Sublethal toxicity of malathion on the proteases and free amino acid composition in the liver of the teleost, Tilapia mossambica (Peters).

Exposure of fish to a sublethal concentration of malathion showed a significant inhibition of acetylcholinesterase (AChE) activity. The levels of protease were markedly elevated with a consequent increase in most of the free amino acids. However, the levels of glutamic acid and valine, phenylalanine and methionine complex remained unchanged, while aspartic acid showed a marked drop. These changes are discussed in relation to the sublethal stress induced by malathion.