Water-soluble vitamins in fish ontogeny

Studies on vitamin requirement at early stages are difficult and vary in quality, both due to the scientific approach and vitamin analysis. Focus has been on water-soluble vitamins that cause dramatic losses of the offspring in practical farming situations or in wild life, like vitamin C and thiamine deficiencies respectively. Practical solutions including vitamin administration through brood stock and larvae diets have confirmed and corrected the vitamin deficiencies. For the other water-soluble vitamins, the situation is not so obvious. Descriptive studies of folate and vitamin B-6 during fish ontogeny have shown a net loss of vitamin during endogenous feeding and a steady transfer of vitamin from the yolk sac into the body compartment, and finally, dramatic increases in body vitamin levels after the start of feeding. The kinetics of mass transfer with ontogeny appears, however, to differ between vitamins. Start of feeding of fish larvae with live or formulated feeds includes several challenges with respect to water-soluble vitamins, including aspects of live feed enrichment and stability, micro-diet leaching, variable feed intakes, immature gastrointestinal tract, variable bioavailability of vitamins and larvae vitamin storage capacity. Consequently, the exact minimum requirements are difficult to estimate and vitamin recommendations need to consider such conditions.