Abstract
Ph.D. (Zoology)
Histomorphology as a tool to assess the health status of five economically important fish species in the Okavango Delta Panhandle, Botswana the Okavango Delta, and an inland freshwater wetland of national and international importance was designated by the Ramsar Convention in 1996. This site is of global importance because of a wide diversity of fish species found in this freshwater ecosystem. The Okavango Delta is also one of the last 'near pristine' sites on the African continent and therefore serves as an ideal reference site to describe the normal histomorphology of selected organs in sentinel fish species which could be used as reference for future toxicological studies. The aim of this study was to assess the health status of five economically important fish species namely, Clarias gariepinus (Burchell, 1822), Clarias ngamensis (Castelnau, 1861), Serranochromis robustus jallae (Gunther, 1864), Serranochromis angusticeps (Boulenger, 1907) and Hydrocynus vittatus (Castelnau, 1861) sampled from the Okavango Delta Panhandle, by describing the normal histomorphology of the liver, gills and gonads of the sentinel species. The sentinel fish species are of significant importance because they form an integral part of the small-scale commercial, subsistence and recreational fisheries in this ecosystem. In the past few decades, fish-health research has focused almost exclusively on
histopathological alterations resulting from pollution caused by exposure to chemicals,
parasitesand pathogens. Limited attention has been devoted to the normal histomorphology
and health status of fish species in various aquatic ecosystems including the Okavango Delta
Panhandle. Also, histopathological evaluations noted only the presence of abnormalities
without quantitative assessment of the extent of the abnormalities within each tissue
section. The absence of baseline normal histomorphology and numerical data however,
makes it difficult to establish cause-and-affect relationships between pathology and
contamination patterns in various fish species. It is imperative therefore, that the normal
histomorphology of organs in fish species occurring in this region should be known so that histopathological conditions maybe accurately diagnosed…