Scientists have rediscovered an incredibly rare blind cave tetra from Brazil for the first time in almost half a century.
Cristiano Moreira and coauthors reported the rediscovery of Stygichthys typhlops in a recent issue of the Journal of Fish Biology.
This eyeless and depigmented tetra was originally described from a single (and only known) fish collected from the town of Jaíba, eastern Brazil in 1962 when a communal well was being dug. No subsequent attempts were made over the next four decades to catch more specimens of this fish, until two expeditions to Jaíba in 2004 by the authors obtained 34 more specimens.
The authors killed and preserved some of the tetras caught for study, and kept the remainder alive to observe their behaviour. They noted that S. typhlops is a midwater swimmer that remains almost still in midwater when undisturbed. The fish adopts an attitude with the body inclined at a 10–40° angle, the head facing either up or down, or moving slowly, with the mouth slightly open.
Stygichthys typhlops is also a solitary species, remaining indifferent to each other and not schooling when kept together. Accidental physical contact results in mutual avoidance movements.
The blind tetra is only known from a single subterranean drainage, the córrego (stream) Escuro system, which runs for about 25 km before discharging into the Rio Verde Grande (in the Rio São Francisco drainage).
Until the early 1990s, the fish was still relatively common in the Jaíba region, according to local inhabitants. Since then, intensive exploitation of the subterranean water source, particularly for irrigation projects, has led to a marked decrease in the water table levels (the Jaíba region is relatively dry and there has been a strong reliance on underground water as a permanent source).
This has led to the drying up of numerous wells, including many of those indicated as previously supporting a population of Stygichthys. The authors conclude that "nless unknown deeper hypogean habitat is present, or the human use of subterranean water is severely reduced, it is unlikely that populations of this species will survive."
For more information, see the paper: Moreira, CR, ME Bichuette, OT Oyakawa, MCC de Pinna and E Trajano (2010) Rediscovery and redescription of the unusual subterranean characiform Stygichthys typhlops, with notes on its life history. Journal of Fish Biology 76, pp. 1815–1824.