to 0.04 mg/kg in the tilapia mariae 0.00 to 0.04 mg/kg in Chrysichthys nigrodigitatus with respective means of 0.02 mg/kg, 0.01 mg/kg and 0.01 mg/kg of the tilpia
This observation can be due to the fact that the rate of accumulation differs for every fish species since various fish species have different migratory and feeding habits as well as different metabolic and excretion (Ntow and Khwaja, 1988). Studies conducted on various fish species by Ntow and Khjawa found no correlation between T-Hg content and size, weight and length of fish under investigation. Lange et al., (1994) also indicated that mercury concentration varies with fresh weight of fish and total length.
Lack of correlation between total length and mercury concentration for several fishes species distributed along the Tasmanian continental shelf has been observed by Thompson, (1985). The results obtained in this study agree with Thompson (1985), who concluded that use of correlation to estimate mercury content and define human consumption limit for a given species could not be done without proper knowledge of the species biology and the particularities of each environment it
These correlations were not significant at p < 0.05. Tilapia mariae recorded a weak strong correlation coefficient r = 0.471 (Table 4.22) at p < 0.05 insignificant in the dry season and recorded r = 0.412 in the wet season (Table 4.23). Tables 4.24 and 4.25 indicate weak positive correlations between pH and mercury in chrysicthys nigrodigitatus for both seasons. Though weak positive, they were not significant at p < 0.05. The positive correlations between pH and mercury which were observed in tilapia mariae and chrysicthys nigrodigitatus in both dry and wet seasons indicated that the T-Hg concentrations increases with an increasing pH however these relationships are not significant at p < 0.05. The inverse of these positive correlations was observed in tilapia zilli in both seasons. The negative correlation coefficients recorded in the tilapia zilli shows that the concentration of total mercury increases with decreasing pH in both dry and wet seasons (Table 4.20 and