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The Many Faces of Aquaculture: An Introduction to Fish Farming

Posted May 04 2011 12:14pm

fishIs there a sight more idyllic, peaceful, and touching than that of a fish farmer tending to his flock? In case you aren’t aware of how fish farming works, here’s a sample day in the life of a fish farmer:

Just before dawn each day, he rises from his water bed, dons his denim board shorts, enjoys a mugful of the fermented fish liver brew he keeps stewing in a bucket beside the front door, leaves his rickety old farmhouse boat, and sets out for a day’s labor. Wherever his paddleboat passes, carp, salmon, tilapia, phytoplankton, algae, and shrimp cease predating each other and crest to greet him. The fish farmer knows each by name and has a wink, chin scratch, and fish flake for every little shy fry cowering behind its mother. At slaughtering time, the old farmer sheds a single, solitary tear – every single time, whether it’s the ornery old catfish with greying whiskers or the months-old tiger prawn just hitting his prime (which, unfortunately for the prawn, is when flavor and texture are at their peak). It’s a simple life, but, all-in-all, an honorable one steeped in tradition, stewardship, and respect for the natural flow of aquatic life.

Okay, okay… how does fish farming really work? Well, it encompasses more than just fish, for one. A more accurate term to use is actually aquaculture, which includes multiple varieties of fish farms, shrimp (and other crustacean) farms, shellfish (oyster, clam, mussel, abalone, etc) farms, and sea ranches (this is the coolest). Let’s dig in.

Humans have been engaging in aquaculture since antiquity, and perhaps even earlier. An Australian archaeologist, Dr. Heather Builth, has gathered evidence that the aboriginal Gunditjmara of Western Victoria  built and oversaw massive eel farms , as early as 6000 BC, that sustained villages and even an industry of smoked eel products. The ancient Chinese started farming carp over 4,000 years ago and wrote the definitive book on the subject somewhere around 500 BC. During the Tang Dynasty, the Chinese discovered that certain species of freshwater carp complemented each other in the same pond, boosting productivity, saving space, and birthing polyculture fish farming. In addition to China, fish farming spread into the Indian subcontinent,  ancient Egypt, the Greco-Roman world , medieval Europe, Hawaii (pre-colonial), and just about everywhere else.

Nowadays, about  half of all fish eaten worldwide comes from aquaculture . To a bunch of health-conscious wild salmon eaters like you folks, that probably sounds like a nutritive disaster. After all, everyone knows that wild trumps farmed, every single time. Right? Well, not exactly, but I won’t get into that right now. Check back tomorrow. This time, I’m going to briefly discuss the various types of aquaculture.

Extensive fish farming utilizes natural photosynthetic production of food (algae, plankton, mollusks, crustaceans) to feed the fish. This type of farming isn’t the most productive, but it requires little labor, low overhead, and very little input from the farmer. You just need water, some fish, and a way to pen them in. Things can obviously get more elaborate, but those are the bare minimum. Most tilapia and carp are farmed using extensive methods.

Extensive farming is obviously the most sustainable and does the least environmental damage, but it isn’t always economically viable and it doesn’t work for every species. Carnivorous fish (which is most of ‘em) need to eat fish, or pellets made from fish. Salmon, for example, eat the fish that eat the plankton; they don’t eat the plankton directly. On the other hand, tilapia, which feed directly on phytoplankton, and carp, which eat benthic animals (bottom feeder), are great for this type of farming because they don’t require food pellets or other, smaller fish for food.

Intensive fish farming uses an external food supply – pellets, fishmeal, corn, soy, even “feathermeal” – to feed the carnivorous fish. The population density is high, antibiotic usage is high, food waste is high, and sewage output is high in intensive fish farming. Water quality is paramount and usually requires a robust water purification system, if the farm is a closed system, like a pond, ditch, or tank. If the farm uses cages in rivers or the open sea, water purification obviously isn’t as necessary.

Either way, intensive fish farming requires constant maintenance and vigilance. If management is poor or funding inadequate, things can get pretty bad: toxic runoff, antibiotic-resistant bacteria, introduction of farmed, perhaps diseased species into wild populations, excess food and waste influencing wild population densities, stressed out fish. Heck, even if management is on top of their game, antibiotics are still a necessity, food is being wasted and eaten by wild sea life, which throws off local wild population densities, and the fish are living in cramped conditions which increases stress. It can be done well, and I’ll get into that next time, but it is difficult to do, and most aren’t doing it.

Traditional shrimp farming took place in brackish water ponds or mangrove swamps, the shrimp’s natural habitats, and often involved other complementary species, like rice or fish. This was subsistence farming, suitable for a family or even an entire village, but not for an industry. Today, shrimp farming displaces mangrove swamps and other coastal systems across China, Thailand, India, and Vietnam, among other countries. There are three primary types of coastal shrimp farms: extensive, semi-intensive, and intensive shrimp farms. Extensive shrimp farming uses low densities, about two or three animals for every square meter of water, and generally do not need to supplement feed supplies. They’re on the coast, so the tide’s enough to keep the water fresh, and extensive farmers often use wild stock. Semi-intensive shrimp farming ups the density to about 10-30 shrimp per square meter, increasing the requirement for food. In semi-intensive farms, shrimp get supplemental shrimp feed, and artificial algae blooms take care of the rest. In intensive shrimp farms, the shrimp populations reach even greater densities and rely almost entirely on supplemental shrimp feed.

Infectious disease is a frequent concern in shrimp farming. It kills profits, sure, but it also infects and kills wild shrimp living near or around the coastal farms. Most shrimp diseases are viral, without any real treatment save for prevention, but preventing viral disease from spreading among shrimp in super-dense living conditions isn’t easy. And then there’s bacterial disease. Most shrimp farms use antibiotics to cull bacterial diseases; one study found that 74% of Thai shrimp farmers surveyed used antibiotics in their operations. As the shrimp population increases in density, larger amounts of antibiotics are required. This leads to resistant bacteria, which is fairly common in both Vietnamese and Brazilian shrimp farms (and, I’d imagine, shrimp farms in general), and, again, spreads to affect wild populations.

Shellfish farming is actually quite impressive. There’s very little active farming required, and, since bivalves tend to be sedentary creatures, farmers don’t worry about their clams escaping to deep water or their mussels fomenting for freedom. Since bivalves are filter-feeders – water passes through their filters, leaving behind algae and other tasty microorganisms – they also require no direct food from the farmers. The filtering also serves as a water purification system. Raised in the same farm as pooping, food-wasting fish, bivalves work especially well, eating the leftovers, cleaning the water of fish waste, and getting big and delicious in the process. All in all, farmed shellfish – scallops, clams, oysters, mussels, and abalone are the big ones – are more sustainable than wild caught shellfish, and live quite similar lives, too.

The world is a massive system with millions of variables, each one interrelated to the next, working (or not) to make sure things flow smoothly. Obviously, we lowly hominids can’t recreate the near infinite complexity of the entirety of nature, but we can make decent attempts at small portions.  Asian rice farmers have been raising carp in their rice paddies for hundreds of years with great success. The carp eat the plankton, preventing the latter from outcompeting the rice for nutrients, comb the bottom soil, which releases more nutrients, and produce a steady source of fertilizer for the rice. There are plenty of other possible aquacultural-agricultural integration permutations  used across the world , like rice/shrimp, fish/grass, fish/duck, fish/pig, fish/chicken, but the fish you come across in the big supermarket probably didn’t have a pig, duck, or rice plant for a friend.

While integrated aquaculture, in many cases, is more cost-effective than either monoculture by itself, the  initial production costs and knowledge required is a large barrier for widespread adoption . That is, you can’t implement sustainable integrated agriculture-aquaculture systems on a large scale without knowhow, planning, and money. Recreating natural symbioses (even on a small scale) isn’t simple.

IMTA is very similar to integrated agriculture-aquaculture systems in that they create mini ecosystems, only IMTA is limited purely to aquatic species. So, instead of rice-fish farms, you’ve got fish-seaweed-bivalve ecosystems-within-a-farm. Very cool. Perhaps the coolest example of IMTA on a large scale is Veta la Palma , a Spanish farm built on a former cattle feedlot that actually improves upon nature. It produces tons of shrimp, bass, bream, and mullet each year. Each fish pond is lined with native plants that maintain nutrient balances in the water. Each fish forages for its own food in water that’s constantly replenished by the tides. Over 250 species of birds (up from 50 before the farm was built) attend to feed on the farmed fish, a practice encouraged by the farmers because it means “the whole system is working.” And, most importantly, they produce fantastic seafood.

They may not have big floppy ears that perk up, but fish can hear; they may not have big brains, but they can learn. Fish ranchers capitalize on both attributes by playing a specific sound every time the fish are fed. Eventually, the fish associate the sound with food and, after plenty of conditioning, will come to the sound every time they hear it. So, rather than keeping the fish in crowded cages, nets, or ponds and feeding them weird pellets, ranchers let their fish range freely in open water, feeding on regular fish fare. When it’s time to harvest, the sound will draw them back. Different species have different recall rates, though; in one ranching test using tilapia and carp in a large reservoir, only 13% of the original tilapia heeded the call, while over 2/3 of the carp came back . But with the original crew came hangers-on – other carp, tilapia, and a few other fish species from the reservoir – and the ranchers’ final haul was over twice as big as the original group of fish. Another type of ranching uses fish with a homing instinct, like the Nepalese mahseer (a type of carp). The mahseer hatches upriver and is fed for about a year, until it grows large enough to be released into the river. It spends a good two or three years in the wild eating (on mother nature’s dime!), growing, and working its way back to the original spawning grounds. The fully grown mahseer always returns to the place of birth, making harvesting a simple task.

Ranching definitely has its benefits. The fish get a more natural diet (although they start on pellets), which the ranchers don’t have to pay for and that doesn’t dose the surrounding environs with excessive nutrients; the fish aren’t crowded into unnatural habitats, lowering both the incidence of disease and parasites and the necessity of antibiotic administration; there are fewer packed crowds of pooping, scaly sewage production facilities to worry about.

As you can see, aquaculture has many faces, some homelier than others. It’s impossible to keep track of all the different types, because everybody does it differently and every species requires its own setup. They are simply too numerous and diverse. Tomorrow, however, I’ll dig through the muck and explain which aquaculture products are worth eating based on nutrition and environmental concerns, because, let’s face it – that’s what it really comes down to, right?

Thanks for reading. Share your thoughts in the comment board and Grok on!

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