Oreochromis leucostictus | |
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Oreochromis leucostictus, male, from a fishpond near Songea, Tanzania, in 2012. | |
Scientific classification | |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Actinopterygii |
Order: | Cichliformes |
Family: | Cichlidae |
Genus: | Oreochromis |
Species: | O. leucostictus |
Binomial name | |
Oreochromis leucostictus (Trewavas, 1933) | |
Synonyms | |
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Oreochromis leucostictus (the blue-spotted tilapia) is a species of cichlid native to Albertine Rift Valley lakes and associated rivers in DR Congo and Uganda. It has now been introduced widely elsewhere East Africa, and is believed to have negative ecological impact, particularly on native tilapias. This species is reported to reach a standard length of up to 36.3 cm (14.3 in), but is usually much smaller. It is exploited by small-scale fishery and aquaculture operations. [2]
Oreochromis leucostictus is a relatively deep-bodied tilapia with a fairly small mouth, narrow, rounded head and high back. Juvenile are pale, countershaded and have around 8 thin faint dark bars on the flank beneath the dorsal fin, with other bars on the head and tail. The fins are faintly spotted and there is a rather vague dark 'tilapia mark' at the based on the soft dorsal fin. Adults of both sexes are characterised by white spotting on the flanks and fins. Mature males are very dark, almost black, sometimes with a blue-green iridescence, and the white spots are very conspicuous. The eye is bright yellow and crossed by an oblique bar. Mature males have elongated filamentous tips to the dorsal and anal fins, but do not have enlarged jaws (in contrast to species like Oreochromis mossambicus ). Young fishes have numerous small slender tricuspid teeth, but they become stouter in larger fish, and sometimes bicuspid. Overall, there are usually 4–6 rows of teeth, occasionally up to 8 in larger fish. The lower pharyngeal bone is slender, with numerous crowded teeth. There are 3–5 upper gill rakers, 1 on the angle and 19–23 lower rakers. The dorsal fin has 15–18 spines and 11–13 rays. The anal fin generally has 3-spines, although a single 4-spined individual has been reported, and 9–11 rays. There are 28–31 scales in the lateral line series. Adults are reported to grow to a total length of 28–30 cm in Lake Victoria, but they mature at much smaller sizes in smaller water bodies, with ripening females reportedly as small as 8 cm. [3]
Oreochromis leucostictus is a typical maternal mouthbrooding cichlid, like all other known members of the genus. During the breeding season, males are conspicuously coloured, defend territories over open sand/mud areas where they construct a 'bower' or mate attraction structure. In this species, the bower is a simple circular pit, dug at depths of less than 60 cm deep, at least along the margins of Lake Victoria. Females visit the bowers of males, laying clutches with one or more, and immediately picking up the eggs in her mouth. The offspring are brooded until they are capable of independent feeding. Like most other members of the genus, the female probably guards them and will retrieve them in her mouth at night or when disturbed. [3]
Oreochromis leucostictus prefers shallow weedy habitats, such as lagoons and bays around the edges of larger lakes. It naturally co-occurs with the Nile tilapia, Oreochromis niloticus, which favours rather deeper waters, so the two species appear to have complementary niches. They feed mainly on bottom sediments or plankton, ingesting mainly microscopic plants and cyanobacteria, along with small invertebrates. [3]
The natural distribution of this fish is in the catchments of Lakes Edward, George and Albert, in Uganda and eastern Democratic Republic of Congo. It was introduced in Lake Victoria into the 1950s, and is now abundant there, having largely supplanted the native endemic Oreochromis variabilis , although the latter is known to persist in some rocky offshore islands. It was later introduced into Lake Naivasha in Kenya, where it hybridised with and then replaced the formerly abundant Kenyan endemic Oreochromis spilurus nigra. [3] Further introductions to Kenya have continued and molecular genetic studies indicate that O. leucostictus has begun to hybridise with endemic populations of O. niloticus at a number of sites, including Lake Baringo [4] and the hot springs around Lake Bogoria. [5] The species has also been widely distributed in Tanzania, probably as a contaminant of Nile tilapia sourced from Lake Victoria and stocked for aquaculture or attempted fishery improvement. [6] Here too, feral populations are becoming established and hybrids with native species such as Oreochromis urolepis have been reported. [7]
The species is fished where it is found, and widely farmed in small-scale fish ponds, but it is known to mature at small sizes in ponds, a trait undesirable for commercial aquaculture, because ponds are quickly filled up with numerous small fish of low market value. This trait is presumably well developed in this species because it is adapted to live in shallow marginal habitats and so is likely to find itself cut off in pools which may eventually dry up and where larger fish are vulnerable to predators such as birds. Thus, it is unfortunate that the species has been so widely distributed. In addition, it seems to have a propensity to hybridise with native Oreochromis species, leading to genetic contamination and creating hybrid swarms, sometimes apparently replacing the native species altogether eventually. Thus, this species seems to be rather a menace to the maintenance of biodiversity and in particular to the maintenance of wild genetic diversity of tilapias, an important food fish throughout the tropics.
Lake Baringo is, after Lake Turkana, the most northern of the Kenyan Rift Valley lakes, with a surface area of 130 square kilometres (50 sq mi) and an elevation of 970 metres (3,180 ft). The lake is fed by several rivers: the Molo, Perkerra and Ol Arabel. It has no obvious outlet; the waters are assumed to seep through lake sediments into the faulted volcanic bedrock. It is one of the two freshwater lakes in the Rift Valley in Kenya, the other being Lake Naivasha.
Cichlids are fish from the family Cichlidae in the order Cichliformes. Cichlids were traditionally classed in a suborder, the Labroidei, along with the wrasses (Labridae), in the order Perciformes, but molecular studies have contradicted this grouping. The closest living relative of cichlids is probably the convict blenny, and both families are classified in the 5th edition of Fishes of the World as the two families in the Cichliformes, part of the subseries Ovalentaria. This family is both large and diverse. At least 1,650 species have been scientifically described, making it one of the largest vertebrate families. New species are discovered annually, and many species remain undescribed. The actual number of species is therefore unknown, with estimates varying between 2,000 and 3,000.
Tilapia is the common name for nearly a hundred species of cichlid fish from the coelotilapine, coptodonine, heterotilapine, oreochromine, pelmatolapiine, and tilapiine tribes, with the economically most important species placed in the Coptodonini and Oreochromini. Tilapia are mainly freshwater fish inhabiting shallow streams, ponds, rivers, and lakes, and less commonly found living in brackish water. Historically, they have been of major importance in artisanal fishing in Africa, and they are of increasing importance in aquaculture and aquaponics. Tilapia can become a problematic invasive species in new warm-water habitats such as Australia, whether deliberately or accidentally introduced, but generally not in temperate climates due to their inability to survive in cold water.
The Nile tilapia is a species of tilapia, a cichlid fish native to the northern half of Africa and the Levante area, including Palestine, and Lebanon. Numerous introduced populations exist outside its natural range. It is also commercially known as mango fish, nilotica, or boulti. The first name leads to easy confusion with another tilapia which is traded commercially, the mango tilapia.
Oreochromis is a large genus of oreochromine cichlids, fishes endemic to Africa and the Middle East. A few species from this genus have been introduced far outside their native range and are important in aquaculture. Many others have very small ranges; some are seriously threatened, and O. ismailiaensis and O. lidole possibly are extinct. Although Oreochromis primarily are freshwater fish of rivers, lakes and similar habitats, several species can also thrive in brackish waters and some even survive in hypersaline conditions with a salinity that far surpasses that of seawater. In addition to overfishing and habitat loss, some of the more localized species are threatened by the introduction of other, more widespread Oreochromis species into their ranges. This is because they—in addition to competing for the local resources—often are able to hybridize.
Sarotherodon is a genus of oreochromine cichlids that are native to the northern half of Africa, with a single species, S. galilaeus, also ranging into the Levant. A couple of species from this genus have been introduced far outside their native range, and are important in aquaculture. Most other species have small ranges and some are seriously threatened. They mainly inhabit fresh and brackish water, but a few can live in salt water. Species in this genus, as well as those in several other oreochromine and tilapiine genera, share the common name "tilapia" and historically they were included in the genus Tilapia.
The Tilapiini are a tribe within the family Cichlidae commonly known as tilapiine cichlids. Formerly this tribe contained many other genera and species, including the economically important Oreochromis and Sarotherodon, but a taxonomic review found that this grouping was paraphyletic and most were moved to Coelotilapini, Coptodonini, Heterotilapini, Oreochromini and Pelmatolapiini. Together, most species in these tribes are called "tilapias". In a more distant past, a number of other, more different genera like Steatocranus also were included in Tilapiini. With these as separate, Tilapiini now is a much more restricted tribe with only three genera and about half a dozen species from Central and Southern Africa.
Tilapia has become the third most important fish in aquaculture after carp and salmon; worldwide production exceeded 1.5 million metric tons in 2002 and increases annually. Because of their high protein content, large size, rapid growth, and palatability, a number of coptodonine and oreochromine cichlids—specifically, various species of Coptodon, Oreochromis, and Sarotherodon—are the focus of major aquaculture efforts.
Throughout much of the tropics, tilapiine cichlids native to Africa and the Levant have been widely introduced into a variety of aquatic systems. In the U.S. states of Florida and Texas, tilapia were originally introduced to curtail invasive plants. In an effort to meet the growing demand for tilapia, humans have farmed these fish in countries around the world. Capable of establishing themselves into new ponds and waterways, many tilapia have escaped aquaculture facilities across much of Asia, Africa, and South America. In other cases, tilapia have been established into new aquatic habitats via aquarists or ornamental fish farmers.
Alcolapia is a genus of small fishes in the family Cichlidae. Their native range is restricted to margins of Lake Natron and Lake Magadi, as well as similar conditions in nearby hot springs, in Kenya and Tanzania. They live in waters that are warm, hypersaline and alkaline. Species from this genus have also been introduced to Lake Nakuru and Lake Elmenteita. They are the only fish in their range.
Oreochromis amphimelas is a species of tilapia cichlid endemic to north–central Tanzania, where it is found in Lake Manyara and a number of other saline lakes with closed basins. Maximum recorded size is 28 cm (11 in) in standard length.
Oreochromis esculentus, the Singida tilapia or Graham's tilapia, is a critically endangered species of cichlid endemic to the Lake Victoria basin, including some of its satellite lakes such as Kyoga, in Tanzania, Uganda, and Kenya. Its common name refers to Lake Singida, but this population is the result of an introduction that happened in the 1950s. This fish is highly valued by local fishermen, who know it as ngege.
The Lake Chala tilapia is a species of cichlid fish that is endemic to Lake Chala, a small crater lake on the border of Kenya and Tanzania. It mostly lives in relatively deep water, at depths between 20–45 m (66–148 ft). It is considered critically endangered by the IUCN, with the two primary threats being deterioration of its habitat due to siltation, and other non-native tilapia species that have been introduced to Lake Chala. Before these introductions, the Lake Chala tilapia was the only fish in Lake Chala. It is very closely related to the similar Jipe tilapia, another highly threatened species from the same general region of Kenya and Tanzania. The Lake Chala tilapia can reach a standard length of up to 30 cm (12 in).
Oreochromis jipe, the Jipe tilapia, is a critically endangered species of cichlid fish native to Kenya and Tanzania, where it is restricted to Lake Jipe and the Pangani River. The population in the Pangani River shows some morphological differences compared to the population in Lake Jipe, and it is sometimes recognized as a separate species, the Pangani tilapia. Whether regarded as one or two species, the Jipe–Pangani tilapia forms a species flock with the threatened Lake Chala tilapia from the same general region of Kenya and Tanzania.
Oreochromis lidole is a species of freshwater fish in the family Cichlidae. This tilapia is native to Malawi, Mozambique and Tanzania, where it is found in Lake Malawi, Lake Malombe, the Shire River and perhaps some crater lakes further north. It is important in fisheries, but has drastically declined; it may already be extinct. This oreochromine cichlid is locally called chambo, a name also used for two other closely related species found in the same region, O. karongae and O. squamipinnis.
Oreochromis variabilis, the Victoria tilapia, is a critically endangered species of African cichlid native to Lake Victoria and its tributaries, Lake Kyoga, Lake Kwania, and Lake Bisina (Salisbury), as well as being found in the Victoria Nile above Murchison Falls. This species can reach a standard length of 30 cm (12 in). This species is important to local commercial fisheries and is potentially important in aquaculture. It is also found in the aquarium trade.
Lake Victoria supports Africa's largest inland fishery, with the majority of the catch being the invasive Nile perch, introduced in the Lake in the 1950s.
The redbelly tilapia, also known as the Zille's redbreast tilapia or St. Peter's fish, is a species of fish in the cichlid family. This fish is found widely in fresh and brackish waters in the northern half of Africa and the Middle East. Elsewhere in Africa, Asia, Australia and North America, it has been introduced as a food fish or as a control of aquatic vegetation. Where introduced, it sometimes becomes invasive, threatening the local ecology and species. The redbelly tilapia is an important food fish and sometimes aquacultured.
Oreochromini is a tribe of cichlids in the Pseudocrenilabrinae subfamily that is native to Africa and Western Asia, but a few species have been widely introduced to other parts of the world. It was formerly considered to be part of the tribe Tilapini but more recent workers have found that the Tilapini sensu lato is paraphyletic. Despite this change, species in Oreochromini are still referred to by the common name tilapia and some of the most important tilapia in aquaculture —certain species of Oreochromis and Sarotherodon— are part of this tribe. In contrast, several species have small ranges and are seriously threatened; a few are already extinct or possibly extinct.
Oreochromis mortimeri, the Kariba tilapia or kurper bream, is a species of cichlid, formerly classified as a Tilapiine cichlid but now placed in the genus Oreochromis, the type genus of the tribe Oreochromini of the subfamily Pseudocrenilabrinae. It is found in the rivers of south central Africa especially the middle Zambezi where it is endangered by the spread of invasive congener Oreochromis niloticus.