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!
Fish of the Week: The Australian Lungfish (Neoceratodus forsteri)
Distribution: Native to the Mary and Burnett river systems, Australia
Maximum Size: 4.9 ft
Fun Fact: The Australian Lungfish “Granddad” has been living in the Shedd Aquarium in Chicago since 1933!
Encyclopedia of Life: Australian Lungfish
Living lungfishes include just six species in three genera. Each genus is endemic to freshwater habitats in Africa, South America, and Australia. The lungfishes (subclass Dipnoi within Sarcopterygii) have an extensive fossil record that extends back to the Devonian period (approximately 416-360 million years ago).
The Australian lungfish is the only living lungfish that breathes through gills, as well as its single lung. They live in deep pools and underwater caves and can survive for days outside of water if kept moist. Members of this species are not sexually mature until they are nearly 20 years old, and females deposit large adhesive eggs on floating plants. They are nocturnal omnivores, feeding on invertebrates, fishes, and plant material.
So long, and thanks for all the fish!