Meeting Abstract
Hagfishes are an ancient group of craniates known to thwart fish predators by deploying large volumes of gill-clogging slime when attacked. This strategy is effective against suction feeding predators, whose attempts to suck a hagfish into their mouth also pull in released slime exudate, which can set up quickly and foul the gills. But what about biting predators? Recent work has shown that hagfish slime does not prevent biting predators from making their initial attack, but instead discourages subsequent attacks. For this this strategy to work, hagfish must be able to survive the initial bite, which led us to wonder whether hagfishes possess adaptations that minimize their risk of damage from biting predators. We tested two hypotheses: 1. Hagfish skin possesses remarkable puncture resistance compared to other fish skins. 2. The lax skin, and its very loose connection to the body of the hagfish helps them avoid damage during biting attacks by allowing the musculature and viscera to slip out of the way of penetrating teeth. To test the first hypothesis, we measured puncture resistance in one species of hagfish and 19 fish species and found that, although hagfish skin is comparable to many fish skins, even those with scales, it is not exceptional in its puncture resistance. To test the loose skin hypothesis, we conducted inflation trials with two species of freshly killed hagfish and found strong evidence of a flaccid body design. We also conducted ballistic puncture tests with isolated mako shark teeth on various preparations of hagfishes and one of their closest living relatives, the sea lamprey, and found that a loose and flaccid body design does indeed prevent damage to the body relative to turgid body designs or those in which the skin is tightly adhered to the body. Our results add a new dimension to our understanding of predator defense in hagfishes.
