The convict cichlid (Amatitlania nigrofasciata) is a fish species from the family Cichlidae, native to Central America, also known as the zebra cichlid. Convict cichlids are popular aquarium fish and have also been the subject of numerous studies on fish behaviour.Robins, C. R., et al. (1991). World fishes important to North Americans exclusive of species from the continental waters of the United States and Canada. Am. Fish. Soc. Spec. Publ. 21: p. 243.
Taxonomy Albert Günther originally described the species in 1867 after Frederick DuCane Godman and Osbert Salvin collected specimens in Central America.Günther, A. (1866). On the fishes of the states of Central America, founded upon specimens collected in fresh and marine waters of various parts of that country by Messrs. Salvin and Godman and Capt. J. M. Dow. Proc. Zool. Soc. Lond. 600–604. In 2007, the species was moved from the genus Archocentrus to a new genus, Amatitlania, based on Juan Schmitter-Soto's study of Archocentus species. However, a 2008 study led by Oldřich Říčan proposed moving the species in Cryptoheros and Amatitlania, including Amatitlania nigrofasciata into the genus Hypsophrys.
The convict cichlid, as traditionally defined, displays significant color variations across its range.Heijns, W. (2001). A convict from the Volcano The Cichlid Room Companion Ed. J. M. A. Azas.Azas, J. M. A. (2002). Cryptoheros, The Small Central American Cichlids The Cichlid Room Companion Ed. J. M. A. Azas. Some of these regional variants are now considered different species. One of these is A. siquia, the Honduran red point cichlid or Honduran red point convict, which ranges from the Atlantic slope of Honduras south to Costa Rica. Two other species formerly included in A. nigrofasciata are A. kanna from Panama's Atlantic slope, and A. coatepeque from Lake Coatepeque in El Salvador; however, the latter is indistinguishable from A. nigrofasciata, leading to the recommendation of regarding it as a junior synonym.
The type species, A. nigrofasciata, which used to cover all these species, is restricted to the northern population ranging from El Salvador to Guatemala on the Pacific slope and from Honduras to Guatemala on the Atlantic slope.
A number of synonyms exist for this species including: Archocentrus nigrofasciatus, Cichlasoma nigrofasciatum, Cryptoheros nigrofasciatus and Heros nigrofasciatus.
Etymology The common name convict cichlid is, like the species name, derived from the vertical black stripes on the body which are reminiscent of the striped prison uniforms of British convicts. Similarly, the species epithet nigrofasciatus literally means "black-striped".
Description
The wild-type of the species has 8 or 9 black vertical bars on a blue-grey body, along with a dark blotch on the operculum. Juvenile convict cichlids are monomorphic until they reach sexual maturity. The male is mostly gray with light black stripes along the body. Males are larger than females, and they have more pointed ventral, dorsal and anal fins which often extend into filaments. In addition, older males frequently develop vestigial fatty lumps on their foreheads. Unusually for fish, the female is more highly coloured. She has more intense black bands across the body, and pink to orange colouration in the ventral region and on the dorsal fin.Sands, D. A Fishkeeper's Guide to Central American Cichlids. Tetra Press. Belgium. 1994. pp 59–60. The maximum standard length has been reported to be 10 centimeters, with total length near .Kullander, S.O., 2003. Cichlidae (Cichlids). p. 605–654. In: R.E. Reis, S.O. Kullander and C.J. Ferraris, Jr. (eds.) Checklist of the Freshwater Fishes of South and Central America. Porto Alegre: EDIPUCRS, Brasil. The body weight of the fish is about . Selective breeding has resulted in a leucistic strain, which lacks the dark barring of the wild type. These are known commonly as white convicts, pink convicts, gold convicts, and A. nigrofasciata "Kongo". The leucistic colouration is caused by a mutation in an autosomal gene and is recessively inherited.Itzkovich, J., et al. (1981). Inheritance of pink body colouration in Cichlasoma nigrofasciatum Günther (Pisces, Cichlidae). Genetica 55: 15–16.
Range and habitat Convict cichlids are native to the lakes and streams of Central America. In particular, the species occurs along the eastern coast of Central America from Guatemala to Costa Rica, and on the western coast from Honduras to Panama. Convict cichlids prefer moving water, and are most frequently found in habitats with cover in the form of rocks or sunken branches.Conkel, D. Cichlids of North and Central America. T.F.H. Publications, Inc., USA. 1993. At four natural habitats of the convict cichlid in Costa Rica, the pH was found to range from 6.6–7.8, while carbonate hardness (KH) ranged from 63 to 77 ppm . The daily water temperature ranged from . Convict cichlids can be relatively tolerant of cool water, allowing them to colonise volcanic lakes at elevations of .
Feral populations
The species also occurs outside its natural range, even being found in Australia, where it can be found in the warm effluent of power stations in Victoria, and in tropical Queensland.Koehn, J. D. and R. F. MacKenzie. (2004). Priority management actions for alien freshwater fish species in Australia. New Zealand Journal of Marine and Freshwater Research 38: 457–472. It has also been captured in Perth, Western Australia, although this initial capture also resulted in its eradication. In addition to Australia, the species has been introduced to Réunion, Japan, Mexico, Colombia, Taiwan, and the USA.Yamamoto, M. N. and A. W. Tagawa. Hawaiʻi's Native and Exotic Freshwater Animals. Mutual Publishing, Honolulu, Hawaii. 2000. p. 200Page, L. M. and B. M. Burr. A Field Guide to Freshwater Fishes of North America North of Mexico. Houghton Mifflin Company, Boston. 1991. p. 432
Feeding In natural habitats, the species has an omnivorous diet composed of plants, algae and various prey including small fish, crustaceans, insects and worms. The fish can protrude its jaw 4.2% of its standard length, allowing it to have a varied diet. Inferior social status and associated stress can affect digestive function in convict cichlids.Earley, R. L., L. S. Blumer, and M. S. Grober. (2004). The gall of subordination: changes in gall bladder function associated with social stress. Proceedings of the Royal Society B: Biological Sciences 271: 7–13.
Reproduction
Life cycle The convict cichlid can reach sexual maturity as young as 16 weeks, though sexual maturity more commonly occurs at 6 months. Sexually mature convicts form monogamous pairs and spawn in small caves or crevices. In the wild, the fish excavate caves by moving earth from underneath large stones.Wisenden, B. D. (1995). Reproductive behavior of free-ranging convict cichlids, Cichlasoma nigrofasciatum. Environmental Biology of Fishes 43: 121–134. Females adhere eggs to the walls of the cave.
Like most cichlids, such as Oreochromis mossambicus, convicts brood (exhibit parental care of) both eggs and free-swimming fry.Keenleyside, M. H. A. Parental Care. In: Cichlid Fishes: Behavior, Ecology and Evolution. Chapman and Hall, London. 1991. pp. 191–208. The eggs hatch approximately 72 hours after fertilization. Until that time the parents expel intruders and potential egg predators from around the nest. They also fan the eggs, moving water with their fins over the clutch to provide oxygenation. They fan the eggs both day and night; at night they use their sense of smell to recognize the presence of the eggs in the dark, and they keep their pelvic fins in contact with the eggs to remain at the right distance for fanning. In darkness the pair recognizes each other and detect predators using their sense of smell.
After hatching, the larvae spend another 72 hours absorb their yolk sacs and developing their fins before they become free-swimming fry.Noakes, D. L. G. Ontogeny of behavior in cichlids. In: Cichlid Fishes: Behavior, Ecology and Evolution Chapman and Hall, London. 1991 pp. 209–224. The fry forage during daylight in a dense school and return to the cave or crevice for the night.Wisenden, B. D. (1994). Factors affecting mate desertion by males in free-ranging convict cichlids (Cichlasoma nigrofasciatum). Behavioral Ecology 5(4), 439–447. Like other cichlids, the parents retrieve their young just before dark, sucking up three or four at a time and delivering them into the nest. The parents anticipate night, using a sense of time; in laboratory experiments convict cichlids continued to retrieve young as night approached even in the absence of any signal, such as dimming light. During the night, the fry bunch up at the bottom of the cave or nest, where the parents fan them.
Both parents remain involved in guarding the fry from brood predators and engage in behaviors to assist feeding such as moving leaves or fin digging (digging up the substrate with their fins). Brood care of eggs, larvae and free-swimming juveniles in the wild can last 4 to 6 weeks, and occurs only once per season for the majority of females. In contrast, females in aquaria are known to breed many times per year with short intervals of 12 or 13 days between broods, as long as suitable rocks or similar surfaces are available for them to lay their eggs on.Wisenden DB (1993)
Mating system Convict cichlids are serially monogamous, so pair bonds may form first before they establish a territory together, or the male and female may each obtain a territory before pairing with each other. Because the convict cichlids are also substrate-brooding, this territory will include a breeding site for the deposition of eggs.
Sexual selection The effect of population density on sexual selection for convict cichlids has been studied. When nest density was greater, the females tended to be larger, which is more accurately explained by density-dependent mate preference and mating competition, as opposed to predation and resource competition. Moreover, as the two nest density regimes were compared, with one high and one low, there was no significant difference in brood survival between the two; however, the convict cichlids did prefer to breed farther away from each other, not in close proximity. This indicates that there are some other costs with breeding in an environment with high population density, an example being energy loss because of the resulting increased aggression when guarding territory.
The female's preference for the male mate has also been examined, in accordance to the male's size and fighting ability. The female cichlid always chooses the larger of the two males if the smaller male is next to the larger male, and if the larger male defeats the smaller male in a fight. If the males are not viewed together at the same time for a comparison to be drawn by the female, the female has no particular preference. Females do benefit by mating with a larger male, as it has been shown that larger males can raise more offspring to independence, are better at chasing predators that might attack offspring, and are better at competing for breeding sites. Male size may act as a more effective indicator of aggression, which may thus repel intruders before they can come closer to the offspring. It has been shown that individuals of significantly greater size relative to their opponent often win fights without much physical contact.
Parental roles