Post-prandial changes in plasma mineral levels in rainbow trout fed a complete plant ingredient based diet and the effect of supplemental di-calcium phosphate

• Maiden report on 24 h post-prandial changes in plasma mineral concentrations in fish.
• Di-calcium phosphate (DCP) improves absorption and utilisation of P, Ca, Mg and K.
• DCP negatively affects absorption and utilisation of micro-minerals Zn, Cu and Se.

Post-prandial changes in plasma mineral levels and utilisation of minerals in rainbow trout fed complete plant ingredient based diets with or without supplemental di-calcium phosphate (DCP) were studied over an 8 week period. Three diets were used: diet M was FM and fish oil (FO) based diet (control); diets VP0 and VP + (V diets) were completely based on plant derived protein and lipid sources. One of the V diets (VP +) was supplemented with DCP to supply 5 g kg− 1 dry matter available phosphorus (P); while the other diet (VP0) was not supplemented with DCP. Change in dietary protein source significantly affected the post-prandial pattern in plasma levels of P (p < 0.05), Ca (p < 0.007), Mg (p < 0.001) and Zn (p < 0.03). Area under the curve analysis indicated that compared to VP0, DCP supplementation in VP + improved plasma levels of P (p < 0.01) and K (p < 0.05); Cu (p < 0.002), Se (p < 0.009) and Zn (p < 0.001) levels were reduced while Ca, Mg and Fe levels were unaffected (p > 0.05). Based on measurement of apparent digestibility, growth and whole body composition analyses, mineral balances were established showing that supplementation of DCP led to significant increase in whole body P concentration and P retention in VP +, comparable to fish fed diet M with significantly (p < 0.05) reduced faecal and non-faecal P losses. There was improved post-absorptive retention (as % of available intake) of Ca (p < 0.05), Mg (p < 0.05) and K (p < 0.05) in VP + compared to VP0. Utilisation of Cu (p < 0.05) and Zn (p < 0.01) was negatively affected. DCP supplementation to complete plant ingredient based diet increased the post-prandial plasma levels, whole body concentration and utilisation of macro-minerals (P, Ca, Mg and K) whereas that of micro-minerals especially Zn and Cu were negatively affected.