Behavioural changes following intraperitoneal vaccination in Atlantic salmon (Salmo salar)

Granulomatous peritonitis is often induced by intraperitoneal vaccination in fish. Peritonitis is a very painful condition in mammals, but little is known about how fish experience this condition. Previous studies have looked at pathological change and feeding behaviour in large groups of fish. Therefore, studies of the effects of vaccination on individual fish are warranted. The aim of this study was to provide a detailed description of the behaviour of individual fish post-vaccination and to test whether behavioural changes indicative of pain and/or stress correlated with pathological changes induced by vaccination. Twelve Atlantic salmon (Salmo solar) were injected intraperitoneally with either saline or an oil-adjuvanted vaccine, and their behaviour was recorded from 30 min before feeding to 4 min after the first food delivery on selected days over a period of 5 weeks. Latency to eat increased in the vaccinated fish 2 h and 6.5 h after injection. Swimming in the lower half of the tank before feeding increased in the control group 1.5 h after injection. There was also a tendency towards a decrease in swim low activity during feeding for vaccinated fish at 2 h and at 3 days after injection compared with both baseline and the control group. Social behaviours were reduced directly after injection, but the original dominance relationships did not seem to be changed by the treatment. The post mortem revealed macroscopic evidence of peritonitis in the vaccinated fish, giving them a significantly higher pathology score compared to control group. There was a positive correlation between pathology score and the latency to eat 2 h, 6.5 h and 3 days after injection, and a moderate, negative correlation between pathology score and swimming low in the tank during feeding at 2 h after injection. In conclusion, intraperitoneal vaccination can induce peritonitis in fish, the severity of which correlates with changes in behaviour. The reduced interest in food and decreased activity observed in the vaccinated fish is similar to what has been reported for other fish species in the acetic acid test, and may thus be general responses to pain in at least some species of teleosts. This study is the first to describe post-vaccination behavioural changes in individual fish. (C) 2011 Elsevier B.V. All rights reserved.