The delicious destroyer that threatens fishing in the Nile

Crayfish are a favourite food in many parts of the world, but not in Egypt, where they are viewed with suspicion. A professor of aquatic ecology wants to change that... and save fishermen's livelihoods.

A crayfish in its natural habitat, the bed of a river. The crustaceans have thrived since being introduced into the Nile.

If there is one thing Magdy Khalil loves to see on his dinner plate, it is a tasty crayfish that has been plucked from the River Nile. In fact, Professor Khalil, an aquatic ecologist at Ain Shams University in Cairo, would like these creatures to become the favourite food of everyone in his country - and not only because they are delicious. The reason is that crayfish, which have the scientific name Procambarus clarkii, can destroy the livelihoods of fishermen along the length of the Nile. Native to the United States and introduced to Egypt in the mid 1980s, the crustaceans have been free to multiply thanks to the absence of any major threat from predators. It is a scenario all too familiar to ecologists, who around the globe have seen populations of countless introduced species, from snails to mammals, grow out of control when natural checks and balances do not exist. The crustaceans, which are smaller versions of lobsters and breathe through gills, cause a headache to fishermen because they cut their nets and eat the catch. They also eat the eggs of the Nile tilapia, a fish native to Egypt that is commonly caught for food. And as if disrupting the Nile's harvest of fish were not enough, crayfish can damage the irrigation canals of the Nile delta through their habit of building burrows that can stretch up to one-and-a-half metres in length. Native to Louisiana, they are believed to have arrived in Egypt courtesy of a fish farmer who thought he was buying shrimp eggs. The eggs hatched into crayfish, which went on to attack small fish being farmed in captivity nearby. "He had his fish farm in the middle of the Nile near Cairo. When he found they destroyed the nets he threw them into the Nile," Prof Khalil says. The only predator the crayfish need fear in Egypt is the catfish, but P clarkii is only vulnerable when very small or when its body is still soft soon after it has moulted its shell to allow growth, something it does about seven times during its lifetime. The catfish's best efforts are nowhere near adequate to keep crayfish numbers down to levels that do not cause significant harm to fishermen. P clarkii is such a hardy creature that it can even thrive in polluted water. "As long as no catching is taking place from the River Nile, their numbers are probably still increasing," says Prof Khalil. In many instances in the past, humans have deliberately introduced species to control pests, a tactic known as biological control. Prof Khalil is adamant this tactic could cause as many problems as it solves were it to be tried with the crayfish. "No, no, no," is his response to the suggestion. "It's very dangerous to introduce another species." The danger is that numbers of the introduced predator could run out of control to such an extent that the animal becomes a pest itself. But while the crayfish may not have any natural predators, and no predators are likely to be introduced to control them, Prof Khalil believes man could take the place of the birds, bass fish and salamanders that in America love nothing more than filling their stomachs with a tasty crayfish. On paper, turning crayfish into a regular on Egyptian dinner plates should not be too difficult a task, since the creatures are a popular food across the world in areas including Australia, Canada, the United States, Africa and Europe. Sometimes the crayfish are boiled alive - a practice animal welfare campaigners consider cruel - or cooked and eaten in pies or even bread. However, despite the popularity of crayfish in other countries, Prof Khalil faces an uphill battle in his quest make them a popular dish in Egypt. Partly because of the bad press crayfish have had, perhaps justifiably, in the country, many people simply do not want to eat them. "They don't like the morphology, the shape of the animal. The media in Egypt, they named the animal the cockroach of the River Nile or the scorpion," Prof Khalil says in a slightly exasperated tone. "It's not natural in the River Nile, so they are afraid to eat it." Prof Khalil is trying to use the Egyptian media to change the image of the crayfish and encourage his countrymen to discard their culinary prejudices. "It's my job to convince people to eat it. I am trying to convince people by newspaper and by television to eat these animals," he says. "They have them in Louisiana, where they are eaten, and it's a big industry. In France and China as well." In Egypt, crayfish meat is relatively inexpensive, selling for about three Egyptian pounds (Dh2) a kilogramme, making it affordable for most families. And if people do not want to eat crayfish, they can still catch them and use the creatures in animal feed, Prof Khalil insists. While it causes fishermen a host of problems, the presence of the crayfish in the Nile also brings benefits, thanks to the animals' fondness for munching on a certain kind of snail. These snails carry the larval stage of a flatworm that causes bilharzia or schistosomiasis, a chronic illness that damages internal organs, impairs growth in children and can cause death in extreme cases. Thousands of larvae escape from the snails into the water and their heads can penetrate the skin of people unlucky enough to be in their vicinity. Ultimately, the parasites infect the lungs, liver and other organs of infected individuals, causing severe damage if the condition is not treated. "That is the most positive thing about these crayfish - it likes to eat the freshwater snails, especially the bilharzia snails," Prof Khalil says. In fact, more than 20 years after the introduction of the crayfish into the Nile, Prof Khalil believes snail numbers have dropped 90 per cent. "Every village water channel we surveyed from 20 years ago or 15 years ago, when we came back we didn't find any snails. It's very useful to Egypt," he says. If the crayfish give such benefits, it begs the question of whether they should be fished at all. If they were eliminated, could the bilharzia snail population grow once again and cause more people to become infected? Prof Khalil insists crayfish stocks are large enough to allow many of the creatures to be caught and eaten without the snail population increasing significantly. "We have a lot of these crayfish to take," he said. @email:[e-mail]