Subterranean Fishes of the World

Country

Types

Holotype: ZSI F313/2 38.85mm TL. The description is based on two specimens (second 42.0mm TL) and although the second is not mentioned as a paratype it should be considered as such (also at ZSI). This is the type species by original designation and monotypy of the cave‑restricted genus Horaglanis.

Distribution

Type locality: A well at an undisclosed location at Kottayam, Kerala, India. Known also from a number of dug out wells in the same area (8^o4'N‑10^o21'N, 76^o13'E‑77^o38'E). The type locality of this species is also the type locality of the Synbranchid Monopterus eapeni and at this site at least the two species coexist. It is not known whether they coexist elsewhere.

Habitat

The only published details are that the fish is found in dug-out wells. It may be an inhabitant of relatively small groundwater voids. Mercy (1981) suggests that they migrate from one well to another through the subsurface drainage system. Francy Kakkasery (pers. comm.) suggests that they live in the water table up to 10m below the surface and that they are only found where laterite is the predominant bed deposit.

Systematics

The anatomy of H. krishnai has been relatively well studied (see references below) and it seems certain that it is rather different in several ways from other members of the family. Menon (1950, 1951a, 1951b) suggested that the differences were the result of regressive evolution and that the animal was only secondarily primitive. Chardon (1968) made a thorough study of several aspects of siluriform anatomy. He noted that the viscera are more typical of the Bagridae than the Clariidae. This and other evidence suggests that the species is a relict, close to the stem of both Bagridae and Clariidae. Although admitting that there were examples of shared derived characters, and of features associated with hypogean life, Chardon suggested that it is primarily primitive. De Pinna (1998) postulates a relationship between Phreatobius and Horaglanis based on similar skull morphology. A recent photograph of Horaglanis krishnai (Plate 6) shows that it is blood red in colour, a very rare condition for fishes (De Pinna, 1998), as is Phreatobius and this may be a synapomorphy for a group containing the two genera. Clearly there is much to be learned about the exact systematic position of this interesting animal.

Jarayam (2006:309) proposed the subfamily Horaglanidinae for the, then, two species in the genus but this has not received support since.

Diogo et al. (2003), also de Pinna (1993) and de Pinna (1998), have suggested, on morphological grounds, that the most basal member of the Family Clariidae is Horaglanis, and that the next most basal is Uegitglanis.

Biological Notes

The Kerala area of south-western India, principally the area of the Western Ghats, is rich in subterranean species. There are at least three unique elements within this subterranean fauna that stand out as of great evolutionary interest.

First, there are at least eleven subterranean fishes: Cobitidae: Pangio bhujia; Clariidae: H. krishnai, Horaglanis alikunhii, Horaglanis abdulkalami; Kryptoglanidae: Kryptoglanis shajii, Kryptoglanis undescribed species; Synbranchidae: Monopterus eapeni, Monopterus roseni, Monopterus digressus; Aenigmochannidae: Aenigmachanna gollum, Aenigmachanna mahabali. What is most remarkable about these fishes is that the Families Kryptoglanidae and Aenigmochannidae were both erected recently (2014 and 2020 respectively) and contain only these species. The erection of new families within teleost fishes is very uncommon and this greatly emphasises the importance of this area.

Second, there is a strongly fossorial amphibian in its own family: Nasikabatrachidae: Nasikabatrachus sahyadriensis Biju and Bossuyt 2003, sister family, genus and species to Sooglossidae, an amphibian family found only in the Seychelles archipelago) (Zachariah et al. 2012).

Third, there are two aberant Crustacea: Euryrhynchidae: Eurindicus bhugarbha De Grave, Arjun and Raghavan 2018 and Palaemonidae: Troglindicus phreaticus Sankolli and Shenoy 1979.

Both the fishes and the Crustacea appear to have originated in Gondwanan times and both have close relatives in Africa. It is hypothesised that the genus Horaglanis is related to Uegitglanis zammaranoi from Somalia (Menon 1951, Silas 2010) and Eurindicus is related to three west African species (the monotypic Euryrhyncoides holthuisi, Euryrhynchina edingtonae and Eurhynchina puteola (De Grave et al. 2018).

There is considerable evidence, both from morphology and molecules, that Horaglanis is very basal within Clariidae. de Pinna (1993, 1998) and Diogo et al. (2003) considered the skull structure of specie swithin the Clariidae and concluded that Uegitglanis was sister to all other species in the family and that Horaglanis was sister to Uegitglanis plus other species making it the most basal of all studied clariids. This conclusion was supported by Pavan-Kumar (2017) who compared mitochondrial COI sequences from one (unnamed) species of Horaglanis and 13 other Clariidae and showed that it is the sister group to all other species in the family (he did not include Uegitglanis in his analysis). [Note than Pavan-Kumar (2017) is a Peerj preprint that had not been refereed so its conclusions need to be taken with caution.]

Museum Holdings

As above plus: BMNH 1981.11.20:1‑3.