Abstract
M.Sc. (Zoology)
Organochlorine pesticides aldrin and methoxychlor were present in the Albasini Dam (Louis Trichardt) in the Limpopo Province of South Africa. This was unexpected as aldrin was banned under the UNEP Stockholm Convention of 2004. Insufficient information is available on the registration and the effects that methoxychlor have on fish in South Africa. One previous study showed that aldrin caused necrosis in the liver and kidney of fish. The aim of this study was to determine the effects of aldrin and methoxychlor on Clarias gariepinus under controlled laboratory conditions. Commonly known as the sharptooth catfish (C. gariepinus), this species was selected as the study species as it is widely distributed in Southern African water bodies (dams and rivers) and have been used extensively in various studies as bioindicators. A semi-quantitative histological protocol as an assessment tool has proven successful in indicating early signs of pollution and the quantification of histological results allowed for the comparison of different studies and selected organs.
The fish were acclimated for 10 days before each exposure in order to reduce stress. The catfish were then exposed to environmentally relevant concentrations of aldrin (0.14 μg/L) and methoxychlor (0.23 μg/L) and at an increased value of aldrin (1.4 μg/L) and methoxychlor (2.3 μg/L) (28.7°C; pH 8) for 96 hours. After the exposure the histology-based fish health assessment was done and includes; (1) calculating biometric indices (condition factor and hepato-somatic index), (2) blood collection from the dorsal aorta to determine the haemoglobin concentration, leukocrit, haematocrit, red blood cell count and white blood cell count, (3) a necropsy was performed to determine any macroscopic abnormalities externally and internally and (4) a qualitative and semi-quantitative histological assessment of the liver and kidneys. The liver and kidney were selected as the target organs because the liver is the main detoxifying organ and the kidney the main excretory organ for toxicants. The target organs were fixed in 10% neutrally buffered formalin for 48 hours. These organs were then dehydrated in an ascending series of ethanol from 30% to 100% ethanol and embedded in paraffin wax. Sections of organ tissues (5 μm) were mounted onto microscope slides with EntellanTM. Histological assessments were done with light microscopy. Using the semi-quantitative histological protocol, the liver index and kidney index were determined. Statistical analyses were done using IBM SPSS software where normality amongst the data was tested using the Shapiro-Wilk test. If...