An important part of fisheries is aquaculture, which deals with the cultivation of aquatic organisms, primarily fish. Fish cultivation in the Republic of Croatia includes mariculture and freshwater fish farming. Cultured fish is an important part of the human diet. Fish can come into contact with various toxic compounds from the environment. Toxicity will depend on the type of chemical compound and the type of fish and the quality of the water. Fish poisoning can be acute, subacute and chronic. It can be caused by increased concentrations of chlorine, copper and various chemical compounds from the aqueous medium, such as nitrogen compounds. Also, fish poisoning is often the result of contamination of fish food with mycotoxins, especially fumonisins, moniliformin, aflatoxin B1 and ochratoxins A, B and C. Persistent organic contaminants can also have a detrimental effect on fish health. In addition, fish can also come into contact with various heavy metals, such as mercury. Toxic substances most often enter the water system through food and water. Therefore, water and food control is an important part of the protocol in protecting fish health.