Effects of melamine and cyanuric acid on growth performance and health condition in Thai economic aquatic animal species

Abstract

The study consisted of three experiments to investigate the effects of melamine (MEL) and cyanuric acid (CYA) in three differences economic aquatic animal species of Thailand i.e. Asian seabass (Lates calcarifer), Pacific white shrimp (Litopenaeus vannamei) and hybrid Clarias catfish (Clarias macrocephalus (Günther) x C. gariepinus (Burchell)). An identical dosages of MEL and CYA were used in each experiment as follows: diet 1 (a control diet without MEL and CYA); diets 2-5 (with MEL and CYA at 2.5+2.5, 5+5, 7.5+7.5, or 10+10 g kg diet); diet 6 (with only MEL at 10 g kg-1 diet); and diet 7 (with CYA alone at 10 g kg diet). In experiment 1, seven experimental isonitrogenous (40%) and isolipidic (12%) diets were formulated. Asian seabass (initial weight of 4.77+0.25 g) were fed three times a day to satiation at 8:00, 12:00 and 16:00 h for 12 weeks. It was obviously indicated that those fish received combined MEL-CYA: 7.5+7.5, 10+10 or MEL alone diets had poor growth and feed conversion ratio (FCR) (P<0.05). Abnormalities were observed in the liver and kidney of fish with combined MEL and CYA supplementation. The renal tubules of fish that were fed with diets 2-5 had golden-brown melamine- cyanurate crystals. Fish given only one type of supplementation (MEL or CYA alone) did not have such crystals in the kidneys. The highest MEL residue in fillet was detected in the fish ingested MEL alone (10 g kg diet). Levels of heat shock protein (Hsp) 70 were elevated in the liver of fish that had ingested MEL/CYA, in combination or alone (diets 2- 7) (P<0.05). There were no significant differences between the treatments (P>0.05) in the level of Hsp70 in the kidneys of the fish. High dosages of MEL-CYA induced the activities of catalase and glutathione peroxidase in liver and kidneys. In experiment 2, seven experimental isonitrogenous (35%) and isolipidic (8%) diets were formulated. The shrimp with an initial body weight of 2.37±0.02 g were subjected to these diets for 10 weeks. The results indicated that all the diets with MEL and CYA singly or in combination had adverse effects on growth and nutrient utilization relative to the control diet (P<0.05). Total protease and trypsin activities were significantly lowered by all diets containing a combination of MEL-CYA or MEL alone (P<0.05). Blood parameters, including total hemocyte count (THC), phenoloxidase (PO) activity, nitroblue tetrazolium (NBT) reduction, and lysozyme activity, were significantly decreased (P<0.05) in shrimp receiving MEL alone (10 g kg diet) and at high combination dosages (10+10 g kg" diet). Moreover, MEL and CYA induced oxidative stress, decreased antioxidant responses, increased lipid peroxidation and caused damaged to hepatopancreas. In experiment 3, seven experimental isonitrogenous (35%) and isolipidic (7%) diets were formulated. The hybrid Clarias catfish with an initial body weight 6.00±0.02 g were randomly distributed into seven dietary treatments and each treatment consisted of 3 replications. Fish were fed twice daily to satiation at 8:00 and 16:00 h for 8 weeks. The results indicated that the supplementation of MEL and CYA had no significant effect on survival rate (P<0.05). However, body weight and specific growth rate (SGR) were significantly lower than the control group. There were no significant differences in FCR among the dietary treatments (P>0.05). The percentages of skin discoloration of fish were significantly increased (P<0.05) in treatment groups than control groups. Blood parameters, including white blood cell count (WBC) and NBT reduction were significantly decreased (P<0.05) in fish exposed to MEL and CYA. When the combination of MEL and CYA up to 7.5+7.5 and 10+10 g kg' diet, catalase (CAT) and glutathione peroxidase (GPX) activities in liver and kidney were significantly higher (P<0.05) than the control groups. The renal tubules of fish that were fed with diets combination of MEL and CYA had gold-brown melamine-cyanurate crystals. In conclusion, this study investigated the responses of three differences of economic aquatic species to MEL and CYA exposures either singly or in combination. Results of the present work indicate that MEL and CYA had many toxic effects evidenced by growth reduction, changed activities of digestive and antioxidant enzymes, and severe histological damage to target organs i.e. kidney in fish and hepatopancreas in shrimp. It was expected that the results from this study can provide basic data for the further studies and it also provided knowledge to farmers for monitoring the contamination of melamine in aquatic diets in the future.