Fish (lat. Pisces) cruisecritic aquatic vertebrate animal with fins and internal gills. There are t

Fish (lat. Pisces) cruisecritic aquatic vertebrate animal with fins and internal gills. There are three classes of live fish: the primitive jawless fish or Agnatha; Cartilaginous (ajkulovidni) fish or Chondrichthyes; and bony fish or Osteichthyes. These groups, cruisecritic although they have different cruisecritic anatomical features, have certain common characteristics related to their common evolutionary origin or their aquatic lifestyle. Fish were the earliest vertebrates and probably evolved from a group of aquatic lower chordates; terrestrial vertebrates evolved from fish.
There are about 20,000 species of fish. They vary in size, from 7,9 mm long pedocipris (Paedocypris) living in tropical swamps of Sumatra, and until 14 m long kitovska shark. Many are brightly colored and have many shapes and patterns for camouflage. They are found in all marine, freshwater and brackish waters throughout the world, at any depth. Members of different species of fish tolerate temperatures of the water freezing to over 38 C. Most are either saltwater or freshwater, but some are physiologically adapted to move from one water environment. Most of the fish born in freshwater cruisecritic spend their adult lives in the ocean, returning to freshwater to spawn; reverse migration occurs in some fish from the ocean. Many fish remain tightly organized groups, others alone and together only during the spawning and feeding. Fish may be carnivorous, herbivorous or omnivorous. Some fish are scavengers on lake or ocean bottoms. Fish are the main source of human food, fish oil, pet food etc.
There are members of the ground vertebratni classes, such as whales and sea snakes that have adapted to aquatic life, but not fish. They breathe air, not dissolved oxygen and their anatomical features reveal the relationship cruisecritic with land animals.
Morphology Lampanyctodes hectoris (1) - operculum (zhabrena cover) (2) - side line (3) - dorsal fin (4) - thick impeller (5) - caudal peduncle (6) - caudal fin ( 7) - anal fin (8) - Photophore (9) - pelvic cruisecritic fins (steam), (10) - pectoral fins (steam)
A typical fish is torpedo-shaped, with a head contains the brain and sensory organs, a corpse with a muscular wall surrounding a cavity containing the internal organs and muscle post-anal tail.
Many fish move through the water with wavy movements of their bodies and control the direction of movement through the fins. All have skin covered with slimy glandular secretions that reduces friction with water, as well as scales, together with mucous secretions form almost cruisecritic waterproof coating. All fish have a lateral line system of sensory organs to detect pressure changes in the water. Possess and gills for breathing located in the channels leading from the throat, or pharynx to the exterior; few fish also have lungs as an additional means of respiration. Except primitive classes in all gill channels are supported by skeletal structures cruisecritic called gill arches. Fish that feed on plankton have spider structures gills that collect small organisms. Fish breathe by taking water in the mouth, which then goes out through the gills; As water passes through the thin-walled gills, dissolved oxygen diffuses through the gill capillaries, and carbon cruisecritic dioxide diffuses into the environment. The circulatory system is closed, cruisecritic so there dvokomorno heart. Blood is red. With few exceptions, the fish are cold-blooded (poikilotermni organisms), that they can not regulate their body temperature, cruisecritic which is the same as that of the environment.
The body of the fish is covered cruisecritic with Multilayered skin. In zhlezdesti skin cells secrete a slimy substance that allows easier movement in the water. The surface of the fish is covered with limestone scales in different shapes and sizes that have a protective role.
There are a variety of ways. Sharks reproduce by internal fertilization and most bear live young. Those species that lay eggs produce large eggs with hard shells. Because embryogenesis in these species is well protected, they give a relatively small number of young, usually only seven to eight. Several of bony fish, including some aquarium species cruisecritic lay their small, unprotected eggs that are fertilized after they exit the water. In most marine representatives cruisecritic eggs float freely in the water and najch