In an earlier post, I told you about the fishes known as brotulas. These are one of the most prominent groups of fish in the deep sea. They tend not to be attractive fish: their lack of outstanding dorsal and tail fins makes them look like something between an eel and a cod, and like many deep-sea fishes they look somewhat flabby and lumpish. There are numerous genera of brotulas out there; the individual in the photo below represents the genus Leucicorus.
Leucicorus belongs to the brotula family Ophidiidae, commonly known as the egg-laying brotulas though Leucicorus' own reproduction has (so far as I have found) not been directly observed. The feature that most immediately sets Leucicorus apart from other brotulas is the eyes: Leucicorus species have very large eyes but the actual lenses are rudimentary or absent (Cohen & Nielsen 1978). It almost looks like they grew bigger and bigger to cope with the low light of the deep sea before they just kind of gave up at some point.
Two species of Leucicorus are currently recognised, each known from separate parts of the world. Leucicorus lusciosus is found in the eastern Pacific, whereas L. atlanticus is known from around the Caribbean. The two species differ in meristic characters and proportions: for instance, L. lusciosus has more dorsal and anal fin rays, but fewer vertebrae and gill rakers, and has a deeper body (Nielsen & Møller 2007). Leucicorus has also been found in the vicinity of the Solomon Islands, but interestingly enough Nielsen & Møller (2007) identified the specimen found as L. atlanticus rather than L. lusciosus, despite the latter species' more proximate distribution. One wonders if perhaps a third species is involved, yet to be recognised.
REFERENCES
Cohen, D. M., & J. G. Nielsen. 1978. Guide to identification of genera of the fish order Ophidiiformes with a tentative classification of the order. NOAA Technical Report NMFS Circular 417.
Nielsen, J. G., & P. R. Møller. 2007. New and rare deep-sea ophidiiform fishes from the Solomon Sea caught by the Danish Galathea 3 Expedition. Steenstrupia 30 (1): 21–46.
Meet the violet demoiselle Neopomacentrus violascens (shown above in a photo by J. E. Randall). This little fish (adults get up to about 7.5 cm in length) is found in tropical waters of the western Pacific, from Japan in the north, south and east to northern Australia and Vanuatu. They usually associate in large schools around inshore reefs, and can commonly be found hanging around outcropping structures over soft bottoms such as coral or rocky outcrops, or wharf pilings (Koh et al. 1997). Violet demoiselles feed on small plant or animal plankton, such as copepods or algae.
The genus this species belongs to, Neopomacentrus, is one of the more recently recognised genera of the damselfish family Pomacentridae. It is similar to two larger genera in the family, Abudefduf and Pomacentrus, but differs from the former in having the hind margin of the preopercle (the anterior one of the bones making up the operculum or gill cover) crenulate or serrate rather than smooth. Pomacentrus has a similar preopercle, but has the suborbital region at least partially naked whereas Neopomacentrus has that region entirely scaly. Neopomacentrus violascens has a distinctive colour pattern, which is mostly a purplish brown, with bright yellow on the caudal fin and the rear of the dorsal fin.
According to Fishbase, individuals of this species form pairs when mating, and the females lay eggs that sink to the bottom and stick to the substrate. The eggs are then guarded and aerated by the males. I have come across reference to this species having been bred in captivity though I get the impression that they are not one of the most commonly kept aquarium fish. This may be because they are somewhat dull in coloration compared to related species, and they are fairly retiring in character. A recent blog post at Zoo Volunteer noted that damselfish species are rarely bred commercially due to the difficulty of providing suitable conditions. Instead, the market for species of this family is usually supplied with wild-caught individuals, commonly collected through the use of cyanide to essentially suffocate the fish until they lose conciousness. Not particularly pleasant for the fish, and arguably not that pleasant for the aquarist either as fish obtained in this method tend to have a much reduced lifespan.
REFERENCES
Koh, J. R., J. G. Myoung & Y. U. Kim. 1997. Morphological study on the fishes of the family Pomacentridae. I. A taxonomical revision of the family Pomacentridae (Pisces; Perciformes) from Korea. Korean Journal of Systematic Zoology 13 (2): 173–192.
Despite how it may look, there is absolutely nothing wrong with this fish. Butis butis is a moderately sized species of fish (up to about 14 cm in length) widespread in warmer waters around the Indian and western Pacific Oceans. They are found in shallow bays and mangrove swamps, often entering into estuaries and lower reaches of rivers. It is known by a range of vernacular names, including crimson-tipped gudgeon or duckbill sleeper. In the aquarium trade, it often goes by the name of crazy fish, in reference to its distinctive habit of swimming hanging vertically head-down or even swimming upside-down. Its predilection for such unusual angles assists it in remaining concealed from both predators and prey; Ryan (1981) noted that the addition of anaesthetic for collection purposes to a pool resulted in the sudden appearance of several specimens of which no sign had been previously seen. Their camouflage abilities are further enhanced by the ability to change colour to a certain degree, from pale to dark. Butis butis are ambush predators of smaller fish and invertebrates that they engulf in their broad jaws with rapid lunges.
Drawing of Butis butis, coloured from an original in Herre (1927) by M. L. Nievera.
The genus Butis belongs among the gobies, a somewhat notorious group of fish from a taxonomic perspective. In the words of the South African ichthyologist J. L. B. Smith, "The Gobioid fishes are one of the major trials of ichthyologists, and when general regional collections are worked up, these fishes tend to be pushed aside, and are apparently often identified with some impatience by those not specially interested" (Smith 1958). This notoriety is mostly due to the small size of many gobies, together with a tendency to the reduction of diagnostic features. Earlier authors classified Butis within the Eleotridae, a group of gobies (commonly known as sleepers, presumably due to their benthic habits) distinguished by having the pelvic fins separate from each other (in other gobies, the pelvic fins are united into a ventral sucker or disc). This, however, is a primitive feature only, and more recent molecular phylogenies have confirmed the paraphyly of Eleotridae in the broad sense. As a result, Butis and some of its nearest and dearest have been separated out into a separate family Butidae (Thacker 2011). However, while the separation of Eleotridae and Butidae seems to be fairly widely accepted, the two groups are still not clearly defined morphologically. Characteristic features of Butis relative to other gobies include (among others) the presence of a complete covering of scales, and a bony ridge above each eye (Smith 1958). In a number of species of the genus, including B. butis, the head is low and long, and the lower jaw distinctly protruding; however, the mudsleeper B. koilomatodon has a shorter, rounder head (this latter species, though originally native to a similar range to B. butis, has become invasive in more recent years in west Africa and Brazil, presumably carried in ballast water). Butis butis differs from other species in the genus in having small secondary scales at the base of most scales on the trunk, and the bony ridges above its eyes are more or less smooth (Herre 1927).
REFERENCES
Herre, A. W. 1927. Gobies of the Philippines and the China Sea. Philippine Bureau of Science Monographic Publications on Fishes 23: 1–352, 26 pls.
Ryan, P. A. 1981. Records of three new freshwater fishes from the Fiji Islands. Pacific Science 35 (1): 93–95.
Smith, J. L. B. 1958. The fishes of the family Eleotridae in the western Indian Ocean. Ichthyological Bulletin 11: 137–163.
Thacker, C. 2011. Systematics of Butidae and Eleotridae. In: Patzner, R. A., J. L. Van Tassell, M. Kovačić & B. G. Kapoor (ed.) The Biology of Gobies pp. 79–85. CRC Press.
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