Just like cows, fish chew their cod

Baddum-tish!  OK, they don't chew their cud, but I can never resist a good pun (although I was seriously considering "Ruminations on the way fish eat" - better?).  I just love this new paper by Gintof et al. about how fish chew, mostly because its an idea that I never would have ever considered.  Basically, they explored whether fish just bolt their food, like lizards and snakes, or whether they engage in "intra-oral prey processing" (= chewing, sometimes sicnetific jargon cracks me up).  After looking at several model fish species, they conclude that yes, fish chew, and they chew about as many times as mammals do.  Its not like mammal chewing (especially herbivores) in that there is little side-to-side motion, but its rhythmic, and thats the most important thing.  This means that the bolting of food by lizards and snakes represents evolutionary loss of chewing, or that the model fish and all mammals both evolved chewing separately (they call this convergent evolution). 

They looked mostly at "basal" fishes like pikes, salmons and arowanas, that is, fish that show the most in common with the ancestors of all fish - I hate to use the term "primitive".  Its significant because it shows that chewing showed up early on in fish evolution.  One theory they put forth for the early appearance of chewing is that the rhythmic pumping of the jaws was necessary to keep fluid moving through the mouth and gills while eating.  Under that view, breathing water through the mouth and gills preadapted all who came after for processing food in their mouth, as opposed to, say, lobsters, whose teeth are in their stomachs.  I would dearly have loved it if they had included a more derived fish like a perch, pufferfish, or the sheepshead (with creepy human-like teeth, shown hereabouts) to show that chewing persisted in other branches of fish evolution, but you can't have everything.

Its a fun paper, you can read it here:

Gintof C, Konow N, Ross CF, and Sanford CP (2010). Rhythmic chewing with oral jaws in teleost fishes: a comparison with amniotes. The Journal of experimental biology, 213 (Pt 11), 1868-75 PMID: 20472774