What Are Some Common Traits Between Fishes and Amphibians?

What Are Some Common Traits Between Fishes and Amphibians?

Image Citation: Couleur (photographer). (2017). Frog Water Pond [photography]. Retrieved from https://pixabay.com/photos/frog-water-frog-frog-pond-amphibian-2211972/

If you were to see a fish and an amphibian sitting next to each other you might not think they have much in common. However, there are more similarities between these two groups of creatures than is immediately obvious.

The class Amphibia is made up of frogs (and toads), salamanders, and long, subterranean creatures called caecilians. Most amphibians spend the first part of their life as aquatic larva with gills and fins on their tails (you may have heard frog larva called “tadpoles”). As adults, amphibians have moist skin and lay eggs with soft-shells that must stay in or around water to avoid drying out.

Already you may notice some similarities with fish. Both groups have gills and fins for at least part of their lives, though most amphibians lose their aquatic traits as adults. They both also have skin and eggs that need to remain moist, and rely on water for reproduction. This sets both amphibians and fish apart from the amniotes (reptiles, mammals, and birds), which have thick, often hard-shelled eggs (or internal eggs in the case of mammals) that don’t need to stay in water.

Both amphibians and fish straddle the line between water and land. While most fish spend their whole lives underwater, there are some species (like lungfish, climbing perch, and mudskippers) that regularly leave the water for extended periods of time. Similarly, there are amphibians that spend their whole lives underwater even as adults (like African clawed frogs and axolotls).

There are also more basic similarities. For example, amphibians and fish are both also vertebrates and ectotherms. This means that they both have backbones (a trait they share with mammals, birds, and reptiles) and don’t generate their own body heat (a trait they share with reptiles and invertebrates).