Fish have a remarkably diverse array of head designs, from snail-crushing redear sunfish to dainty zebrafish that feed on plankton and wide-mouthed bewhiskered catfish, but they all have one thing in common: they all suck. Corrine Jacobs and Roi Holzman, from the University of Tel Aviv, Israel, explain that fish rapidly expand and open their mouths to slurp up water, sweeping in any tasty morsel within range, ‘yet it is unclear how variable suction flows are across species’, the duo says. Together, Jacobs and Holzman filmed water being sucked into the mouths of fish ranging from oscars, knifefish and goldfish to tetras and even an amphibian (the tiger salamander) to find out how much their slurps differed, and they were amazed to find how little variation there was.

No matter how large or small the fish's mouth, they rarely slurped in water that was more than a mouth's width away and the suction always peaked at the instant when the fish's mouths were at their widest gape, although the fish with the largest mouths always produced the fastest gush of water. So, instead of adapting their suck to suit their diet, all fish – and probably other suction feeders – use pretty much the same style of slurp despite their vast array of head designs. And Jacobs and Holzman suggest that the reliability of a fish's slurp may have allowed them to experiment with other head designs as they evolved to vacuum up different dinners.