News last update:6 Aug 2012

Mineral leaching: a problem in aquaculture?

Mineral leaching from faeces, excess feed and chemical compounds from aquaculture sites may cause negative impacts on the environment. However, growing awareness can assist the industry to avert potential risk. In the latest Feed Mix, Santosh Lall* explains the current situation.

As most fish species and shrimps are raised in cages in the open sea or in ponds, fecal and feed waste (containing high levels of minerals) accumulate at the bottom of net-pens and flow directly in the aquatic environment. This leaching of minerals has a direct effect on the mineral concentrations of the ecosystem and may have a negative effect on the animals and plants living near these cages. The excessive minerals stimulate phytoplankton production and increase oxygen demand. Such nutrient enrichments also have the potential to stimulate the development of macro-algal beds and to influence organisms that live near seabeds.

Too high concentration in diet
Although several nutritional strategies are in place to reduce organic and inorganic enrichment of recipient waters, fish feeds contain trace elements at a higher concentration than required due to limited information on their requirement and bioavailability from feed ingredients. In order to minimize the adverse effects of trace elements on benthic organisms, particularly in their reproduction, recruitment success and survival, there is a need to develop proper models based on mineral bioavailability, feed consumption and excretion, water current and flow and other environmental factors.

The necessity to increase research efforts to better define the dietary requirements of trace elements of major concern particularly for zinc, iron, copper and manganese as well as measure their bioavailability and retention in the body of fish is obvious. The best option for now is to minimize zinc, iron, copper, cadmium and manganese concentrations in feeds and to consider use of highly available forms of inorganic and organic trace elements in supplements.

*Dr. Santosh Lall is a Group Leader of Aquatic Animal Health & Nutrition at the Institute for Marine Biosciences of the National Research Council of Canada, Halifax, Nova Scotia. He is also an adjunct professor at Dalhousie University, Halifax and Atlantic Veterinary College, University of Prince Edward Island, Charlottetown. Dr. Lall received his MSc. and Ph D. degree in Nutrition from the University of Guelph, Canada.

The full article can be read in Feed Mix 16.4. Not a subscriber yet, please click here to subscribe or to sign up for a free sample copy. 

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