A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

Do fish fart? Plus: angels dancing on the head of a pin (cont.)

November 10, 2000

Dear Cecil:

A quick question which I have been unable to find an answer to: do fish fart?

Cecil replies:

When you get a question like this you think, This is a golden opportunity to brighten up scientists' dull lives. I sent urgent inquiries all over the globe. Best response on the subject of whether fish fart: "They do if they're male."

Fish flatulence hasn't been a major focus of biological research, so the following is somewhat tentative. To some extent the answer depends on how you define "fart." Many fish have a swim bladder that they inflate or deflate as necessary to maintain buoyancy. Usually any expelled gas exits from the mouth and would properly be considered a burp. However, the sand tiger shark, Carcharias taurus, gulps air into its stomach at the surface, then discharges it out the back door to attain the desired depth. Surely this qualifies as flatulence in the common sense of the term.

But purists may object that this isn't true farting — that is, a by-product of digestion. We then get into a somewhat speculative realm. In theory any animal's metabolism produces carbon dioxide, while bacteria in the gut produce methane. Both must be purged lest the fish lose the ability to control its buoyancy. Carbon dioxide is typically eliminated via gas transport to the gills; methane has to escape some other way. However, actual sightings of farting fish are rare — and let's face it, underwater this isn't a phenomenon that could be easily concealed. Some experts say digestive gases are consolidated somehow with the fish's feces, which are packed into a gelatinous tube and then expelled. (Frequently the fish then eats this — not for nothing is the study of fish called ichthyology.) The point is, no farts.

Some fish observers claim they see a telltale bubble or two escape from the stern of a fish after it has gulped air at the surface (I've heard this said of tarpon). But again, this isn't strictly a product of digestion. On the Web I've seen the claim that inasmuch as coral is made of calcium carbonate, which when combined with stomach acid produces carbon dioxide, coral-eating fish ought to produce farts in abundance. If true, it seems to me, the critters in the vicinity of a typical coral reef should emit forests of bubbles unequaled since the days of Lawrence Welk — not the impression one usually gets. Then again, few visit reefs specifically for the purpose of detecting fish farts. In short, Alan, much research remains to be done. Maybe you could organize an expedition and let us know.

Alan gets, how shall we say, off the hook

Dear Cecil:

Your recent article is full of gas! [Long rant omitted in which author disputes Cecil's claim that little research has been done on fish farts.] During three summers, 1957-1959, I worked for the U.S Fish & Wildlife Service in Alaska. In 1959, as an ichthyological graduate student, I was in charge of a research project on herring, Clupea harengus. At that time, a herring fishing industry still existed in Alaska and we were attempting to tag herring in order to study their population size, migration patterns, etc.

Herring are schooling fish and easily lose scales if handled. Placing a tag in them could be very traumatic, leading to high mortality, unless they could be calmed down so as not to struggle while a tag is being inserted. My job, then, was to determine a proper time/ temperature-dependent dosage of fish tranquilizer that would not kill fish outright but quiet them down slowly and allow them swift recovery. A precise formula would have to be used on large open sea tagging operations. No one had ever done this before.

Over the course of two months, I observed herring behaviour in my seawater lab aquaria and experimentally narrowed down dosages to an optimum range. As the narcotic effect occurred, the herring relaxed, began to lose their upright orientation, and gas bubbles were released from what appeared to be the anus! I immediately thought: "I'm observing a phenomenon never previously reported in the ichthyological literature: herring farts!"

I then dissected some herring specimens and discovered that, in addition to the presence of a pneumatic duct, herring had a small posterior extension of the air bladder which opens alongside the anal opening. I searched the early herring literature and discovered that several members of the herring family, Clupeidae, also have such an opening. By location, the gas release I observed appeared to be farts but, technically, they were not.

In a previous summer, I had worked on one of the herring purse-seiners and discovered that while attempting to encircle a large school of herring with a purse-seine, the herring may "sound," i.e., begin swimming downward and deeply in order to escape the now encircling wall of netting. When a seine-boat captain surrounds a school, he and crew must work quickly to cinch up cables on the "purse" bottom before the herring "sound."

Here, however, was the serendipitous bonus of my summertime discovery adventure: the primary visual cue that a captain uses to determine whether or not a herring school has "sounded" is when an enormous cloud of bubbles appears at the surface. It means that, somehow, acting as a single school, the herring, in unison, send up a giant, bubbly (noisy?), silver "fart" which confuses the predator, in this case human fishermen, and the school survives another day! I do not know whether or not anyone has seen herring use this "farting"escape mechanism against natural predators but I suspect it occurs normally since many other similar diversionary tactics are used in the sea, e.g., squid ink.

I wrote this up in my summer research report to the US Fish & Wildlife Service and when I told my summer story to fellow graduates students at the University of British Columbia Institute of Fisheries, I became known as the guy who discovered fish farts!

Indeed, while completing his PhD dissertation on the physical and physiological effects (on swimbladders) of passing young migrating salmon through hydroelectric dam turbines, one of my colleagues, Dr. Harold Harvey, named the excretory expulsion of swimbladder gasses by young salmon in my honor. He called it "exkrejsiation"!

In the interest of ichthyological truth and wisdom, I remain, sincerely …

Cecil replies:

Just proves what I've always said. Pick any question, no matter how bizarre, and there is always someone, somewhere, who has devoted his life (or at least several summers) to researching the answer.


Dear Cecil:

In your discussion of angels dancing on the head of a pin in The Straight Dope Tells All, page 133, you write, "Martinus Scriblerus … is a pseudonym of a sort in common use among Enlightenment satirists." This is a little misleading: it's the name of a fictional author invented by Alexander Pope, John Arbuthnot, Jonathan Swift, John Gay, and Thomas Parnell, founders of the Scriblerus Club and coauthors of The Memoirs of Martinus Scriblerus. Haven't got a copy of this handy to see if the passage indeed turns up in chapter seven, but we'll leave that to you.

Cecil replies:

Told you my 18th century files were a mess. I have, however, located the indicated volume, said to be the origin of the satirical claim that Scholastic philosopher Thomas Aquinas once debated how many angels could dance on the head of a pin. Turning to chapter seven, we see Pope and his fellow smart alecks indeed poked fun at some of Aquinas's more esoteric speculations. However, the question of how many angels can dance on the head of a pin isn't among them. Thus, while we know Aquinas did argue whether several angels can be at the same time in the same place (solemn conclusion: no), we still aren't sure who gave the discussion its modern comical twist. Alan, since you have nothing to do now that Prof. Krejsa has plumbed the depths of fish farts, see what you can do with this.

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