Oreochromis mossambicus (Peters, 1852), Mozambique Tilapia


1. Introduction

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Figure 1: Mozambique tilapia (Free Image by: Image basket)


This is the Oreochromis mossambicus, more commonly known as the Mozambique Tilapia. You may have seen it in some of our reservoirs in Singapore, kept as pets or even used for aquaculture in many areas around the world.

Their presence around the globe has been attributed to them being intensely farmed for food in many countries all over the world, including India, Brazil, USA and Australia. However, when farms decided to stop breeding these animals, they managed to make their escape into many local reservoirs and lakes. Now they form established communities which can provide many benefits to these new environments but at the same time can pose very dangerous threats. In some areas, they have even been considered as highly invasive.

In Singapore, they were not introduced as food. Rather, it is likely they were brought in as ornamental animals or for religious releases. Therefore, responsible ownership and management of this fish is necessary to ensure that the remaining natural habitats of Singapore remain healthy.

2. Distribution

Distribution of Oreochromis massambiscus in Africa.PNG
Figure 2.Distributions of Natural Populations of Oreochromis mossambicus. Image from Google Maps. Edited by Cheyenne Phillips.
As the name suggests, they are typically found in Mozambique but there are natural populations that spread all the way down to South Africa.

However, thanks to the aquaculture industry, this species of Tilapia has been introduced worldwide and has even infiltrated natural habitats in Sri Lanka and Australia. It was even used a stable source of protein in South East Asia during the Japanese Occupation. It is now said that this animal is found in 5 continents and in approximately 94 countries at last count. As recently as 2010, they have been found in some of our reservoirs in Singapore, including Bedok Reservoir and Pulua Tekong Reservoir. If you would like to know where the legal fishing points are in Singapore, you can refer here.

3. Morphology

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Figure 3. Annotated image of Oreochromis mossambicus with main identifying features (Image by: Cheyenne Alexandria Phillips, Annotated by: Cheyenne Alexandria Phillips)

The O. mossambicus shares many characteristics with other Cichlids. For example, across their bodies are straight vertical lines that are only of a slightly different colour than the rest of the body. This feature allows the fish to appear to change colour in response to stress or biological and social cures (See Biology). Their body pattern is typically made up of 2 horizontal lines and 6 to 7 vertical bars, however these may be difficult to see as the bars are not completely realized in this species. Their tails also have a orange tinge. They also have large and well-developed eyes, giving them their excellent eyesight. These animals are sexually dimorphic, meaning that the males and females can be differentiated by key morphological differences. However, these differences are not very easy to see. Males are usually more brightly colored than females and have a more orange tail. They also can develop secondary structures such as long extensions to the soft dorsal and anal fins and an exaggerated jaw.

3.1 Distinguishing features

Taken from Tilapine Fishes of the Genera Sarotherodon, Oreochromis and Danakilia:
  1. Genital papilla of male simple or within a shallow distal notch
  2. Jaws of sexually mature males enlarged, often causing the upper profile to become concave.
  3. Female and non-breeding male silvery with 2-5 mid-lateral blotches and some of a more dorsal series. Breeding male black with white lower parts of head and red margins to dorsal and caudal fins.
  4. Vertebrae 28-31, mode 30.
  5. Dorsal spines XV-XVII, mode XVIl; Total dorsal rays 26-29, mode 28.
  6. Anal spines III.
  7. Lower gill-rakers, 14-20, modes 17 or 18
  8. Pharynegeal teeth very fine, the dentigerous area with narrow lobes, the blade in adults longer than dentigerous area.
  9. Causal fin not densely scaled.

3.2. Diagnosis

Body compressed; caudal peduncle longer than deep. Scales cycloid. A knob-like protuberance present behind upper jaw on dorsal surface of snout. Upper jaw length shows sexual dimorphism, and mouth of male larger than that of female. First gill arch with 20 to 22 gillrakers. Lateral line interrupted. Spinous and soft ray parts of dorsal fin continuous. Dorsal fin with 15 to 18 spines and 10 to 13 soft rays. Anal fin with 3 spines and 9-10 rays. Caudal fin truncated. Colour in spawning season, pectoral, dorsal and caudal fins becoming reddish; colour males shows much brighter orange tail than female.

4. Aquaculture

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Figure 4: Global Aquaculture Production (Figure by: FAO FishStat)

In the 1930s, O. mossambicus, was introduced in Asia to control aquatic weeds. Later on, among other species, O. mossambicus have been used for aquaculture to provide food for populations around the globe as it was a relatively easy species to breed and rear for food. They also can tolerate a large range of environmental factors such as temperature, salinity, pH and more. However in 1980s, the use of O. mossambicus declined as it was discovered that their growth could be naturally stunted and result in a less productive harvest.

Today, there are still many individuals around the globe who have set up their own private Tilapia aquacultre farms in their homes. The global community is not only very large but also very supportive. Many private farmers publish 'to-do' videos on youtube or have private blogs educating the masses on the practice. As polycultures are usually used, there is little information on specific methods to farm O. mossambicus and therefore many in the community share different opinions on the best methods to breed a sustainable O. mossambicus culture.

If you are interested in starting your own private aquaculture farm, here are several sites and youtube channels you may wish to review:

Other more formal sources which account for larger, commercial farms include:

5. Biology

5.1 Feeding Habits

This fish feeds on a varietyof food types including aquatic vegetation, bentic algae, several types of plankton (including phytoplankton and zooplankton) and some fish larvae. These feeding habits are not fixed and the O. mossambicus can adapt based on their environments and seasons or time patterns their habitats can experience. Hence, they are seen to occupy an intermediary position between the primary producers in lakes and the other trophic levels.However the young can feed on plankton and periphyton or green algae and even small crustaceans. Thus, there is some consensus that while adults mainly are detritus consumers, young can be omnivorous.

There are some exceptions to this: In some ponds in Hawaii, it was found that the adults were consuming their own young.

5.2 Fighting Behaviour





Male O. mossambicus are known to be territorial, especially in the company of females. They can be aggressive toward each other and have been documented fighting in order to gain access to a specific territory. This is one of the aspect's that increases a males sexual attractiveness towards females. During fights, males have been known to take on a specific 'fighting pattern' on their bodies; the flanks are paler with irregular dark markings and a grey belly. They fight in a distinct matter, first by circling each other, followed by tail beating, ramming and head to head ramming.The defeated male will lose the fight colours quickly and perform 'appeasement displays'. If possible it will flee and rarely fight back. However, if they are kept in tanks with no means of escape, the defeated male can suffer fatal blows from his opponent. Female O. mossambicus can also be aggressive when protecting fry. They develop dark-stripes across the forehead, dark opercular region and chin and a dark, almost black eye. Males are known to become a deep blue-black colour to black colour on their main body during breeding.

5.3 Mating and Reproduction

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Figure 5: Spawning pits formed by Oreochromis species : a. O. mweruensis, b. O. mossambicus, c. O. karomo, d. O. macrochir, e. O. lidole. All drawings are to scale (Taken from: Tilapias: Biology and Exploitation, Beveridge and McAndrew, 2000).

In addition to territory, the size of the male as well as the size of the spawning pit (which is usually dug out from the mud, sand or the benthic substrate) that the male can construct is indicative to a female that an individual may be a suitable mate. This behavior is common among many tilapia species. The size of the pit depends on the species (see above figure) and size of the male individual. Generally the larger the fish the larger the pit. Despite being territorial, males territories are relatively small and tend to be in close proximity to one another. This results in them forming a 'lek' or breeding arena where they crowd together and display themselves to females.This also affects how males build their spawning pits and overcrowding could easily lead to a male building a smaller brooding pit.

In addition, males have a specific courtship behavior to attract females to mate with them. Males point their heads down and close the unpaired and pelvic fins while performing a high frequency low amplitude tail-quivering display.
There isn't a determined and specific age of sexual maturity in this species. Instead, their age of sexual maturity varies depending on environmental conditions. Reports in South East Asia suggest that spawning occurs when the fish are relatively young, about 2-3 months old while in Nicaragua, the only start breeding when they are about 5 to 6 months of age. They are also notorious brooders: females can spawn up to five broods in a 133 day period.

5.4 Parental Care




O. mossambicus are mouthbrooders, which means they carry their eggs and young in their mouth until they are large enough to fend for themselves.They are maternal mouthbrooders, which means the female fish will carry the fry in her mouth and not the male fish. Females will move away from male territory after spawning, carrying the fry in her mouth to join other females to form small brooding groups. The eggs will hatch approximately 3 to 5 days after spawning. Fry can then swim outside the mothers mouth but actively seek entrance if they sense danger. They have been observed to do this behavior before the mother calls them back to her with a down-ward pointed head position. However the female preforms this action less frequently as brooding progresses, encouraging the fry to learn to fend for themselves.

5.5 Hybrids

If O. mossambicus is raised in a polyculture with these other fish, they are likely to interbreed, forming the following hybrids:

1. O. mossambicus X O. u. hornorum
2. O. mossambicus X O. niloticus
3. O.mossambicus X O. Sarotherodon melanotheron

Hybrids are usually known as Red Tilapia.These hybrids were also bred in aquaculture farms.

6. Ecological Roles

Because they occupy an intermediary position between the primary producers and the rest of the trophic web, O. mossambicus has two main ecological roles: they help in the circulation of nutrients and support the populations of other piscivores (i.e. fish eaters) in a water body. However, because of these ecological purposes, they have the potential to provide benefits and pose threats, depending on the environment they are introduced to.

6.1 Benefits to Ecology

These fish contribute to the diet of several piscivores and so a directly ecological benefit would be a food source for bird species like the Least Grebe (Podiceps dominicus) and the Pied-billed Grebe (Podilymbus podiceps). As they are important in the recycling of nutrients in a water body, they have been known to improve productivity of lakes and reservoirs they have been introduced to. For example, when O. mossambicus was introduced in a reservoir in Sri Lanka, the overall productivity of the lake improved. In Thailand, this ecological function has several advantages when fish cultures are incorporated in rice plantations. These advantages include:

  • production of fertilizer for rice due to nutrient re-cycling by fish which increases rice yield;
  • increase in revenue from rice and fish cultivation;
  • availability of food for poorer households; and
  • reduction in pest and weeds due to the presence of the fish.

With such benefits, it is no wonder that fish culture is not only being introduced in rice plantations but the movement has spread across Asia and reached countries in Africa and Latin America.

6.2 Threats to Ecology

However, it is also a highly invasive species. It has been listed as one of the top 100 most invasive species on the planet. In addition, they have been described to be the 'model invaders' as they have the following biological characteristics:
  • they are able to tolerate a wide range of ecological conditions
  • they are generalists, i.e. they do not have specific diets
  • they produce very rapidly with maternal care
  • they can successfully compete with native fish through their aggressive behavior.

Evidence of their harmful effects can be found on a global level. In Central America, native cichlid populations have been declining in Lake Nicaragua probably because of the competitive displacement by O. mossambiscus. Endemic pupfish in Mexico have been cited to suffer from similar problems with this species. Aquatic vegetation could also suffer from overgrazing by O. mossambicus and could limit resources for other fishes as well as act as a highly effective top-down control for aquatic macrophytes.

In Singapore, these fish used be to commonly found in the local reservoirs. However, their numbers seem to be dwindling. This has been attributed to the introduction of African sharp-tooth catfish (Clarias gariepinus), a carnivorous catfish that has a taste for O. mossambicus. This top-down population control method is not only used in Singapore but also very commonly used all around the globe.


7. Conservation

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Figure 6. IUCN status of O. mossambicus (Photo by: IUCN)


Currently, the O. mossambicus is categorized as near threatened under the International Union for Conservation of Nature (IUCN) Red List. This is mainly because of its ability to hybrid with the Nile Tilapia at very fast rates. The concerns regarding it being over-exploited for food or being controlled through predation has yet to suggest any contribution towards its conservation status.In Singapore, it is not protected under the Convention of International Trade of Endangered Species (CITES) and can be kept as pets in the home. This also means it has the potential to be used for private aquaculture farms.

8. Taxonomic Hierarchy

Kingdom
Animalia
Phylum
Chordata
Class
Actinopterygii
Order
Perciformes
Family
Cichlidae
Genus
Oreochromis
Species
Mossambicus

9. Phylogeny

O. mossambicus is a species under the family Cichlidae, which is one of the most widely studied species by evolutionary biologists. It is one of the most species-rich families with estimates of the number of species ranging from 1300 to 1870. Up until 1983, the phylogeny of this family was based on morphology. Even then, the categorizations were challenged frequently. Greenwood (1978) derived a classifications of four types when the pharyngeal apophyseal morphology was examined in greater detail, of which Regan's original description and sub-categories of the family could be divided into. They are the Tylochromis, the Tilapia, the Haplochromis and the Cichla. Stiassny's analysis based on the observations he made of the morphology of the back of the jaw resulted in the elimination of 3 of Regan's original categories namely Pelmatochromis, Steatocranus and Pterochromis. Tilapia was later further split by Trewavas(1983) into several genera including Tilapia, Oreochromis and Sarotherodom.


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Figure 7. Phylogeny Tree of Tilapiine cichlids based on the ND2 gene. ( Image from Klett and Meyer, edited by Cheyenne Alexandria Phillips)

The use of determining phylogenical relations between Cichlids started occuring in the 1830s. Figure 5 shows the results of one such attempt using the ND2 gene. A-Tilapia refers to the monophyly of the three west African Tilapia species; B-Tilapia refers to the other monophylectic group of Tilapia species that are found in Western and Eastern Africa; C-Tilapia are the 'New Cross cichlid and are not clearly defined by all methods. Against the Tilapia, the Oreochromis have shown clear distinction and monophyly.

10. Synonyms

Chromis (Tilapia) mosaambicus (Peters, 1852)
Tilapia mosammbica (Jones and Sarojini, 1952)
Oreochromis mosaambica (Trewavas, 1983)

11. Type

Lectotype: W.C.H. Peters' collection in the Zoologisches Musuem der Humboldt Universitat Berlin.
Paralectotypes: Zoologisches Musuem der Humboldt Universitat Berlin, ZMB 2806: 88mm standard length, ZMB 16035: 3 specimens 74-115mm standard length

12. Glossary


dorsal fin: The fin located on the back of the fish
caudal peduncle: The narrow portion at the end of the fish that connects the tail to the main body
protuberance: something that protrudes
gill arch: a series of bony arches that support the gills
gillrakers: Bony processes that project from the gill arch to help the fish in suspension feeding.
Lectotype: A specimen later selected to serve as the single type specimen for species originally described from a set of syntypes.
Paralectotype: Any additional specimen from among a set of syntypes, after a lectotype has been decided among them.

13. References


Abdel-Fattah M. El-Sayed (2006) Tilapia Culture. CABI Publishing: Oxfordshire, UK.
Food and Agriculture Organisation of the United Nations. (2015). Retrieved on 26 October 2015 from http://www.fao.org/fishery/species/2408/en
IUCN. (2007). 2007 IUCN Red List of Threatened Species. Retrieved on 23 October 2015 from http://www.iucnredlist.org/details/full/63338/0
Klett, V. & Meyer, A. (2002) What, if Anything, is a Tilapia? -Mitochondrial ND2 Phylogeny of Tilapiines and the Evolution of Parental Care Systems in the African Cichlid Fishes. Society for Molecular Biology and Evolution 19(6):865-883
Ng, HH and Tan, HH (2010) An Annotated Checklist of the Non-native Freshwater Fish Species in the Reservoirs of Singapore. COSMOS 6 (1): 95-116.
Russell D.J., Thuesen P.A. and Thomson F.E. (2012) A review of the biology, ecology, distribution and control of Mozambique tilapia, Oreochromis mossambicus(Peters 1852) (Pisces: Cichlidae) with particular emphasis on invasive Australian population. Rev Fish Biol Fisheries 22: 533-554.
Sultana, S. (2010) Mozambique Tilapia: Oreochromis mossambicus. BdFISH Feature. Retrieved on 23 October 2015 from
http://en.bdfish.org/2010/02/mozambique-tilapia-oreochromis-mossambicus/
The Fish Site (2005) Farming Tilapia: Life History and Biology. Retrieved on 18 November 2015 from
http://www.thefishsite.com/articles/58/tilapia-life-history-and-biology/
Trewavas, E. (1983) Tilapiine Fishes of the genera Sarotherodon, Oreochromis and Danakilia. Trustees of the British Museum (Natural History), London.
Turner, G.F. & Robinson R.L. (2000) Reproductive biology, mating systems and parental care. In M.C.M. Beveridge & B.J. McAndrew (Eds.) Tilapias: Biology and Exploitation. Kluwer Academic Publisher: Great Britain : 33-58.