Convict cichlid

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".[13]

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.[21] It has also been captured in Perth, Western Australia, although this initial capture also resulted in its eradication.[22] In addition to Australia, the species has been introduced to Réunion, Japan,[2] Mexico,[12] Colombia,[23] Taiwan,[24] and the USA.[25][26]

Series of images of reproduction. Top to bottom: 1. Female with eggs, 2. One-day-old larvae, 3. Three-day-old larvae, 4. Five-week-old fry.

The convict cichlid can reach sexual maturity as young as 16 weeks, though sexual maturity more commonly occurs at 6 months.[20] 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.[14] 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.[29] 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.[30][31] In darkness the pair recognizes each other and detect predators using their sense of smell.[32]

After hatching, the larvae spend another 72 hours absorb their yolk sacs and developing their fins before they become free-swimming fry.[33] The fry forage during daylight in a dense school and return to the cave or crevice for the night.[34] 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.[35] During the night, the fry bunch up at the bottom of the cave or nest, where the parents fan them.[36]

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).[14] Brood care of eggs, larvae and free-swimming juveniles in the wild can last 4 to 6 weeks,[14] and occurs only once per season for the majority of females.[14] 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.[37]

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.[38] Because the convict cichlids are also substrate-brooding, this territory will include a breeding site for the deposition of eggs.[39]

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.[40]

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.[41] 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.[39]

Convict cichlids are a biparental species, so the parents will usually cooperate by carrying out tasks specific to their individual parental roles when raising their offspring. This is common in cichlid fish, and studies have shown coordination between the female and male.[42] The female tends to remain with the brood and perform activities involving the brood fanning the eggs, whereas the male tends to patrol the area to chase intruders and defend from predators.[42][43] Both parents are able to carry out all of the parental care tasks to a certain extent. However, because they are biparentally custodial, each sex will still focus on a specific set of behaviors in particular, which is susceptible to change during the brood cycle.[44] In fact, it is observed that when one of the mates is removed, either parent is still able to raise the offspring independently by having the capacity for all the parental behaviors. As the young offspring grow and become free-swimming fry, the parental activities are distributed more equally between the parents, which appears to be typical behavior in other types of cichlids as well.[42]

The different ways in which this biparental sex role specialization can be influenced was studied by manipulating the presence and absence of the mate as well as the presence and absence of an intruder. The former variable was considered because the specialization of parental roles only occurs when both parents are present, while the latter variable was considered because it is thought that biparental care in these cichlids was an evolutionary consequence of the protection of offspring from intruders. When both mates are present with no intruder, both parents may stay with the offspring by resembling single parents because each parent is addressing only the offspring and not its mate, or one parent may be concentrated on activities associated with the offspring while the other parent concentrates on patrolling and defending the area. Under these isolated conditions, a more equal sharing of parental behaviors tends to occur. However, when both mates are present and an intruder is introduced, the male spends more time chasing intruders while the female remains with the offspring more. When the intruder is present but a parent is by itself, the widowed male tends to leave the offspring unattended and instead attacks the intruder or predator. Therefore, the conclusive finding is that the male rarely remains with the offspring when the female is absent, and the female rarely confronts the intruder when the male is absent.[42]

Convict cichlids may show extended biparental care and adopt unrelated young of the same species of similar or smaller body size compared to their own biological offspring. The parents may benefit by adopting smaller young by taking advantage of the dilution effect, which is when the risk of predation for an individual is reduced because the group size is larger. Another reason that has been considered is that foreign young that are larger than the biological offspring may be a direct predatory threat to them. However, it has been shown that as the biological offspring develop and become stronger swimmers, the parents are less active about rejecting larger foreign young, but when they do reject, often foreign young are rejected before they are large enough to be perceived as a direct threat to the biological offspring. Thus, it can be concluded that the brood adoption and rejection rely more heavily on the protection of the biological offspring from differential predator instead of from larger adopted cichlids.[45]

Breeding convicts is as simple as having a male and a female in the same tank with adequate water quality and feeding. There is no special conditioning required. Due to their prolific breeding in captivity, there is a very low demand for Convict fry, and one may easily find their aquarium overstocked with an inbreeding population of Convicts without any avenues for adoption.

Ideal tank mates for convict cichlids consists of robust similar sized fish. Such fish include T-Bar cichlids, Honduran red points, Green Terrors, Jewel cichlids, Salvini, Jack Dempsey, (Keep in mind as Dempseys outgrow the convicts territorial issues will become a problem.) Pictus catfish, plecostomus, as well as other convicts. Other fast moving fish such as Giant Danios can be used as dither fish. Also remember, if you have a breeding pair Convicts in a 40-gallon or smaller you will be most likely be unable to keep the convicts with any tank mates. But if your tank mates have established any type of dominance they will however breed and live together.