Dangers of fish invasion

2008-12-06 00:00

Plecos, the common name given to a number of armoured catfish species from South America, may look attractive and harmless in a fish tank or pond, but there is a potentially sinister side to them, as the website plecoinvasion.org shows. This is the website of an international organisation dedicated to documenting and trying to prevent the spread of these fish around the world because of the environmental and socio-economic damage they can cause. Unfortunately, plecos have been identified in rivers in the Empangeni area.

Professor Paul Skelton, managing director of the SA Institute for Aquatic Biodiversity (SAIAB) in Grahamstown, explains that these fish have several characteristics that make them successful invaders. They grow to a large size, can breathe air and when breeding protect their eggs to ensure that their brood survives. They also spread because their extensive armour plating and spines protect them. There are few indigenous predators that could successfully feed on them once they attain a certain size. “So they compete with indigenous species for space in the environment.”

He outlines the dangers that these fish could pose to local fisheries and ecosystems. “As they are very heavily armoured they tend to get caught in fishing nets easily, but are extremely difficult to remove from nets, so they seriously disrupt fishing activities and nets quickly become dysfunctional and tangled. They are not good for food as they consist of mostly bones and bony plates.

“There are subsistence fisheries in some areas that could be negatively impacted by a pleco invasion. If they become established and spread further north they could even affect subsistence fisheries in parts of Mozambique. In addition, plecos burrow in muddy banks extensively and they might affect structures such as farm dams or even cause increased erosion of river banks.”

Skelton says plecos are being studied in other parts of the world both as interesting natural creatures but also because of their proven invasive characteristics. “In Mexico they have been intensively studied as invasive organisms for several years. No studies have been done on them here yet. However, the SAIAB intends investigating the Empangeni invasion as soon as possible. It will also help to establish if there are other pleco invasions in the country.”

The owner of Exotic Pets outlets in Northdale and Victoria Road, Anwar Mohammed, said plecos sell very well because they are omnivores, eating algae, excess food and even dead fish, thus helping to keep fish tanks clean. The different varieties also have beautiful colours and interesting shapes. He buys fish from importers who bring them into the country. “Common plecos are the cheapest, with rarer varieties like the bristle-nosed, red-spotted or leopard pleco more expensive. We sell them from four or five centimeters to about 15 centimetres long. However, they can grow to as much as 50cm long, and can start becoming a problem from about 20cm. To keep a fish that size you have to have a large tank or a pond. That’s when people may be tempted to release them.”

Mohammed said he is willing to take back plecos that become too large for people to keep, and swop them for smaller ones. He also offered to do this for people who did not buy them from his stores, rather than have then released into the wild. He has large tanks and a pond where he keeps them. “You could say we run a retirement home for plecos,” he said.

what are plecos?

Known as “plecostomus”, “algae eaters” or plecos (family name Loricariidae) this is the largest family of catfish with over 80 described genera and 800 described species. They are freshwater fish native to central and south America, and are found in tropical Costa Rica, Panama, and South America, but many species have small natural ranges. Most are nocturnal. They are a bottom-dwelling species that eat algae, invertebrates and detritus, and one genus, Panaque, is known to eat wood. Many species can also breathe air, making them robust, which may be one of the reasons they are often found in the aquarium trade. Plecos supplied to the aquarium trade are collected from the wild or bred by breeders in several countries, including South Africa. There is no way to tell the sexes apart without dissecting them.

They have caused problems in environments in many areas of the world where they have been released. They have been collected in several states in the United States, Canada and Mexico, and populations have also been recorded in Australia, Europe and Asia.

In addition to the ecological impacts, the socio-economic consequences of armoured catfish invasion can be severe. In Mexico, their invasion has been linked to reduced water quality and the collapse of large freshwater fisheries. For example, the Infiernillo Reservoir tilapia fishery in southern Mexico supported 46 000 people through fishing and processing jobs. After plecos entered the reservoir, the fishery experienced a 70% to 80% reduction in tilapia production. Subsequently, unemployment rose and led to the emigration of young people from affected communities.

— Sources: www.pleco

invasion.org and SAIAB

want to get rid of a pleco?

If you want to get rid of an armoured catfish, either:

• Destroy it;

• Take it back to the place where you bought it; or

• Take it to Anwar Mohammed at Exotic Pets in Victoria Road or Northway Mall. He can be contacted at 033 397 1261.

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