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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 social
    environments, 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 sizegraded
    groups 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 of
    the Small (SS). Grading (overall mean of the four grading groups) improved growth rate by
    10% compared with ungraded controls, but the effect was also significantly affected by
    social environments, because in the latter half of the experiment overall growth was
    improved 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 rank
    correlations 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, the
    degree of mean rank position changes varied between the experimental groups and was
    higher 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 three
    groups. Growth rate differences may be the product of different degrees of interactions
    among individuals, and based on the higher overall growth rates in the groups with larger
    size variation (i.e. SL, LS) it is concluded that juvenile halibut should not be too intensively
    size graded.

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