Africa, Environment, Headlines, Middle East & North Africa

Fooling Fish to Grow and Multiply

Cam McGrath

ALEXANDRIA, Nov 18 2010 (IPS) - Surrounded by glass jugs and beakers full of bubbling green slime, Mohamed Ashour appears to be experimenting with a new formula for pea soup. As part of his daily rounds, the Egyptian researcher checks the valves on the tubing connecting each vessel, ensuring their verdant-hued contents are adequately aerated.

Microalgae, essential to rearing juvenile hatchery fish, being cultured in a lab in Alexandria. Credit: Cam McGrath

Microalgae, essential to rearing juvenile hatchery fish, being cultured in a lab in Alexandria. Credit: Cam McGrath

It is a tedious task, but an important one. The colonies of microalgae brewing inside the glass vessels form the basic building block of a marine hatchery food chain. The harvested microscopic organisms are consumed by tiny zooplankton, which in turn are devoured by hungry seabass during their initial 30-day larval phase.

Fish that survive this critical stage and mature into fry are reared in nurseries, then shipped as fingerlings to fish farms throughout Egypt. There they are fattened up for about two years to reach commercial size before being sold to markets and fish restaurants.

Last year, Egyptian fish farms produced over 6,000 tons of marine finfish. The government hopes to double this amount within three years, and is pressing the country’s six marine hatcheries to expand fingerling production. And that means a lot more green goo.

“The scale of any mariculture operation will depend on your ability to produce sufficient supplies of microalgae,” says Ashour.

While marine hatcheries are usually thought of as facilities for breeding and raising juvenile fish, up to 70 percent of floor space is allocated to producing food – microalgae, phytoplankton and zooplankton – for the voracious little larvae. Feasting larval seabass, about the size of aphids, increase their body weight by about 10 percent a day.

“It is possible to grow microalgae in ponds outdoors, but the problem is every culture will be different because of changes in temperature, humidity and water salinity,” Ashour explains. “It is much better to produce it in a lab where you can control the conditions – but then there are space limitations.”

At the National Institute for Oceanography and Fisheries (NIOF) hatchery in Alexandria where Ashour works, staff scale up stock cultures of microalgae from test tubes to increasingly large vessels, ending in giant tubs ready for harvesting. The green slime is added to the saline water in the hatchery’s larval rearing tanks, where seabass, sea bream and sole fry begin feeding as soon as their yolk sacs are exhausted.

More than two million fertilized eggs are hatched in the facility’s four fibreglass tanks each year, says Mohamed Abdel Razek Eissa, director of aquaculture at NIOF.

“The larvae are very sensitive,” he asserts. “The survival rate during the first 100 days is 40 percent max, but the average is about 25 percent. That’s still higher than the wild rate, where more eggs hatch but the larvae have no protection from predators.”

Egypt began its marine hatchery programme in the mid-1990s to relieve pressure on declining wild fish populations. While hatcheries now produce over three million fingerlings a year, more than 80 million are collected from the estuaries and lagoons of the Mediterranean Sea to seed marine aquaculture projects.

“For freshwater species such as tilapia our hatcheries produce enough fry for all projects, but we still have problems with marine fry,” explains Mohamed Fathy Osman, chairman of the General Authority for Fishery Resources Development (GAFRD). “We get most of them from the sea, and in the case of mullet, we collect 100 percent from the sea.”

Demand for marine fry has put aquaculture in direct competition with traditional fishermen, who blame the explosive growth of fish farming operations for their declining catch. In an effort to protect wild stocks, GAFRD has given mariculture operators until 2013 to switch to hatchery seed.

“In less than three years a ban on collecting marine fry from the sea will come into effect,” says Eissa. “After that, marine aquaculture projects will only be able to use hatchery fry.”

A recent expansion of the NIOF hatchery has increased its capacity five-fold to 500,000 fingerlings a year. Egypt’s two other government hatcheries are capable of producing up to 1.7 million fingerlings, while three private hatcheries have a combined annual capacity of one million fingerlings.

“It will be impossible for our existing hatcheries to fill the gap (in fingerling production), even if they expand,” says Eissa. “We need to build new hatcheries.”

But it is not just about expanding facilities; scientists are looking at ways of making hatchery broodstock more productive.

NIOF researchers have been experimenting with artificial environmental conditions to control the reproductive cycle of seabass. The aim is to induce the fish to spawn out of season, permitting hatcheries to collect fertilized eggs year-round.

Initial results are encouraging. In August, while outdoor temperatures in Alexandria hovered around 35 degrees Celsius, Eissa’s team lowered the water temperature in four indoor breeding tanks to 15 degrees Celsius and dimmed the lights. The conditions simulated those of the fish’s natural winter spawning grounds off Egypt’s northern coast.

“We tricked them into thinking it was time to spawn,” says Eissa, adding that the experiment resulted in over 110,000 viable eggs from five broodstock pairs.

Now that the electricity bill has arrived, Eissa has come to the conclusion that induced summer spawning, while feasible, is too costly to be practical. However, the technique could be used to stagger spawning over three seasons, increasing commercial productivity.

“Producing fry in different seasons would allow marine aquaculture projects to continually replace fingerlings as they mature into bigger fish,” he explains.

Advances in hatchery production are expected to narrow the gap between wild and hatchery fry culture. Fishers, however, fear Egypt’s aggressive mariculture growth will outpace any hatchery gains.

“Increases in aquaculture production always come at the expense of (traditional) fishing and wild stocks,” warns Eid Mostafa, an Alexandria fisher.

Fathy concedes that the government waited too long to develop its marine hatcheries. Efforts to create a sustainable mariculture industry, while conserving wild fish populations, will require a shift in focus from building new fish ponds to expanding hatchery facilities.

“We need a much stronger foundation to build on,” he says.

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