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Fish farming

Fish farming is the principal form of aquaculture. It involves raising fish commercially in tanks or enclosures, usually for food, though often to seed sport-fishing areas. A related area is mariculture.

Table of contents
1 Recycling Systems
2 Irrigation ditch or pond systems
3 Cage systems
4 Classic Fry Farming
5 Links

Recycling Systems

One of the largest problems with aquaculture is that it can use a million gallons of water per acre per year. Recycling solves that problem.

The largest-scale pure fish farms use a system derived (admittedly much refined) from the New Alchemists in the 1970s. Basically, large plastic fish tanks are placed in a greenhouse. A hydroponic bed is placed near, above or between them.

Tilapia are raised in the tanks. Tilapia are able to eat algae, which naturally grows in the tanks when the tanks are properly fertilized.

The tank water is slowly circulated to the hydroponic beds where the Tilapia waste feeds a commercial crop such as parseley. Carefully cultured microorganizms in the hydroponic bed convert ammonia to nitrates, and the pants are fertilized by the nitrates and phosphates. Other wastes are strained out by the hydroponic media, which doubles as an aerated pebble-bed filter.

This system, properly tuned, produces more edible protein per acre than any other known.

A wide variety of plants can grow well in the hydroponic beds. Most growers concentrate on herbs, which command premium prices in small quantities all year long. The most common customers are restaurant wholsalers.

Since the system lives in a greenhouse, it adapts to almost all temperate climates, and may also adapt to tropical climates.

The main environmental impact is discharge of water that must be salted to maintain the fishes' electrolyte balance. Current growers use a variety of proprietary tricks to keep fish healthy, reducing their expenses for salt and waste water discharge permits. Some veterinary authorities speculate that ultraviolet ozone disinfectant systems (widely used for ornamental fish) may play a prominent part in keeping the Tilapia healthy with recirculated water.

A number of large, well-capitlized ventures in this area have failed. Managing both the biology and markets is complicated.

A classic book is: "Freshwater Aquaculture: A Handbook for Small Scale Fish Culture in North America" by William McLarney

Irrigation ditch or pond systems

These use irrigation ditches or farm ponds to raise fish. The basic requirement is to have a ditch or pond that retains water, possibly with an above-ground irrigation system (many irrigation systems use buried pipes with headers).

This is a low-investment way to produce fish from an existing structure. Often the fish sell for premium prices since they are fresh, and produced inland. If the ponds raise sport species, they can be advertised as "fishing ponds," and access can be sold directly to fishermen.

The basic scheme is to store one's water allotment in ponds or ditches, usually lined with bentonite clay. In small systems the fish are often fed commercial fish food, and their waste products can help fertilize the fields. In larger ponds, the pond grows water plants and algae as fish food.

Some of the most successful ponds grow introduced strains of plants, as well as introduced strains of fish.

Control of water quality is crucial. Fertilizing, clarifying and pH control of the water can increase yields substantially, as long as eutrophication is prevented and oxygen levels stay high. Salting the water is not recommended because it can salinize the fields. Yields can be low if the fish grow ill from electrolyte stress.

Cage systems

These use synthetic fiber cages in existing water resources. The advantage is that many types of water can be used (rivers, lakes, filled quarries, etc.), many type of fish can be raised, and the fish farming can coexist with sport fishing and other forms of use.

However, fish are vulnerable to disease, poaching, and low levels of dissolved oxygen.

In general, pond systems are easier to manage, and simpler to start.

Classic Fry Farming

Trout and other sport fish are often raised from eggs to fry or fingerlings and then trucked to streams and released.

Normally, the fry are raised in long, shallow concrete tanks, fed with fresh stream water. The fry receive commercial pelletized fish food.

While not as efficient as the New Alchemists' method, it is also far simpler, and has been used for many years to stock streams with sport fish.


One of the best sites is