Meeting Abstract
Hagfishes defend themselves from fish predators by releasing exudate from their slime glands when they are attacked. The slime exudate contains condensed mucus and protein threads, which combine with seawater and expand to form an ultra-dilute, viscoelastic material. Recent work has shown that slime release repels further attacks by fish predators by lodging in their gills and putting them at risk of suffocation. In this study, we explored the biophysical mechanisms that allow the slime to clog fish gills. Using a custom apparatus designed to measure the flow rate of test solutions through a screen, we found that the slime’s ability to impede flow initially increased strongly and linearly as a function of concentration, and started to plateau at an optimal concentration of 45 mg/L of mucus. We performed similar trials with hydrogels formed from suspended xanthan gum and psyllium husk and found that hagfish slime is 120 and 130 times more effective at impeding flow than these materials, respectively. We found that the mucus alone has an optimal clogging concentration of 102 mg/L, suggesting that the mucus and threads act synergistically to disrupt flow and that the mucus is responsible for most of the clogging effect. We also tested the hypothesis that the threads perform a distinct function from the mucus, which is to allow the slime to catch on and and persist on the gills. Flushing experiments were consistent with this hypothesis, with thread presence having a strong positive effect on the ability of the slime to impede flow after repeated flushing with seawater. Our results provide insights into the mechanisms of gill clogging by hagfish slime and raise new questions about how it performs so well at such low concentrations.
