For example, hagfish don’t have scales and aren’t true vertebrates (or are considered primitive vertebrates) mudskippers are amphibious fish that can live outside water lungfish use lungs instead of gills to breathe lampreys lack paired fins, and tuna are warm-blooded.Īlso, not all fish groups come from fish lineages. There are several exceptions to the common definition of a fish. Exceptions Hagfish are the only animals that have a skull but no vertebral column. Although interesting, it remains unclear if there was ever an advantage of a hinged jaw.įurthermore, fish may have evolved from a creature similar to a coral sea squirt whose larva resembled primitive fish in very important ways. The diversity of these jawed creatures may prove the evolutionary advantages of a jawed mouth. The first jaws were found in fossils and they lacked any teeth. However, an extant clade, the lampreys may have pre-dated the ancient pre-jawed fish. These jawless fish lineages are mostly extinct now. Additionally, the earliest fish lineages were the Agnatha or the jawless fish.Įarly fish from fossil records are represented by a group of small armored and jawless fish. The earliest chordates formed skulls and spinal columns, which helped to evolve craniates and vertebrates. Fish began to evolve during the Cambrian explosion approximately 530 million years ago. Evolution and Origins Oilfish contain high levels of wax esters, which are indigestible to humans.įish have been evolving and changing for a very, very long time. For example, pet fish mostly eat freeze-dried and frozen foods including bloodworms, brine shrimp, krill, and plankton. It also helps fish find the different nutrition they need in a variety of foods.Īdditionally, pet fish may have a bit of a different diet than fish you find in the wild.

It offers a wider range of food options for aquatic animals. This means that they can eat both plants and meat. What do fish eat? Most species of fish fall into the omnivore category. Variations exist but they all provide motion, maneuverability, and stability.įor a list of incredible facts about fish, make sure to read ‘ 10 Incredible Fish Facts.’ Diet Fish eat crustaceans, plants, shrimp, and worms. Fins for movement: Most common are a tail fin, a pair of side fins, a dorsal fin, and an anal fin.They also help fish sleep and are sensitive enough to detect the movement of food and predators. Swim bladders: Specialized organs fill with air to keep the fish afloat and in some species help them survive with low oxygen levels.As with the water habitat, although all fish have gills, not all creatures with gills are fish. Gills to breathe: Fish have gills throughout their life cycle.However, not all creatures that live in water are fish. Water habitat: All fish live in bodies of water, whether it is freshwater or saltwater.Even warm-blooded fish such as tuna and mackerel sharks have only “regional endothermy” or warm-bloodedness limited to certain areas. Cold-bloodedness: All fish are ectothermic or cold-blooded, meaning they cannot regulate their internal body temperature.Regardless, all fish have some characteristics in common that distinguish them from other animals. Ray-finned fishes are of the class Actinopterygii, while lobe-finned fishes are of the class Sarcopterygii. There are three superclasses into which fish are grouped: Bony fish (Osteichthyes), jawless fish (Agnatha), and cartilaginous fish (Chondrichthyes). We may soon have over 35,000, or even 40,000 known species! 5 Fish Characteristics There are three superclasses into which fish are grouped: Bony fish, jawless, and cartilaginous fish. No one really knows how many different types of fish exist in the world, more are being discovered constantly. Fish are the most diverse group among vertebrates, with over 33,000 different types of fish species. Instead, there are 3 main classes, groups, or types of fish: bony fish (Osteichthyes), jawless fish (Agnatha), and cartilaginous fish (Chondrichthyes). “Fish” is a term used to refer to lampreys, sharks, coelacanths, and ray-finned fishes, but is not a taxonomic group, which is a clade or group containing a common ancestor and all its descendants. They usually have gills, paired fins, a long body covered with scales, and tend to be cold-blooded.

Cat goes fishing all fish