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**Evolution and Fossil History:**
– Fishlike animals with notochord and eyes appeared during Cambrian explosion.
– Jawed vertebrates emerged in the Silurian period.
– The Devonian period saw an increase in fish diversity.
– Bony fish became dominant after the end-Devonian extinction event.
– Tetrapods evolved from lobe-finned fish during the Carboniferous period.
– Notable fossils include Dunkleosteus, a giant Devonian armoured placoderm.

**Classification and Diversity:**
Fish are a paraphyletic group.
– Some tetrapods have evolved fish-like body shapes through convergent evolution.
– Osteichthyes includes all tetrapods.
Fish account for over half of vertebrate species.
Fish exhibit a wide range of sizes, swimming abilities, body shapes, and habitats.

**Anatomy, Physiology, and Adaptations:**
Fish bodies are adapted for efficient swimming.
– Swim bladders help adjust buoyancy.
– Scales provide protection and camouflage.
Fish have a closed-loop circulatory system with a single-loop circulation.
– Gills are crucial for gas exchange in fish.
– Various adaptations in fish include efficient respiration, digestion, excretion, and sensory systems.

**Behavior, Reproduction, and Feeding Habits:**
Fish exhibit diverse reproductive strategies and behaviors.
– Reproductive strategies can be oviparous, viviparous, or ovoviviparous.
– Courtship rituals and parental care are common.
Fish have varied feeding habits including carnivorous, herbivorous, omnivorous, and filter-feeding species.
– Feeding behavior can involve ambush or pursuit tactics based on species and habitat.

**Habitats, Respiration, and Sensory Systems:**
Fish inhabit diverse aquatic environments like freshwater, saltwater, and brackish habitats.
– Coral reefs and large river basins are centers of fish diversity.
– Some fish migrate between freshwater and saltwater habitats.
Fish have specialized respiratory systems, including gills for gas exchange and adaptations for breathing air.
– Sensory systems in fish include the lateral line system, vision, electroreception, and olfactory lobes for navigation and survival.

Fish (Wikipedia)

A fish (pl.: fish or fishes) is an aquatic, anamniotic, gill-bearing vertebrate animal with swimming fins and a hard skull, but lacking limbs with digits. Fish can be grouped into the more basal jawless fish and the more common jawed fish, the latter including all living cartilaginous and bony fish, as well as the extinct placoderms and acanthodians. Most fish are cold-blooded, their body temperature varying with the surrounding water, though some large active swimmers like white shark and tuna can hold a higher core temperature. Many fish can communicate acoustically with each other, such as during courtship displays.

Temporal range: 535–0 Ma Middle CambrianRecent
Bala shark, a bony fish
Bala shark, a bony fish
Scientific classificationEdit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Olfactores
Subphylum: Vertebrata
Groups included
Jawless fish
Armoured fish
Spiny sharks
Cartilaginous fish
Bony fish
Ray-finned fish
Lobe-finned fish
Cladistically included but traditionally excluded taxa

The earliest fish appeared during the Cambrian as small filter feeders; they continued to evolve through the Paleozoic, diversifying into many forms. The earliest fish with dedicated respiratory gills and paired fins, the ostracoderms, had heavy bony plates that served as protective exoskeletons against invertebrate predators. The first fish with jaws appeared in the Silurian and greatly diversified during the Devonian, the "Age of Fishes".

Bony fish, distinguished by the presence of swim bladders, emerged as the dominant group of fish after the end-Devonian extinction wiped out the apex placoderms. Bony fish are further divided into the lobe-finned and ray-finned fish. About 96% of all living fish species today are teleosts, a crown group of ray-finned fish that can protrude their jaws. The tetrapods, a mostly terrestrial clade of vertebrates that have dominated the top trophic levels in both aquatic and terrestrial ecosystems since the Late Paleozoic, evolved from lobe-finned fish during the Carboniferous, developing air-breathing lungs homologous to swim bladders. Tetrapods are usually not considered to be fish, making "fish" a paraphyletic group.

Fish have been an important natural resource for humans since prehistoric times, especially as food. Commercial and subsistence fishers harvest fish in wild fisheries or farm them in ponds or in breeding cages in the ocean. Fish are caught for recreation, or raised by fishkeepers as ornaments for private and public exhibition in aquaria and garden ponds. Fish have had a role in human culture through the ages, serving as deities, religious symbols, and as the subjects of art, books and movies.

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