CONICET | Buscador de Institutos y Recursos Humanos

This study aims to evaluate the effect of different sources of inorganic phosphate, monosodium phosphate (MSP), monocalcium phosphate (MCP) and monoammonium phosphate (MAP) included in a diet for rainbow trout on growth performance, nutrient digestibility, nutrient retention efficiency and discharge of nutrients to the water. Rainbow trout (Oncorhynchuss mykiss) with an initial weight of 120 grams (25 fish per tank) were fed during 56 days with four experimental diets: basal diet containing 430 g kg?1 protein, 210 g kg?1 lipids and 6.7 g kg?1 total P (Control), basal diet plus 4 g P kg?1 from MSP, MCP and MAP. Both MSP and MAP resulted in higher levels of phosphorus (P) apparent digestibility (≈90%) compared to MCP (70%), increasing the global digestibility of the nutrient in feed. The retention efficiency of P in fish tissues was increased near to 15% over the Control when MSP and MAP were used as P supplement, whereas in concordance with the lower digestibility observed in MCP, P retention efficiency from this phosphate source was lower than the other products. Total P discharge to the water was similar for MSP, MCP and MAP. However, values from MCP indicated that this P source produces more solid discharges to the water through faeces due the lower digestibility of the salt within the gut of the fish. Among phosphate salts evaluated, fish fed MSP and MCP did not showed differences for soluble or solid N discharged fractions, but fish fed the diet with MAP inclusion released a higher amount of N in its dissolved form to the water. From an environmental impact viewpoint, MAP seems to be more disadvantageous than the other inorganic P sources evaluated in this study since its non?protein soluble N fraction is not utilized by fish.