Fish as a pet
The name fish refers to a diverse group of vertebrates from several evolutionary lineages. It describes a living organism rather than a taxonomic group. As members of the Chordata phylum, fish have characteristics in common with other vertebrates. These characteristics include gill slits at some point in the life cycle, a notochord. Alive fish are divided into five classes, each unique to the four classes of familiar air-breathing animals: amphibians, reptiles, birds, and mammals. For example, jawless fish (Agnatha) have gills in pouches and no limb girdles. Lampreys and hagfishes are examples of extant agnathans. As the name implies, the skeletons of fish in the Chondrichthyes class (from chondr, “cartilage,” and ichthyes, “fish”) are cartilage. Sharks, skates, and rays are cartilaginous fish. Examples include the tiny seahorse, the 450-kg (1,000-pound) blue marlin, flattened soles and flounders, boxy puffers, and ocean sunfishes. Unlike cartilaginous fish scales, those of bony fish grow throughout their lives and are made up of thin, overlapping bone plates. Bony fish also have an operculum that covers their gill slits.
General behaviour of fish
In addition to their normal senses of sight, smell, hearing, touch, and taste, fish also use unique lateral line water-current detectors to sense their environment. Perception is aided in the few fish that produce electric fields by a technique best described as electrolocation. Depending on the fish’s various adaptations, one or more of these senses are frequently prioritized over others. Fish with large eyes may have a diminished sense of smell, whereas fish with small eyes mostly rely on scent to hunt and dine.
Special behaviour of fish
Fish that exhibit specialized behaviour mostly focus on three essential life activities: feeding, reproducing, and evading predators. For example, sardines’ schooling behaviour on the high seas is primarily a defence mechanism to ward off enemies. Still, it is also influenced by their needs for food and reproduction. Beaked parrot fishes, which feed on coral and move in tiny groups from one coral head to the next, cannot move like predatory fishes, which are frequently solitary creatures that lie in wait to dart for their prey abruptly furthermore, several predatory fish, including tunas, frequently school in aquatic habitats.
How do fish sleep?
Fish sleep in a seemingly listless state, keeping their equilibrium but moving slowly since they do not have genuine eyelids. Most can flee if they are assaulted or disturbed—certain species of fish sleep by lying on the bottom. Most catfish, a few loaches, some eels, and electric fish are exclusively nocturnal; they spend the day hiding in holes, dense foliage, or other safe havens while actively searching for food.
How do fish communicate?
In many cases, communication is crucial between individuals of the same species or between two or more species, particularly when it comes to breeding behavior (see Reproduction below). A huge fish of a completely different species and the small, so-called cleaner fish may communicate visually. In order to get rid of gill parasites, the larger fish frequently lets the cleaner into its mouth. Even though the larger fish is often a predator, the cleaner is distinguished by its unique color and behavior and is therefore not consumed. Pheromones, which are particular molecules that transmit messages, are often used in chemical communication.
Reproduction cycle
Fishes reproduce in various ways, but most lay a large number of small, fertilized eggs dispersed outside their bodies. Pelagic fishes typically leave their eggs dangling in open water. Many freshwater and shore fish lay their eggs in vegetation or on the bottom. There are those with sticky eggs. Out of hundreds, thousands, or even millions of eggs laid, only a few people often reach adulthood due to the high mortality rate of both the young and eggs.
Males generate sperm in two (or sometimes one) testes inside the body cavity, typically as a milky white fluid known as milt. Each testis in bony fish has a sperm duct that connects to a urogenital aperture located behind the vent or anus. The duct ends in a cloaca in cyclostomes, sharks, and rays. The pelvic fins may occasionally be altered to aid the transfer of milt to the eggs at the female’s vent or on the substrate where the female has put them. In a few cases, auxiliary organs—such as the claspers of many sharks and rays—fertilize females internally.
Parental behaviour, whether by the male, female, or both, and somewhat stereotyped but intricate courtship and behaviour ensure successful reproduction and, in many cases, defines of the eggs and the young. Certain fishes create their nests by blowing a cluster of mucus-covered bubbles at the water’s surface (gouramis), sticklebacks construct their nests consisting of plant materials and kidney-excreted sticky threads, and cichlids hollow out depressions in the sand bottom. These structures are where the eggs are laid. Certain types of catfish and cichlids use their mouths to incubate their eggs.
Rather stereotyped but frequently intricate courtship and parental behaviour, either by the male, female, or both, ensure successful reproduction and, in many cases, defence of the eggs and the young. Certain fish species prepare their nests in different ways. Cichlids, for example, hollow out depressions in the sand bottom; sticklebacks use plant materials and kidney-excreted sticky threads to form their nests; and gouramis blast bubbles covered in mucus at the water’s surface. In these structures, the eggs are laid. Eggs are incubated in the jaws of certain species of catfish and cichlids.
Diversity status
Fish have been around for almost 450 million years and have adapted to fit into nearly every form of aquatic ecosystem. Terrestrial vertebrates are highly modified fishes that evolved into tetrapod (four-legged) terrestrial vertebrates after colonizing land habitats. Many fishes fit the conventional image of a fish as a slippery, streamlined aquatic animal with fins and gills, but far more fishes vary from that stereotype than conform. For instance, the body can be greatly shortened in some instances, elongated in others, flattened in some (mostly bottom-dwelling fishes), laterally compressed in others, and have elaborately extended fins that form intricate shapes or are reduced to non-existent fins. The mouth, eyes, nostrils, and gill openings can also vary greatly in position. There have been air breathers in several evolutionary branches.
