Theraps coeruleus (Stawikowski & Werner, 1987), the small blue corrientera Juan Miguel Artigas Azas T his beautiful little fish is one of the smallest fast-water cichlids in Central America. It makes up for its small size by intriguing breeding behavior accompanied by a sequence of color changes that must be seen to be believed. Classification Original description.— Rainer Stawikowski, a German aquarist and editor of the DATZ (Die Aquarien und Terrarien Zeitschrift) magazine, with special fondness for American cichlids, visited México in April of 1983 in the company of Uwe Werner and H. G. Breidohr, and again in April 1987 in the company of Uwe Werner, Ingomar Kranz, and Ernst Sosna, on two ichthyological explorations. They focused on cichlids intended for their personal collections and eventually the German aquarium hobby from the state of Chiapas. Four years later, after they had kept and bred Theraps coeruleus and T. lentiginosus (its closest relative) from Rio Chacamax (Usumacinta drainage), they determined, after realizing striking differences in size, life col- oration, and other aspects between these two species, that the “little blue” (or “Kleinen Blauen”) as they had called it, was sufficiently different to propose its recognition as a new species. In this decision they also considered that the recently described Theraps rheophilus Seegers & Staeck, 1985, with a type locality in Nututun (“Place among rocks” in the Mayan language) in the Chacamax, Usumacinta drainage was perhaps a synonym of Theraps lentiginosus. Río Mizol-Há, affluent of Río Tulija in the Grijalva-Usumacinta drainage in Chiapas, México. A clear water mountain river habitat of Theraps coeruleus. 14 Volume 18 (4) October 2009 Synonymy.— None. Diagnosis.— Theraps coeruleus is smaller (males up to 15 cm or 5.9" TL) than T. lentiginosus (males up to 25 cm or 9.8" TL). Theraps coeruleus differs from Theraps lentiginosus in life coloration, both in normal and more noticeably in breeding coloration. Theraps coeruleus was placed in the genus Theraps Günther, 1862 (type species is Theraps irregulare) by its describers in the same sense that T. rheophilus had been placed in the genus Theraps by Staeck & Seegers (1985). The genus Theraps Günther, 1862, was redescribed by Robert Allgayer (1989) for elongated (2.5 to 3.32 times the depth in the standard length) rather compressed cichlids, with a long head (2.84 to 3.76 times in the standard length) and a terminal or subterminal mouth, a long caudal peduncle (0.9 to 1.48 its length in its height), and ctenoid scales, among other traits. T. coeruleus is recognized by Allgayer as part of the genus Theraps and subsequently reaffirmed by Warren Burgess (2000). It should be noted, however, that in spite of the apparent relationship of Theraps coeruleus and T. lentiginosus with the type species of Theraps, namely T. irregulare, other species considered in Theraps because of elongated shape (e.g., Theraps wesseli) probably comply with the diagnosis more likely because of convergent evolution than because they share a monophyletic origin. Etymology.— The term coeruleus (sometimes referred to as caeruleus) stems from Latin meaning “sky blue”, in reference to the color of the females and also the breeding color of the parental fish. Types.—The holotype (specimen ZFMK 15501) is a 95 mm (3.7") TL specimen collected by I. Kranz, E. Sosna, R. Stawikowski, and U. Werner on April, 21 1987 in a tributary of Río Mizol-Há at Francisco I. Madero, Mexico. The A female Theraps coeruleus in normal coloration in the Río Tulija, Chiapas, México. The blue dorsal fin with black blotches is typical for females of this species. paratypes (ZFMK 15502-05) consist of 4 individuals 77, 81, 78, and 74.5 mm (3.0, 3.2, 3.1, and 2.9" respectively) TL from the same lot as the holotype. foraging areas, normally away from the very strong currents, but visit the slower flowing areas in smaller numbers or during breeding. Hardly ever are they found in stagnant water. Distribution Type locality.— Tributary of Río MizolHá at Francisco I. Madero, approximately 30 km (18.6 miles) south of Palenque, Chiapas, Mexico. Distribution.— Theraps coeruleus is restricted to the middle zone of the Tulija river and its affluents in the GrijalvaUsumacinta river system in the state of Chiapas, México, around 100 meters (330 ft.) above sea level. Habitat.— The habitat of Theraps coeruleus is characterized by mountain rivers wider than five meters (16 ft.) of clear cool water, in a temperature ranging approximately between 20 to 27°C (68 to 81°F). River beds are normally composed of boulders, rocks, gravel, and sand, although some backwater areas covered with layers of sunken leaves are also present. Theraps coeruleus choose the moderately fast flows as preferred Water transparency is often well over ten meters (33 ft.), although normally rivers where Theraps coeruleus inhabit are less than three meters deep (10 ft.). Water is alkaline with pH measurements from 7.5-8.4, General Hardness ranges from 11-22° GD, and KH from 7-28° (Stawikowski and Werner, 1998). Other cichlid species often found with Theraps coeruleus include Thorichthys socolofi, Chuco intermedium, Paratheraps bifasciatus, Rocio octofasciata, Paraneetroplus omonti, and ‘Cichlasoma’ salvini. Other commonly associated fish species include the characinids Brycon guatemalensis and Astyanax mexicanus; poeciilids Poecilia mexicana, Priapella compressa, Xiphophorus helleri, and Pseudoxiphophorus bimaculatus; atherinid Atherinella alvarezi and pimelodid Rhamdia laticauda, among others. Volume 18 (4) October 2009 15 the rocks, hiding in the crevices, or below the rocks. Individuals of all sizes group loosely together, swimming against the current while searching for edibles among the rocks. During feeding, they exhibit little or no aggression among themselves or to other fishes. Females of Theraps coeruleus establish territories in holes of sunken trunks or, when not available, in small excavated burrows at the base of a rock. The more elevated from the bottom the nest is, the better. Photo taken in the Río Tulijá, Chiapas, México. Natural history Description.— Theraps coeruleus is a small, elongated, laterally compressed cichlid. Males reach only 15 cm (5.9") and females grow no larger than 10 cm (3.9") TL. They have a rounded head, a pointed snout and a rather small, slightly subterminal, mouth located in the lower part of the head. Lips are rather large and teeth are easily visible on the jaws. Fins (except for the caudal) are short and rounded and the caudal peduncle is long with a long sub-truncated caudal fin. The traits indicate the rheophilus nature of the cichlid. The basic coloration is beige, darker in the dorsal area, and clear to white in the ventral area. Eight to ten black blotches line up in the middle part of the flanks, distributed from the end of the caudal peduncle to the opercula, the middle one being the most conspicuous of them all. Second is the blotch at the caudal peduncle. The blotches are the beginning of the black bars that surround the body dorsally. The first three bars have their origin in the anterior and upper part of the eye cavities, the first one extending frontally to the tip of upper 16 Volume 18 (4) October 2009 lip. A less intense line of dark blotches is present in the dorsal part of the flanks, the third and fifth of those blotches are fused together in what looks like a circular band surrounding the insertion of the dorsal fin. Females also show two or three black blotches in the dorsal fin. Females, in particular, have a sky blue coloration in the ventral area and the lower part of the head. Cheeks in males are yellow. Fins are sprinkled with light blue dots. Unpaired fins have a red base with contrasting blue rays. Females have the black blotches on the dorsal fin ringed in blue. The dorsal fin has a red margin on the spinous area. While this is a basic description of the color patterns, Theraps coeruleus is a fish that exhibits at least four color morphs during their reproductive cycle, as explained in the text below. Feeding.— Theraps coeruleus feeds in the fast flowing areas of rivers with rocky and/or sandy beds, picking in the sand in rock pebble areas. Although I am not aware of stomach examinations, after having observed this fish underwater on multiple occasions, it seems apparent that they feed on invertebrates encrusted in Unlike its sibling species T. irregularis, at least in my observations, this species does not seem to turn over pebbles in search for hiding invertebrates, although further observations may be necessary to corroborate this. Breeding.— Breeding in Theraps coeruleus is one of the most fascinating acts in Central American cichlids. The elaborate color changes involved with breeding phases, as well as the mating system, are unique. The more colored females, with a beige base color and a strong blue in the lower head, chest, and belly, are the first to colonize the breeding area. They look for zones of slower water flow and search for a cave that will become their nest. Holes in sunken tree trunks, separated from the bottom, are by far the most desirable places, as evidenced by the fact that larger, more aggressive females hold every available hole. The second most preferred locations are caves formed naturally by rocks, which sometimes have to be enlarged in the adjacent substrate. On other occasions, caves are dug up from below rocks in the sand on which they lay. When a female becomes territorial, she expresses this mood with a row of six to eight large contrasting white blotches longitudinally on her flanks. The white blotches take the place of the black blotches that are seen in normal coloration. The coloration of the female then intensifies, and two large black blotches ringed in blue become prominent on the middle part of the dorsal fin. Males of all sizes, normally greenish-yellow in base coloration with eight to ten black blotches in a longitudinal arrangement on the middle part of their flanks, detect territorial females and patrol by their territories. Females remain at the entrance of their caves and normally ignore passing males. Patrols can extend for hours. A chosen male, always larger than the female, eventually is courted back and both potential mates circle each other in the territory. After the pair is established, coloration changes for both individuals and they start chasing all intruders away. At this point, the specific name coeruleus becomes apparent, as both males and females develop a fantastic sky blue coloration all over body and fins, with just a black blotch visible on the middle of their flanks. The spawning surface is cleaned by both fish for eggs to be placed and fertilized. About two hundred (depending on the size of the female) yellow ovoid eggs of approximately 2.1mm (0.08") length per 1.7mm (0.07") width (Coleman & Galvani, 1998) are attached to the ceiling or walls of the spawning cave, and fanned with the pectoral fins by the female. The female remains at the entrance or inside the spawning cave while the male patrols the immediately surrounding area. Eggs take about two days to hatch under aquarium conditions. Four days later the little wrigglers, having consumed their heavy yolk sacs, become free swimming and venture outside the cave. Males, regardless of size, constantly visit nests of territorial females and hope to be chosen as breeding partner. The female, when interested, will come out and court a chosen one; the male of a pair is always larger than the female. At this point another coloration change takes place in the parents when a black pattern appears on the sky blue base color, with six incomplete bars going down from the top to the now black blotches found longitudinally on the middle part of their flanks, highly contrasting with the light blue background. A black “U” is also formed just below the anterior base of the dorsal fin. danger approaches, fry are quick to disappear below the surrounding rocks, and just the parents remain, apparently guarding nothing. After the danger is perceived to have disappeared, the fry start popping one by one from their hiding places. As there are no studies in the wild Parents herd their babies in the moderately fast flowing water. The babies forage on the surface of the rocks, presumably from small encrusted larvae, detritus, and aufwuchs. When a perceived Volume 18 (4) October 2009 17 After spawning in the breeding cave, both male and female become sky blue (with a black blotch on mid-flank) which gave them their specific name. Females remain inside the cave fanning eggs while males stay outside chasing away intruders. on this fish it is hard to assess how long parents will guard their babies, but juvenile fish of about two centimeters (0.8") length are seen wandering among the rocks, where they efficiently take refuge in little crevices when danger approaches. When they reach about four centimeters (1.6") length they are seen grouping with adults searching for food. Conservation status Theraps coeruleus is not listed in the Mexican Official Norm NOM-059- ECOL-2001 or the IUCN Red List of Threatened Species. The habitat remains stable in its entire range. Aquarium maintenance Theraps coeruleus is a beautiful cichlid with a moderately aggressive disposition but it is by far not the easiest cichlid to be successfully kept and bred. This fish is shy, and if the conditions are not right, this shyness becomes extreme and apparently becomes stressful, and they do not last very long. To compen- sate for this shyness and to ensure its well-being, this fish requires an assemblage of dither fish, as well as proper lighting. A dark environment promotes shyness. Dither fish are ignored and just occasionally very small fish (livebearer fry) will be eaten. Caves and rocks are necessary in the aquarium. The minimum tank size I would personally recommend is 300 liters (75 gallons); I have kept mine in a 1.5 m (60") long 400 liters (100 gallon) aquarium, which seems to be perfect for this fish. Of course, I am sure some people would be successful in smaller tanks but you cannot expect to see natural behavior there. Considering the natural conditions in which this fish inhabits it is easy to understand its requirement for very good water quality, because when water conditions go wrong, Theraps coeruleus is very prone to bacterial infections and eventual death. Of special consideration is the amount of dissolved oxygen and temperature. The fish suffer in low oxygen environments as can easily be seen by a rise in respiration rates. It is best to keep water chemistry close to natural conditions, with pH above 7.0 and hardness above 5 GD. Water temperature is important, and water either too cold or too hot can easily damage the fish. Of special concern is not to keep them in water which is too warm: a range of 20-28° Celsius (68 to 83°F) is acceptable, with the middle temperatures preferred. Taking all this into consideration, coloration and behavior are optimal. Feeding is not a problem, as they will greedily accept whatever is offered to them. I tend not to offer foods too rich in protein or fat to my fish, to prevent digestion problems. Flake or frozen foods are accepted with no problems and the fish can be kept long term on this regime without any apparent problem. I believe that if the fish is kept in the proper conditions the main problem to 18 Volume 18 (4) October 2009 solve in breeding them is to overcome their natural shyness. Proper water conditions, dither fish, good lightning, abundant food, and companions that are not too aggressive are the key. More aggressive companions will stress T. coeruleus and prevent them from forming territories. If these conditions are met then the fish will most likely breed for us. For a breeding cave, an inverted flower pot with an open base works very well in my experience. tiful, lively, and challenging beauty, with interesting and intriguing behavior. For taxonomists, the relationship of Theraps coeruleus with the closely related Theraps lentiginosus populations of Usumacinta and Grijalva rivers, different among themselves, provides grounds for thought. Theraps coeruleus is indeed one of the more shining jewels of the wonderful Mayan land. Once pairs form and breeding procedures start, things will normally go well, although often the first breeding attempts by the fish result in failure. Fry accept brine shrimp as their first food and they normally prosper in the community aquarium, many of them even reaching adulthood there. Of course this happens only if there are no efficient fry predators in the tank, and enough cover is provided. Allgayer, R (1989) Révision et redescription du genre Theraps Günther 1862. Description de deux espèces nouvelles du Mexique (Pisces, Perciformes, Cichlidae). Revue Francaise des Cichlidophiles 10 (no. 90): 4-30. Theraps coeruleus do better in a group of six or more individuals, and although they are not overtly aggressive, they can show intraspecific aggression, although they rarely are lethal to each other, especially if the space conditions are right. References Burgess, W.E. (2000) The Cichlasoma story. Herichthys, the break-up. Tropical Fish Hobbyist 48(11): 44-54. Coleman, R.M. & A.P. Galvani (1998) Egg size determines offspring size in neotropical cichlid fishes (Teleostei: Cichlidae). Copeia 1988: 209-213. Günther, A (1862) Catalogue of the fishes in the British Museum. Catalogue of the Acanthopterygii, Pharyngognathi and Anacanthini in the collection of the British Muesum. Catalog of Fishes 4: 1-534. Kullander, S.O. (1983) A revision of the South American cichlid genus Cichlasoma (Teleostei: Cichlidae). Swedish Museum of Natural History, Stockholm. Miller, R.R. (2005) Freshwater Fishes of Mexico. University of Chicago Press, Chicago. Seegers, L. & W. Staeck (1985) Theraps rheophilus nov. sp., ein ungewöhnlicher Cichlid Mexicos aus der Cichlasoma Verwandtschaft. Die Aquarien- und Terrarien-Zeitschrift 38(11): 499-505. Stawikowski, R & U. Werner (1987) Neue erkenntnisse über die buntbarsche um Theraps lentiginosus mit der beschreibung von Theraps coeruleus spec. nov. Die Aquarien- und TerrarienZeitschrift 40(11): 499-504. Stawikowski, R & U. Werner (1998) Die Buntbarsche Amerikas Band 1.Eugen Ulmer GmbH & Co, Germany. Comments Interestingly enough, Robert Miller (2005) in his book Freshwater Fishes of México, considered Theraps coeruleus as a synonym of T. lentiginosus, but validates T. rheophilus. The reasons for this decision are not expressed but it certainly puzzles people familiar with these fish, because clearly T. coeruleus is a valid species. Theraps coeruleus is indeed a wonderful fish. For behavioral researchers, it provides an excellent opportunity to study interesting breeding tactics and coloration changes, never studied before, as far as I know. For aquarists, it is a beau- Breeding partners guard their babies together; at this point they change coloration again, this time showing striking bars in the upper middle part of the flanks. Fry hide under rocks or leaves when a perceived threat approaches. Photo taken in the Río Tulijá, Chiapas, México. Volume 18 (4) October 2009 19