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First published online January 31, 2006
Journal of Experimental Biology 209, 702-710 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02067

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Hagfish slime ecomechanics: testing the gill-clogging hypothesis

Jeanette Lim, Douglas S. Fudge^*, Nimrod Levy and John M. Gosline

Department of Zoology, University of British Columbia, 6270 University Boulevard, Vancouver, BC, V6T 1Z4, Canada

^* Author for correspondence at present address: Department of Integrative Biology, University of Guelph, Guelph, ON, N1G 2W1, Canada (e-mail: dfudge{at}uoguelph.ca)

Accepted 27 December 2005

Hagfish are able to produce substantial amounts of slime when harassed, but the precise ecological function of the slime is unclear. One possibility is that the slime acts as a defence against gill-breathing predators, whose gills may become entangled with the slime's mixture of mucins and fibrous threads during an attack. We previously demonstrated that hagfish slime does not bind water tightly, but instead behaves like a fine sieve that slows water down via viscous entrainment. These properties are consistent with the gill-clogging hypothesis, which we tested here by quantifying the effects of hagfish slime on water flow through an artificial gill model and real fish gills. Our results indicate that the slime is capable of clogging gills and increasing the resistance that they present to the flow of water. We also characterized the behaviour of slime release from live hagfish and the effect of convective mixing on the formation of slime in vitro. Our observations show that exudate is locally released from the slime glands as a coherent jet and that hagfish do not appear to use their slime as a protective envelope. We found that convective mixing between the exudate and seawater is necessary for proper slime formation, but excessive mixing leads to the slime's collapse. We suggest that the loose binding of water by the slime may be an optimal solution to the problem of delivering an expanding jet of flow-inhibiting material to the gills of would-be predators.

Key words: biomechanics, slime, hagfish, gill resistance, predator defence, Eptatretus stoutii