Mammals are those living species that are warm-blooded, have fur, and give birth to the young ones, not by eggs.
Fish are cold-blooded water or marine species. They lay eggs but do not have fur, hair or lungs and instead, have scales on their bodies.
They do not nurse their babies as mammals do with milk. But some of the water or marine creatures like the whale, porpoise, and dolphins come under mammals, even though they inhabit exactly the same environment as that of fishes. Fish are neither amphibians nor mammals. Mammals do not have the process of filtering the air from the water for respiration like a fish (using gills). Small fishes feed on other aquatic matter, while large predators like sharks feed on small fish as food. All fish are classified into three evolutionary categories, which are Osteichthyes, Agnatha, and Chondrichthyes. Osteichthyes are bony fishes and Chondrichthyes are cartilaginous fish. The majority of the fish come under the category of bony fish and have a proper skeleton just like humans. While species like skates, rays, sharks, or chimera come under the cartilaginous category. The warm-blooded mammals like humans do not have gills, they have lungs, unlike the fish which have cold blood. Fish can control body heat to some extent. Their life is only possible in the water.
You can get more insight here on our herring facts and is a bird and animal article on this website.
What family does fish belong to?
Every living species is divided into a particular kingdom, phylum, class, order, family, and genus. Fish is not a scientific term, rather is a general term for the species which do not fit into any of the sub-vertebrate categories like classes Reptilia, Amphibia, Aves (birds), or Mammalia. Fish are egg-laying water species. Both tiny and big fish like sharks have small teeth. Fish are neither amphibians nor mammals. A group of fish is called a 'school'.
Fish have many families, and they all belong under the phylum Chordata. Fish are broadly classified into these three main categories, which are Chrondrichthyes - cartilaginous fish, Osteichthyes - bony fish (ray-finned group and lobe finned group) which is also the largest group, and Agnatha - jawless fish. Different species of fish are classified under different families and classes. Like, sawfishes (Pristidae), guitarfishes (Rhinobatidae), Australian lungfish (Ceratodontidae), South American lungfishes (Lepidosirenidae), African lungfishes (Prototeridae), and many more.
Is fish an order?
According to scientists, there are approximately 70 orders or even more orders of fish in the world. Fish is not an order in itself, but all the species have different orders according to their characteristics. Like, Lepisosteiformes, Cypriniformes (minnows, carps, and suckers), Acipenseriformes (sturgeons and paddlefishes), Siluriformes (North American catfishes), Salmoniformes (trout and salmon), Esociformes (pikes and pickerels), Scorpaeniformes (sculpins), and Perciformes (temperate basses, sunfish, perches, drums).
Fishes are classified under the kingdom Animalia, and phylum Chordata. Chordata species have a notochord and a tubular nerve chord at their back. Fish are under the vertebrate subphylum and are not warm-blooded. Fish are those vertebrates that inhabit the water and have gills to breathe, but they are not amphibians. They are ectoderms and will consist of either a bone set or cartilage. The fins that fish have help in protecting the bodies. Even the sharks, whales, and dolphins, which are mammals, do not have hair on their bodies, but have lungs and do not belong to one particular class.
What are the three categories of fish?
All the fish species available in the world are broadly classified under three categories of fishes, which are Chrondrichthyes - cartilaginous fish, Osteichthyes - bony fish (ray-finned group and lobe-finned group), and Agnatha - jawless fish. There are 50 Agnatha fishes, 600 Chrondrichthyes fishes, and 30,000 Osteichthyes fishes.
Bony fish have are aquatic vertebrates and possess a skeleton of bones. They also have an air bladder and gills to breathe air. They have color vision as well. They are also called Osteichthyes and the majority of the fish today come under this category. Bony fish are those standard fish that come to our mind when we talk about fish. These fishes have a spindle shape, are oval, and are flattened. Their skin is protected by the protective scales. They are further divided into two major subgroups, which are lobe-finned and ray-finned fish. The ray-finned fish have fins made of webs of the skin which are altogether held by the bony spines. Their fins are directly attached to their skeleton system. Lobe-finned fish possess fleshy fins and they are joined by a single bone to the body.
The cartilaginous fishes have cartilages, unlike the bony skeletons of the bony fishes. This cartilage gives external support to the fish. Because of this external support, only these fish grow in good size. Cartilaginous fish have a different breathing pattern as that of a bony fish. Bony fish have coverings on the gills. Cartilaginous fish can breathe by spiracles too other than gills. These spiracles are like the openings present on the top of the head of the skates and rays. The cartilaginous fish have dermal denticles or placoid scales. These scales are very different from the scales of the bony fish.
Lampreys (Agnatha) are those species that are jawless and come under vertebrates. These vertebrates have narrow and long bodies. They do not have scales and have a small range of teeth in the mouth. They are further divided into non-parasitic and parasitic fishes.
Which is the oldest class of fish?
The oldest class of fish which are even in existence today are the Agnatha, which consists of the lampreys (class Cephalaspidiformes) and the hagfishes (class Myxini). This group of fish does not have biting jaws like humans. They do not have scales and are very long. They are derived from the Paleozoic era.
The lampreys are hagfishes are associated with the Carboniferous period which was about 350,000,000 years ago. The body characteristics of this category of animal help understand the evolutionary features. They swim at the bottom areas of the ocean all their life and prey on different types of arthropods there. The gills which they have served as the food filters for them. Only lampreys (class Cephalaspidiformes) and hagfishes (class Myxini) are available today who survived in the group of Agnatha. These two fishes are very slimy in texture, but not like dolphins. They survive by parasitic mode of nutrition or show scavengers behavior on small fishes.
Dolphins and whales come under the category of warm-blooded animals but sharks are cold-blooded. Fish are not warm-blooded and do not give birth to young ones. Fish are not like other legged-amphibian creatures who survive both on the surface and water. Yet they show some common characteristics as of them. Fish do not have hair on their bodies.
Here at Kidadl, we have carefully created lots of interesting family-friendly facts for everyone to enjoy! If you liked our suggestions for is a fish a mammal, fin-tastic facts for kids on fish classes, then why not take a look at how long do gorillas live, cool facts to know on this forest animal or how do mirrors work, amazing physics facts revealed for curious kids?
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