Effect of manganese and iron at a neutral and acidic pH on the hematology of the banded tilapia (Tilapia sparrmanii)

Results of experiments on the effects of iron and manganese (1.75 mg ferric chloride and 4.43 mg manganese chloride per litre) on 8 haematological parameters in fish (Tilapia sparrmanii) at pH 5.0 and pH 7.4 are summarized. The observed effects and possible mechanisms involved, are discussed briefly. Manganese caused greater stress at neutral pH than under acidic conditions; this was attributed to the fact that the toxicity of manganese depended not on the total concentration of the metal but on the available concentration of oxidized manganese. In contrast to manganese, iron caused an increase in numbers of red blood cells. Changes in the physico-chemical characteristics of the water could alter the toxicity of metals already present in the system.