You might have read the title of today’s article and thought, "That must be a mistake!" After all, how can there be no such thing as a fish? Surely, fish are real, aren't they? Well, according to a certain group of scientists, this might be more accurate than you think. In fact, the idea that there is "no such thing as a fish" has become a surprising but scientifically grounded statement. Let me explain why.

The Traditional Definition of Fish

The common definition of a fish, as found in dictionaries like the Oxford English Dictionary, describes it as a "limbless cold-blooded vertebrate animal with gills and fins living wholly in water." At first glance, this seems straightforward. Fish are cold-blooded creatures with bones that live in water—so we think of animals like sharks, tuna, salmon, clownfish, and even the mysterious anglerfish.

"Limbless cold-blooded vertebrate animal with gills and fins living wholly in water”

Oxford Dictionary

However, there’s an issue: while these animals do meet the basic description, they are not all closely related. For instance, the lungfish—an aquatic species—shares more in common with cows than with salmon. Yes, you read that correctly: the lungfish (a cold-blooded, water-dwelling creature) is genetically closer to a warm-blooded land mammal like a cow than it is to a fish like a salmon. This revelation might challenge everything you thought you knew about the fish category!

Taxonomy: The Science of Classifying Life

To understand why this is the case, we need to delve into taxonomy. Taxonomy is the science of classifying living organisms. It is often described as the "tree of life," a system based on the idea that all living things are connected through common ancestors. Over millions of years, different species have evolved from shared ancestors, leading to the biodiversity we see today.

In this system, living creatures are classified into hierarchical categories: Kingdom, Phylum, Class, Order, Family, Genus, and Species. For example, humans fall under the Kingdom Animalia (the animal kingdom), the Class Mammalia (mammals), and the species Homo sapiens. These categories show where animals evolved from and their genetic connections to one another.

However, when it comes to "fish," the situation is much more complicated. Fish are not all descended from a single common ancestor. In fact, the diversity of life in the oceans and rivers is enormous, and many of the animals we call "fish" evolved in vastly different ways.

A Fascinating Fact: Sharks Are Older Than Trees!

To put this into perspective, consider this astonishing fact: sharks are older than trees. Fossils of sharks date back around 450 million years, while the oldest known trees appeared about 360 million years ago. Sharks, in other words, are around 90 million years older than trees and over 200 million years older than dinosaurs. This means that life in the ocean predates the existence of life on land by millions of years, and over that time, evolution has produced a wide variety of species.

"I imagine that Fish have no word for water".

Terry Prachett

Among these species are animals like sharks, which are vastly different from other so-called "fish" in terms of their evolutionary history. The lungfish, for example, is a type of fish that actually has lungs and can breathe air, just like humans and other land animals. Despite living underwater, lungfish are more closely related to amphibians, reptiles, birds, and mammals than to many other "fish" species.

Lungfish: The Link Between Fish and Land Animals

The lungfish is particularly important in understanding the history of life on Earth. It is one of the closest living relatives of all amphibians, reptiles, birds, and mammals. This means that humans share a common ancestor with lungfish, dating back around 390 million years ago. This is why lungfish are more closely related to cows (which have lungs) than to salmon (which do not have lungs).

So, from an evolutionary perspective, classifying animals like lungfish and salmon under the same "fish" label doesn’t make much sense. The differences in their evolutionary history are vast, despite their similar appearance.

Does It Matter?

You may be wondering, does it really matter if we call something a "fish" or not? For everyday people—whether they are fishermen, fishmongers, or diners in a restaurant—the term "fish" works just fine. It’s a convenient way of grouping certain animals based on their appearance, behaviour, and culinary use. But from a scientific standpoint, the term "fish" is problematic.

In fact, the term is so misleading that it has little value to scientists who study animal evolution. After all, if we consider lungfish and salmon to both be "fish," then technically, humans, frogs, ostriches, and even lizards could also be considered fish, since they all share a common ancestor with lungfish. Clearly, this isn’t helpful when trying to understand the evolutionary relationships between species.

The Limitations of Language and Categories

The main takeaway from this discussion is that the word "fish" can be limiting and imprecise, especially when it comes to understanding the vast diversity of life in the oceans and rivers. While the word is useful for practical purposes, such as in fishing or cooking, it doesn’t reflect the complicated evolutionary histories of these animals.

Ultimately, this highlights the limitations of language in describing the natural world. Just because an animal looks like a "fish" and lives underwater doesn’t mean it belongs in the same category as another animal with similar characteristics. As we continue to learn more about the diversity of life on Earth, we must be open to rethinking how we categorise and define the animals around us.

Vocabulary List:

1. Taxonomy (noun) –  The science of classifying living organisms.
   • Example: The taxonomy of these fossils.
2. Common ancestor (adjective/term) –  The shared ancestor from which different species evolved.
   • Example: An early mammal species, is a common ancestor of whales, cats, humans, and all other modern mammals.
3. Evolution (noun) –  The process by which different kinds of living organisms have developed and diversified from earlier forms.
   • Example: The forms of written languages undergo constant evolution.
4. Lungfish (noun) –   A type of freshwater fish that has lungs and can breathe air.
   • Example: A lungfish has lungs.
5. Species (noun) –  A group of organisms that are capable of interbreeding and producing fertile offspring.
   • Example: It was an unknown species.
6. Diversity (noun) –  The variety of different types of living organisms in a given area.
   • Example: There was considerable diversity in the style of the reports.
7. Culinary (adjective) –   Relating to cooking or the kitchen.
   • Example: I do have many culinary skills.

Discussion Questions and Topics:

1. What is the problem with classifying all underwater animals as "fish"?
2. How are lungfish more closely related to cows than to salmon?
3. Why is the term "fish" considered limiting by scientists?
4. What other common terms do you think might be misleading or imprecise when it comes to classifying animals?
5. Before reading this article, did you ever question the usefulness of the term "fish"?
   • Why or why not?
6. How do you think categorising animals by appearance affects our understanding of evolution?
7. Do you think scientists should change the way we use the term "fish"?
   • Why or why not?