Effect of Citric Acid on Growth and Red Coloration of Red Porgy (Pagrus pagrus)

This study investigates the effect of dietary citric acid supplementation on the growth and red coloration of red porgy (Pagrus pagrus). Red porgy (~0.5 g) were fed one of four diets: (a) an unsupplemented control, (b) a diet containing astaxanthin at 0.06 g/kg, (c) a diet containing citric acid at 30 g/kg, or (d) a diet containing both astaxanthin at 0.06 g/kg and citric acid at 30 g/kg. After two months, fish reached ~6 g with no differences in growth between groups. Astaxanthin increased the total carotenoid concentration in the skin from 3.16 to 45.15 μg/g in fish fed the astaxanthin-supplemented diet and from 2.61 to 50.07 μg/g in fish fed the diet supplemented by both astaxanthin and citric acid, producing a distinctive red skin color. Diet composition did not affect the melanin concentration of the skin, which ranged 57.60-68.18 μg/g and did not differ between groups. Dietary supplementation of citric acid did not affect growth or coloration in red porgy, thus alternative means of administering citric acid should be sought, for example, adding citric acid to the rearing water or injecting it into the fish body