In situ chelation of phosphorus using microencapsulated aluminum and iron sulfate to bind intestinal phosphorus in rainbow trout (Oncorhynchus mykiss)

Excess phosphorus (P) in freshwater ecosystems increases primary production which, left uncontrolled, may lead to eutrophication, accelerating the ageing process of receiving water bodies. To limit phosphorus release resulting from freshwater aquaculture, we propose to incorporate microencapsulated P-chelating agents into fish diets. In a first trial, alum (Al2SO4) and ferrous sulfate (FeSO4) were encapsulated by spray-chilling in a hydrogenated lipid matrix. Two practical diets incorporating one of these two chelating elements (6 g/kg) were fed to fish for five weeks (w), and P release from resulting feces was compared. In a second trial, a similar approach was used to evaluate the impact of increasing supplementation of encapsulated alum (3, 6, 15 g/kg of diet). Feces from the fish fed with the diets incorporating alum and ferrous sulfate released 62 % and 54 % respectively less P than feces from fish fed with control diets. The second experiment revealed a negative correlation between the level of encapsulated Al2SO4 included in the diet and phosphorus released by the feces (y = 0.18x2 ˗ 4.78x + 62.7; R2 = 0.93). Feces from feed incorporating Al2SO4 at 0, 3, 6 and 15 g/kg released 62 %, 52 %, 39 %, and 32 % of the total fecal P after 14 days respectively. Fish fed encapsulated Al2SO4 have similar growth performance and mineral status. Incorporation of encapsulated P-chelating agents into fish feed offers an opportunity to manage P release from fish feces. Long-term feeding studies are required for validation of dietary Al2SO4 and FeSO4 impacts on potential toxicity and growth/environmental performance following chronic feeding of encapulated P chelating agents.

Mots clés

Fish farming; Pollution; Phosphorus solubilization; Encapsulating; Ferrous sulfateAlum