An uncommon presentation of fungal infection in Atlantic salmon fry

Fungal infection in fry from several families of Atlantic salmon Salmo salar are reported. Moribund fry had a conspicuous cranial defect that corresponded with 18.3% mortality. The lesion was characterized by a domed, epithelium-covered swelling centered over the optic tectum. The swelling was an oedematous reaction to the extension of a fulminating necrotizing mycotic stomatitis and branchitis into the cranial tissues including the ventral meninges. The genus and species of the fungal pathogen were not identified, although histological examination was consistent with an oomycete. The % mortality of fry in each separately reared family ranged from 1.0 to 63.3%. An analysis of variance revealed significant differences in mortality among families (P<0.0001), and no significant difference between replicates of each family, reared apart. A possible genetic basis for resistance to fungal infection is discussed..