Vertebrates (pdf)

	First record of the estuarine goby Eutaeniichthys gilli Jordan & Snyder, in Hong Kong
	Macaques as seed predators and dispersal agents in Hong Kong
	Piranha = man-eating fish?
	Bat Pollination in the Climber Mucuna birdwoodiana
	Rattus sikkimensis occupies bird nest box on Kau Sai Chau

Piranha = man-eating fish?

by Cheung Sze Man

Piranha 食人魚 refers to some of the members of the subfamily Serrasalminae (Family Characidae, Order Characiformes). In the Tupi-Guarami language, pira means fish and ranha refers to teeth (Schleser, 1997). Some sources (e.g. Schulte, 1988) state that the word 'Piranha' means scissors. Native to the Neotropics, most piranha species can be found in the Amazonia and Orinoco River Basins. They thrive in big rivers, swamps and estuaries. Piranhas are notorious for their cruel feeding habit but most rumors of their fierce behaviour are very much exaggerated while they do attack injured animals crossing rivers, some piranha species only feed on invertebrates, fish fins and fruits dropping from overhanging riparian plants.

Although most heart-breaking rumours on piranhas are untrue, we should never ignore their impact on the ecosystem when they are introduced to places out of their natural ranges. Exotic piranhas may compete with native fauna for available space and food resources and they may also prey on indigenous fish and break the balance of the ecosystem. Apart from ecological impacts, released piranhas a bite cleaners during pond maintenance work (e.g. 29 September 1998 Ming Pao and 01 December 1998 Sing Tao Daily).

Because of such concern, in some parts of the world regulations have been implemented to restrict or even ban the import/export and possession of piranhas, especially the Red-bellied piranha (Pygocentrus nattereri). Over 20 states in the US ban the keeping of piranha and in some states even scientific organizations need to apply for possession permits. A hot debate has been stirred up by the mass media in Mainland China since November 2002 on whether the keeping of piranha should be banned. This debate urged the Mainland Central Government to issue an emergency notice to stop the importation and possession of piranhas. All the P. nattereri in the market had to be confiscated and all the stocks/exhibition in zoos and public aquariums had to be destroyed by fisheries officers.

On 27 August and 19 September 2003, I visited two of the largest wholesale markets in Guangdong: Qingping and Huadiwan pet markets and Qingping food market at Guangzhou. I also conducted a survey at Dongmen market and neighboring aquarium shops at Shenzhen on 03 December 2003. The results from all 3 visits for both pet and food markets at Guangzhou and Shenzhen showed that no P. nattereri were being sold. Only approximately 20 individuals of phytophagus serrasalmin silverdollar Myleus spp. were found at a single shop at Huadiwan pet market at Guangzhou and a single pacu, Piaractus brachypomus, was recorded in an aquarium shop at Shenzhen.

Pretending to be a potential customer, the author asked the aquarium shopkeepers about the sale of piranhas. All the respondents independently expressed that they did sell a certain amount of piranhas before the implementation of the regulation but now hardly dare to do so because of the heavy punishment (CNY $ 50,000 maximum fine for selling any piranhas; note that the average annual wage of staff and workers per capita in urban areas of Guangdong in year 2002 = CNY $ 17,500; National Bureau of Statistics of China Website, 2003; US $1 = CNY $8.28). Moreover neither the profit of selling piranha, nor demand for piranha, are very high, unlike the profitable arowana trade that can still power a huge underground black-market. Several freshwater food fish stall owners said that they did not need to take the risk since they could offer a lot of other fish species to their customers. These observations from the three visits to Guangzhou and Shenzhen did not imply that there would be no more piranhas in the markets, but at least people in the Mainland China have become well aware of the implementation of the regulation.

In Hong Kong, piranhas are still occasionally found in both aquarium shops and food markets. In the past three months (September to November 2003), Pygocentrus nattereri was recorded in at least 15 aquarium shops distributed in the New Territiories and Kowloon. Usually each shop selling P. nattereri keeps a supply of around 10-15 individuals (2 cm-25 cm TL) at any one time. Other serrasalmins were also recorded in small quantities, including Myleus rubripinnis, M. schomburgkii, Piaractus brachypomus, Pygocentrus piraya, Serrasalmus spilopleura, etc.

Piranhas have become less and less common in local food markets in recent years but some freshwater fish stalls in the New Territories always stock around 10 individuals of piranhas for sale (20-30 cm TL). When asked about the origin of the fish, some shopkeepers told the author that they were from the Mainland China, and some were even said to be wild-caught from the countryside of Hong Kong!

In the past few years, I have also recorded some sightings of piranhas (Table 1). In August 2001, I witnessed several women releasing 3 adult piranhas (around 30 cm TL) into Kowloon Reservoir for religious purpose. They said the red colour of the red-bellied piranhas could bring them good luck. All my records so far have been recorded from reservoirs and man-made ponds in a town park. The piranha issue in Mainland China raised the question regarding whether controls on the import and possession of piranha are also needed in Hong Kong. As studies such as Bennett et al. (1997) have shown that tropical P. nattereri cannot withstand temperatures < 10^oC, it is suspected that piranha may not survive through the winter in Hong Kong. Although P. nattereri is renowned for their aggressive behaviour, scientific evidence on their actual impact on the natural ecosystem is scant. This does not imply that piranha pose no harm to native fauna but rather stresses the need for further field observations and experiments to determine the cold tolerence and ecology of exotic piranha in Hong Kong. In fact, phytophagus serrasalmins such as Myleus spp. and Piaractus brachypomus) are good aquarium and food fish.

Relevant government departments should consider whether regulations should be imposed to either ban the whole subfamily Serrasalminae, or just ban the true piranha (P. nattereri). In the long-term, government departments and the scientific community should raise the awareness of the general public on the environmental consequences of irresponsible disposal of aquarium fish. Putting unwanted predatory exotic fish (as in the piranha case) to sleep by freezing or using tranquilizer is not a good thing to have to do, but at least causes less harm to native fauna and the environment. Communication with religious organizations can help to spread the message on the negative impacts brought about by releasing exotic animals. In addition, we should analyze perceived information objectively and scientifically, including those from the mass media, in order to make reasonable and effective strategies to prevent and tackle the invasive species problem.

Bennett, W.A., Currie, R.J., Wagner, P.F. & Beitinger, T.L. (1997). Cold tolerance and potential overwintering of the red-bellied piranha Pygocentrus nattereri in the United States. Transactions of the American Fisheries Society 126(5): 841-849.

Schleser, D.M. (1997). Piranhas---everything about selection, care, nutrition, diseases, breeding and behavior. Barrons's Educational Series, Inc. New York. 88 pp.

Schulte, W. (1988). Piranhas in the Aquarium. T.F.H. Publications. New Jersey. 56 pp.

Table 1. Sighting records of Red-bellied piranha Pygocentrus nattereri in Hong Kong in the past three years (2001-2003)