| Lithoxus | |
|---|---|
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Siluriformes |
| Family: | Loricariidae |
| Subfamily: | Hypostominae |
| Tribe: | Ancistrini |
| Genus: | Lithoxus Eigenmann, 1910 |
| Type species | |
| Lithoxus lithoides Eigenmann, 1910 |
|
| Species | |
| Synonyms | |
|
Paralithoxus Boeseman, 1982 |
|
Lithoxus is a genus of catfishes (order Siluriformes) of the family Loricariidae. It includes eight species, L. boujardi, L. bovallii, L. jantjae, L. lithoides, L. pallidimaculatus, L. planquettei, L. stocki, and L. surinamensis.[1][2]
Contents |
Lithoxus is supported as a monophyletic sister to Exastilithoxus. Together, these two genera form a well-supported clade.[1]
Lithoxus range from the Oyapock drainage along the border between Brazil and French Guiana, through Suriname west to the Tacutu River along the border between Guyana and Brazil and south to the Uatama and Trombetas rivers of Brazil.[1] L. boujardi originates from the Approuague and Oyapock River basins in French Guiana. L. bovallii inhabits the Ireng River basin in the upper Negro River drainage in Guyana. L. lithoides is distributed in the Essequibo in Guyana and the upper Corantijn River basin in Suriname. L. pallidimaculatus is from the Suriname River basin in Suriname. L. planquettei is known from Atlantic coastal drainages from the Maroni to the Kaw River basins in French Guiana. L. stocki originates from the Maroni and Mana River basins in French Guiana. L. surinamensis inhabits the Gran Rio River basin in the upper Suriname River drainage in Suriname.[2]
In 2008, the discovery of L. jantjae spread the known distribution of the genus to include the Orinoco River; this species is restricted to the Ventuari River above Tencua Falls.[1]
Lithoxus contains some of the most dorsoventrally flattened fishes in the world.[3] They can be distinguished from most loricariids by having a round instead of oval lower lip. The lower lip is large and round as in Exastilithoxus with the edge sometimes frilled, but not with the barbels seen in Exastilithoxus.[3]
Lithoxus species have a unique, enlarged, thin-walled stomach from which the intestine exits dorsally.[3] The stomach is expanded, thin-walled, and clear and is used in breathing air. A thin, clear tube exits the main body of the stomach anterodorsally, terminating at the pylorus just anterior to the posterior extent of the stomach. The intestine tends to have less coils than other members of Ancistrini. The expanded stomach is slightly larger in males; this is due to the males having more space due to a difference in the relative size of the gonads.[4]
Colouration in Lithoxus species is typically slate gray to tan with a few lighter markings on the body; there are occasionally bands in the pectoral and caudal fins. The ventral surface ranges from white to slightly lighter than the sides. The abdomen is naked (scaleless and unplated). The caudal fin is slightly forked.[3]
Breeding males develop extremely long odontodes on the leading edge of the pectoral fin spine.[3]
Lithoxus species grow to about 4.1–8.6 centimetres (1.6–3.4 in) SL.[5][6][7][8][9][10][11]
Lithoxus species are rheophilic, meaning they prefer to inhabit fast-moving water.[1] Lithoxus is said to inhabit both rivulets and medium-sized creeks. Lithoxus have been collected from riffles on the main-stem Essequibo River in Guyana. These peripheral habitats are among the first parts of the river to dry and the respiratory stomach may have evolved to handle this periodic drying.[3] The flattened morphology suggests that Lithoxus species live under rocks.[3] L. boujardi frequently occurs in fast flowing waters of principal rivers or creeks where the substrate is rock or sand.[5] L. bovallii, L. lithoides, and L. surinamensis live in stony rivulets.[6][7][8][9][11] L. lithoides clings to rocks in the rapids.[7] L. planquettei has been found in little forest tributaries (3–4 metres or 9–13 ft wide) with shallow depth, a rocky bottom, and a strong current, often with cascades.[9] In the dry season, L. planquettei has been found in a split brook with very little water input, suggesting that it is a pioneer species which is capable of colonizing difficult environments which are nutritionally poor.[9]
Lithoxus have a unique air-holding stomach.[3] Lithoxus (along with its sister, Exastilithoxus) are fairly unique among loricariids in that they subsist entirely on a diet of insect larvae.[3] The large size and small number of eggs suggest that parental care is well developed, but nothing is known of the breeding habits of Lithoxus.[4]