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European Seabass - varying protein proportions

Biological filters designed for the removal of ammonia, which is continuously excreted by fishes, are an integral part of any recirculation aquaculture system, which is intensively used for the production of aquatic organisms (Brunty et al. 1997). One of the most important criteria for designing a closed culture system, which reuse the water, is the amount of nutrients excreted by the cultured fish. An undersized biofilter is not able to control the ammonia and nitrite concentrations within the water and therefore poor water quality will prevail. On the other hand, over sizing a biofilter will unnecessarily drive up the costs of investment for the system (Van Wyk 1999) as well as the running costs during operation.

The quantity of ammonia excreted by fish is related to the quantity of nitrogen supplied by the protein contained in feed (Brunty et al. 1997). Using an optimized food under appropriate culture conditions will lead to a good food conversion. In combination with a low content of protein in the food there is a potential to reduce the disposal of nutrients. Potentially, this will lead to a reduction of the water treating effort, in particular by applying a smaller biological filter. Consequently, energy and cost savings are possible.

Carnivorous fishes are of special interest regarding the European marine finfish production. This type of production still depends on the supply of natural proteins originating from the fishery. Due to the nutritional requirements of carnivorous fishes, the composition of the fish feed contain still high amounts of fish meal and fish oil. Fish meal and fish oil supply essential amino acids and fatty acids that are deficient in plant proteins or vegetable oils (Naylor et al. 2000).

A reduction of fish meal proteins in the food would lead to a lower nutrient discharge, especially nitrogen, but also to a reduced pressure of the fish meal markets by reducing the demand for the feed industry. In the present study the European Seabass (Dicentrachus labrax) was fed with three different types of fish feed, containing varying protein levels of 50 %, 42 % and 30 %. The nutrient excretion within the system was analyzed and it was examined whether a reduction of proteins in the fish feed is possible and whether it allows the application of smaller biofilters. Prior to the main experiment a recirculation system was stocked with fish and the design was continuously optimized.

The results reveal that European Seabass is also able to grow when fed with feed containing a reduced protein level, but growth performance is also reduced. The excretion of ammonium of the group fed with the 30 % level is explicitly lower than the excretion of the other groups. Nevertheless, the reduced amount of excretion is compensated by the increased amount of food required for adequate growth rates, therefore a reduction of the biofilter size could not be achieved.

 

References:

Brunty, J. L., Bucklin, J., Davis, J., Baird, C. D., Nordstedt, R.A., 1997, The influence of feed protein intake on tilapia ammonia production, Aquacultural Engineering 16, S. 161-166

Naylor, R.L., Goldburg, R. J., Primavera, J.H., Kautsky, N.,Beveridge, M.C.M., Clay, J., Folke, C., Luchenco, J., Mooney, H., Troell, M., 2000, Effect of Aquaculture on world fish supplies, Nature Vol. 405, pp. 1017-1024

Van Wyk, P.,1999, Chapter 4 - Principles of Recirculating System Design, In: Van Wyk, P., Davis-Hodgkins, M., Laramore, R., Main, K.L., Mountain, J., Scarpa, J., Farming Marine Shrimp in Recirculating Freshwater Systems, Florida Department of Agriculture and Consumer Services, p. 90ff


 

 
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