- have gills with which they take oxygen from water
- have limbs modified into fins
- have scales covering their bodies
- are ectothermic, sometimes called "cold blooded." This means that their body temperature varies with the water temperature.
Fish are a very diverse group and live throughout fresh and salt water habitats. There actually two major groups of fishes: Cartilaginous Fishes (including sharks, skates, and rays), and Bony Fishes (like tuna, salmon, and carp).
Below, you will see some of the fishes that Signals of Spring - ACES scientists are tracking.
Cartilaginous (Kart-ill-adj-in-us) Fishes:
This group of fishes includes sharks, skates and rays. These animals have been on Earth for almost 450 million years! Their bodies are made of the bony substance that makes up your nose and ears, called cartilage. They have no true bones.
The bodies of Cartilaginous Fishes are covered in spiny "tooth-like" scales that are sharp to the touch. Unlike bony fishes, these fishes have five or more gill openings on the sides of their bodies.
Skates are cartilaginous fishes with a flattened body and a long tail. They usually live on the sea bottom. There are many different types of skates that live in shallow and deep waters ranging from tropical to much colder temperatures. Rays have similar body shape, but these fish have a poisonous stinger.
Sharks are probably the best-known Cartilaginous Fishes, but unfortunately they have a bad reputation. There are actually very few shark attacks on humans each year, and scientists believe that these incidents are mostly by accident when the fish mistake humans for tastier prey like sea lions and seals. While certain species of shark are certainly fierce, others, like the Whale Shark, are harmless to us; they eat only plankton.
The bony fishes are an incredibly diverse group. They come in all shapes and sizes, colors and patterns and live in almost all watery habitats, both salt and freshwater.
This group of animals is called bony fishes because their skeleton is bony, unlike the cartilaginous fishes. Bony fishes also have one gill opening on each side with a covering on it, called an operculum. They take water in through their mouths which then passes over their gills.
Many bony fishes have a special structure called that helps them to regulate their depth in the water. This organ is called a swim bladder. A swim bladder is balloon-like structure that is filled with air and helps to regulate buoyancy, which means that the animal doesn't sink if it stops swimming. Unlike cartilaginous fishes, the scales of bony fishes are not embedded in their skin; if you touch a fish, you are likely to find that scales have fallen out into your hand.
Some of the many examples of diverse bony fish including parrotfish, flounder, frogfish, pufferfish, and salmon.
Photos credit: NOAA