What the Fish? Episode 1: You Are All Fishes

What is a fish?

When most people hear the word fish, they think of Nemo (clownfish), tunas, cichlids, and sharks. Everyone knows what a fish “is”, but why? It turns out that identifying the characteristics that define fishes is a daunting task, and with good reason! Fishes, as we think of them, are actually a paraphyletic or "unnatural" group. When scientists say “fishes”, they are discussing a group of organisms that includes all the descendants from a common ancestor.  So, the correct grouping of fishes includes us, the tetrapods (amphibians, turtles, crocodiles, birds, squamates, mammals, and countless extinct forms).

Yes, you are a fish. Now that your view of the world has been forever altered, let us explain. In general, there are three main groups of fishes still living today; the cartilaginous fishes (e.g., sharks, rays, skates, chimeras), the ray-finned fishes (e.g., goldfish, tuna, cichlids, clownfish, and our beloved anglerfish from the logo), and the lobe-finned fishes (e.g., coelacanths, lungfishes, frogs, birds, humans).  While terrestrial (or land) vertebrates such as frogs, dogs, and humans are classified as tetrapods within the lobe-finned fishes evolutionary lineage, we owe our earliest vertebrate origins to an aquatic environment. In short, just as humans are mammals, mammals are tetrapods, and tetrapods are all fishes. Welcome to the club!

So…what the fish?

As ichthyologists, scientists, and researchers that study fishes, we primarily study the cartilaginous fishes (greater than 1,000 species), the aquatic lobe-finned fishes (e.g., lungfishes, coelacanths, eight living species), and the ray-finned fishes (greater than 35,000 species). This podcast series will predominantly focus on fishy issues related to these evolutionary lineages. Fishes have thrived in aquatic environments that vary from the rivers and streams near your backyard to the deepest recesses of the ocean. The evolutionary history, biology, and ecology of fishes are as diverse as they are fascinating, and we look forward to discussing the vast biodiversity of fishes with you. Thanks for listening, and enjoy this ongoing podcast series!