|
Is aquaculture sustainable if it costs 4 kg of fish to make 1kg of salmon? |
|
|
Written by Sadasivam Kaushik, Institut National de la Recherche Agronomique for the Consensus project [1]
First of all, the term "Aquaculture" covers a wide range of species. Currently, more than 250 species of fish and crustaceans are farmed around the world. The impact of aquaculture will naturally vary, depending on what species is farmed and what type of farming method is involved. Some species are naturally ‘carnivores' (fish eaters like salmon are better termed piscivores), others can be omnivores or herbivores. Salmon farming is only one part of aquaculture. So, it would be more appropriate to discuss this question specifically for salmon (and other purely piscivorous fish) farming, rather than as a general question on the sustainability of aquaculture per se.
In nature, wild salmon thrive on natural prey. The ecological efficiency of conversion of prey to predator is about 1 to 10 (meaning a predator requires 10 times their mass or energy from preys to gain 1 unit of biomass or energy). This means that some 10kg of the normal prey of wild salmon would be required to produce 1Kg of salmon flesh. Some authors have added in a value of by-catch, which could add a further 2-5Kg to this figure.
Salmon feeds contain fish meal and fish oil which are derived from small pelagic fish which are not used for direct human consumption. With current feeds and feeding practices and the efficiency with which the feeds are converted into edible fish, the total amount of wild fish used to make one ton salmon is between 2.7 and 3.5 tons. Already big changes are also occurring to reduce the levels of fish meal and fish oil in the feeds for salmon which should lead to lower figures in the coming decade.
If all feed-based aquaculture[1] were to use feeds rich in fish meal and or fish oil, and that if they all require 4 kg of wild-catch fish to produce 1 kg of aquaculture product, then this could arguably be defined as an unsustainable practice, but this is not the case.
[1] EU funded project on sustainable aquaculture in Europe www.euraquaculture.info [2] Feed-based aquaculture : farming of fish or shrimp using man-made formulated feeds |
|
Last Updated ( Thursday, 12 August 2010 )
|
Fish feed