Abstract
Simple SummaryAquaculture effluents with high levels of phosphorus (P) and nitrogen (N) contribute to eutrophication in the aquatic ecosystem. The environmental impact of phosphorus and N aquaculture waste may be diminished by modifying diet ingredients that improve phosphorous (P) digestibility, and therefore, reduce the P in metabolic waste. The content of P in fishmeal is high (30 g/kg), but the inclusion of fishmeal in the diet is reducing due to its high costs and limited accessibility; therefore, the addition of an inorganic P source is necessary to ensure a satisfactory level of available P in fish diets. Consequently, the present study aimed to evaluate the effect of four different inorganic P sources on P digestibility and excretion in rainbow trout (Oncorhynchus mykiss), as one of the most relevant aquaculture species. Monosodium/monocalcium phosphate with 2% of sodium source presented a P digestibility similar to monoammonium phosphate, but with lower nitrogen and phosphorus excretion into the environment, which is advantageous from a nutritional, environmental and industrial point of view (biofilters and recirculation systems in fish farms).This study was conducted to evaluate the apparent availability and P and N excretion in rainbow trout (Oncorhynchus mykiss) using different inorganic phosphorus sources. With this goal, fish (153 ± 14.1 g) fed four inorganic P sources were assayed: monoammonium phosphate (MAP, NH4H2PO4), monosodium/monocalcium phosphate (SCP-2%, AQphos+, NaH2PO4/Ca(H2PO4)2·H2O in proportion 12/88), monosodium/monocalcium phosphate (SCP-5%, NaH2PO4/Ca(H2PO4)2·H2O in proportion 30/70) and monocalcium phosphate (MCP, Ca(H2PO4)2·H2O). Phosphorus (P) digestibility, in diets that included MAP and SCP-2% as inorganic phosphorus sources, were significantly higher than for SCP-5% and MCP sources. In relation to the P excretion pattern, independent of the diet, a peak at 6 h after feeding was registered, but at different levels depending on inorganic P sources. Fish fed an MAP diet excreted a higher amount of dissolved P in comparison with the rest of the inorganic P sources, although the total P losses were lower in MAP and SCP-2% (33.02% and 28.13, respectively) than in SCP-5% and MCP sources (43.35% and 47.83, respectively). Nitrogen (N) excretion was also studied, and the fish fed an SCP-5% diet provided lower values (15.8%) than MAP (28.0%). When N total wastes were calculated, SCP-2% and SCP-5% showed the lowest values (31.54 and 28.25%, respectively). In conclusion, based on P and N digestibility and excretion, the SCP-2% diet showed the best results from a nutritional and environmental point of view.
Highlights
Aquaculture is still a sector with a great growth potential, with improvements in fish feed formulations being essential to achieve a greater expansion
European Union Regulation [18], can be found on the market, being categorized according to the Ca/P ratio (Figure 1). This is due to commercial phosphates coexisting without a defined chemical composition, in the case of mixtures of monocalcium phosphate (MCP), dicalcium phosphate (DCP), phosphoric acid, carbonate and impurities
Around 200 rainbow trout with an average weight of 130 g were moved by an auAround rainbow trout with average located weight of g were moved by an authorized service200 from the fish farm
Summary
Aquaculture is still a sector with a great growth potential, with improvements in fish feed formulations being essential to achieve a greater expansion. Due to the greater inclusion in the diet of plant protein sources and their low P digestibility, the inclusion of an inorganic P source in feed is required. European Union Regulation [18], can be found on the market, being categorized according to the Ca/P ratio (Figure 1) This is due to commercial phosphates coexisting without a defined chemical composition, in the case of mixtures of monocalcium phosphate (MCP), dicalcium phosphate (DCP), phosphoric acid, carbonate and impurities. This undefined chemical composition is explained by the appearance of unwanted collateral reactions, events difficult to avoid at the industrial scale.
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