Mental Floss

Two More Odd Things I Just Learned About Fish

Matt Soniak

When I'm not blogging for mental_floss, I can usually be found wearing bright orange rubber pants and gutting, cutting and selling fish at my local Whole Foods (and winning awards for it). Sometimes, my two worlds collide and I find some scientific research involving my ocean-dwelling friends that begs for a blog post. This is one of those times.

1. Catfish are seriously terrifying

The order Siluriformes (we know its members as catfish) is diverse group. It contains 34 recognized families, which contain over 400 genera, which contain some 3,000+ known species. Some of these catfish have long been known to be venomous, but the number of venomous species and their distribution on the evolutionary tree have only recently been examined and documented.

Jeremy Wright, from the Department of Ecology and Evolutionary Biology at the University of Michigan, Ann Arbor, recently published the results of a histological and toxicological investigation into venomous catfish.[1] He cataloged 158 venomous species and looked into the biological effects of their venom (the venoms have neurotoxic and hemolytic[2] properties and can produce "severe pain, ischemia, muscle spasms and respiratory distress" (though a single species' venom may not produce all of these effects). Wright's results allowed him to estimate the total number of venomous species and he writes that his results indicate that approximately 1250-1625+ catfish species should be presumed venomous. If his numbers are accurate, venomous catfish may outnumber the combined total of all other venomous vertebrate species.

I, for one, welcome our poisonous catfish overlords and am immediately switching to oyster po' boys.

2. Pipefish will break a few eggs to make an omelet

pipefish /

Researchers radioactively labeled a batch of eggs prior to their transfer to a male so they could trace nutrient uptake from these eggs and found that the labeled amino acids wound up in the father's brood pouch, liver and muscle tissues. The research suggests that the blood vessels in the fathers' brood pouches allow them siphon away nutrients from their eggs. This seems to be done for the father's own use, and not for the redistribution of nutrients among the other eggs since the labeled amino acids weren't observed in the rest of the eggs!

1Jeremy J Wright. "Diversity, phylogenetic distribution, and origins of venomous catfishes." BMC Evolutionary Biology 2009, 9:282. doi:10.1186/1471-2148-9-282.

2Hemolytic venoms have the particularly gruesome effect of breaking down the flesh. The blood vessels exposed to the venom lose their ability to contain the blood, the clotting effect is suppressed, and the flesh in the area fills with fluid and dies.

3Gry Sagebakken, Ingrid Ahnesjö, Kenyon B. Mobley, Inês Braga Gonçalves, Charlotta Kvarnemo. "Brooding fathers, not siblings, take up nutrients from embryos." Proceedings of the Royal Society B. Published online before print November 25, 2009. doi: 10.1098/rspb.2009.1767