by James Morris

What’s the plural of fish? Fish? Or fishes?

It turns out that both are correct, but it depends on what you mean. If there are many fish of the same species, it’s “fish.” If there are many fish (fishes?) of different species, it’s “fishes.”

For example, if I see a tank full of goldfish, I might say, “That’s a lot of fish.” But, if I consider the ocean, I might say something like, “There are many fishes in the sea.”

Figuring out plural forms in biology can sometimes be tricky. One fungus, two fungi. One hippopotamus, two hippopotami. One nucleus,l two nuclei. But one octopus, two octopuses, not two octopi.

This is because “octopus” is Greek, not Latin. To convert a Latin noun that ends in “-us” to its plural form, you usually change “-us” to “-i.” Because “octopus” is Greek, its plural form should technically be “octopodes,” but that doesn’t sound right and you almost never see it.

In this way, octopus is like platypus: it’s platypuses, not platypi or platypodes.

Louse becomes lice. Mouse becomes mice. But grouse doesn’t become grice. The plural of grouse is simply “grouse.”

Similarly, tooth becomes teeth and goose becomes geese. But moose doesn’t become meese. If you are referring to more than one moose, it’s just “moose.”

Like moose and grouse, there are many other organisms in which the singular and plural forms stay exactly the same: deer/deer, sheep/sheep, and even species/species.

What’s the plural of pancreas? Pancreases? No, it’s pancreata. Similarly, stoma becomes stomata.

Ovum becomes ova and millennium becomes millennia. In the same way, datum becomes data. So, be sure to write, “The data are interesting” not “The data is interesting” even though the latter might sound better and is even more commonly used. One day, it might even be considered completely acceptable.

That’s because languages are living and evolve, not unlike organisms themselves. Charles Darwin likened the evolutionary process to the way that languages change over time: languages with common origins are similar, but have also become distinct. Think of Latin and its “children,” including French, Spanish, Italian, and Portuguese.

In On the Origin of Species, Darwin wrote,

It may be worth while to illustrate this view of classification by taking the case of languages . . The various degrees of difference in the languages from the same stock, would have to be expressed as groups subordinate to groups; but the proper or even only possible arrangement would still be genealogical; and this would be strictly natural, as it would connect all languages, extinct and modern, by the closest affinities, and would give the filiation and origin of each tongue.

We can still see the roots of modern languages, as well as how they have changed over the course of time. In the case of English, its Germanic origins are clear, but it has also incorporated many words from other languages, including Latin and Greek, especially in the sciences. Although it’s easy to make many English words plural by simply adding an “s,” the plural forms of Latin and Greek words are more complicated, as many of these examples illustrate.

I recently spoke to a scientist who said that while “fishes” is still used by some biologists, it’s going out of style in everyday English, providing another example of the changing nature of language.

And that’s no fish story.

© James Morris and Science Whys, 2017.