| Summary: | M.Sc. === The tigerfish, Hydrocynus vittatus member of the Alestidae, are ferocious and fierce predators capable of consuming prey up to 40% of their size. In South Africa H. vittatus can be found in the major east-flowing rivers from the Limpopo River to the Phongolo River flowing into the Pongolapoort Dam making up the southernmost population. The Pongolapoort Dam also known as Lake Jozini is located in the high-rainfall subtropical region of northern KwaZulu-Natal. The Pongolapoort Dam wall was completed in 1973 to make it the fifth largest dam in South Africa with a total surface area of 2 445.9 x 106 m2. It was primarily built for the irrigation of sugar-cane in the surrounding regions. The Fish Health Assessment Index is used as a quantitative index that identifies morphological alterations and assigns them a score for statistical comparison. The main purpose of the macroscopic Fish Health Assessment Index is to detect gross changes in the health of fish populations through necropsy early enough for remedial actions to be put into place. Histopathology is used as an important diagnostic tool for detecting infectious and non-infectious diseases and can therefore be used to assess the health of fish populations by analysing selected target organs. Catch and release (C&R) angling has become a very widely promoted conservation tool as sport angling continues to increase. Anglers release their fish under the assumption that the fish will survive; however, the end results have been shown to vary greatly, from death of the fish to sub-lethal end points such as exhaustive exercise, injury and/or air exposure which will affect the fitness of the fish. The first aim of the study was to determine the health status of H. vittatus and C. gariepinus from the Pongolapoort Dam by means of a histology-based fish health assessment protocol applied to a total of 45 H. vittatus specimens collected in February 2009 (n = 30) and July 2009 (n = 15) and a total of 19 C. gariepinus specimens collected in October 2009 (n = 10) and April 2010 (n = 9). In the H. vittatus specimens DDT was found in the axial muscle; the concentrations of these in February 2009 (5 403.9 ng∙g-1 lipid) and July 2009 (5 537.4 ng∙g-1 lipid). The Mean Index values showed that the Kidney Index (IK), Gill Index (IG) and Fish Index (IFISH) were higher in fish from the February survey while the Liver Index (IL) was higher in those collected during July. Liver alterations identified included intercellular oedema, granular degeneration, vacuolation, nuclear pleomorphism and lymphocyte infiltration. Kidney alterations included dilation of the glomerulus capillaries, vacuolation and hyaline droplet degeneration. Gill alterations identified included telangiectasia and hyperplasia of the secondary lamella, congestion, and rupture of pillar cells.
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