DEVELOPMENT OF THE OLFACTORY ORGAN OF THE ARCTIC CHARR, SALVELINUS-ALPINUS (L) (TELEOSTEI, SALMONIDAE)

The structure of the olfactory epithelium in developing Arctic charr, Salvelinus alpinus, was studied by light and scanning electron microsc opy. Embryos, larvae, free-swimming fry, and individuals up to the age of 96 months after hatching were studied. In larvae about 10 days aft er hatching, microvillar and ciliated olfactory receptor cells were lo cated in a pit and no nares were differentiated. Fifty days after hatc hing, two nares were present on each side of the head, and about 20 da ys later one or two lamellae had started to differentiate and were vis ible as an elevation in the caudal part of the floor of the olfactory chamber. Six months after hatching there were 5-10 club-shaped lamella e, which in older fish acquired a more disk-like appearance. The numbe r and size of lamellae increased with the size of the fish, reaching t he maximum number, 10-15 per rosette, 18-30 months after hatching. At 18 months, secondary folding of the lamellae had started. Eighteen mon ths later, differentiated secondary lamellae were present and most of the central raphe was composed of indifferent epithelium. The olfactor y receptors were located in the depressions between the secondary fold s. The development of the olfactory organ is discussed in relation to the results of behavioural studies.