The effect of varying forms of dietary ascorbic acid on the nutrition of juvenile tilapias (Oreochromis niloticus)

An 8-week growth study was conducted to evaluate the utilisation of L-ascorbic acid (AA), the sodium salt of L-ascorbic acid (NaAA), glyceride coated L-ascorbic acid (GCAA), the barium salt of L-ascorbic acid 2-sulphate (AA2S) and ascorbyl palmitate (AP) in diets for Oreochromis niloticus. All five forms were added to the basal diet, containing no ascorbic acid (AAF) on an equimolar basis to supply 125 mg ascorbic acid/100 g of dry diet. In terms of growth, feed conversion and protein utilisation diets containing all forms of ascorbic acid performed well. Fish fed AAF performed poorly and showed clinical signs of ascorbic acid deficiency such as haemorrhage, caudal fin erosion, exophthalmia, and 7% exhibited spinal deformity. Fish fed diet AAF also exhibited depressed haematocrit, haemoglobin, hepatosomatic index and muscle and liver glycogen compared with fish fed diets containing the vitamin C forms. Total ascorbate concentrations in 10 tissues were lowest in fish fed diet AAF and lower in fish fed AA2S than for the other ascorbic acid forms. When supplied in semipurified diets on an equimolar basis the five forms of ascorbic acid evaluated supported similar performance and alleviated signs of deficiency.