Dietary citric acid improves phosphorus and calcium availability and intestinal morphology of Nile tilapia Oreochromis niloticus

Citric acid is an organic acid, which has been used as a feed additive because it has a reasonable cost, pleasant taste, and fast assimilation, showing positive effects on the growth and health of some livestock and aquatic species. This study aimed to evaluate the effects of increased levels of citric acid (0, 10, 20, 30, and 40 g/kg) in an isonitrogenous (280.00 g/kg of digestible protein) and isoenergetic diet (12.98 MJ/kg of digestible energy) on growth performance, body composition, apparent digestibility of nutrients and minerals, hematology, pH in stomach and intestine, and intestinal histomorphometry of Nile tilapia juveniles. Fish (n = 200, initial average weight of 14.59 +/- 0.81 g) were randomly distributed in 25 experimental tanks (five replicates per treatment) and fed experimental diets over a 40-day period. Increasing levels of citric acid supple-mentation resulted in a decrease in the pH of the experimental diets (P = 0.021). However, no significant differences in pH levels were observed in the stomach and intestine among the treatments (P > 0.05). Citric acid supplementation did not significantly (P > 0.05) affect the growth performance variables, body composition, or the apparent digestibility coefficients (ADC) of dry matter, crude protein, gross energy, ether extract, and ash of the diets. Fish fed diets with 10 and 30 g/kg citric acid exhibited higher values for total leukocytes (P = 0.043) and total plasma protein (P = 0.019) compared to the control group. Diets supplemented with 20 g/kg citric acid showed a higher ADC value for phosphorus (P = 0.027) and calcium (P = 0.032) compared to the control. Additionally, fish fed with diets containing 20 g/kg citric acid demonstrated higher values for villus height (P = 0.002) and width (P = 0.048), crypt depth (P = 0.035), and villus: crypt ratio (P = 0.014) compared to the control group. In conclusion, the supplementation of 20 g/kg citric acid improved the availability of phosphorus and calcium and positively influenced the intestinal morphology of Nile tilapia juveniles.