Toxicity of melamine, an adulterant in fish feeds: experimental assessment of its effects on tilapia.

Unscrupulous inclusion of melamine in fish feeds can be harmful to fish and may be hazardous to human health. An eight-week feeding trial examined the effects of melamine (inclusion levels; 5-30 g kg⁻¹ feed) on the growth performance, feed efficiency, histopathological changes and melamine residues in sex-reversed red tilapia, Oreochromis niloticus (L.) × O.mossambicus (Peters). Fish which received melamine-containing feeds grew less, utilized feeds less efficiently and performed poorly, besides exhibiting defects such as fin erosion, anorexia, sluggish swimming behaviour, paling/darkening of skin and low survival. Melamine concentration in the fish reflected its inclusion level in the feeds, and the content was higher in the viscera than in the fish fillet or whole fish. Histopathological alterations were evident in the kidney, liver and gills of fish subjected to melamine treatment - the severity of lesions corresponded to its dosage. Enlargement of renal tubules was observed in the kidney of fish fed with ≥10 g melamine kg⁻¹ feed, although, crystals were not deposited. Fish subjected to melamine insult had more prominent lesions in liver than in kidney. Toxic effects on the gills manifested as epithelial hyperplasia of the primary and secondary lamellae. The anomalies were severe at higher intake levels of melamine.