The Titicaca orestias, Lake Titicaca orestias, or Lake Titicaca flat-headed fish (Orestias cuvieri), also known by its native name amanto, is a likely extinct freshwater killifish from Lake Titicaca in South America. It belongs in the pupfish genus Orestias, endemic to lakes, rivers and streams in the Andean highlands. With a total length of up to , it was the largest member in that genus. In the hope that an undiscovered population remains, it is listed as Data Deficient by the IUCN. Despite its common name, it is not the only Orestias from Lake Titicaca.
Its mouth was nearly turned upwards, thereby giving the flat head a concave shape. The head took up nearly a third of the whole body length. The upperside was greenish-yellow to umber. The lower jaw was black. Its scales were oddly light coloured at their centre. The scales of the young were blotched.
The Titicaca orestias became extinct due to competition by introduced trout like the lake trout, brown trout, or the rainbow trout as well as Argentinian silverside from the 1930s to the 1950s. A survey in 1962 failed to find any Titicaca orestias.
History
Orestias cuvieri is a species of killfish that belongs in the genus Orestias. Other related species of Orestias live in the region, forming a species flock.
Anatomy
The Titicaca orestias was characterized by a unique pattern of pores on the head. Large thick scales lined the median dorsal ridge and thinner smaller scales surrounded the ridge. Between these two areas of skin were patches with no scales. Unlike most other species of Orestias, the scales of the adult O. cuvieri were granulated. The concave dish shape of its body and jaw further helped distinguish O. cuvieri from other species of Orestias. The anatomy of O. cuvieri closely resembled a species of trout which is now found in Lake Titicaca, a similarity which has led many researchers to hypothesize that competition between the two groups was the reason for the extinction of O. cuvieri.
Size
Each species of Orestias has varying size. The Titicaca orestias was the largest species in the genus. The maximum recorded size is in standard length and in total length, which is considerably larger than most other species; only O. pentlandii at up to and , respectively, comes close.
Coloration and markings
With regard to the coloration of the amanto during their lifetime, specimens present black melanophores laterally as a band on the lateral line and as small groups on the upper lateral sides. Small melanophores cover the fins giving them a grayish color. The grayish color fades to white on the dorsum and belly; juvenile pigmentation pattern persists with little modification in adult males and females. This information shows that the color of the Orestias in question depends on what part of the body is being considered.
Life history
Reproduction
Nothing has been published about the reproduction of the Titicaca orestias, but in other Orestias species of Lake Titicaca, the males become more orange or yellow in color when they are spawning. During their reproductive stage, the females lay somewhere between 50 and 400 eggs, each of which has a yellowish filament up to about 2.5 mm in diameter. As an adaptation to solar radiation, the eggs develop a black protective coat, derived from melanophores, around the embryo sac.
Ecology
Range and habitat
The freshwater fish belonging to the genus Orestias are found in high-altitude isolated lakes in the Altiplano region of South America, ranging from Peru to Chile. Lake Titicaca, which is on the border of Peru and Bolivia, contains a wide variety of Orestias fish. This large lake was once the home to Orestias cuvieri before their extinction.
Population, trends and predation
At one time, there were as many as 30 native fish species in Lake Titicaca, of which 28 species belonged to the genus Orestias. In the middle of the 20th century, there were many attempts to introduce exotic species to the lake. Two of these introductions were successful: rainbow trout introduced in 1942 and silverside (Odontesthes bonariensis) in the early 1950s. The success of the silverside meant the decline of the Titicaca orestias, since the larger silversides were observed to eat them. As long as the silverside continued to flourish, it meant difficult times for the amanto. Fifty years ago, there was no sign of Orestias cuvieri in Lake Titicaca and the species was presumed to be extinct.
Feeding
O. cuvieri mainly ate smaller fish.