Connect to share and comment

Slimy green revolution

Humanity suffers from a severe shortage of protein. American scientists working in Haiti have a novel solution: pond scum.

 A child fishes in Cité-Soleil, Haiti

Haitian children try to catch fish in the neighborhood of Cité-Soleil. (Photo by Eduardo Munoz/Reuters)


CAMBRIDGE, Mass. –  Scientists call it “low-resource aquaculture” or “periphyton aquaculture technology.”  To you or me, it’s pond scum.  And it is the bare-bones, low-cost feed of choice for fish farmers in developing countries from Haiti to Bangladesh.


Aquaculture is booming worldwide, growing about 10 percent annually.  This year, farms will supply half of the fish consumed by humans worldwide.


But now, the price of fish feed — which accounts for about half of a commercial farm’s costs — is skyrocketing. This rising cost is threatening the future of the industry. In poorer countries it is posing challenges to aid workers who are promoting aquaculture as a solution to the protein shortage that leaves millions malnourished each year.


“The feed costs are always rising,” said Ana Milstein, an aquaculture researcher at the Agricultural Research Organization in Dor, Israel.


This is in part a matter of supply and demand. Farming some popular species requires large amounts of wild fish. For example, to produce one pound of farm-grown salmon requires up to five pounds of seafood caught in the wild.


While that five-to-one ratio is a subject of controversy, scientists say high ratios are not sustainable. Over the past decade, aquaculture’s consumption of fishmeal and fish oil has doubled. These days, aquaculture consumes 68 percent of the world’s fishmeal production, and 88 percent of the fish oil, according to a recent study.


Environmental factors are also contributing to the rise in fish feed prices. For example, El Nino has decreased output at fisheries in Peru, a main supplier of anchovies for fishmeal.


The price hike has become so pronounced that the U.S. government is offering subsidies to offset feed costs of domestic producers. The American Recovery and Reinvestment Act is releasing up to $50 million in stimulus funds for that purpose.


Meanwhile, researchers at feedstuff companies like Monsanto and Cargill are looking for replacement ingredients. But impoverished countries may already have a head start. Out of necessity, they’ve turned to cheap, home-grown, plant-based feeds. Haiti is farming fish on a vegetarian diet of periphyton, the green slime found in ponds, thanks to assistance from the Marine Biological Laboratory in Woods Hole, Massachusetts.


The low-tech pond-scum system was a major breakthrough, says William Mebane, superintendent of Woods Hole’s Aquaculture Engineering Division. He admits that some of his lab’s earlier efforts were misguided. In 2002, for example, he and his colleagues devised a scheme to press local plants into fish pellets using a device powered by a bicycle. The pellets were intended to feed tilapia, an easy-to-farm fish that eats plants rather than other fish.


“We crafted a pellet that was nutritious and palatable to the fish, and a method to make it with available materials,” he said. “But our misstep was, we did not understand the culture well enough. Haitians spend four to six hours daily collecting water and firewood, so they had no time to work on the pellets.”


So later, he adopted the pond scum idea, which was initially developed in Asia and refined in Israel for organic aquaculture. To boost the output of periphyton, he suggested adding compost made of animal and plant waste, such as mango rinds. The compost, which is confined to a corner of the pond, acts like a tea bag, filtering in nutrients as the breezes and fish move the water. The periphyton grows throughout the pond on bamboos posts where the fish can graze.


“Fish can grow as fast with periphyton as a commercial diet,” said Mebane.


The compost recipe was easy: mix equal amounts of greens and browns, that is, plant and animal waste. But convincing fish farmers that throwing waste into the ponds would promote fish growth was another matter. There were doubters, so Mebane enlisted village seniors to collect plant and animal waste for the ponds, in the process giving them a means to contribute to the community. These were known as “poo patrols.”


“Each person had a shovel and a basket and was shown what to collect and how to maintain the compost,” said Mebane.


In L’Acul, Haiti, a mountainous area about 64 kilometers north of Port au Prince, the poo patrols spawned an unexpected business opportunity. People with animal and plant waste wanted to sell it, so they hid it. Some people created an informal cartel, hoarding manure. “There’s no better capitalist than a person who makes $1 a day,” says Mebane. “They all have cell phones, and word travels through Haiti faster than Paul Revere,” he added.


 All this underscored the pond scum scheme’s potential for creating business opportunities.


Twice a year, aquaculture project leader Madam Enes wraps her 80-pound harvest of tilapia in banana leaves, hoists it onto her head and walks two hours to the market to sell them. And she keeps some to eat. Other villagers trade their fish for rice rather than eating them. “It’s like a 401(k). They don’t want to touch it,” said Mebane, who added that the ponds would do better if they were harvested every couple weeks to thin them out. The fish are eaten only for special holidays, a practice Mebane hopes will change over time.


A joint project of Bangladesh and Israel, funded by the U.S., figured a way around that problem by adding a second, smaller fish that farmers will readily eat. They chose two kinds of carp, both herbivores that eat periphyton like the fish in Haiti.


The technology is good in Asia, where the unit of production is the family farm,” said Milstein of the Agricultural Research Organization in Israel, which collaborated with Bangladesh Agricultural University.


During the rainy season the ponds are filled with large and small carp. Each pond is farmed weekly, yielding enough small carp to fill a fist. This improves the protein in the farmers’ diets. “It got the attention of other farmers in the area, so there was a dissemination of the technology,” Milstein said. The small fish measure 5 to 10 centimeters long and can be eaten whole. 


The ponds fit well into the lifestyle in Bangladesh’s wet and rural landscape. Villagers site the ponds in holes that are left when new homes are elevated to protect them from flooding during monsoons.


The assistance project was completed last year, but the villagers are continuing to use the technology. Milstein is now researching other materials on which the periphyton can grow. She and her partners in Bangladesh would like to extend the fish technology to other species like prawns or shrimp, but so far they have not gotten funding.


“It is difficult to find funding for these projects, especially these days,” she said. “In the Western world the objective of aquaculture is profit. It’s not a family business, but an industry. In Haiti the goal is profit and feeding the family.”


But periphyton aquaculture technology isn’t likely to solve everyone’s problems. It is aimed at small ponds rather than large fisheries. Said Mebane, “It doesn’t produce as much fish as with a commercial diet, which has densities of 300-400 pounds of fish compared to 30 pounds with periphyton in Haiti.”