Eating without using your mouth seems like an impossibility to many vertebrates, but not to hagfish, according to a study to be published in a forthcoming issue of the journal Proceedings of the Royal Society B: Biological Sciences.
Hagfishes (Myxini) are a group of ancient vertebrates with vile feeding habits: these scavengers feed by plunging their writhing bodies into the body cavities of dead and dying animals and eating their way out.
Chris Glover, Carol Bucking, and Chris Wood hypothesised that this disgusting feeding habit may lend itself to novel methods of nutrient acquisition through the skin (particularly since the salt concentration of hagfish tissue is the same as that of seawater, suggesting that dissolved substances can cross this barrier easily), and set out to test this hypothesis in their study.
Using the Pacific hagfish (Eptatretus stoutii) as their study organism, the authors investigated their potential to absorb amino acids through skin and gill surfaces.
The authors stretched a piece of hagfish skin over the rim of a glass tube. The glass tube was immersed in a flask containing seawater that had added food colouring, and radioactively-labelled amino acids and sugars added to it while the fluid in the glass tube contained a solution with the same concentration of salts as hagfish tissue.
After a few hours, radioactivity was observed in the fluid in the glass tube as the amino acids were absorbed through the skin (and into the tube).
The authors also noted that the skin was highly selective in what was absorbed, since the food colouring remained outside the glass tube and in the flask.
The fact that the absorption rate increased with increasing concentration of amino acids up till a certain point indicated that a specific active transport mechanism was involved (when all of the transport sites are involved in moving the amino acids across the skin, increasing amino acid concentration at this saturation point will not increase the rate of absorption).
The authors’ calculations suggest the relatively large area of the skin could absorb nutrients at around the same levels as the digestive tract and that the skin could actually absorb nutrients faster than the intestines.
According to lead author Chris Glover, the ability to absorb nutrients through the skin and gills of the hagfish may be an adaptation to an environment in which meals are infrequent and there is fierce competition for the carcasses.
For more information, see the paper: Glover, CN, C Bucking and CM Wood (2011) Adaptations to in situ feeding: novel nutrient acquisition pathways in an ancient vertebrate. Proceedings of the Royal Society B: Biological Sciences DOI:10.1098/rspb.2010.2784