It was an unlikely nursery but during this time the initial stirrings of life on Earth took place. Rudimentary plants took a foothold on the harsh landscapes and primitive soft-bodied animals, encased within some form of armour plating, thrived in the oceans. The evolutionary highway had many off-ramps and thousands of bizarre animal experiments conducted by Mother Nature came and went, leaving only the strongest and most efficient to survive.

One animal in particular was unlike anything that had ever come before. Its soft, fleshy body, covered in scales or light armour plating, was supported by an internal framework of bones, an unheard of concept. Until then no animal had been made with the hard parts on the inside.

These were the first of the vertebrates, precursors to the modern fishes and their skeleton allowed for the attachment and support of muscles, giving them superior speed and maneuverability. They also sported a sophisticated sensory and nervous system. This newcomer flourished and soon commanded all bodies of fresh and salt water.

Today, fish, with over 20,000 species, account for nearly half of all vertebrate species on the planet. They are found anywhere there is water, and a few places where there isn't.

They have adapted to myriad aquatic habitats from the frozen arctic to the tropics, subterranean caves and the abyssal depths, and even within the bodies of other animals. In form and function they cover the gamut from the beautiful to the bizarre.

In order to survive and flourish, an animal must be able to respire, escape predators, catch prey, defend themselves and reproduce, and fish have found some ingenious ways to achieve these. But it is nearly impossible to find a common denominator when discussing fish. To every rule, there is an exception, and nowhere is this more true than with fish. As the naturalist Pierre Teihard de Chardin said, fishes are "an assemblage of monstrous complexity."

It can be said that fish live in water and breathe by pumping water over an intricate and very effective system of gills, but some, such as the lungfish, can spend considerable lengths of time out of the water, able to breathe through rudimentary lungs, and the fresh water eel often makes treks overland, able to absorb oxygen through it's skin. The bichir of the upper Nile must gulp air at the surface and would drown if held underwater, and some African catfish dig a burrow in the mud, line it with mucous and live there during droughts for up to three years.

To defend themselves fish use a variety of tactics. Safety in numbers forces some to form huge schools while others use speed or maneuverability. Heavily muscled and streamlined fish such as the tuna are capable of speeds in excess of 40 miles per hour while smaller fish that inhabit the maze of the coral reef rely more on agility. Large teeth and powerful jaws, poisonous spines, electricity and even the power of flight are also employed by various species. Feeding tactics include everything from attack and ambush to grazing.

Shapes of fishes cover the geometric and artistic spectrum from the ordinary to the outrageous, often allowing them to mimic their surroundings. A trumpet fish can pass off as a piece of coral, while the frogfish resembles a rough piece of sponge. With the help of feathery appendages or skin tags some seem to have no shape at all and might blend in with weeds on the bottom. And some, such as the seahorse, look nothing like a fish.

Colours are also critical to survival. Some fish are painted from a palette of drab, muted colours, or an array of pastels, while still others advertise their presence with bright neon colours, bold stripes or bright splotches. Colouration is displayed in a variety of ways for different effects. It enables some to blend in with the background and breaks up the overall outline of others in an attempt to confuse potential prey. And many, such as flatfishes and sculpins are able to change their colour to match their surroundings.

Methods of reproduction in fish boggle the mind. For many, the female lays eggs which are fertilized by the male. This may happen out in the open, in the security of a den or even in the mouth of one of the happy couple. Many, such as the capelin and grunion, suffer great hardships as they are tossed ashore by the surf in their mating ritual. Salmon must prolong the inevitability of death in order to meet their sole obligation in life. Internal fertilization and live birth is also quite common among many sharks, rockfishes and surfperches along Canada's coasts. Sometimes, as in the case of the seahorse, the male carries the fertilized eggs. Some fish, such as swordtails or groupers, also change their sex, and during this procedure may undergo a period of hermaphroditism.

But nowhere is mating more bizarre than in the case of some deep water anglerfish. The tiny male, only about one and a half inches long, latches on to the much larger female which can be up to 45 inches long, and over time his body becomes a fixed appendage of hers, a mere sperm producing organ of the female.

Fish are many things to many people. To some they are an aquatic treasure whose beauty and behaviour fascinates us. To others they are the largest, most indispensable, and tenuous, source of food on the planet, a resource that must be protected at all cost, for their destiny is linked very closely with our own.