Blind Characin

The specimens were collected from two shallow wells, at Fazenda do Seu Roque which is still occasionally used as a source of water for cattle, and the shallow, abandoned well at Fazenda do Lajeado. Both have similar physico-chemical characteristics, with the pH and conductivity typical of limestone drainages (Fazenda do Seu Roque: pH 6.98, conductivity 0.683 μsm cm−1, 25·3°C and salinity 0·02; Fazenda do Lajeado: pH 7·0, conductivity 0·647 μsm cm−1, 25·8◦ C and salinity 0·02%). Laboratory and field observations demonstrate that this species is predominantly a midwater swimmer; when undisturbed, it remains almost stationary in midwater, with the body inclined at a 10-40° angle, head facing either up or down, or moving slowly, with the mouth slightly open. It is apparently solitary and when in groups (in laboratory), they remain indifferent to each other, not schooling and if there is contact by chance, it is followed by mutual avoidance movements, usually (but not always) with the smaller individual withdrawing for a short distance, some intraspecific agonistic biting attempts during feeding were also observed. The surface feeding behaviour in the laboratory of recently captured individuals, associated with the fact that phreatic waters are generally food-poor, suggests that in nature, these fish concentrate at the upper part of the aquifer where food input is higher in these sectors, as organic matter washes down from the surface. Ostracods were also observed in radiographs of the stomachs of five of the 16 specimens preserved in the field. Specimens were collected with hand nets and minnow-traps baited with commercial fish pellets and dry cat food. During collection with hand-nets in wells, the fish reacted with a quick fleeing movement only when the net was at close range. This reaction plus the limited responsiveness to live prey as initially observed in the laboratory, indicates a low dependence on mechanosensory systems, probably associated with the loss of the lateral line on the body. There is no clear reaction to light, because they are either insensitive to it or behaviourally unresponsive to light conditions (Ref. 84216).

Stygichthys typhlops, the blind tetra or Brazilian blind characid, is a species of fish in the family Characidae and the only member of the genus Stygichthys. It is endemic to caves in northern Minas Gerais, Brazil. Like other cave-adapted fish (e.g. the cave form of the Mexican tetra), the Brazilian blind characid is blind and lacks pigmentation. It reaches up to about 4.6 cm (1.8 in) in standard length. It is solitary and when kept together in an aquarium, individuals are indifferent to each other.

Initially only known from a specimen collected in 1962, it was rediscovered in 2004 by researchers led by the ichthyologist Dr Cristiano Moreira from the University of São Paulo. According to locals it was relatively common in the Jaíba region until the early 1990s, but generally not seen afterwards as extensive water extraction had significantly lowered the water table, resulting in many wells and springs drying out. This represents a serious threat to the continued survival of Stygichthys typhlops. It is recognized as an endangered species by Brazil's Ministry of the Environment.

Although there are many cave-adapted catfish species in mainland South America, there are only two known cavefish species from other orders: Stygichthys typhlops and the knifefish Eigenmannia vicentespelaea.

Habita um riacho subterrâneo. Troglomórfica especializada, não possui pigmentação ou olhos. Nada na coluna d'água e não e são arritmicos, não mostrando nenhum padrão de atividade consistente com ativividades circadianas ou ultradianas, o que indica um longo período de isolamento em ambiente freático (Moreira et al., 2010). Aparentemente solitário e provavelmente um micro-carnívoro (Moreira et al. 2010).

Lençol freático na drenagem do córrego Escuro, afluente do rio Verde Grande, Jaíba, bacia do rio São Francisco, Minas Gerais; encontrada apenas em duas localidades (Moreira & Trajano, em Rosa & Lima, 2008; Moreira et al., 2010)