A study on enrichment of the rotifer Brachionus “Cayman” with iodine and selected vitamins

Brachionus “Cayman” is a widely used live feed organism in fish larvae culture. Our previous studies indicate that these live feeds may not fulfill the nutritional requirement of marine fish larvae. The present study aimed to enrich rotifers with the micronutrients thiamine, vitamins C, A, and E, and iodine up to the levels found in copepods, the feed for fish larvae in the wild. Various levels of these micronutrients were supplemented along with the basal diet: Baker's yeast–pronova oil–live Chlorella (65:25:15 DW). Thiamine was supplemented as thiamine HCl, vitamin A as retinyl palmitate, vitamin C as Stay C or ascorbic acid polyphosphate, vitamin E as dl-α-tocopherol and iodine as Lipiodol®, ethyl esters of iodized fatty acids from poppy seed oil. Rotifers were cultured with these supplemented diets for 4 days. There was a significant positive relationship between dietary and rotifer concentrations of thiamine, vitamins C and E, and iodine, as indicated by the regression equations: thiamine y = 0.73x + 30, r = 0.88; vitamin C: y = 0.023x + 125, r = 0.91; vitamin E: y = 0.078x − 12, r = 0.96; and iodine: y = 0.88x + 5, r = 0.96, y being the rotifer concentration and x being the concentration of active component in the diet, both in mg kg− 1 DW. Compared to copepod levels, the control diet gave sufficient amounts of thiamine in the rotifers (25 ± 14 mg kg− 1 DW). The highest level of vitamin C enrichment did not give copepod levels of vitamin C (500 mg kg− 1) in rotifers, but by extrapolation the diet should contain 16 g kg− 1 vitamin C from Stay C to obtain this level. This corresponds to 4.6% Stay C in the diet. A dietary concentration of 1.6 g kg− 1 DW of α-tocopherol is needed to enrich rotifers up to copepod levels (110 mg kg− 1), while 52 mg kg− 1 dietary iodide would be needed to obtain the lower range of copepod levels of iodine (50 mg kg− 1). There was no significant relationship between dietary and rotifer vitamin A concentrations (y = 0.0097x + 5.4, r = 0.57). Control rotifers contained 4.9 ± 0.5 mg kg− 1, while rotifers enriched with the highest concentration of 200 mg kg− 1 vitamin A contained 7.0 ± 1.7 mg kg− 1 vitamin A. However, both control and enriched rotifers contained sufficient concentrations of vitamin A to cover the requirement in fish larvae.This study shows that concentrations of thiamine, vitamin C, vitamin E and iodine increase almost linearly in Brachionus in response to simultaneously increasing dietary concentrations. This indicates that rotifers can be enriched up to copepod levels with these nutrients, to satisfy marine fish larvae requirements. Vitamin A was not increased in the rotifers by dietary retinyl palmitate under the conditions used in the present study.