Trace mineral nutrition in fish and shrimp: Working towards optimum performance and sustainability in a rapidly evolving industry
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by the Alltech Mineral Management Technical Team, USA
quaculture is one of the fastestgrowing food-producing sectors in the world. Nutrition, specifically trace minerals, is just one of several key aspects that must be considered in successful, profitable and sustainable farm management. Trace minerals are absorbed from the marine environment through gills or the body surface, but they seldom meet the total requirements for farmed aquatic species and must be provided in the diet through supplementation (Katya et al., 2017). Trace minerals, which are required in milligram or microgram amounts, are essential elements required for normal life processes and cellular metabolism. They form components of body fluids, hormones and biological compounds such as haemoglobin. Of particular importance are copper (Cu), iron (Fe), manganese (Mn), zinc (Zn) and selenium (Se), which are associated with proteins within metalloenzymes responsible for catalytic function (Lall, 1989). Supplementing the right amount of trace minerals ultimately contributes to the maintenance of health, fertility, hatchability and immunity, as well as performance parameters, including growth rate, feed efficiency and flesh quality. A general summary of the functions of these trace minerals is provided in Figure 1.
Figure 1: Key trace minerals and their physiological and metabolic benefits in aquatic species
Figure 2: Effect of trace mineral source (inorganic vs. organic) and level (commercial levels vs. 2/3 commercial levels) on final body weight and FCR in Atlantic salmon reared in low oxygen conditions (Kausoulaki et. al. 2019).
Trace mineral requirements in aquaculture: What needs to be explored?
Although a delicate balance of trace mineral nutrition is required to maintain physiological processes (Lall, 1989), the exact trace mineral requirements for different aquaculture species are still being explored and are hence a subject of much debate. Excess mineral intake, either dietary or environmentally, can cause toxicity, while a deficiency can compromise immunity, therefore increasing susceptibility to disease. Lall (2003) recommends the following ranges of dietary trace minerals in fish (See Table 1). The perspective from the National Research Council (NRC) is that there is much to be explored on the knowledge of trace mineral requirements for farmed fish and shrimp. Their recommendations for dietary trace minerals in all livestock species have yet to differentiate between trace mineral sources and forms (See Tables 2 and 3). This can influence dietary inclusion rates, as well as physiological factors like mineral bioavailability and absorption and interaction with other dietary feed components.
Form and level affect function: Feed ingredient sources and mineral interactions
An increase in the demand for aquafeed and limitations on the availability of fish meal has directed the industry to either reduce the amount of fish meal in diets or explore other alternatives, such as plant meal (DomĂnguez et al., 2020). This can present a range of nutritional challenges. Plant meal often contains high amounts of phytic acid, which is a known antagonist. Phytic acid binds strongly to mineral ions, making them unavailable for absorption by aquatic species (Prabhu et al., 2016; DomĂnguez et al., 2020). In diets containing high levels of plant protein, mineral supplementation is necessary to improve growth and bone development, especially in carnivorous salmonid and marine fish. Trace mineral composition and bioavailability can also differ markedly among aquatic feed ingredients and complete feeds, which can result in exceptionally high trace mineral
22 | August 2020 - International Aquafeed