Abstract
M.Sc.
Metal ions have become an increasing source of pollution in the natural waters
of South Africa. This phenomenon is related to the rapid industrial, mining and
agricultural activity growth along rivers, especially in the Upper catchment of the
Olifants River, Mpumalanga. In general, metal ions have - negative effects on the
physiology of fish and other aquatic biota in metal polluted waters.
In this study. the sublethal effects of, manganese were determined by exposing
the freshwater fish, Oreochromis mossambicus, to this metal in an experimental
flow-through system. The exposure times were divided in acute (96 hours) and
chronic (26 days) exposures, both at 23 ± 1°C.
The results obtained showed changes in the general, haematological, metabolic,
osmoregulatory variables, as well as the differential white blood cell counts.
These changes indicated several effects in the physiology of a mossainblais
after sublethal manganese exposure. Significant differences (P < 0.05) were
found between the haematological variables of the control and exposed fish.
During chronic exposure, an oxygen deficiency developed due to , the epithelial
lifting of gill lamellae. As a result of hypoxia the red blood cell numbers,
haemoglobin-, haematocrit and lactate concentrations increased to uplift the
depleted oxygen situation.
The significant differences (P < 0.05) found in the sodium, potassium,. calcium
and chloride concentrations are mainly as a result of gill damage. Manganese
showed a disruptive influence on the structural organization of the gill.
The differential white blood cell counts performed , showed significant
fluctuations. This leucocytosis and leucopenia are normal reactions of the
fishes’ body against infections of foreign substances, such as metal ions. It was
concluded that the general haematology, metabolism, osmoregulation and
differential white blood cell counts can, be used as indicators in detecting the
effects of sublethal manganese exposure on fish.