Something’s fishy about this bladder

I had to teach a lab on fish recently. I’m not big on vertebrates, as I think they are highly overrated. However, I guess it’s necessary for humans to know a little about fish since we happen to have vertebrae, too. Don’t be embarrassed by that, though. Vertebrates only make up a small percent of all the animals.  About all you and I can claim is to be interesting, fringe creatures. We add variety to the world! Still, a whole lab on fish seems excessive. 

Anyway, the lab led to a discussion of fish bladders. Fish don’t really have bladders like you and me. I mean, they live in water and can just go in the pool whenever they want. No need to hold onto anything. What they have is an oblong bladder filled with gas. This is located internally just below the spine. By regulating the amount of gas in the bladder, fish regulate their buoyancy and depth in the water. Me? I depend on the buoyancy of fat to keep me afloat.

This fish bladder has been known about for centuries. Anciently it was called the vesica pisces: fish bladder. Before scientists there were philosophers.  Philosophers are people who sit around and ask questions. The early scientists did this also. More recently, however, scientists seem to have evolved into people who sit around, have all the answers and must not be questioned. 

One question early philosophers asked was, “How do you make an accurate equilateral triangle?” About the only tools they had were a straight edge and a compass. You know, the kind of compass that allows you to draw an accurate circle by placing the point in one position and then rotating the pencil around the point with a set radius.

I don’t think they actually used pencils then because they hadn’t been invented yet. But they did discover that if you drew one circle, and then placed the point of the compass on the edge of the circle and drew another of the same radius, you created two overlapping circles. The overlapping portion of the circles made a pointed oblong shape like a football, although the NFL hadn’t been invented yet either. They called this the vesica pisces because it looked to them somewhat like a fish bladder. 

This alone probably doesn’t mean much to enlightened modern folks, except that they also discovered that if you draw a straight line directly through the center of the circles the line also bisects the sides of the vesica pisces. Then, if you draw straight lines from the midpoints of the vesica pisces sides to the pointed end of the football, you create a perfect, equilateral triangle. If you draw a line from the midpoints of the sides to the other end of the football, you make a second equilateral triangle, upside down. 

This explains the Pisces constellation of stars. I always thought it looks more like a V than a fish. However, come to think of it, a fish is sort of shaped like two equilateral triangles attached base to base. In fact, a vesica pisces, with the sides extended slightly on one end, is the universal symbol for a fish, and the early Christian church. 

I have to admit that the triangle, as well as the number three, are significant concepts, in spite of the fact that I hated trigonometry. It takes three legs to make a stable chair, three plaits to make a braid, three tenses to express time, and three primary colors. Is it an accident that the vesica pisces is a symbol for the Holy Trinity? 

Who knew that geometry and trigonometry grew out of fish bladders? Much of our modern world is based on the number three and the triangle. I mean, there are three little pigs, three blind mice, three little kittens, three bears, three wishes, and three strikes and I’m out.

Gary McCallister, .(JavaScript must be enabled to view this email address), is a professor of biology at Colorado Mesa University.


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