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Best among unequals? Effect of size grading and different social environments on the growth performance of juvenile Atlantic halibut
Imsland, A.K.; Jenssen, M.D.; Jonassen, T.M.; Stefansson, S.O. (2009). Best among unequals? Effect of size grading and different social environments on the growth performance of juvenile Atlantic halibut. Aquacult. Int. 17(3): 217-227
In: Aquaculture International. Springer: London. ISSN 0967-6120, more
Peer reviewed article

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Keywords
    Growth; Social environment; Hippoglossus hippoglossus (Linnaeus, 1758) [WoRMS]; Marine

Authors  Top 
  • Imsland, A.K.
  • Jenssen, M.D.
  • Jonassen, T.M.
  • Stefansson, S.O.

Abstract
    In order to study the effect of rearing juvenile halibut in different socialenvironments, individually tagged juvenile halibut were size-graded into two size classes(Large, L, and Small, S) with ungraded fish as control. After ca 6 weeks, the two sizegradedgroups were again graded into two size classes creating four experimental groups:Large of the Large (LL), Small of the Large (SL), Large of the Small (LS), and Small ofthe Small (SS). Grading (overall mean of the four grading groups) improved growth rate by10% compared with ungraded controls, but the effect was also significantly affected bysocial environments, because in the latter half of the experiment overall growth wasimproved by 11 and 12% in the two groups with larger size variation (i.e. SL and LS,respectively) compared with the two other groups (i.e. LL and SS). Significant size rankcorrelations were maintained during the experiment, these were higher in the ungraded(Control) group and the SS and LL groups than in the SL and LS groups. Further, thedegree of mean rank position changes varied between the experimental groups and washigher in the SL (20.7) and LS (25.6) groups than in the Control (10.5), LL (15.1), and SS(15.4) groups. This could possibly indicate a stronger social hierarchy in the last threegroups. Growth rate differences may be the product of different degrees of interactionsamong individuals, and based on the higher overall growth rates in the groups with largersize variation (i.e. SL, LS) it is concluded that juvenile halibut should not be too intensivelysize graded.

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