Cypriniformes II (Loaches and Relatives)

(Loaches and relatives)

Class: Actinopterygii

Order: Cypriniformes

Number of families: 4 of loaches and relatives

Evolution and systematics

Fossils of this order date as far back as the Oligocene (about 38 million years ago), and have been found in North America, Europe, and Asia.

Cypriniformes are in the superorder Ostariophysi, together with the Gonorhynchiformes, Characiformes, Siluriformes, and Gymnotiformes. This superorder is characterized by having a Webberian apparatus, i.e., the first four or five vertebrae, called ossicles, are modified and connect the inner ear with the swim bladder. Because of this, they can hear very well, which is an advantage in murky fresh waters. This may explain why this group has been so successful inland, while being absent from the marine environment. Another distinguishing characteristic of fishes in this superorder is the production of an alarm substance, a chemical released by their skin when damaged, which helps to warn conspecifics of possible danger.

There have been a number of classifications for the order Cypriniformes. The most commonly employed is that of Nelson (1994), in which the order is divided into two superfamilies. The first superfamily, Cyprinoidea, includes one family and eight subfamilies (Cyprininae, Gobioninae, Rasborinae [=Danioninae], Acheilognathinae, Leuciscinae, Cultinae, Alburninae, and Psilorhynchinae), and has a total of 210 genera and about 2,010 species. The second superfamily, Cobitoidea, includes four families: 1) Gyrinocheilidae, or algae eaters; 2) Catostomidae, or suckers, which includes three subfamilies (Ictiobinae, Cycleptinae, and Catostominae), 3) Cobitidae, or loaches, which includes two subfamilies (Cobitinae and Botiinae); and 4) Balitoridae (=Homalopteridae), or river loaches, which includes two subfamilies (Nemacheilinae and Balitorinae). The superfamily Cobitoidea has a total of about 70 genera and 690 subspecies. This is considered the most primitive within this order. The Cobitoidea represent the scope of this chapter.

Physical characteristics

From a morphological viewpoint, the Cobitoidea is not a very well-defined group (it could be said that it was largely put in place to differentiate all noncyprinid families of the Cypriniformes). Therefore, it is difficult to generalize in terms of major morphological characters. For example, the algae eaters, fishes in the family Gyrinocheilidae, lack pharyngeal teeth, while the number of teeth in fishes in other families is extremely variable, reflecting a great deal of ecological adaptations to different types of food. Sometimes the lateral line is complete, in other families it is incomplete or even absent. The algae eaters are further characterized by having a ventral mouth that has been modified for feeding on algae on hard substrate and by having inhalant and exhalant gill openings. The suckers (Catostomidae) have one row of 16 or more pharyngeal teeth and have four sets of chromosomes, a condition called tetraploidy. The loaches (Cobitidae) have an elongated body with a subterminal mouth and three to six pairs of barbels; the river loaches (Balitoridae) have three or more pairs of barbels near the mouth.

Distribution

Suckers occur in China, northeastern Siberia, and North America. The remaining families in this group are native to Eurasia and Africa, with some species having been introduced in other parts of the world. The algae eaters are found in parts of Southeast Asia and Borneo; loaches are found in Europe, Asia, and in Morocco (North Africa), with one species introduced in North America; the river loaches are found throughout most of Eurasia.

Habitat

Like the rest of the Cypriniformes, the families included in this chapter contain all freshwater fishes. They are mostly benthic, feeding and reproducing at or near the bottoms of rivers and streams, especially those that are medium to small in size. Several species are troglomorphic, i.e., blind and depigmented, and living in caves.

Behavior

Fishes in this group can be effective swimmers because of their need to adapt to fast-moving currents. Some members of the family Catostomidae use their ventral mouths to adhere to the bottom and thus avoid being swept away by currents. These fishes usually have a reduced swim bladder that prevents them from rising to the surface of the water (their least preferred habitat).

Feeding ecology and diet

There is a great variety of feeding habits and items in this group. Some fishes eat algae, others, such as those in the Chasmistes spp. in the family Catostomidae, are midwater planktivores, and most feed on aquatic insect larvae, worms, crustaceans, and detritus from the bottom. A large proportion of species in several families, including the Cyprinidae, have a mouth that is essentially ventral, which allows them to feed from the bottom. Others, such as some representatives of the family Balitoridae, have barbels around the mouth that help them locate food. These barbels can be so sensitive that they can sense an imminent thunderstorm. Members of this superfamily are preyed upon by other fishes and some aquatic reptiles and mammals.

Reproductive biology

Some species, such as the longnose sucker (Catostomus catostomus), can engage in rather extensive upstream migrations prior to spawning. In many cases, two males compete for a single female, but not much is known about the genetic role played by each male. Some fishes, like the members of the family Catostomidae, are tetraploid, having four sets of chromosomes instead of the usual two, but only two sets are functional. The evolutionary meaning of this is unknown. Hybridization occurs among species in all the families, raising the question of the validity of the systematics.

Conservation status

The IUCN Red List includes 65 species from these four families: two (Chasmistes muriei and Moxostoma lacerum) are Extinct; two are Critically Endangered; six are Endangered; 27 are Vulnerable; seven are Lower Risk/Near Threatened; one is Lower Risk/Conservation Dependent; and 20 are Data Deficient. Many of these species have a very restricted range and live in small streams that are very sensitive to pollution.

Significance to humans

Many species, particularly those in the Gyrinocheilidae, are commonly sold in pet shops because they are believed to be useful in keeping aquaria clean of algae. Others, such as the hillstream loaches of the family Balitoridae, are important as ecological indicators because of their sensibility to minor environmental change. A few species can occasionally be seen in fish markets, but since most are small, they are rarely of any commercial value. Others, such as those living in caves, are of scientific value because of their interest from an evolutionary standpoint.

Species accounts

Resources

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[Article by: Aldemaro Romero, PhD]