Table 1 lists biotin requirements for various species.
The commercial form of biotin is fairly stable to air and heat in dry multivitamin premixes but sensitive to light and high humidity. Pelleting and heat have little effect on biotin activity in feeds, but oxidative rancidity severely reduces biotin bioavailability (Halver, 1989). Much of the biotin in feed ingredients exists in a bound form, epsilon-N-biotinyl-l-lysine (biocytin), which is a component of protein. The bioavailability of biotin from biocytin varies widely, depending on the digestibility of the proteins (Baker, 1995). Low-temperature fish meals were found to contain on average 0.4 mg biotin per kg but ranged between 0.36 mg and 0.8 mg per kg (Mæland and Sandnes, 1999).
Intestinal microflora also affect biotin requirements (Sugita et al., 1992). Depending on the resident microbial population, the biotin requirement may be increased, due to bacterial usage of biotin or decreased, due to bacterial production (Sugita et al., 1992). Rainbow trout fed practical diets supplemented with 0.11 ppm of biotin where shown to respond to stress better than fish fed diets that were not supplemented (Koppe et al., 1993).
The requirement for biotin can be increased with a reduction in dietary lipid levels (Poston and McCartney, 1974; Walton et al., 1984). However, with typical dietary lipid levels found in fish diets, this is not likely (Robinson and Lovell, 1978; Walton et al., 1984).
