Catfish have opted for one of two different ways to feed. They either slurp up whatever takes their fancy, or scrape it off surfaces with their mouths. How scrapers evolved from slurpers intrigues a team of Belgian scientists led by Peter Aerts at the Universiteit Antwerpen. Sam Van Wassenbergh explains that the first thing you have to do if you want to understand how slurpers become scrapers is to understand how slurping relatives of modern scrapers feed now; they may have some of the attributes necessary to make the transition from slurping to scraping(p. 116). So, Van Wassenbergh and his colleagues filmed and analysed the feeding techniques of an African and a South-American bottom-feeding slurper, both of which are closely related to modern scraping feeders, and compared them with a more distantly related slurper. The team found that the bottom feeders' brain cases barely rotated at all while they were feeding, just like their scraping cousins. They also suggest that catfish with deep and narrow heads may be able to get closer to the ground when slurping food up, and this feature could have allowed the scraper's suction-feeding ancestors to make the lifestyle change.

Van Wassenbergh, S., Lieben, T., Herrel, A., Huysentruyt, F.,Geerinckx, T., Adriaens, D. and Aerts, P. (
). Kinematics of benthic suction feeding in Callichthyidae and Mochokidae, with functional implications for the evolution of food scraping in catfishes.
J. Exp. Biol.