Rainbow trout “eyed ova” from a regional trout hatchery were
placed in an aerated, re-circulating laboratory aquarium, maintained
at 10–15 C with a biological
filter to detoxify faecal
ammonia. Lipid was extracted from an additional 2050 rainbow
trout eggs to determine their vitamin D content by a chick toe–ash
bioassay [8]. The hatched
fish were reared on a semi-purified,
vitamin D-free diet, prepared in the form of soft gelatin pellets
(Table 1). The trout were kept in total darkness except for 10 min
each day, during feeding, when the aquarium room was lit with a
dim 60 W incandescent ceiling light with a minimum wavelength
emission of about 400 nm.