SPC/Fisheries 25/WP.99
14-18 March 1994


(Noumea, New Caledonia, 14-18 March 1994)

On the introduction of exotic freshwater
fish species to the South Pacific


Hugh Dunnit & Hans Kneesun-Boompsadaisy
Goliath Consultants Inc,
Upper Choirboy, Hampshire


The freshwater fish fauna of the South Pacific is relatively depauperate and in many cases the complement of species in freshwaters is comprised mainly of secondarily derived marine species. The African cichlid Oreochromis mossambicus was introduced to many of the countries of the region to improve yields from freshwaters and to provide a suitable species for aquaculture. Other introduced species include the carp (Cyprinus carpio), rainbow trout (Onchorhynchus mykiss) and black bass (Micropterus salmoides). Further introductions are being considered in Papua New Guinea for the Sepik-Ramu river system to improve yields for the large indigenous population.

Not all fisheries introductions are for food, however. One example is the mosquito fish, which was introduced to prey on mosquito larvae and hence reduce the biomass of mosquitos and the incidence of malaria. Another is the grass carp, Ctenopharyngodon idella, In this paper we consider other selective freshwater fish introductions for the purpose of domestic security.


Urban crime in the South Pacific

As populations grow and societies in the region become more urbanised there is a parallel growth in the incidence of crime, particularly housebreaking. Indeed most of the developed world appears to be experiencing massive rise in opportunistic theft from houses and cars. To combat this there has been an enormous growth in the security industry, with the development of better alarms, motion sensors, video and audio equipment and the creation of whole armies of security guards.

Such security is expensive and opportunistic thieves are no respecters of income and will rob from whatever house they can. Clearly, the growth in personal incomes and wealth in the South Pacific will be compromised by the threat of robbery. A regional initiative is required and one that is appropriate to the conditions of the region and the lifestyle of the inhabitants. Perhaps one solution is some form of biological security that is both effective and affordable. The solution may be in the introduction of selected species of freshwater fish from the Amazon River system in South America.


Species proposed for introduction to the South Pacific for domestic security

Several South American fishes have life history characteristics that recommend them for use in domestic security.

The first of these is the Piranha (Serrasalmus rhombeus) (Figure 1). This inhabitant of the Amazon is renowned for its extreme ferocity and Piranhas can be driven in to a feeding frenzy within seconds through the scent of blood in the surrounding water. Although not large (maximum size @ 35 cm) the Piranhas possess extraordinarily powerful and sharp dentition and in schools can overwhelm and skeletonise a large animal in minutes.

The second is the electric eel (Electrophorus electricus) (Figure 1), which is a large (@ 2.5 m) fish, capable of rendering a powerful electric shock that will stun or even kill a large mammal. The electric shock is generated from specially modified muscle tissue, which comprises about half the somatic tissue of the electric eel. The electric eel generates a pulse of electricity lasting only about one second but may be as high as 1.0 Ampere and 500 volts, sufficient to severely shock a human being. Schools of electric eels can easily render unconscious large mammals such as deer, horses, peccaries and capybara, following which they can be consumed.

The third is a small (~ 2.5 cm) parasitic fish from the Amazon, the Candiru (Vandiella cirrhosa)  (Figure 1). This tiny catfish lives mainly on the blood of other fishes. They attach themselves to the gills and will force their way into body apertures, such as the urethra, where they bite into the tissue and consume blood from the lesion. They are sensitive to urine and uric acid and will follow the trail of persons relieving themselves in rivers and enter the urethra. When they swim into the urethra of humans, it can be difficult to pull the fish out by the tail because the umbrella-like spines near the head may extend and prevent its removal. Forced extraction may cause lacerations of the urethral mucus membranes, which has caused death by haemorrhaging. Remedies have ranged from penile amputation and suprapubic cystotomy to application of native herbs that softens the spines of the Candiru so that it can be removed without trauma


Security procedures

To protect a house we suggest that homeowners construct a deep moat or pond around their dwelling and stock it with the fishes mentioned above. A system of lockable cantilever bridges can be used to gain access and isolate house when in residence or when the property is vacated  (Figure 2).

Effectively each homeowner would live on a small island surrounded by an aquatic barrier or moat containing the electric eel, Piranha and Candiru. A stout fence should be erected around the edge of the island to prevent persons falling in to the water accidentally. To gain access to the house, a criminal would have to wade or swim through the moat.

The bottom of the moat should be lined with broken glass so as to cut the feet of any malefactor wishing to swim or wade across and gain entry to the house. The liberation of blood in the water will drive the Piranha in to a feeding frenzy and they will school and attack the criminal as he bleeds in the water. No doubt too the electric eels will join in and incapacitate the villain where he can be readily consumed by the fish in the moat.

The householders can then inform the police who may wish to recover the bones and teeth for identification purposes. The beauty of this system is that it will relieve pressure on the police force and judicial system as the criminal makes a more beneficial contribution to society as fish food.

Should the housebreaker fortuitously not be attacked by the electric eels or the Piranha then there is a good chance that he will suffer the invasive penetration of the Candiru in to the urethra. Studies have shown that the tension and stress of burglaries results in loss of sphincter and bladder muscle control. The spontaneous emission of urine in the water will act as a guide to the Candiru and the burglar, if wearing normal relatively loose fitting clothing will be invaded by the fish.

Naturally the malefactor may not realise this and indeed make away with some property. However, the subsequent blockage in the urethra and inability to urinate will force the criminal to report to hospital where, once the penile obstruction has been identified as a fish, this can be reported to the police, and an arrest made, leading hopefully, to the recovery of property.

It might be argued that thieves could cross the moat in a small boat. A metal fence set in the middle of the moat will prevent this although it is unlikely that opportunistic thieves will be carrying a canoe or dinghy with them.


Maintenance of the guard-fish stocks

The Piranha and electric eel can be fed daily on household refuse, whilst the Candiru will live by parasitising both these larger fish. The moat water should be kept clean and changed from time to time and it is recommended that every care and attention is given to ensuring that these fishes do not establish themselves in the natural freshwater systems.


Establishing a domestic fish-based security system

The main requirement for this security method is a pond or moat surrounding a house. This can be easily dug with a small excavator or by a gang of workmen at a cost of a few hundred dollars. Small grants for this are currently available under the SPRADP regional aquaculture support funds currently being administered by SPC's Fisheries Programme. It may be possible to hire prisoners from the local corrective institution for a nominal sum. For example prison labour has been used in Fiji to construct fish ponds for aquaculture.

The three exotic species can be obtained from a recently established company, Piscurity Inc, based in Manaus, Brasil, with branches in Suva, Port Moresby Auckland and Guam. A detailed review of fish-security systems is given by Dr Vas de Ferens of FAO in his report 'Ancillary uses of cultured fish populations in the tropics' (FAO Fisheries Paper 99, 1992).


Future developments

The optimum use of a domestic fish security system as described here would include some form of harvestable recovery for food besides protecting buildings and possessions. Such multi-purpose aquaculture has been employed in Asia, where fish are cultivated in rice paddy fields to reduce pest infestation and for food (see Rice-fish research and development in Asia, ICLARM Conference Proceedings 24, 1992).

The Piranhas are an edible species, however, the electric eel is unlikely to appeal as a source of food and the Candiru is far too small to be harvested and eaten. Current research is aimed at finding dangerous fish species from South America and elsewhere that could be used both for security and food.


  1. Breault, J. L. (1991) Candirú: Amazonian parasitic catfish. Journal of Wilderness Medicine, 2: 304-312.
  2. dela Cruz, C. R., Lightfoot, C., Costa-Pierce, B. A., Carangal, B. R., & Bimbao, M. P. (1992) Rice-fish research and development in Asia. ICLARM Conference Proceedings 24. 457pp.
  3. Marshall, N. B. (1965) The life of fishes. Wiedenfeld & Nicholson, London. 402pp.
  4. Sterba, G. (1963) Freshwater fishes of the world. Viking Press. New York. 877pp.

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