Spotted tilapia

Taxobox
name = Spotted Tilapia

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image_caption = A spotted Tilapia in an aquarium
regnum = Animalia
phylum = Chordata
classis = Actinopterygii
ordo = Perciformes
familia = Cichlidae
genus = Tilapia
species = "T. mariae"
binomial = "Tilapia mariae"
binomial_authority = Boulenger, 1899

Description

The spotted tilapia ("Tilapia mariae") is a fresh and brackish water fish of the cichlid family⁷. 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 spines¹. 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 adults¹. They also have two to six dark spots between the bars on the middle of their side¹ and they generally reach a maximum length of 300mm³. Spotted mangrove cichlids have a rapid growth rate and maturation time³. They also have high fecundity, simple food requirements and extensive tolerance of environmental variables such as water temperature, salinity, and pollution³. 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 species³ and research has found that internal reproductive androgenic factors can overrule the effect of size on dominance encounters in this species⁶.

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 areas³.

Breeding and Parental Care

Like several other tilapiine cichlids, the spotted mangrove cichlid is notable for its adaptability and prolific breeding ⁷. Spotted mangrove cichlids breed when they are about 150mm long and generally breed year long with peaks in November, March-April and July-September⁴. They lay up to 1800 eggs usually on submerged logs, rocks or plants and the eggs hatch after approximately three days³.

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 care⁴. 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 substrate². 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 predators². 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 predators². Parental care continues until the fish are about 2.5-3cm¹. 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 area².

Ecology

Spotted mangrove cichlids feed mainly on plant matter¹ and males and females never feed at the same time. Instead, one will feed while the other stays close by and then they will switch². 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 adults⁴. 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 die⁴. Spotted mangrove cichlids are important ecologically as well as commercially and as a result are commonly exploited and cultured⁴.

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 decrease⁴. Spotted mangrove cichlids are strong, aggressive and very territorial and have the ability to disturb the habitat of other fish populations⁴.

potted 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 Indonesia⁵. Captive individuals were then dispersed throughout Australia by the industry of fish fanciers⁵. Then, some spotted mangrove cichlids escaped or were released and self-sustaining populations arose⁵. The expansion of the spotted mangrove cichlid species in Australia has potential adverse effects on the native fish faunas that currently exist in Australia⁵. 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 pondage³. 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 permit⁸. 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 species⁸. The NSW fisheries have the right to seize the fish and destroy them if necessary⁸.

References

1. Allen, G.R., S.H. Midgley and M. Allen. Fieldguide to Freshwater Fishes of Australia. CSIRO Publishing:Australia, 2002.
2. Annett, Cynthia A., Raymond Pierotti and Jeffrey Baylis. (1999). Male and female parental roles in the monogamous cichlid, Tilapia mariae, introduced inFlorida. Environmental Biology of Fishes. 54, pp.283-293.
3. Caldwater, P.L., G.N. Backhouse and R. Fallu (1980). Occurrence of exotic tropical fish in the cooling pondage of a power station in temperate south- eastern Australia. Australian Journal of Marine and Freshwater Reserve. 31, pp541-546.
4. King, R. P. and L. Etim (2004). Reproduction, growth, mortality, and yield of Tilapia mariae Boulenger 1899 (cichlidae) in a Nigerian rainforest wetland and stream. Journal of Applied Ichthyol. 20, pp.502-510.
5. Mather, P.B., and A.H. Arthington (1991). An assessment of genetic differentiation among feral Australian tilapia populations. Australian Journal of Marine Freshwater Reserve. 42, pp721-728.
6. Schwanck, Erikki (1980). The effect of size and hormonal state on the establishment of dominance in young males of Tilapia mariae (pisces: cichlidae). Behavioural Processes. 5, pp.45-53.
7. FishBase species | genus = Tilapia | species = mariae | year = 2006 | month = October
8. “Tilapia - Oreochromis mossambicus (Mozambique mouthbrooder)”. New South Wales Department of Primary Industries: Fisheries. Updated 16 Mar. 2008. Accessed 12 May 2008. .