Effect of different inorganic phosphorus sources on growth performance, digestibility, retention efficiency and discharge of nutrients in rainbow trout (Oncorhynchus mykiss)

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Aquaculture, Vol.495, 568-574, 2018
Oncorhynchus mykiss - Trucha arcoíris - Fosfatos - Fosfato inorgánico
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. Juvenile rainbow trout (Oncorhynchus mykiss) with an initial weight of 120 g were fed for 56 days four experimental diets: basal diet containing 430 g kg(-1) protein, 210 g kg(-1) lipids and 6.7 g kg(-1) total phosphorus (P) (Control), and three experimental diets consisting in the basal diet plus 4 g P kg(-1) from MSP, MCP and MAP, respectively. Both MSP and MAP resulted in higher levels of P apparent digestibility (approximate to 90%) compared to MCP (70%), increasing the dry matter digestibility of the nutrient in the feed. The retention efficiency of P in fish tissues was increased by nearly 15% units over the Control when MSP and MAP were used as P supplement, whereas in agreement with the lower digestibility observed in MCP, P retention efficiency from this phosphate source was lower than the other sources. Total P discharge to the water was similar for MSP, MCP and MAP (4.12-4.58 g kg(-1) BW fish gain). However, fish fed with MCP showed higher solid/particulate P discharge to the water through faeces due to the lower digestibility of this P-source within the gut of the fish. Among the phosphate salts evaluated, fish fed MSP and MCP did not show differences for soluble or solid N discharged fractions. However, fish fed the diet supplemented with MAP released a higher amount of non-protein N fraction to the water, probably as undigested ammonium through the faeces released by fish

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