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In-depth: Fish Farming
Is There Something Fishy About Your Dinner?
by Robin Marks
Ooo, that baked salmon sure looks good... crusty seasonings on the outside, nice pink flakiness inside... a spritz of lemon, and mmmm...
But wait a second -- where's this nice-lookin' fish from?
One quarter of all the fish eaten by humans in the world is raised on farms. Many people view aquaculture - the farming of fish and other seafood - as a way to bridge the gap between declining food-fish populations and rising demand for fish and other seafood. In most cases,
But aquaculture isn't without its risks. A fish farmer should know how to raise fish and should be aware of the impact a fish farm can have on the environment, the economy and consumers.
Environmentally speaking, in some respects fish farms are the water-bound cousins of hog and cattle farms - they face some of the same issues. A dense population of penned-in fish generates a significant amount of waste that enters the surrounding waters, posing a waste management problem. And similar to land-based farm animals, farmed fish living close together on restricted diets are more susceptible to disease than are their wild relatives. Therefore, their diet often includes antibiotics, and these, too, add to the pollution created by the farm.
And as with farmed livestock, the extent of resources required to feed farmed fish can be environmentally problematic. Some farmed aquatic animals, like shrimp and that tasty herb-crusted salmon, are carnivorous. Their diet in captivity usually consists of fishmeal, a processed combination of herring, mackerel, sardines and other small fish caught in the wild. Stocks of these smaller species may feel the pinch of overfishing as they are gathered as food for their larger cousins. Indeed, some researchers estimate that every pound of fish raised solely on fishmeal requires the extraction of two pounds of fish from oceans and rivers. In other words, such farming practices can actually consume more fish than they produce, rather than supplementing wild food-fish stocks.
Occasionally, farmed fish can escape and become part of a nearby wild population, potentially jeopardizing the integrity of the native fish's gene pool. The consequences of hybrid fish in a wild population are likely to vary from species to species and aren't yet well understood. However, scientists have observed some negative effects.
Among tilapia, a fish widely farmed in habitats where it doesn't naturally live, escaped fish have been found to threaten or reduce native populations in many parts of the world, sometimes eating the young of other species or the plants they rely on. And although farmed male salmon are much less successful breeders than wild males, one study of salmon in Norway found that when farmed males did succeed in producing hybrid offspring, the hybrid males were smaller than their wild counterparts, which enabled them to sneak in and fertilize a female's eggs without being noticed. This means that the second-generation escapee is four times more likely to reproduce.
From a consumer standpoint, farmed fish may have a nutritional advantage: Some studies have shown that the fishmeal diet fed to farmed salmon gives them higher levels of desirable omega-3 fatty acids. This benefit can be negated, however, by toxins in the fish. One 2005 study found that the levels of pesticides, PCBs and dioxins were as much as 10 times higher in farmed salmon than in wild Pacific salmon.
Despite their potential negative impacts, fish farms play an increasingly important role in providing people with protein, particularly in the developing world. That role is so important, in fact, that in 2005, the World Food Prize, sometimes likened to a Nobel, was awarded to Indian scientist Modadugu Gupta, who developed a method of fish farming that can be done sustainably by small farmers. Aquaculture offers a number of other advantages: jobs in local communities, the opportunity for researchers to closely study specific species and the potential to offset threats to wild stocks in danger of being overfished.
So how can farmers take advantage of the potential benefits of aquaculture while mitigating some of the environmental risk? Through a variety of approaches, fish farmers can strike a balance between food production and environmental stewardship.
The problems of escaped fish would be lessened if farms raised only fish native to their area. Alternatively, pens with hard walls, rather than nets, act as more effective containers. The best method of preventing escapes - though certainly not the cheapest - is to separate the farm from the open water by digging a pond and pumping the ocean or river water into it. Although more protective pens would better secure the farmed fish stock, the tradeoff is that the consumer would likely pay for the pens in the form of higher-priced fish. Because aquaculture relies so heavily on feed made from wild-caught fish, scientists are working to develop plant-based feeds that produce fish with as much of the valued omega-3 fatty acids as those raised on fishmeal. Although they haven't yet succeeded in finding a substitute food for carnivorous fish, recent research indicates that fishmeal may only be necessary for a short period before the fish are harvested. And some farmers have succeeded in switching their omnivorous fish to an entirely vegetarian diet.
A different approach, and one that deals with fish farming's waste management issue, is to farm fish along with shellfish or plants that help to filter some of the waste from the water. Some farms have adopted what are known as integrated multitrophic aquaculture systems, in which nutrients are recycled. For example, fish waste might be used to fertilize ocean plants, which can then be used to feed other animals, such as shellfish.
Another approach, known as integrated rice-fish culture, also shows promise. This is the practice of farming rice and fish in the same area, which the Chinese have been doing for 2,000 years. The rice paddies provide the fish with a steady stream of pests and weeds to eat, and the fish, in turn, fertilize the rice with their waste. This approach is especially desirable because the fish get most of their nutrition naturally. Integrated rice-fish culture could offer a reliable source of local food for people in the developing world, who are growing food to feed themselves (as opposed to growing food for export), provided enough farmers could be taught this practice.
Award-winner Gupta goes a step further with his fish farming: He teaches people to make use of microenvironments and nutrient-rich waste that already exist. For example, in low-lying countries like Laos and Bangladesh, the rainy season fills ditches left behind by road and housing construction, creating ponds big enough to serve as single-family fish farms. Even very poor farmers who don't own land can cultivate their meals this way.
In our hungry world, fish farming plays a variety of roles, from providing delicacies for a chef's table to offering a more stable existence for many people around the world. With dedication and ingenuity, farmers and the governments that regulate them can make aquaculture both economically viable and less threatening to the environment. And they will need to, not only to protect the planet, but also to safeguard the very resources on which they, and so many others, rely.
USA Today: "Pros and Cons of Fish Farming"
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