Spotted tilapia
| Spotted Tilapia | |
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| Spotted tilapia (adult) in an aquarium | |
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| Species: | P. mariae
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| Binomial name | |
| Pelmatolapia mariae (Boulenger, 1899)
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The Spotted tilapia (Pelmatolapia mariae[1]) is a West African fresh and brackish water fish of the cichlid family.[2] It is also commonly known as the spotted mangrove cichlid or black mangrove cichlid. Spotted mangrove cichlids have a short rounded snout and three anal spines.[3] They are dark olive green to light yellowish in colour and have eight or nine dark bars on their sides which are more evident in young spotted mangrove cichlids than adults.[3] They also have two to six dark spots between the bars on the middle of their side[3] and they generally reach a maximum length of 300mm.[4] Spotted mangrove cichlids have a rapid growth rate and maturation time.[4] They also have high fecundity, simple food requirements and extensive tolerance of environmental variables such as water temperature, salinity, and pollution.[4] These characteristics allow spotted mangrove cichlids to rapidly populate many areas that have an appropriate habitat. Typically spotted mangrove cichlids tend to be an aggressive and territorial species[4] and research has found that internal reproductive androgenic factors can overrule the effect of size on dominance encounters in this species.[5]
Habitat
Spotted mangrove cichlids are native to Africa from the Côte d'Ivoire to Ghana, and Benin to Cameroon. They have also established large feral populations outside of their native ranges, such as in Florida and Australia. Spotted mangrove cichlids live in a variety of habitats. They have been found in both still and flowing waters, in shallow and deep water, in places where there is both little or no coverage and in rocky and debris-strewn areas.[4] Spotted mangrove cichlids are quite common and are found in rivers near the coasts of Africa, near the Côte d'Ivoire.
Breeding and parental care
Like several other tilapiine cichlids, the spotted mangrove cichlid is notable for its adaptability and prolific breeding.[2] Spotted mangrove cichlids breed when they are about 150mm long and generally breed year long with peaks in November, March–April and July–September.[6] They lay up to 1800 eggs usually on submerged logs, rocks or plants and the eggs hatch after approximately three days.[4]
Spotted mangrove cichlids are monogamous fish who engage in biparental care, and research has found that the size of the eggs tend to increase with the amount of parental care.[6] The males and females both have very specific roles in parenting and work together to ensure the well being of their offspring. The females prepare the nest by clearing an area on rocky substrate.[7] After spawning, the females take care of all embryo tending while males stay about two to three meters away and remain mostly inactive except for an occasional feeding or chasing away of predators.[7] When the offspring become two to three days old they rise off the nest and form a school. This causes a dramatic change in parental role as the male becomes active and the female begins to spend more time away from the young, guarding ahead of the school by chasing away predators.[7] Parental care continues until the fish are about 2.5–3 cm.[3] This biparental behaviour could help explain why black mangrove cichlids are able to live in many different habitats and become dominant over other fish populations in the same area.[7]
Ecology
Spotted mangrove cichlids feed mainly on plant matter[3] and males and females never feed at the same time. Instead, one will feed while the other stays close by and then they will switch.[7] There are a number of factors that contribute to the natural mortality of spotted mangrove cichlids. Their predators include Malapterurus electricus which preys on the eggs of spotted mangrove cichlids, and Hepsetus odoe and Parachana obscura which prey on the adults.[6] Spotted mangrove cichlids are also prone to heavy intestinal infection caused by nematode parasites which causes death. Also, they sometimes get swept away from their streams by flooding caused by rain into small residual pools over the banks of the stream where they become stranded. Then, when the rain stops the pools dry out they die.[6] Spotted mangrove cichlids are important ecologically as well as commercially and as a result are commonly exploited and cultured.[6]
Problems with Spotted Mangrove Cichlids
One main problem with spotted mangrove cichlids is they tend to become the dominant fish in many lakes, rivers and canals. They have even been found to at times comprise over half of the total fish biomass and therefore, they cause other previously dominant fish populations to decrease.[6] Spotted mangrove cichlids are strong, aggressive and very territorial and have the ability to disturb the habitat of other fish populations.[6]
Spotted Mangrove Cichlids in Australia
It is believed that spotted mangrove cichlids got to Australia through a series of events. First it is thought that all Tilapia populations derived from the importation of small numbers of individuals for the freshwater aquarium industry from Singapore or Indonesia.[8] Captive individuals were then dispersed throughout Australia by the industry of fish fanciers.[8] Then, some spotted mangrove cichlids escaped or were released and self-sustaining populations arose.[8] The expansion of the spotted mangrove cichlid species in Australia has potential adverse effects on the native fish faunas that currently exist in Australia.[8] Since they tend to become the dominant fish where they live, their expansion into Australia could be harmful to the other existing fish populations. Another way in which spotted mangrove cichlids have become a pest in Australia is that they have been found living in the cooling pondage of the Hazelwood power station in Victoria, Australia as well as in the creek just below the pondage.[4] The water temperature in Victoria is far too low for them to survive outside this habitat they have created, however it is a nuisance for the power station that they live here.
Reaction to Spotted Mangrove Cichlids in Australia
Since spotted mangrove cichlids are considered to be a class 3 noxious fish in Australia it is illegal to possess, sell or buy this species in New South Wales, Australia without a permit.[9] NSW fisheries are closely monitoring the populations of spotted mangrove cichlids and heavy fines of up to $11,000 apply for being in possession or caught buying or selling this species.[9] The NSW fisheries have the right to seize the fish and destroy them if necessary.[9]
References
- ^ Dunz, A.R. & Schliewen, U.K. (2013): Molecular phylogeny and revised classification of the haplotilapiine cichlid fishes formerly referred to as “Tilapia”. Molecular Phylogenetics and Evolution, Available online 29 March 2013 doi: 10.1016/j.ympev.2013.03.015
- ^ a b Froese, Rainer; Pauly, Daniel (eds.). "Tilapia mariae". FishBase. October 2006 version.
- ^ a b c d e Gerald R. Allen; Stephen Hamar Midgley; Mark Allen (2002). Field guide to the freshwater fishes of Australia. Western Australian Museum. ISBN 978-0-7307-5486-2. Retrieved 4 February 2012.
- ^ a b c d e f g Cadwallader, P. L.; Backhouse, G. N.; Fallu, R. (1980). "Occurrence of exotic tropical fish in the cooling pondage of a power station in temperate south-eastern Australia". Marine and Freshwater Research. 31 (4): 541–546. doi:10.1071/MF9800541.
- ^ Schwanck, E. (1980). "The effect of size and hormonal state on the establishment of dominance in young males of Tilapia mariae (Pisces: Cichlidae)". Behavioural Processes. 5: 45–53. doi:10.1016/0376-6357(80)90048-0.
- ^ a b c d e f g King, R. P.; Etim, L. (2004). "Reproduction, growth, mortality and yield of Tilapia mariae Boulenger 1899 (Cichlidae) in a Nigerian rainforest wetland stream". Journal of Applied Ichthyology. 20 (6): 502–510. doi:10.1111/j.1439-0426.2004.00545.x.
- ^ a b c d e Annett, C. A.; Pierotti, R.; Baylis, J. R. (1999). "Male and female parental roles in the monogamous cichlid, Tilapia mariae, introduced in Florida". Environmental Biology of Fishes. 54 (3): 283–293. doi:10.1023/A:1007567028017.
- ^ a b c d Mather, P. B.; Arthington, A. H. (1991). "An assessment of genetic differentiation among feral Australian tilapia populations". Marine and Freshwater Research. 42 (6): 721–728. doi:10.1071/MF9910721.
- ^ a b c "Tilapia". State of New South Wales. Retrieved 2012-02-05.