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Sarotherodon melanotheron

By Jenna Beras

Geographic Range

In its native range, Sarotherodon melanotheron is found only in freshwater lagoons and brackish, or slightly salty, waters along the coast of West Africa from Senegal to southern Cameroon. This species has been introduced to many countries in Europe and Asia as well as the southern United States. (Pullin and Lowe-McConnell, 1982; Pullin and Lowe-McConnell, 1982; Pullin and Lowe-McConnell, 1982)

Habitat

Sarotherodon melanotheron is confined to brackish water in lagoons (bodies of water cut off from the ocean by reefs of sand) and estuaries, or areas where freshwater rivers meet the ocean. In these habitats, the salinity of the water is always fluctuating due to the fact that in the wet season, flooded rivers extend the freshwater zone seaward, reducing the salt concentration of the waters in which the tilapia live. Though blackchin tilapia prefer brackish water, a few subspecies of this genera can survive and reproduce in freshwaters, such as the Senegal River, and may occasionally venture into salt waters. The depth of water in which these fish live varies with the changing tide. On average, however, they are found living at around 3 m below the surface of the water. The aquatic homes of S. melanotheron are often surrounded by dense thickets of mangrove trees.

The waters in which these fish live range in temperature from 18 to 33 °C. Sarotherodon melanotheron is stenothermic and cannot survive in temperatures that vary greatly from this range. (Trewavas, 1983)

  • Range elevation
    0 to 1200 m
    0.00 to 3937.01 ft
  • Average depth
    3 m
    9.84 ft

Physical Description

Blackchin tilapia are named for patches of black or melanic areas that usually occur on the neck and throat. In the young of the species, these black spots are absent. The pattern in which these patches occur differs among geographically isolated populations of these fish and is thus a good distinguishing feature among the subspecies of S. melanotheron, of which there are three : S.m. melanotheron (Ivory Coast to Benin), S.m heudelotii (Senegal to Guinea) and S.m. leonensis (Sierra Leone to Liberia). As for the coloration of the rest of the blackchin tilapia's body, the lower body is usually a pale blue and the back is often metallic golden yellow or orange. In males, the operculum is gold. In females, it is transparent and appears a deep mauve because of the blood that flows through the gills underneath it. There is little size dimorphism between the sexes, except that males possess a slightly larger head.

In terms of body structure, blackchin tilapia have an emarginated caudal fin, a small mouth, small teeth shaped in slender shafts and spoon-shaped crowns, a lower jaw that takes up 27 to 34% of the head, and 11 soft dorsal rays. These fish possess a lateral line system, an adaptation for mechanoreception in water. Blackchin tilapia are distinguished from other similar species of tilapia by their low number of vertebrae (26 to 29, usually 27 to 28), 12 to 19 lower gill rakers, 14 to 16 dorsal spines, and a deep preorbital bone.

Blackchin tilapia tolerate salinity ranges of 0 to 45 ppt and can live in an environment with dissolved oxygen levels as low as 0.1 ppm and carbon dioxide levels as high as 70 ppm. (Pullin and Lowe-McConnell, 1982; Trewavas, 1983)

  • Sexual Dimorphism
  • sexes colored or patterned differently
  • Range mass
    25 to 50 g
    0.88 to 1.76 oz
  • Range length
    20 to 28 cm
    7.87 to 11.02 in
  • Average length
    25 cm
    9.84 in

Development

The eggs of S. melanotheron are orange, relatively large (0-3 mm) and brooded in the mouth of the male parent. While in the egg, adhesive structures, whose function is not known, were observed to form on a four-day-old embryo, disappearing almost as quickly as they arose. Fry range from 2 to 11 mm at the time of hatching. A few days after hatching, the young no longer have contact with the parents but are quick to form schools with each other in order to avoid potential danger. (Trewavas, 1983)

As blackchin tilapia mature, black patches begin to form on the lower head and pectoral girdle. These spots apparently become more intense when the fish approach breeding age. Before it reaches adulthood, S. melanotheron appears to go through an intermediate stage in which the gonads are mature and black spots have formed but the body is still small. In fact, these young individuals may be anywhere from 51 to 88 mm, far below their adult size of 200 to 288 mm. (Pullin and Lowe-McConnell, 1982)

Reproduction

Female blackchin tilapia take the initiative in courting males and each female begins to dig a pit for eggs before a male has been chosen. If the male is stimulated to react to the female's advances, he forms a pair bond with her. This bond remains firm and the male begins to take an active part in digging and defending the pit that the female has started. Once the pit has been prepared, the female releases her eggs externally in large batches and these eggs are immediately fertilized by the male. The male does not take the eggs into his mouth until all have been laid, and in some circumstances, delays picking up the eggs for an extended period. This delay is evidence that the pair bond between male and female may be weak and that S. melanotheron is not monogamous. Though the exact mating system of this species is not known, it can be hypothesized that, because the male engages in the parental care, the female may have more mating opportunities. This would suggest a polyandrous system. (Shaw and Aronson, 1954)

Sexual maturity in S. melanotheron can be determined by the presence of a golden colored operculum in the male and a transparent operculum in the female. The smallest known mature male and female were 69 mm and 78 mm respectively. Blackchin tilapia generally breed every 22 days though there are sometimes periods of inactivity for 2 months or more. They spawn throughout the year, but somewhat less during the rainy season. Females produce anywhere from 200 to 900 eggs but the number of eggs that can be incubated by the male ranges from less than 20 to over 700. The eggs are fertilized externally and incubated for 4 to 6 days in the mouth of the male before hatching. Once hatched, the young fry may remain in the mouth of the male for up to 19 days before being released. (Eyeson, 1979; Trewavas, 1983)

  • Breeding interval
    Blackchin tilapia generally breed every 22 days though there are sometimes periods of inactivity in this species for 2 months or more (Eyeson 1979).
  • Breeding season
    Blackchin tilapia spawn throughout the year, but somewhat less during the rainy season (Trewavas, 1983).
  • Range number of offspring
    20 to 700
  • Range time to hatching
    4 to 6 days
  • Range time to independence
    14 to 19 days
  • Average time to independence
    15 days
  • Range age at sexual or reproductive maturity (female)
    1 to 4 years
  • Range age at sexual or reproductive maturity (male)
    1 to 4 years

Mouth-brooding is a form of parental care in which a fish incubates the eggs in its mouth until the yolk is sufficiently reduced and the young can swim freely. While mouth-brooding is a common practice in tilapia, S. melanotheron is unique in the fact that the male of the species, rather than the female, is the mouth brooder. In this sense, parental care is solely paternal. Male blackchin tilapia scoop fertilized eggs into the mouth and the young are kept there for anywhere from 14 to 19 days (the eggs hatch inside the mouth at 4 to 6 days). Once the young are released, males, for a brief period, may rescoop them into the mouth if danger approaches. In a matter of days the fry are left to fend for themselves (Pullin and Lowe-McConnell 1982). (Eyeson, 1979)

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • male
      • female
  • pre-hatching/birth
    • provisioning
      • male
    • protecting
      • male
  • pre-weaning/fledging
    • provisioning
      • male
    • protecting
      • male

Lifespan/Longevity

In the wild, S. melanotheron reaches sexual maturity between 1 and 4 years of age. Often they can live as long as 9 years.

In captivity, blackchin tilapia are raised for food consumption by humans and a lifespan much past maturity is rare. (Pauly, 1976)

  • Range lifespan
    Status: wild
    9 (high) years
  • Typical lifespan
    Status: wild
    0 to 9 years

Behavior

Immature blackchin tilapia exhibit schooling behavior and travel in groups to avoid potential danger. When sexual maturity is reached, female S. melanotheron seem to display more aggressive behavior than males. Males are more territorial and actively defend the pit or pits in which their females lay eggs.

Sarotherodon melanotheron feeds nocturnally due to the shallowness of the lagoons and estuaries it inhabits. Feeding during the day would put these fish in danger of terrestial predators such as birds.

At times when predators are few, tilapia have been observed to feed on the surface of the water where phytoplankton are abundant. (Pauly, 1976; Shaw and Aronson, 1954)

Home Range

No information could be found on the size of the home range of S. melanotheron.

Communication and Perception

Little is known about the communication and perception of S. melanotheron. Because they are schooling fish, however, it is presumed that some form of visual communication or mechanoreception may be in play between members of this species. (Pullin and Lowe-McConnell, 1982)

Food Habits

Blackchin tilapia feed primarily on filamentous algae, microorganisms, and organic material from dead and decomposing plants and animals. The stomach contents of these fish also include granules of mud and sand implying that they suction feed on the bottom of their aquatic habitat. Juveniles are much more carnivorous than adults and add small crustaceans and zooplankton to their diet. (Pauly, 1976)

  • Animal Foods
  • mollusks
  • aquatic crustaceans
  • zooplankton

Predation

The main predators of S. melanotheron are humans. Humans in many parts of the world rely on tilapia as an essential food source and exploit them heavily. Predatory birds as well as larger fish may also pose a threat to blackchin tilapia. Blackchin tilapia avoid predators by feeding mainly at night. (Pauly, 1976)

Ecosystem Roles

Blackchin tilapia are primary and higher-level consumers in the ecosystems they inhabit. They are also prey for larger fish and predatory birds. (Pauly, 1976)

Economic Importance for Humans: Positive

In its native habitats in Africa S. melanotheron is used by poor coastal dwellers for food and livelihood in capture fisheries and enhanced fisheries. The introduction of blackchin tilapia to the waters of North America, Europe, and Asia has extended the breadth of these benefits. People all over the world use this fish as a food staple as well as a source of income in both the commercial fishery business and the aquarium trade. (Pauly, 1976; Pullin and Lowe-McConnell, 1982)

Economic Importance for Humans: Negative

Sarotherodon melanotheron is a potential pest and could disrupt the ecosystems in waters where it is introduced. (Pullin and Lowe-McConnell, 1982)

Conservation Status

Blackchin tilapia are not currently endangered. Due to the fact that this species has been introduced in many waters around the world, its overall numbers are actually growing. In its native African habitat blackchin tilapia could eventually face extinction due to overfishing. (IUCN, 2004; Pauly, 1976)

Contributors

Allison Poor (editor), University of Michigan-Ann Arbor.

Jenna Beras (author), University of Michigan-Ann Arbor, Kevin Wehrly (editor, instructor), University of Michigan-Ann Arbor.

Glossary

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

World Map

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

brackish water

areas with salty water, usually in coastal marshes and estuaries.

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

detritivore

an animal that mainly eats decomposed plants and/or animals

detritus

particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).

estuarine

an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.

external fertilization

fertilization takes place outside the female's body

fertilization

union of egg and spermatozoan

food

A substance that provides both nutrients and energy to a living thing.

herbivore

An animal that eats mainly plants or parts of plants.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

introduced

referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.

marsh

marshes are wetland areas often dominated by grasses and reeds.

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

World Map

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pet trade

the business of buying and selling animals for people to keep in their homes as pets.

phytoplankton

photosynthetic or plant constituent of plankton; mainly unicellular algae. (Compare to zooplankton.)

planktivore

an animal that mainly eats plankton

polyandrous

Referring to a mating system in which a female mates with several males during one breeding season (compare polygynous).

polymorphic

"many forms." A species is polymorphic if its individuals can be divided into two or more easily recognized groups, based on structure, color, or other similar characteristics. The term only applies when the distinct groups can be found in the same area; graded or clinal variation throughout the range of a species (e.g. a north-to-south decrease in size) is not polymorphism. Polymorphic characteristics may be inherited because the differences have a genetic basis, or they may be the result of environmental influences. We do not consider sexual differences (i.e. sexual dimorphism), seasonal changes (e.g. change in fur color), or age-related changes to be polymorphic. Polymorphism in a local population can be an adaptation to prevent density-dependent predation, where predators preferentially prey on the most common morph.

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

year-round breeding

breeding takes place throughout the year

zooplankton

animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)

References

Eyeson, K. 1979. Studies on egg production, spawning, and fry development in Tilapia melanotheron. Ghana J. Sci., 17(1): 25-34.

IUCN, 2004. "2004 IUCN Red List of Threatened Species" (On-line). Accessed October 17, 2005 at www.redlist.org.

Pauly, D. 1976. The biology, fishery and potential for aquaculture of Tilapia melanotheron in a small West African lagoon. Aquaculture, 7: 33-49.

Pullin, R., R. Lowe-McConnell. 1982. The Biology and Culture of Tilapias. The International Conference on the Biology and Culture of Tilapias: 1-351.

Shaw, E., L. Aronson. 1954. Oral Incubation in Tilapia macrocephala. Bull. Amer. Museum of Natural History, 103: 379-415.

Trewavas, E. 1983. Tilapiine Fishes of the genera Sarotherodon, Oreochromis and Danakilia. London, England: Trustees of the British Museum (Natural History).

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