|dc.description.abstract||The objectives of this research were to assess the resources use for producing aquaculture feeds and to determine the waste loads of nutrients to the culture system (system loads), along with the solution to reduce nutrient loads by applying enzyme in aquatic feeds. In the first study, the literature was searched for works that allowed the estimation of land, water, nutrients, and energy embodied in the common feedstuffs used in aquaculture feeds. Results demonstrated that the embodied energy of salmon and trout feeds were greater than for other aquatic feeds. Whiteleg shrimp feed required the greatest amount of land to produce plant-based ingredients. Tilapia and pangasius feeds exhibited the highest average water requirement per unit of production.
In the second study, feed samples obtained from major aquaculture countries were analyzed for concentrations of carbon, nitrogen, and phosphorus in order to estimate system and environmental loads in natural waters. The result indicated that system waste loads for nitrogen ranged from 54.83 g/kg (or kg/tonne) for tilapia to 90.30 g/kg for channel catfish. System load of phosphorus ranged from 10.55 g/kg for salmon to 18.32 g/kg for channel catfish. System waste loads for carbon ranged from 350.74 g/kg (or kg/tonne) for salmon to 650.57 g/kg for channel catfish.
In the third study, 17 minerals elements in aquaculture feeds were analyzed by ICP-AES to quantify levels of minerals and to estimate loads from data on concentrations of elements in
feeds. Concentration of macro and micro-minerals was generally found to be higher in feed samples than in bodies of cultured species. Also, P, Mg, Cu and Zn concentrations were found to be significantly higher than animals requirement levels in the feed samples. System loads for macro-minerals and micro-minerals S, Ca, and K were found to be highest for channel catfish.
In the fourth study, this study was designed to determine the effect of carbohydrase and phytase enzymes supplemented to the diet on growth performance and nutrient retention of channel catfish. The results obtained indicate supplementing carbohydrase or phytase into diets did not result in significant (P>0.05) improvement in the growth performance of fish. Supplementation of diets with phytase 2000 IU/kg improved P retention and ash content in the fish, resulting in a reduction in P system load.||en_US