Hippoglossus hippoglossus L

Physical damage among farmed Atlantic halibut, comprising injuries to eyes, pectoral fins and tails, first becomes apparent post-weaning. This study examined social interactions in farmed halibut, to determine whether potentially serious aggression occurred in fish of different age classes in which injury has been reported. Specific aims were to understand the context in which such behaviour happens and to examine individual variations in aggressiveness. Behavioural data were collected via direct observation and video footage from halibut of six size classes in Norway and the UK. Food was delivered to experimental tanks, one pellet at a time, to enable the Ž identification of consumers and the registration of all social activity. In five size classes 45–3000 . g , potentially damaging contact among fish, occurred solely during feeding and comprised Ž . targeted aggression nips and chases and collisions due to misdirected feeding attempts. Feed intake was positively correlated with levels of aggression, and fish were most aggressive early in a feeding session. A mean 85% of attacks were directed at fish that had won pellets from aggressors. The frequency of aggression declined markedly with fish size, and no aggression was Ž . observed in the largest size class 2.5–10 kg . Our studies indicate that the majority of aggression occurs early in hand feeding sessions, when fish are particularly hungry. To reduce the occurrence of this behaviour, we suggest that feed should be delivered by a combination of hand and automatic feeders. In this way, feed can be well-dispersed and provided throughout the day, ) Corresponding author. Tel.: q44-141-330-4769; fax: q44-141-330-5971. Ž . E-mail address: [email protected] K. Greaves . 0044-8486r01r$ see front matter q2001 Elsevier Science B.V. All rights reserved. Ž . PII: S0044-8486 00 00476-2 ( ) K. GreaÕes, S. TuenerAquaculture 193 2001 139–147 140 thereby preventing a build-up of hunger levels and ensuring that fish are fed to satiation. q 2001 Elsevier Science B.V. All rights reserved.