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The Fishes - Habitats, And Types

Introduction

California scorpion fish

The Fish is a group of animals that live and breathe in water.
All fishes are vertebrates (animals with backbones) with gills for breathing. Most fish have fins for swimming, scales for protection, and a streamlined body for moving easily through the water.

Fishes live in nearly every underwater habitat, from near-freezing Arctic waters to hot desert springs; from mud in dried-up tropical ponds to the deepest ocean abyss. Special antifreeze chemicals in the blood of Antarctic icefish enable them to survive in water below 0° C (32° F). Desert pupfish found in hot springs of western North America live in temperatures higher than 40° C (100° F). Killifish release their eggs, or spawn, as the dry season begins in the tropics of South America and Africa, leaving their eggs to dry in the ground until the rains return six months later. In the deep ocean, where sunlight never reaches, many fishes cooperate with glowing bacteria to create their own light for communication and to attract mates and prey.

With approximately 25,000 recognized species, fishes make up the most diverse vertebrate group, comprising about half of all known vertebrate species. New fishes continue to be discovered and named at the rate of 200 to 300 species per year. With this vast number of different fishes comes a diversity of sizes and shapes, from huge whale sharks that reach 12 m (40 ft) in length to the smallest vertebrate, the stout infantfish (Schindleria brevipinguis), measuring only about 7 mm (0.3 in) long.

Fishes are generally streamlined with a pointed snout and pointed posterior and a broad propulsive tail. Unlike the shape of a human body, a fish's body shape is ideal for speeding through the water without creating excess resistance. This torpedo-shaped body is typical of the fastest-swimming fishes, the billfish and the tunas. One billfish, the sailfish, can swim in bursts of over 110 km/h (70 mph). Tunas are built for long-distance endurance as well as speed, swimming as fast as 50 km/h (30 mph) and migrating as far as 12,500 km (7700 mi) in only four months. Other fishes come in a wide variety of shapes. The snakelike eels, flat halibuts, and boxy puffers are all slower swimmers that have evolved distinctive bodies best adapted to their specific habitats. Unlike fishes that swim through the open water, these fishes have adapted to life in caves, on the ocean floor, and among coral reefs where speed is less important than camouflage or maneuverability.

Fishes are an important source of protein for millions of people worldwide. Since the early 1970s, 70 to 100 million metric tons of fish are caught each year for food (see Fisheries). People consume about 70 percent of fish caught, and nearly 30 percent are used as animal feed that helps produce other forms of protein. Fish protein represents about 25 percent of the total animal protein consumed by the world's population, second only to beef.

Habitats of fish

Freshwater Sponge

Fishes may be classified as either freshwater or saltwater species.
Although freshwater lakes and rivers comprise less than 0.001 percent of the volume of water on earth, 40 percent of fish species are found there. Most of the rest are found in the salty oceans, while only 2 to 3 percent are found in somewhat salty, or brackish waters. Similarly, most marine fishes are found associated with the seafloor or with other natural or artificial features, such as reefs or docks. These structures offer them protection from predators or serve as focal points for feeding and social interactions. The variety of seafloor habitat has enabled fish to diversify while the relatively uniform habitat of open waters has not. Only 13 percent of fish species live primarily in the open ocean.

Fish are not randomly distributed in the world's waters. For example, the continental shelves, shallow areas of the ocean typically 200 m (650 ft) deep or less, with abundant light from the sun and nutrients from the continents, contain most of the ocean's fishes. This habitat promotes large populations of tiny invertebrate animals that are in turn eaten by fishes. Similarly, the upper 200 m (650 ft) of the ocean holds 78 percent of marine fish species. The warm, well-lit waters near coral reefs also promote a rich diversity of fish species.

Fish are not randomly distributed in the world's waters. For example, the continental shelves, shallow areas of the ocean typically 200 m (650 ft) deep or less, with abundant light from the sun and nutrients from the continents, contain most of the ocean's fishes. This habitat promotes large populations of tiny invertebrate animals that are in turn eaten by fishes. Similarly, the upper 200 m (650 ft) of the ocean holds 78 percent of marine fish species. The warm, well-lit waters near coral reefs also promote a rich diversity of fish species.

Fish and humans

Drying fish at Nakamura Port

It is impossible to overstate the importance of fish to human populations around the world. Throughout history, humans have used fish protein as a food source, with wild caught fish providing the bulk of fish protein. Fish have also been farmed in large quantities for more than 2000 years in China. Recent advances in fish farming (see Aquaculture), especially with some African cichlids (see Tilapia), have alleviated hunger in many parts of the world. In industrialized countries, farm-raised fish provide relief for overfished stocks of wild fish. Fish also have served as a source of recreational pleasure for many people. The catches from sports fisheries (see Fishing) are far larger than commercial catches from most freshwaters and in marine waters close to large population centers. Aquariums provide an intimate acquaintance with the aquatic world. More than 20 million home aquariums are kept in the United States alone. Among the many fish kept in aquariums, the most common are minnows, characins, and cichlids.

Some fishes may be dangerous to humans, although in most cases the danger is easily avoided. The stonefish is one of the most venomous vertebrates known, with enough toxin in the sharp dorsal spines to kill an adult human that steps on one (see Rockfish). The toxin of the pufferfish, or fugu, is deadly when eaten. Sharks have perhaps the worst but least deserved reputation for aggressiveness, for only a few of the species have been known to attack humans. Many larger fish when provoked are capable of inflicting wounds on humans. For example, moray eels, as sinister as they appear, do not go out of their way to attack humans, but will bite if provoked.

Threatened fishes

Landing a fish catch

Humans are far more dangerous to fish than fish are to humans.
Sharks kill about 30 people per year, while an estimated 700,000 metric tons of sharks are harvested or killed by people each year. Several species of sharks, including the great white, have been greatly overfished. Sharks are particularly susceptible to overfishing because most species need many years to grow to reproductive maturity.

Many stocks of wild fish have been harvested beyond their natural capacity to sustain their populations. Most recently, the collapse of the cod fishery in the Northwest Atlantic has heightened concerns over our ability to responsibly manage natural marine resources. Since the closing of those commercial fishing grounds, evidence is mounting that the fish populations are beginning to recover, although the recovery may take decades. Stocks of fish, like the bluefin tuna, that cross international borders or are found on the high seas are of special concern because they are particularly difficult to manage. Even large marine stocks once thought immune to the effects of overfishing, like the Pacific sardine and the Peruvian anchovy, have declined dramatically. In spite of these problems, fisheries can be successfully managed to reduce the effects of previous overfishing and to prevent further abuse. Proper management requires timely and accurate data on fish populations and harvest, as well as the ability to strictly enforce the protection of vulnerable fish stocks.

The most seriously threatened fishes are found in freshwaters of the world, especially in the environmentally sensitive and industrialized areas of the northern hemisphere. Many unique freshwater species are found only in a small area because of the isolation by land barriers. Thus, water pollution or habitat destruction in streams can be devastating to fish populations or even entire species. With increasing human populations, the effects are bound to intensify unless preventive actions are undertaken. Fortunately, significant advances in our knowledge of the effects of pollutants and habitat change have improved habitat restoration and pollution control.

Fish Types

American Eel

Fishes may be divided into two distinct groups, jawless fish and jawed fish.
The jawless fish are represented by two families of distantly related eel-like fish, the hagfish and the lampreys. Both fishes have tongues equipped with numerous small teeth and lack paired fins and a bony skeleton. Although these two families include only a handful of living species, the fossil record shows they were once a highly diverse group that also included fish whose head and trunk were covered with a hard bony shell.
Hagfish are the vultures of the abyss, feeding on carcasses of dead fish and other animals.
Lampreys, in contrast, feed on live fish by attaching their sucking disk to their host and rasping away tissue with their toothed tongue.

Great White Shark In Spencer Gulf

With more than 2000 different species, catfish (named for whiskerlike feelers on their jaws) are a diverse collection of tenacious fish that have adapted to life in a variety of environments. One type of catfish, Clarias batrachus, commonly known as the walking catfish, is native to shallow ponds in eastern India and Southeast Asia. When droughts cause shallow ponds to dry up, the walking catfish is capable of traveling across land to move to deeper ponds. It uses its pectoral fins and tail to slither across the ground, or "walk," in search of a suitable new pond, surviving on oxygen stored in an air chamber in its gill arch.

The jawed fish may also be separated into two major groups: bony fish, which have skeletons made of rigid bone, and cartilaginous fish, which have skeletons made of elastic cartilage. There are nearly 1000 species of cartilaginous fish, including sharks, rays, and chimaeras, or ratfish. Sharks and rays live in relatively shallow ocean waters and occasionally freshwater, while chimaeras are found only in the ocean, mostly in deep water. Sharks have an age-old reputation for savagery, but only a few of the approximately 370 species deserve this reputation.
Most sharks, like the spiny dogfish, are predators of small fish and invertebrates, while the largest, such as megamouths, whale sharks, and basking sharks, feed by filtering tiny invertebrates from the water. The nearly 200 species of rays are essentially sharks flattened like a pancake that have adapted to life on the ocean floor.
The bony fishes encompass by far the largest diversity of fish, with about 24,000 species inhabiting nearly every body of water on the earth. They are divided into two groups-the lobe-finned fish and the ray-finned fish. Lobe-finned fishes include the lungfish, a small group of primitive air-breathing fish, and the coelacanth, the single living species of a group long thought to be extinct.

The river lamprey is one of a number of lampreys common to North America and its surrounding waters. The lamprey shown here is facing forward with its jawless mouth completely open. The African lungfish is one of three species of lungfish. All lungfish have fleshy fins with strong muscles supported by a core of bones. This lungfish is equipped with both a lung and rudimentary gills. During the dry season, the African lungfish is able to survive by curling itself into a tight ball with its tail covering the eyes. Mud adheres to the body mucous, forming an impervious casing. The lungfish then becomes dormant, or estivates, until the rainy season again fills the pool, softens the mud casing, and releases the fish.

The ray-finned fishes are divided into two major groups, the primitive sturgeons and paddlefish, and the more evolved new-finned fishes. Most of the common and well-known fish species are new-finned fish, including the herrings, which support one of the largest fisheries in the world, and the eels, which are found in nearly all marine habitats. Other new-finned fishes include the ostariophysans-minnows, characins, and catfish-which inhabit the freshwaters of the tropics and surrounding areas. Salmon have adapted to the coasts of northern oceans by living part of their lives in freshwater and part in the ocean. There are over 9000 species of perch, including tunas, jacks, billfishes, sunfishes, and darters, making it the largest vertebrate order. Perches and their relatives are the dominant fishes in tropical marine waters. Closely related to the perches are the flatfish, which look and swim like normal fish when young, only to lay on one side of their body as adults after one eye migrates to the "top" side.

The Hake Fish

Silver Hake

Hake is common name for any of several related soft-rayed, marine, acanthopterygian fishes. All hake fishes are carnivorous.
Certain hakes called codlings are found on both sides of the North Atlantic Ocean and are characterized by elongated, largeheaded fishes with large, sharp teeth. They have two dorsal fins, the second long and slightly notched near the middle. The anal fin is also long and notched, and the pelvic fins are placed far forward, ahead of the pectorals. This feature has led to the English name forkbeard for the common European species, also known as hake's dame. The red hake is the common American species and is about 60 cm (about 24 in) long. This fish and the white hake are sought for their oil and for their air bladders, used in making isinglass.

The true hakes are found on both sides of the Atlantic Ocean, in the Mediterranean Sea, and in the Pacific Ocean, off the United States, Chile, and New Zealand. The common European hake is slender, reaching 1.2 m (4 ft) in length, with a long, pointed snout. Unlike the silver hake, found mostly between Cape Cod, Massachusetts, and Cape Sable, Nova Scotia, Canada, the European hake is not valued as food. The name hake has also been applied to the northern kingfish, a member of the drum family.

In eastern North America, the name hake is also applied to several marine food fishes related to Merluccius but placed in the genus Urophycis. These fishes resemble Merluccius but are distinguished by long, slim pelvic fins and by a small barbel at the tip of the chin. Economically important members of this genus include the white hake (U. tenuis) and the red hake (U. chuss).

The Swordfish

Swordfish

Swordfish is a common name applied to a large, marine, acanthopterygian (spiny-finned) fish found in tropical and subtropical seas. The swordfish averages about 113 kg (about 250 lb), but individual fish have been caught that weigh more than four times that much.
Swordfish live in temperate and tropical seas throughout the world. They remain near the water's surface during the day, diving to deep waters to feed, chiefly on smaller fishes. A swordfish typically swims through a school of mackerel, haddock, or other fish swinging its sharp-edged, swordlike snout from side to side to stun its prey. It then turns around and swims back through the school to feed, swallowing the prey whole in its toothless mouth. A swordfish may also impale its prey.

The swordfish has a large dorsal fin, lacks pelvic fins, and is characterized by the fusion and prolongation of the bones of the upper jaw to form a rigid, swordlike beak that often constitutes one-third of the total body length. Swordfish feed on large mollusks and on other fish; the adult swordfish has no teeth. Swordfish meat is edible and nutritious, and swordfish hunting is a profitable sport. Swordfish are hunted with harpoons as well as with big-game fishing equipment. The swordfish is also known as the broadbill, and the name swordfish is sometimes applied to the gar pike and to the cutlass fish.

The Dragonfish

Dragonfish

The Dragonfish is also called sea moth and belongs to about five species of small marine fishes comprising the family Pegasidae and the order Pegasiformes.
Dragonfish are found in warm Indo-Pacific waters. They are small (to about 16 centimetres [6 1/2 inches] long), elongated fish encased in bony rings of armour. The armour is fused on the head and body but not on the tail, which is thus flexible. The pectoral fins are large, horizontal, and winglike; the pelvic fins consist of a few fingerlike rays. The mouth is small and toothless and is placed below an elongated, bony snout.

Little is known about the natural history of the dragonfish. Their relationships to other fish groups are also in doubt. One of the best known dragonfish is Pegasus volitans, a blue-eyed, brown or deep-red fish found from India to Australia.

The Porcupine Fish

Porcupine Fish

The Porcupine Fish is a spiny, shallow-water fishes of the family Diodontidae, found in seas around the world, especially the species Diodon hystrix. The porcupine fish is related to the puffer.
The prcupine fishes range from 30 to 90 cm (12 to 36 in) long. When threatened, the fish may swallow water or air, inflating its body into a bristling ball. The upper teeth are fused, as are the lower, producing a beaklike mouth used for feeding on coral and mollusks-hence the family name, which means "two-toothed." The skin is usually spotted. The porcupine fish is related to the puffer.

Porcupine fishes are short and broad-bodied, with large eyes, beaklike teeth, and skins set with spines, hence the name. These spines are short and permanently erect in some species, such as the burrfishes of the genus Chilomycterus. In the others, such as those of the genus Diodon, the spines lie against the body except when the fish is inflated. The skins of porcupine fishes, inflated, dried, and sometimes provided with a light bulb inside, are commonly sold as curios. The porcupine fish (Diodon hystrix) is a common and widely distributed member of the family. Found throughout the world, it is a dark-spotted, brownish fish reaching a maximum length of about 90 centimetres (3 feet).

Source:
- "fish." Encyclopædia Britannica from Encyclopædia Britannica 2007 Ultimate Reference Suite. (2007)
- Microsoft® Student 2007 [DVD]. Redmond, WA: Microsoft Corporation, 2006.