Pathophysiological changes associated with dietary melamine and cyanuric acid toxicity in red tilapia

This study examined the adverse effects of feed-delivered melamine (MEL) and cyanuric acid (CYA) in red tilapia. Diet 1 (without MEL and CYA), diets 2–4 (with MEL and CYA at 2.5, 5 and 7.5 g kg⁻¹ diet, respectively) and diets 5 and 6 (with either MEL or CYA at 10 g kg⁻¹ diet) were examined. MEL alone lowered both growth and FCR (P < 0.05), and CYA alone reduced the FCR of tilapia. Protein efficiency ratio and apparent net utilization of fish on diets 2–6 were poor (P < 0.05). The renal tubules of fish ingested MEL-CYA combination had melamine–cyanurate crystals. On the other hand, diets with only one chemical did not induce such crystals. MEL and CYA in whole body, fillet or viscera reflected their dietary inclusion levels. The levels of Hsp70 were increased in the liver of fish that ingested MEL and CYA, in combination or singly (P < 0.05). However, in the kidney, such an increase was visible only in the fish that received diet 4 (P < 0.05). Combination of MEL and CYA at inclusion levels > 5 g kg⁻¹ diet induced the activity of catalase in liver and the activity of glutathione peroxidase in liver and kidneys. Therefore, these adulterants should not be included in fish feeds.