Variabilichromis moorii

Species of fish

Variabilichromis moorii has no common name and is a species of freshwater cichlid endemic to Lake Tanganyika in eastern Africa. It is a small ovate bodied fish named for an early collector of fish from the lake, John Edmund Sharrock Moore (1870 1947) who was a cytologist, zoologist and led an expedition to Lake Tanganyika and who discovered this species. Juveniles are usually yellow, and adults are dark brown to black in color. It reaches a total length (TL) of Currently it is the only member of its genus. V. moorii feeds on algae, zooplankton, and benthic invertebrates. It is also found in the aquarium trade.

V. moorii is the only member of the genus Varibilichromis, as well as a member of the tribe Lamprologini. It had previously been in the genus Neolamprologus, but in 1985, Colombé & Allgayer created the new monotypic genus Variabilichromis in order to account for a more ancestral supra orbital bone structure. This was rejected by Poll's (1986) classification, but supported by Stiassny (1997).

V. moorii exhibit sexual dimorphism as adult females tend to be larger than adult males. Adults are black with electric blue edges on their tail, pectoral, and dorsal fins, whereas juveniles are yellow.

V. moorii is a substrate breeder, with a male and female pair providing biparental care to their eggs and the young after they hatch. This species exhibits serial monogamy, where a male and female are monogamous for at least one spawning cycle. A female lays 200–500 eggs per brood, usually under an overhanging rock or within a rock crevice. Eggs take at least 3 days to hatch and newly hatched larvae are approximately (TL). They remain in the larval stage for 4 to 5 days, attached to the substrate by their head glands. They then develop into free swimming fry and swim in a tight school close to the spawning site. Parents may defend the brood for up to 100 days, which is when fry reach about (TL).

Spawning cycles in V. moorii correspond to the lunar cycle, with egg laying taking place just before the full moon. This lunar related reproductive periodicity is rare in freshwater organisms and far more common in organisms in marine environments. This periodicity probably evolved to decrease risk of predation when the fry are in their most vulnerable stages (as eggs and larvae), since the moon is at its brightest and the parents can best defend against nocturnal fry eating fish. Such nocturnal predators also tend to avoid or move away from light and thus hunt less during the full moon. This lunar synchronicity confers greater benefit to V. moorii compared to other freshwater fish species because of V. moorii’s location in the tropical zone where the moonlight is more intense (since it is more perpendicular to the surface) and V. moorii tend to live in shallow waters that are easily penetrated by moonlight.

V. moorii have individual territories for feeding and territories shared with a mate when spawning and raising their young.

Individual V. moorii territories are defended for their food resources and territory owners will defend more aggressively against individuals of species with similar diets, including conspecifics. V. moorii feeding territories in deeper areas are larger than those in shallow areas. Population density decreases with greater depth, so a large territory in a deep area can be more easily defended from competitors than a similarly sized territory in a shallow area. There is also lower algal productivity at greater depths because less light is available for photosynthesis, which also contributes to larger territories with increasing depth.

V. moorii parents have a total defended territory that is several times larger than the core area (which is the area where the parents spend most of their time and where the brood is located). The male and female divide the total territory into roughly equal subterritories without much overlap, with the brood located in between these two subterritories. The subterritory borders are not fixed and will shift throughout the day, depending on the presence of intruders. Upon seeing an intruder, a parent will quickly dart out of the core territory to chase the intruder away. V. moorii attack fry eating fish entering their territory more often if their brood is larger. This is reasonable because the parents have a higher rate of return on parental investment in a large brood compared to a small one. V. moorii parents attack fry eating fish more often than other types of fish, meaning they can concentrate their defensive efforts on the fish most dangerous to their fry. Rates of attack do not decrease significantly even as fry get older and larger because the environment has high predation pressure and even older fry will be quickly eaten without defense from the parents.

V. moorii parents typically chase away other fish that enter their territory, but they are less aggressive toward members of the cichlid species N. mustax which are yellow in color, resembling V. moorii fry. N. mustax is the only other cichlid in V. moorii's habitat which is yellow. Experiments have shown that V. moorii are more aggressive toward black fish compared to yellow fish of the same size and shape. N. mustax feed on benthic invertebrates and preferentially feed in V. moorii territories where benthic invertebrates much more abundant. This is due to V. moorii parents driving away other zoobenthivorous fish species, which often also prey on V. moorii fry. Unlike other zoobenthivorous fish, N. mustax do not prey on V. moorii fry; if they did they would certainly be driven away.