WWW.WAS.ORG • WORLD AQUACULTURE • MARCH 2024 61 Agricultural runoff: Melamine is also used as a fertilizer in some countries. It enters surrounding water bodies from agricultural runoff from fields treated with fertilizers containing the chemical (Chen et al. 2013). Sewage effluent: Sewage effluent containing melamine is often discharged into the environment, contaminating nearby water bodies (Johannessen et al. 2022). Melamine resulting from sources mentioned above is detected in various aquatic environments, including surface water such as rivers, lakes, oceans, their sediments, and groundwater (Rauert et al. 2020). In rivers and lakes of the USA, melamine and cyanuric acid (a metabolite of melamine) were together found at levels between 0.017-3.650 µg L-1. Tap water and bottled water samples had concentrations of 0.515 µg L-1 and 0.075 µg L-1, respectively. Mean concentrations of 0.182 µg g-1 dw of melamine and 0.0262 µg g-1 dw of cyanuric acid were determined in lake sediments near Seoul, and in Japan 10-400 ng g-1 dw melamine concentrations were measured in river sediments. Melamine’s stability and resistance to degradation allow it to persist once discharged into the aquatic environment. Melamine adversely affects many aquatic organisms at high concentrations, but in some cases, it affects early life stages at low concentrations. Studies have shown that exposure to melamine causes toxicity in fish, crustaceans, and other aquatic organisms. Melamine also accumulates in the tissues of aquatic organisms, especially fish and shellfish, through ingestion and absorption. If contaminated fish and shellfish are eaten, it may cause melamine to go up the food chain and put human health at risk (Liu et al. 2014). Melamine in Aquaculture Aquaculture plays an important role as a main source of animal protein in global diets. Fish feed accounts around 60% of the total cost incurred in aquaculture and as the amount of protein in fish feed determines its price, some feed manufacturers may boost protein levels artificially using melamine. Reports from numerous countries have indicated the presence of melamine, up to 150 parts per million, in fish meal and fish feed (Karunasagar et al. 2009). Fish are systemically poisoned by cyanuric acid and melamine. Catfish organs were found to contain insoluble melamine cyanurate crystals, as reported by Pirarat et al., (2012). He suggests that aquatic animals may be able to metabolise and biotransform these hazardous substances due to the dispersed nature of extrarenal crystals throughout the body. Following significant decreases in the RBC, Hb, and PCV (Packed Cell Volume) levels of the exposed fish, the haematology of C. gariepinus was adversely affected. According to Iheanacho et al., (2020), the harmful effects of melamine and melamine-formaldehyde compounds may be the cause of this substantial impairment of erythrocyte production, Hb biosynthesis, and hematogenesis. Melamine and cyanuric acid have also been found in shrimp feeds. In Pacific white shrimp, L. vannamei, growth performance and feed utilization were negatively affected by MEL and CYA exposure, with reductions in mean weight gain, average daily gain, and specific growth rate, and an increase in the feed conversion ratio. Exposure to these substances also damaged the cells of the hepatopancreas, leading to the generation of oxidative stress, increased lipid peroxidation and decreased antioxidant and immune responses, demonstrating that the hepatopancreas of shrimp is sensitive to MEL and CYA (Nuntapong et al. 2019). Oxidative stress and disrupted antioxidant defence systems were observed in the liver and kidney tissues of Heteropneustes fossilis, Cyprinus carpio and zebrafish when fed with melamine and cyanuric acid-tainted feed. High levels of melamine in the diet lead to decreased feed conversion efficiency, growth, and protein retention and can also lead to kidney damage, tissue damage and oxidative stress in fish (Reimschuessel et al., 2008). Melamine at high levels in the diet results in decreased growth and survival rates in Rainbow trout. Histopathological analysis revealed damage to liver and kidney tissues. Melamine is absorbed and accumulated in the muscle tissues in Atlantic salmon fillets. High doses led to decreased growth and feeding rates, damaging the hepatopancreas, gills, and midgut tissues of freshwater crayfish resulting in increased mortality. According to Phromkunthong et al. (2012), melamine incorporation in fish feed affects growth performance, feed efficiency, histological alterations, and residues in red tilapia. In addition to showing abnormalities such as fin erosion, anorexia, slow swimming behaviour, paling or darkening of the skin and low survival, fish who received feeds containing melamine also grew less, used their feeds less effectively, and performed poorly. Fish treated with melamine showed clear histopathological changes in their kidney, liver, and gills; the extent of the lesions correlated with the dose. Renal tubule enlargement was noted in the kidneys of fish given 10 g of melamine or more kg−1 diet. While it is known that melamine is toxic to animals, including humans, the severity of toxicity depends on the dose, duration of exposure, and individual susceptibility. Melamine is potentially dangerous to aquatic animals, including fish, crustaceans, and mollusks because it can form crystals in the urinary system, which can cause kidney failure and injury. The formation of these crystals can also cause blockages in the urinary tract, leading to inflammation and tissue damage (Anderson et al. 2008). Concentrations of melamine that are toxic to aquatic animals vary depending on the species, the duration of exposure, and the environmental conditions. FIGURE 3. Effects of Melamine on Aquatic Animals FIGURE 4. Remediation of melamine (CONTINUED ON PAGE 62)
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