The role of heavy metals in fish nutrition

Aquaculture is one of the most dynamic sectors of the agro-industrial complex, currently providing nearly half of the world’s fish consumed by humans. One of the key factors in the effective development of aquaculture is feed quality, which directly affects fish growth, health, meat quality, and consumer safety. Particular attention in recent studies is given to the content of heavy metals in fish feeds, as they may have both essential (vital) and toxic significance for fish. This article examines the dual nature of the impact of heavy metals on the fish organism: on the one hand, trace elements such as copper, zinc, selenium, manganese, and iron are indispensable for normal biochemical and physiological processes, including immune response, antioxidant defense, growth, metabolism, and enzyme system functioning. On the other hand, an excess or contamination of feeds with toxic forms of these elements, as well as with metals like lead and arsenic, may lead to a range of adverse health effects in fish, such as disrupted enzymatic activity, tissue damage, reduced growth rates, altered behavior, and increased mortality. The paper summarizes up-to-date scientific data on the role of heavy metals in the micromineral nutrition of fish, their routes of entry, absorption, and mechanisms of action in both physiological and toxic concentrations. Species-specific reactions to deficiencies or excesses of these microelements are presented, along with the main sources of heavy metal contamination in feeds, particularly due to raw material components and technological processing. Special attention is given to the bioaccumulation of heavy metals in fish tissues, their potential transfer through the food chain, and the implications for the safety of aquaculture products. These findings can be useful for improving feed quality control systems, formulating balanced diets, and enhancing the overall biosecurity of fish farming.