Subterranean Fishes of the World

Hubbs (1938:264) used the generic name Caecorhamdella for this species but this was obviously a mistake since the correct name is used three pages later. The generic name was misspelt Caecohamdia by Wolf (1934, 1938).

Country

Types

The description was based on a syntype series of two individuals: BMNH 1926.7.28:1‑2. This species is the type species by monotypy of the genus Caecorhamdia.

Distribution

Known only from the type locality: Guacharo Cave (or Oropuche, Oropouche, or Cumaca Cave) Trinidad (10^o30’N, 61^o30’W).

Habitat

Guacharo Cave is a vadose cave with a stream running through it. The fishes tend to be concentrated in the resurgent sump at the end of the cave. It is thought that the main body of the population is concentrated in the groundwater supplying the cave and nothing is known of this habitat (Darlington 1995). It is highly likely that the large population of Oilbirds (Steatornis caripensis) provided much of the food supply for the aquatic biota. Whether the fishes feed directly on bird products (faeces, dead bodies), or consume invertebrates that do, is not known. Rutherford (2019) counted a population of 1400 individuals in the cave. This is a very significant increase on the 200 reported by Snow (1962). Holland et al (2009) describe the ecology and habits of this bird.

Systematics

Norman (1926) erected the genus Caecorhamdia "in order to draw attention to this interesting fish". He realised however "that this procedure is somewhat unsatisfactory, for, were the eyes developed, the [fishes] would be probably be identified with the species Rhamdia queleni [sic]". Mees (1974:160-165) examined one preserved specimen and living animals at the type locality. His observations indicated that neither generic nor specific distinctions were merited. Instead of synonymising the cave form completely with R. quelen he gave it subspecific status. In common with the cave form of Poecilia mexicana there is a suggestion that a fully evolved troglomorphic fish is undergoing intogression with an epigean form. At Guacharo Cave it is possible to observe all degrees of pigmentation and eye morphology, from pure quelen at the entrance to pure urichi at the end of the cave (observations made by Jack Price; John Endler pers. comm.; Romero 1983:82). Silfvergrip (1996) does not recognise the subspecies. If a troglomorphic, and stygobitic, fish is resident in the area of this cave it will require a separate status and name. Rhamdia urichi seems sensible. However, recent studies by Romero and co-workers (Romero and Creswell 2000, Romero and Creswell 2000, Romero et al. 2002) suggests that the troglomorphic form may have been replaced by an epigean morph. It still remains possible that the troglomorphic form exists in more remote passages, none of which have ever been entered.

Phillip et al. (2013) comment: "A troglomorphic form of Rhamdia cf. quelen had been misidentified as a separate species, Caecorhamdia urichi Norman (1926), and is now considered a synonym of R. cf. quelen.

Biological Notes

Kenny (1995) provides the following very useful observations. They strongly support a view that there was never a highly evolved subterranean fish in the cave and that the syntypes (BMNH 1926.7.28:1‑2) were at the unpigmenred and small-eyed end of the spectrum of variability. (Text courtesy of Amy Deacon).

Caecorhamdía urichi

Given the extreme variability of eye development, pigmentation and barbel length in the blind catfish of the Oropouche Cave, l am inclined to the view that Caecorhamdia urichi was conspecific with Rhamdia quelen. Mees (1974) suggests subspecific status for the blind catfish of the Oropouche Cave. l question this. l have maintained in captivity several specimens and not only the degree of eye formation is variable, but barbel length and colour. Some are pigment free and short barbelled, others range through grey to a very dark grey with longer barbels, and some are even spotted. Moreover, there is no doubt that the pigment-free forms do in fact develop pigmentation in prolonged exposure to illumination. Mees actually visited the Oropouche Cave with Jack Price and Victor Quesnel and spent some time trying to collect specimens. He collected two. Perhaps his methods may not have been up to it. Had he employed a mask and snorkel and chumming he might have seen the very wide variation which l have seen, and had he used a small seine he would certainly have collected more.

Museum Holdings

As above plus: BMNH 1926.7.28:3, RMNH 26733 (Mees 1974).