In contrast to terrestrial animals, fish can ingest minerals from food or directly from water. Although micro- and macro-elements are needed in small quantities, they play a key role in many metabolic processes. Trace mineral and macromineral deficiencies may go unnoticed due to an absence of clear clinical symptoms in fish. Absorption processes are determined by various factors, mostly mineral concentrations in water but also other water parameters. The required dietary supplementation of macronutrients and micronutrients is very difficult to determine, and the amount of nutrients absorbed by fish from water is equally difficult to measure. Interactions between elements should also be taken into consideration. Many authors emphasize that phosphates may reduce the absorption of most micronutrients. Also, the current parameters of the water can affect the bioavailability. Some elements such as calcium, chlorine and sodium can be absorbed from ambient water in a quantity sufficient to meet the demand for this element. Other elements, however, require supplementation in a diet. For example, studies indicate the need for supplementation of phosphorus, zinc, copper and manganese. Most research concentrates on feedstuff as a source of micro- and macronutrients. Meanwhile, information concerning bioavailability of minerals directly from water is scarce. The aim of this study was to analyse literature from a different perspective, and concentrate on water as a source of minerals in fish nutrition. Measurements of water parameters such as temperature, pH, nitrate and nitrite levels and the amount of dissolved oxygen are a regular component of environmental control in fish farming. Determination of micro- and macro-element levels, however, remains uncommon in aquaculture. Measurements of these parameters could suggest which elements need to be supplemented and which are found in water in amounts that satisfy the needs of the fish.

21.3.2016