The physiological effects of salmon lice infection on post-smolt of Atlantic salmon

The physiological effects of salmon lice infections on post-smelt of Atlantic salmon were examined by experimentally infecting hatchery reared post-smelts with infective copepodids. Even at high infection intensities, ranging from 30-250 lice per fish, early chalimus stages did not have severe, physiological effects on the fish. There was a sudden increase in fish mortality after the appearance of preadult I stages. Infected fish were then suffering due to lesions and osmoregulatory failure. Plasma chloride level increased significantly and total protein, albumin and haematocrit decreased significantly in infected compared to uninfected fish. All infected fish became moribund before adult lice appeared. Infection intensities above 30 salmon lice larvae per fish thus appear to cause death of Atlantic salmon post-smelt soon after the lice reach their pre-adult stage. (C) 1996 The Fisheries Society of the British Isles