AGUA AZUL, Honduras — A common Bible story says Jesus fed 5,000 people with five loaves and two fish, which scholars surmise were tilapia. But at the Aquafinca fish farm here, a modern miracle takes place daily: Tens of thousands of beefy, flapping tilapia are hauled out of teeming cages on Lake Yojoa, converted to fillets in a cold slaughterhouse and rushed onto planes bound for the United States, where some will appear on plates within 12 hours. Americans ate 475 million pounds of tilapia last year, four times the amount a decade ago, making this once obscure African native the most popular farmed fish in the United States. Although wild fish predominate in most species, a vast majority of the tilapia consumed in the United States is “harvested” from pens or cages in Latin America and Asia. Known in the food business as “aquatic chicken” because it breeds easily and tastes bland, tilapia is the perfect factory fish; it happily eats pellets made largely of corn and soy and gains weight rapidly, easily converting a diet that resembles cheap chicken feed into low-cost seafood. “Ten years ago no one had heard of it; now everyone wants it because it doesn’t have a fishy taste, especially hospitals and schools,” said Orlando Delgado, general manager of Aquafinca. Farmed tilapia is promoted as good for your health and for the environment at a time when many marine stocks have been seriously depleted. “Did you know the American Heart Association recommends eating fish twice a week?” asks the industry Web site, abouttilapia.com. But tilapia has both nutritional and environmental drawbacks. Compared with other fish, farmed tilapia contains relatively small amounts of beneficial omega-3 fatty acids, the fish oils that are the main reasons doctors recommend eating fish frequently; salmon has more than 10 times the amount of tilapia. Also, farmed tilapia contains a less healthful mix of fatty acids because the fish are fed corn and soy instead of lake plants and algae, the diet of wild tilapia. “It may look like fish and taste like fish but does not have the benefits — it may be detrimental,” said Dr. Floyd Chilton, a professor of physiology and pharmacology at Wake Forest Baptist Medical Center who specializes in fish lipids. Environmentalists argue that intensive and unregulated tilapia farming is damaging ecosystems in poor countries with practices generally prohibited in the United States — like breeding huge numbers of fish in cages in natural lakes, where fish waste pollutes the water. “We wouldn’t allow tilapia to be farmed in the United States the way they are farmed here, so why are we willing to eat them?” said Dr. Jeffrey McCrary, an American fish biologist who works in Nicaragua. “We are exporting the environmental damage caused by our appetites.” Defenders of tilapia aquaculture point out that this young and rapidly growing industry has begun improving standards and toughening regulation. The two-year-old Aquaculture Stewardship Council, the brainchild of the conservation organization WWF and I.D.H., a Dutch sustainable trade program, is rolling out an inspection program for tilapia farms independent of the industry. Those that choose to participate — and pass — will receive labels identifying their product as “responsibly farmed.” In a nod to its growing popularity, this year tilapia’s will be the first of 10 fish certification programs to be initiated. Aquafinca, which began adopting more environmentally friendly cultivation in 2006 to better appeal to large corporate customers like Costco, this year became the first farm to pass an initial inspection. Proponents say tilapia aquaculture will only grow in importance because it provides food and jobs in a world of declining fish stocks and rising population. “There are going to be more farmed fish each year,” said Kevin Fitzsimmons, a biologist at the University of Arizona. “Think about it: if we tried to get beef from hunting, there would be a lot of hungry people.” From Africa to the World Native to lakes in Africa, this versatile warm-water fish was deployed by many governments in poor tropical countries around the world in the second half of the 20th century to control weeds and mosquitoes in lakes and rivers. In a cistern or pond, a few fish yielded dietary protein. In retrospect, that global dispersal “maybe was not the best idea,” said Aaron McNevin, a WWF biologist who is coordinating the development of standards for tilapia farms, because tilapia “is one of the most invasive species known and very hard to get rid of once they are established.” Today, wild tilapia has squeezed out native species in lakes throughout the world with its aggressive breeding and feeding. By the 1990s, businesses saw opportunity in farming this hearty species, which tolerates crowding and does not need expensive meat-based feed. Using selective breeding, scientists created today’s industrial strains: big, fleshy fish with tiny heads and tails, and intestines that allow them to absorb food faster. Farmed tilapia reaches its sales weight of about two pounds in roughly nine months of intensive feeding. “Nature is for maintaining species; what we do is make fillets,” said Danilo Sosa, a technician at the tilapia breeding pens of Nicanor Fish Farms, outside Managua, Nicaragua, plopping a tilapia used for breeding on a wooden table and scanning the chip in its gut that identifies its breeding line. Last year, more than 52 million pounds of fresh tilapia were exported to the United States, mostly from Latin America, as well as 422 million more pounds of frozen tilapia, both whole and fillet, nearly all from China, according to the United States Department of Agriculture. The growth has been abetted by the creation and marketing of new products like fleshy “tilapia loins” — even though fish do not possess that anatomical feature. For United States shoppers picking up tilapia from China or Honduras or Ecuador, there is little guidance. “It’s such a complicated job for consumers to decide what to eat, with aquaculture production expanding so rapidly,” said Peter Bridson, aquaculture research manager of the Monterey Bay Aquarium, which produces the popular Seafood Watch, an independent consumer guide to buying sustainable fish. The new sustainability standards being developed for aquaculture will be tailored by species to address their diverse environmental risks. For tilapia, that means fish cages can be placed only in lakes where tilapia already live, and must be designed to prevent escapes. To limit overtaxing of lakes, the new guidelines establish water quality rules for oxygen and phosphorus, a product of fish waste. Fish farms may not use prophylactic antibiotics. But even the new rules allow for some practices considered unacceptable in the United States, where cage farming in lakes is generally forbidden. In many states, tilapia must be housed in specially designed pens with roofs to prevent birds from carrying the fish elsewhere; their waste is often collected to use as fertilizer rather than released. Also, the new standards allow for baby fish to be fed testosterone even though markets like Whole Foods will not buy hormone-treated seafood.