Loach

Loaches are a diverse group of freshwater fishes belonging to the suborder Cobitoidei. These fish are benthic, which means they live on the bottom of water bodies. You can find them in rivers and creeks across Eurasia and northern Africa. They represent one of the most varied groups of fish in the world. There are 1,249 known species within the Cobitoidei suborder. These species are organized into 107 different genera and 9 distinct families.

Because loaches are so diverse, they do not share a single body shape. Their physical forms, or morphologies, vary greatly from one species to another. Some loaches are very small, such as the 23 mm long miniature eel-loach, Pangio longimanus. Others are much larger, like the imperial flower loach, Leptobotia elongata. This larger species can reach 50 cm in length and weigh up to 3 kg. Most loaches have narrow, elongated bodies with small cycloid scales. These scales are often tucked away under the skin. Many species also have three or more pairs of barbels near their mouths. These whisker-like organs help them sense their surroundings.

Scientists classify loaches into several different families based on their traits. The family Cobitidae includes spined loaches, which often have a special bone structure. The Botiidae family consists of pointface loaches. Some loaches belong to the Gastromyzontidae family, which are known as hillstream loaches. Other families include the Vaillantellidae, known as longfin loaches, and the Barbuccidae, or scooter loaches. There are also the Serpenticobitidae, which are called snake loaches. Other groups include the Balitoridae (river loaches), the Ellopostomatidae (square-head loaches), and the Nemacheilidae (brook loaches).

To understand how loaches are related, scientists look at their osteology, or bone structure. Many shared traits among loaches come from modifications in the neurocranium, which is the part of the skull that holds the brain. Specifically, changes in the ethmoid bones help unite the Cobitoidei suborder. Many loaches also possess a suborbital spine. This is a movable spine located just below the eye. In the genus Acantopsis, this spine sits between the eye and the snout tip. While once thought to be a trait unique to certain families, it is now seen as a trait from a common ancestor.

The history of loach classification has changed significantly over time. The name Cobitoidei comes from the genus Cobitis, which Carl Linnaeus described in 1758. At the start of the 20th century, researchers only recognized two families. During the early 1900s, ichthyologists Fowler and Hora identified the Balitoridae and Gastromyzontidae families. For a long time, Botiidae and Nemacheilidae were considered subfamilies of Cobitidae. However, they were eventually elevated to full family status in 2002. Modern molecular phylogenetics, which studies genetic relationships, has helped resolve many confusing links between these groups.

Loaches live in many different types of environments. Many families prefer rocky mountain streams at high elevations. However, almost all of these families also have species that live in lowland areas. Some Cobitidae species live in broad, flat terrain by burrowing into the sand of riverbeds. In some extreme cases, loaches have adapted to life in total darkness. At least three families contain troglomorphic species, which are animals specifically adapted to living in caves. These species are often blind due to their dark habitats.

Humans have many connections to loaches through nature and trade. In East and Southeast Asia, some loaches are important food fish found in markets. Many other species are popular in the aquarium trade. People enjoy keeping fish like the clown loach, the kuhli loach, and the dwarf chain loach in home tanks. In an aquarium, loaches are often fed sinking discs of food. While loaches are native to the Old World, some have moved to new places. The oriental weatherfish, or dojo loach, has been introduced to parts of the United States.