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Abstract

Two methods for assessing the status of an individual rainbow trout Oncorhynchus
mykiss within a group hierarchy, radiographic determination of individual food intake
and analysis of brain serotonergic activity, were compared. The results showed that
individual food intake, measured as the average share of the group meal, and brain
serotonergic activity, measured as brain levels of 5-hydroxyindoleacetic acid (5-HIAA)
or as 5-HIAA/5-HT (serotonin) ratios, were inversely correlated with each other,
suggesting that both methods could be used as indicators of the position of the rainbow
trout in a dominance hierarchy. In addition, specific growth rate correlated significantly
with brain 5-HIAA/5-HT ratios.
The results indicate that the increase in brain 5-HIAA/5-HT ratios in subordinate
individuals is caused by an increased use (release) of 5-HT in these fish, and not by an
increase in the level of tryptophan, the amino acid precursor of 5-HT. The relationships
between social rank, food intake, growth, stress and brain serotonergic activity of fish in a
social hierarchy are discussed.

Item Type:	Article
Authors/Creators:	Winberg, S and Carter, CG and McCarthy, ID and He, ZY and Nilsson, GE and Houlihan, DF
Keywords:	Feeding rank, hierarchy, serotonin, tryptophan, rainbow trout
Journal or Publication Title:	Journal of Experimental Biology
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