Author: Brittan & Böhlke, 1965
FBname: Blind tetra
Comments: 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).