Why Are FISH Shaped The Way They Are?

This article was written by Stephanie

There are more fish than any other kind of vertebrate - not surprising since our planet is mostly water.

Now to our question – why ARE fish shaped the way they are? To answer that, it is important to understand

the environment in which fish live. This affects their shape and how they survive.

First of all, fish are cold-blooded animals. Mammals, including humans,

are ‘warm-blooded’- their bodies can control their own temperature.

Mammals can grow a layer of fat or fur to protect them from the cold,

or they can take shelter in a cave. If they get hot, they can sweat or

hide in the shade. Fish cannot do this. Their body temperature is the

same as the environment around them - cool-water or warm-water.

When the water temperature goes up to high or down to low, they

must move somewhere else if they are to survive.

Fish can live in amazingly different environments. Some have been

found in the deepest of the oceans at around 11,000 metres (that is

deeper than Mt. Everest is high!). Others can live in mountain lakes at 4,500 metres above sea

level. That’s a difference of 15,500 metres. Humans can survive in only a portion of that range.

So what makes fish so good at living in different locations? Adaptation! Evolving over millions of years, fish

have adapted themselves to their environment.

The Flounder or Flatfish Family of fish are all flat, with both eyes on top of the head

and the mouth underneath. Many species of flounder or sole live off the west coast

of BC. They can feed along the ocean bottom and look out for enemies above

at the same time. Their skin is speckled on top to look like sand.

The Deep-Se a Angler Fish

lives in extremely deep water in

the Pacific Ocean off California

where it is under tremendous

pressure from the water above and

where hardly any light reaches. The

angler fish resists the pressure by being very

round in shape, with soft, thin bones and

jelly-like flesh. In fact, it is almost all water. As the angler 

fish can’t use its eyes to hunt for food, it has developed a thin organ

dangling from the top of its head, like a fishing line. Tiny bacteria at

the tip produce bioluminescence (light), which attracts prey. Thus,

drawn by the light, the food comes to the fish!

The Northern Pike is a hunting fish that lives in fresh water. It is

long and slender, with fins placed far back on its body. With a quick

burst of speed, the pike can race out of hiding and capture its prey.

Pike are common in the Peace region of northern BC.

The Tuna is a large fish that can swim

very fast, up to 77 kilometres per hour.

It has a wide body that narrows to be

very thin by the caudal (tail) fin. This

aerodynamic shape and fast side-toside movement of the fin is why the

tuna is able to swim so fast. This helps it

escape from predators. Many species of

tuna live off BC’s coast.

The American Eel doesn’t even look

like a typical fish. It is a snake-shaped fish

with extremely small scales, which give

its body a smooth appearance. Unlike

salmon, eels migrate from fresh to salt

water to spawn. American Eels are very strong swimmers. They swim

all the way from Lake Ontario out to the Sargasso Sea, an area way

off in the North Atlantic Ocean to lay their eggs - a distance of about

6,000 kilometres!

Littlest but not least important as an example of adaptation is a

population of Lake Chub, which live in the wetlands draining the

hot springs in Liard River Hot Springs Provincial Park in northern

British Columbia. They are small minnows that have adapted to

these warm waters and we mean really warm (for fish) at

 temperatures from

 15 to 26°C, during summer. As far as

 we know, this is the only place where chub survive in

 water that is this warm.