Effects of dietary inorganic phosphorus levels on growth, liver and intestinal morphology and digestive enzymes in fingerling obscure puffer (Takifugu obscurus)

Phosphorus (P) is involved in extensive metabolism and fish attain most of P from their diets. However, little is known about the optimal supplemented amount of P in diet for Takifugu obscurus (obscure puffer). To explore the effects of P on growth performance, tissues mineralization, digestive organs structure, and digestive capability, six diets supplemented with at 0, 2, 4, 6, 8 and 12 g/kg P were prepared and fed to obscure puffer (11.92 ± 0.19 g) for 56 days. The results showed that the highest final body weight, specific weight gain rate and protein efficiency ratio were observed in puffer fed diet supplemented with 6, 8 and 12 g/kg P. Dietary inorganic P supplements markedly increased P and calcium concentrations of the whole-body, muscle and vertebrae. The crude lipid content of whole body and muscle, plasma cholesterol and triglyceride content were reduced with increasing inorganic P supplement. For digestive capability, hepatic and intestinal structure and villi length of intestine were also significantly improved in puffer fed 6, 8 and 12 g/kg inorganic P diet. Moreover, hepatic and intestinal lipase activities were significantly enhanced in fish with raising inorganic P supplement in diet. Hepatic and intestinal amylase activities were markedly increased in puffer fed 8 g/kg inorganic P diet. The present study indicated that optimal dietary inorganic P level could promote growth by improving liver and intestinal morphology, vertebrae mineral deposition and increasing digestive capability in obscure puffer, which suggested that the range of supplemental inorganic P is estimated to be 4.5–6.4 g/kg based on the broken-line analysis of whole body and vertebrae P content. •Based on growth and vertebrae P content, the addition range of P in diet of obscure puffer was estimated to be 4.5–6.4 g/kg..•P supplement facilitate the growth improving intestinal structure, villi length, activities of intestinal lipase and amylase.•Phosphorus supplement may spare more protein for fish growth via decomposing lipid and carbohydrates as energy.