Subterranean Fishes of the World

Country

Types

Holotype: MZB 17174 male 66mm SL.

Paratypes: MNHN 2009-0154 male 69mm SL, MZB 17175 male 78mm SL, ZMUC P771680 female 62mm SL, ZMUC 771681 male 80mm SL, ZRC 51874 female 51mm SL.

Distribution

Type locality: Alam Moko cave, Oempo village, Tongkuna district, Walengkabola, Muna Island, southeastern Sulawesi Province, Indonesia. 5°10'27.5"S, 122°35'00.6"E. Known also from Gua Moko and Moko Morete in the same area.

Habitat

All three sites from which this species is known are anchialine caves (Bishop et al. 2015, van Hengstum et al. 2019).

The Alam Moko, Gua Moko and Moko Morete are anchialine caves with an upper layer of fresh to weakly brackish water above layers of saltwater. Sharp picnoclines were observed, especially in Moko Morete, the longer of the caves. Passages develop towards the sea, located 400-500 m to the east. Fresh water flows into the sea through springs that we succeeded to locate and partly explore (Franck Brehier, pers. com.). In Moko Morete a strong tidal flow causes an inflow of saltwater.
Alam Moko is a vast blue hole close to 30 m in diameter with direct exposure to daylight, surrounded by cliffs up to 6 m high. One passage develops to the west, but it is too narrow to allow the passage of a diver. The main passage develops to the east. It is in complete darkness, 16.5 m deep and about 65 m long ending in a collapse of stones. Moko Morete opens in a vast blue hole. An underwater passage to the west can be followed 10 to 15 m, but then it becomes too narrow. It may lead to Gua Moko. The main passage begins to the east. With 403 m, it is one of the longest sumps explored on Muna so far. The maximum depth is 21 m. The inner part is huge, ending in a collapse due to the very soft nature of the limestone. The cave still needs to be thoroughly explored. Only the few first meters are exposed to daylight. Gua Moko begins with a dry passage that leads to a lake about 50 m long. The sump begins thus in total darkness, is 43 m long and 14 m in depth. The cave is 116 m and completely lightless. [Information from Nielsen et al. 2009].

Systematics

Molecular and morphological studies by Moller et al. (2016) show that Diancistrus typhlops forms a monophyletic group with D. jeffjohnsoni (type locality: Sweers Island, Gulf of Carpentaria, Australia, 17°08'S, 139°36'E) and D. tongaensis (type locality: Epi Island, Vanuatu, 16°47'S, 168°21'E). These three in turn form a monophyletic group with the sister species Dinematichthys iluocoeteoides (type locality: Batu Islands, Indonesia). The four species in this group have a sister relationship with a group consisting of Ogilbia cayorum, Ogilbia sp., Ogilbichthys sp. and the subterranean species Typhlias pearsei. The same studies show that these species are in the newly proposed Family Dinemtichthyidae (they were previously in Bythitidae) which is diagnosed by unique morphological synapomorphies in the male copulatory apparatus.

Biological Notes

Diancistrus typhlops belongs to a viviparous family. Recently, however, a rare instance has been observed within the Dinematichthyini, where viviparity appears doubtful (Didymothallus criniceps Schwarzhans and Møller, 2007), and it is also not proven for D. typhlops. The two females have eggs up to 0.8 mm in diameter, but no embryos were found. The 62 mm SL female had about 250 eggs 0.6-0.8 mm in diameter. The four males have a well-developed intromittent organ and histological sections of the testes of one of these (MNHN 2009-0154) show numerous spermatophores in the testicular duct. The presence of long, retrorse fangs indicates that they can take relatively large prey. The only identifiable stomach content, judged from radiographs, is two 2 mm long gastropods. The absence of eyes indicates that the species has evolved under dark cave conditions. The specimens were easily caught in hand nets. They kept close to the rocks often upside down. In Moko Morete an interesting nocturnal migration was observed as dozens of fish from the lightless parts of the cave appeared in the blue hole after dark. There was much more food available in the blue hole than in the oligotrophic cave habitat as the blue hole was exposed to daylight all day long. It was not without risk to stay in the blue hole as many specimens were eaten by snakes. Except for some possibly introduced marine fish in the Alam Moko blue hole the only fish found in the caves was Diancistrus typhlops. A number of crustaceans were observed and caught in traps: Copepoda (Harpacticoida - Tisbe?, Cyclopoida - Oithonidae), Amphipoda (Melitidae - Grandidiereli sp.) and Decapoda (Natantia). The salinity in the caves varied between 5-10 ppm in the surface layers and about 30 ppm in the bottom layers with a sharp halocline at 15-20 m depth. [Information from Nielsen et al. 2009].

Museum Holdings

As above only.