WHAT IS A FISH?

The answer to this question is a lot more complicated than you might think. Read this article to learn some weird and wonderful things about different kinds of fish. The drawing below shows some of the major fins and body parts of a rockfish.

True fish are cold-blooded, aquatic vertebrates that generally have streamlined bodies with fins. There are 3 classes of fish. Two classes of fish have cartilaginous skeletons and one class has a bony skeleton. Feel the wiggly part of your nose or the top of your ears so you know what cartilage feels like.
The most ancient class of fish includes the primitive jawless fish like hagfish and lampreys. They are descendants of jawless fish that lived about 400 million years ago (long before the dinosaurs). Hagfish are fished for their skin which is used to make “eel skin” a very fine leather for wallets and purses.

The other class of cartilaginous fish includes the sharks and they definitely have jaws. Skates, rays and rat fish are in the same class as the sharks. They all have jaws and they can also have teeth and pointy little scales (placoid scales) that look like their teeth. Some sharks carry their developing young but most of these fish lay their eggs in egg cases. The photo on the left shows a young skate (Raja binoculata) shortly after it hatched from an egg case. The third class of fish is most the common and diverse, the bony fish. They generally have fins, gills and scales and generally lay eggs. There are thousands of different kinds of bony fish from goldfish to tuna, from hatchet fish to lantern fish. You can really let your imagination go wild and there is probably a fish that looks that way!
Most of the fish you are probably familiar with are bony fish and most of the worlds fisheries are for bony fish. How many can you think of? With bony fish there is an exception to every rule though. Check out some the fish that don’t follow the “fish rules”.
What does your favourite fish look like?

The body shape, the type of tail and where the mouth is can give clues about the biology of that fish. Predators that chase their prey are usually stream-lined, have a mouth that points straight ahead and a strong tail for swimming. Surface feeders feed on small plankton and insects and have a small upward pointing mouth and large eyes. Bottom fish are usually flat. Crevice and burrowing fish are usually eel-like, with fins running the length of their body and blunt wedge-shaped mouth. Deep sea fish are often really crazy looking with enormous jaws and a tiny body. In other words fish shapes make sense.
In the Pacific, off Canada’s west coast some of the most important fisheries are for salmon (Can you name all 6 species?), herring, halibut, hake, black cod, rockfish, and lingcod. What do you know about these food fish?

Sharks can be easily over-fished because they grow slowly, mature late, (some don’t spawn for the first time until their thirty years old) and because they produce a small number of young. Because sharks are top predators, their removal can impact the whole ecosystem. Shark finning is a really wasteful fishery where the shark’s fins are sliced off and the rest of the body is thrown back. Shark fins soup is a delicacy that can sell for $150 a bowl. This is not a sustainable fishery.
A recent study in Nova Scotia, Canada, looked at shark populations over the last 15 years. They found that in the North Atlantic many shark species had declined drastically. Populations of great white sharks had dropped by 79 percent and hammerhead shark numbers dropped by 89 percent. The loss of these top predators has been blamed mainly on overfishing. Sharks are often caught accidentally in longlines that are fishing for swordfish or tuna (see fishing methods).

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