Hagfish don't score high on the fish charisma scale. They are very unattractive, have a reputation for devouring victims from the inside out and, if attacked, they instantly release litres of repulsive slime. However, despite their repelling habits, Douglas Fudge from the University of Guelph is intrigued by hagfish slime. He says ‘It's like nothing else in biology because they produce it so quickly and in such large quantities and it's reinforced with fibres.’ Fudge has been working on the material properties of hagfish slime ever since his PhD and explains that the creatures exude a viscous milky white secretion – pre-slime – packed full of microscopic packets (vesicles) carrying a highly absorbent glycoprotein called mucin. These vesicles suddenly explode upon contact with seawater, releasing the mucin and producing mature slime. But how do hagfish prevent the mucin vesicles from exploding inside their slime glands before the vesicles contact seawater? Fudge wondered if something in the pre-slime was stabilizing the vesicles to prevent them from rupturing too soon. Teaming up with undergraduates Julia Herr and Tim Winegard, the trio decided to find out what hagfish pre-slime is made of (p. ).
‘Tim is our hagfish wrangler extraordinaire who worked out how to work with fresh slime,’ says Fudge. Fishing the animals out of holding tanks and slipping them into anaesthetic, Winegard gently stimulated the animals and collect samples of the milky pre-slime for analysis. Spinning the pre-slime in a centrifuge, Winegard separated it into three layers with protein fibres at the bottom, mucin vesicles in the middle and the clear fluid that they were suspended in at the top. Sending the clear fluid to Mike O'Donnell at McMaster University and Paul Yancey at Whitman College for chemical analysis, Fudge discovered that the fluid contained very high levels of two methylamines, TMAO and betaine, as well as a variety of inorganic ions including potassium, sodium and chloride.
Having found the recipe for hagfish pre-slime fluid, Fudge was curious to find out whether it might stabilise the mucin vesicles before they contact seawater. Reasoning that the TMAO and betaine in the fluid would have a higher osmotic pressure than the vesicles and should dehydrate the vesicles and prevent them from rupturing, Fudge and Herr decided to test whether the methylamines could stabilise the vesicles. But even when Herr added solutions of 1200 mmol l−1 of TMAO and betaine to the vesicles, most of the vesicles exploded within 20 s of contact, while others took longer to burst.
Maybe something else in the fluid was stabilising the vesicles; but when Herr made a solution containing all of the known constituents of the slime fluid from off the shelf chemicals, the vesicles still ruptured. ‘This was not what we were expecting,’ says Fudge, so Herr collected some of the natural fluid from the pre-slime and tried that to see if it prevented the vesicles from bursting. Amazingly it did not.
So the pre-slime fluid was not able to stabilise hagfish mucin vesicles and prevent them exploding before contact with seawater. Having found the recipe for hagfish pre-slime, Fudge is still keen to find out why hagfish mucin vesicles do not rupture in the animal's slime glands, what mechanisms are at play when the vesicles rupture in seawater and why some vesicles rupture faster than others.
