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Hydrodynamic and phylogenetic aspects of the adipose fin in fishes

Reimchen, T. E.; Temple, N. F.


T. E. Reimchen

N. F. Temple


The adipose fin on fishes is a highly conserved and enigmatic, small, non-rayed fin that has persisted from the Mesozoic on some basal teleosts such as salmonids. Using juvenile steelhead, Oncorhynchus mykiss (Walbaum, 1792), ranging from 5 to 18 cm standard length, we experimentally test the effects of adipose fin removal on swimming performance in a variable velocity flow chamber and quantify, with seven independent trials, amplitude and frequency of caudal fin movement at multiple flow velocities (range 10-39 cm.s-1). Results demonstrate that adipose fin removal on smolts produces an average 8% (range -3% to 23%) increase in caudal fin amplitude relative to unclipped fish across all velocities. However, we observed no effects in trials with smaller fish (12 cm). Consistent with speculations in the literature, our results show that the adipose fin may function to control vortices enveloping the caudal fin during swimming or, alternatively, function as a passive precaudal sensor of turbulent flow. Phylogenetic persistence of this trait among multiple groups of early bony fishes is probably due to its hydrodynamic attributes rather than developmental constraints, and the current widespread practice in fisheries of removing the adipose fin as a marking technique may have significant biological costs.


Reimchen, T. E., & Temple, N. F. (2004). Hydrodynamic and phylogenetic aspects of the adipose fin in fishes. Canadian Journal of Zoology, 82(6), 910-916.

Journal Article Type Article
Acceptance Date May 21, 2004
Publication Date Jun 1, 2004
Journal Canadian Journal of Zoology
Print ISSN 0008-4301
Publisher NRC Research Press
Peer Reviewed Peer Reviewed
Volume 82
Issue 6
Pages 910-916
Keywords vestigial trait, salmonid, adipose fin, swimming dynamics, fish phylogeny
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