Abstract
Water resources are frequently under inspection as pollution increases.
Therefore an urgent need has arisen for sensitive bio-monitoring tools in toxicant
impact assessment to indicate the effect of pollution on fish health in polluted
aquatic ecosystems. Histopathological assessment of fish tissue allows for early
warning signs of disease and detection of long term injury in cells, tissues or
organs. Various biochemical and biological studies of fish have been used to
assess the consequences of environmental toxicants on fish, but histology is able
to enhance and add quality to the research carried out by identifying cellular
alterations and quantifying the results.
The aim of this study was to assess the degree of pollution in the Marais Dam
(MD) and Rietvlei Dam (RVD) in the Rietvlei Nature Reserve (RNR) by
determining the health status of the sharptooth catfish, Clarias gariepinus, using
fish histology as a bio-monitoring tool.The MD and RVD situated within the Sesmyl Spruit serve to provide the area
with water and are separated by a natural wetland. The dams were chosen for
their elevated levels of toxicants. Four sampling surveys, two low flow and two
high flow, were carried out over a period of two years. During each survey twenty
fish were sampled per dam. Water and sediment were sampled for metal and
endocrine disrupting chemical analysis. A standardized health assessment
protocol employed to determine the effects of the toxicants included analysis of
blood constituents, fish necropsy, calculation of condition factor and
organosomatic indices, and a qualitative and quantitative histological assessment
of three target organs: the gills, liver and gonads.
These organs were removed and processed according to standard techniques
for histological assessment. Histopathological alterations of each organ were
identified (qualitative assessment) and subsequently quantified by means of a
standard methodology of criteria to assess and compare fish health (quantitative
assessment). The total index (Tot-I) values from the quantitative histological
assessment were statistically analyzed using the ANOVA method.
Potential endocrine disrupting chemicals and metals in the water of both dams
were present at levels that could be toxic. The degree of pollution was more
severe in MD than RVD. Examination of tissue from the gills, liver and gonads
revealed marked histopathological alterations. The quantitative histological
assessment indicated that fish collected from MD were in a significantly more
severe histopathological condition than those of RVD. These results indicate that
the wetland may still function as a natural filter. The qualitative and quantitative
histological assessment objectively compared C. gariepinus specimens from MD
and RVD and the effects of the toxicants on the health of the fish.
Dr. G.M. Pieterse