Phosphorus availability from inorganic phosphorus sources in yellowtail (Seriola quinqueradiata Temminck and Schlegel)

This study was conducted to select an appropriate inorganic phosphorus (P) source with higher P availability, judging from apparent availability of P and non-fecal P excretion, in yellowtail (270 ± 44.6 g) fed five inorganic P sources. Albumin based purified diets with five inorganic P sources were used: potassium phosphate monobasic, KH2PO4; sodium phosphate monobasic, NaH2PO42H2O; calcium phosphate monobasic, Ca (H2PO4)2H2O; calcium phosphate dibasic, CaHPO42H2O, and calcium phosphate tribasic, [Ca3(PO4)2]3Ca(OH)2. The results showed that the P sources significantly influenced P availability in yellowtail. Apparent phosphorus availability (APA) values for K (96.1%), Na (94.8%), and Ca (92.4%) phosphate monobasic sources were significantly (P < 0.05) higher than for sources using Ca phosphate di- (59.2%) and tribasic (48.8%). The pattern of non-fecal P excretion, based on monitoring every hour for 24 h after feeding, showed that the peak height at 5 h after feeding differed, depending on the availability of inorganic P sources. The fecal P content was found to be significantly (P < 0.05) less in yellowtail fed monobasic inorganic P sources of K (0.56 mg/g dry fecal matter), Na (0.63 mg/g dry fecal matter), and Ca (0.9 mg/g dry fecal matter) than dibasic (9.1 mg/g dry fecal matter) and tribasic (9.9 mg/g dry fecal matter) sources of Ca. In contrast, non-fecal P content was significantly (P < 0.05) higher with monobasic sources of K (3.5 g soluble P/kg dry feed fed), Na (3.5 g soluble P/kg dry feed fed), and Ca (3.4 g soluble P/kg dry feed fed) than with dibasic (2.6 g soluble P/kg dry feed fed) and tribasic (2.4 g soluble P/kg dry feed fed) sources of Ca. These indicated that intestinal absorption was lower with those di- and tribasic sources of Ca compared to mono basic sources of K, Na, and Ca. In this study, both availability and non-fecal excretion measurements suggested that K, Na, and Ca mono basic are highly available inorganic P sources for yellowtail.