Influence of feeding regime on intraspecific competition, fin damage and growth in 1+ Atlantic salmon parr (Salmo salar L.) held in freshwater production cages

Abstract

The feeding behaviour, growth and feed conversion ratio (FCR) of cage-held Atlantic salmon parr (Salmo salar L.) were studied when in 576 m 3 (12 m  12 m  4 m) commercial freshwater cages under ambient water temperature (8.84 AE 3.53 1C) and photoperiod (11.02 AE 2.05 h) for 205 days. The e¡ect of feeding regime on ¢n damage was also investigated. Six groups (n 5 31234 AE 2051 ¢sh group À1 , initial stocking density 1.25 AE 0.14 kg m À 3 ) were fed to satiation using either (a) an imposed regime involving scheduled, ¢xed ration feeding every 10 min from dawn till dusk or (b) on demand from dawn till dusk using commercial interactive feedback systems. During feeding, there were no signi¢cant di¡erences in aggression although swimming speeds and turning angles were signi¢cantly higher in ¢sh under the imposed regime. On-demand feeding signi¢cantly reduced the incidence of dorsal ¢n damage. There was no clear relationship between ¢sh size, feed regime and the incidence of ¢n damage until 1 week before the ¢sh were transferred to marine cages, when the smallest ¢sh under each feeding regime had the highest incidence of ¢n damage. Interestingly, growth did not di¡er between regimes, but ¢sh under the imposed regime were signi¢cantly overfed and achieved higher FCRs.

Behavioural indicators of welfare in farmed fish

“…For example, cage-held Atlantic salmon parr and smolts exhibited increased swimming speeds and performed sharper turns during feeding when they received a uniform, temporally predictable ration to perceived daily satiation. However, fish fed to daily satiation using demand feeding technology did not significantly change their swimming speeds and performed moderate turns during feeding (Noble et al 2007b, c). Fish can also exhibit increasingly complex swimming manoeuvres during feeding in response to underfeeding (Andrew et al 2004).…”

“…However, increased swimming activity prior to and during a meal can also be a sign of underfeeding or a poorly designed feeding regime (e.g. Andrew et al 2004;Noble et al 2007b, c). Therefore, care must be taken to avoid underfeeding as the ensuing feeding frenzy could be interpreted as a positive indicator of welfare.…”

“…Some authors, e.g. Rose (2002Rose ( , 2007 and Cabanac et al (2009), argue that Table 1 Examples of behavioural changes in responses to aquaculture procedures or stressors that could be used as species-specific operational welfare indicators in farmed fish Beaumont et al (1996) Juvenile lake chubsuckers Erimyzon sucetta Scheduled (vs. on demand): : swimming speed and turning angles Noble et al (2007b, c) this is not possible because their behaviour is simple and reflexive and they lack a neocortex. Yet, a growing body of evidence related to cognitive (Braithwaite 2006), neuroanatomic (Portavella and Vargas 2005;Rodriguez et al 2006) and emotional (Sneddon 2007;Yue et al 2008) aspects of fish behaviour provides strong support for sentience (the ability to feel) in fish.…”

“…food-anticipatory activity (see also section ''Group swimming behaviour'') when a scheduled feeding regime was used as opposed to fish receiving random feeding (Sánchez et al 2009). However, imposed fixed regimes can increase the incidence of fin damage and injury as compared to demand feeding (Noble et al 2007b, so a farmer should bear this in mind when making decisions on utilising a fixed ration or demand feeding strategy. In addition, the use of self-feeders has been shown to improve feed conversion ratio and growth in rainbow trout (Alanärä and Brännäs 1996) and can also be beneficial for their welfare (Suzuki et al 2008).…”

“…The techniques for delivering food should be appropriate for the particular species (Alanärä and Brännäs 1996;Alanärä et al 1998;Andrew et al 2002;Noble et al 2007b). For instance, bottom-feeding flatfish have been shown to have improved welfare (measured as feed intake and feeding motivation) when fed sinking pellets compared with floating pellets (Kristiansen and Fernö 2007).…”