Info about Fishing
What is a fish?
With their fluid movements and dazzling array of patterns, colours, and shapes, fish are a constant source of fascination. Today's extraordinary diversity of types stems from prehistoric ancestors, which were some of the earliest complex living creatures on Earth, making dinosaurs look like recent newcomers...
• The evolution of fish
Fossils of fish remain date back over 500 million _T years, making them the oldest group of vertebrates (animals with backbones) on the planet. The earliest evidence of their existence comes from fossilized bony scales unearthed from rocks of the Cambrian period, but the first fish whose entire outline is known dates back to the subsequent Ordovician era.
Named Arandapsis, this fish is also the earliest known complete vertebrate. Just 15cm (6in) in length, it had a very simple body structure, with no fins, and depended entirely on its tail for propulsion. Its backbone or notochord was composed of stiff cartilage rather than bone. There are clear signs of gills for breathing in Arandapsis, but jaws - believed to have adapted from the first of the series of gill arches - had not yet developed at this stage in the evolutionary process.
• Jaws!
Roughly 80 million years after the appearance of the earliest fish, jawed fish started to evolve. Jaws aided feeding and therefore survival, because fish no longer had to depend on tiny creatures and vegetable matter which they could swallow whole. There was a rapid increase in types of fish and much larger fish also began to develop, some of which became fearsome predators.
The most notorious of these are the sharks, whose lineage dates back over 400 million years, with remarkably few changes since then. But evolution did not stop there: fossils show that feeding techniques continued to develop over many millennia. For example, Lepidotes developed greater jaw mobility, enabling it to suck in prey directly, rather than having to seize it.
• Skeletons from the past
Sharks, along with their close relatives such as rays and skates, are known as cartilaginous fish, because their skeleton is predominantly cartilage, coated with bone for extra support. By contrast, the skeleton of bony fish or teleosts, which form the class Osteichthyes, is made up entirely of bone. Fossil records date them as living approximately 400 million years ago. Since then, they have undergone remarkable diversification, and today there are more than 20,000 different species, making them the largest group of fish on the planet and the biggest class of vertebrates.
There are three subdivisions, of which the oldest are the actinopterygians. They are often called ray-finned fish, and are characterized by bony spines in the fins. Originally, these fins were largely immobile, but changes in the bone structure in later osteichthyans, such as Perleidus from the Triassic period (about 240 million years ago) ensured much greater mobility.
• The emergence of modern fish
Unlike actinopterygians, the fins of sarcopterygian bony fish were equipped with muscles. This was a vital distinction, and a feature that can still be seen in lungfish, one of the few survivors of the group. Lungfish can breathe atmospheric air directly, rather than relying entirely on their gills. It is thought that amphibians probably evolved from sarcopterygians; the muscular fins provided the means for movement out of the water, and so began colonization of the land.
While only seven species of sarcopterygian or lobe-finned fish remain, there are more than 21,000 descendants of the actinopterygians. By the Eocene era, roughly 66 million years ago, teleosts were becoming established in fresh water, and some types are obvious ancestors to contemporary fish. Hypsidoris, for example, was very like the catfish of today, with trailing sensory barbels around its mouth and protective spines on each pectoral fin. Some teleosts were giants of 4m (13ft) or more, and their descendants still exist. They include the bony tongues, which have bony plates in their tongues that are used like teeth to hold food.
The arowana (Osteoglossum bicirrhosum) is a living descendant of the giant teleostfish of the past. It is greatly prized in Asia as a symbol of wealth and longevity.