Abstract
M.Sc. (Zoology)
Oreochromis mossambicus was used as the test organism. The fish were exposed to environmentally relevant concentrations of DDT alone, to a mixture of DDT with chlordane, zinc and nitrates (DCZN), and to chlordane zinc and nitrates (CZN) under controlled laboratory conditions for 96 hours. Each treatment comprised sixteen individuals (n = 16). At the end of the exposure period, blood parameters including haematocrit, leukocrit and haemoglobin concentration were measured in each fish. The liver and gonads were examined for histological alterations using a qualitative and semi-quantitative histological assessment protocol. All quantitative variables were compared statistically among treatment groups using R statistical software (R version 3.3.2) at a confidence level of 95%.
There was a significant decrease in the haemoglobin concentration in the mixture exposures (DCZN; p = 0.007831, CZN; p = 0.02036) and a significant decrease in haematocrit for the CZN (p = 0.005577) exposure with reference to the control group. An upward trend in the leukocrit was observed in the mixture exposure groups with significantly higher values in the CZN group (p = 0.02786). Liver alterations quantified by the liver index were significantly higher in the DCZN mixture exposure (p = 0.02621). There was no significant difference in the gonad index among the exposure groups. These results suggest that a possible interaction between DDT and CZN resulted in increased adverse effects in the liver and blood of the fish exposed to the mixture compared to DDT single exposure. Therefore, DDT may not be solely responsible for the decline in fish health status reported in the previous studies.