Recirculation Aquaculture Systems (RAS)

Recirculation Aquaculture Systems (RAS)
RAS represent a new and unique way to farm fish. Instead of the traditional method of growing fish outdoors in open ponds and raceways, this system rears fish at high densities, in indoor tanks with a "controlled" environment. Recirculating systems filter and clean the water for recycling back through fish culture tanks.

New water is added to the tanks only to make up for splash out and evaporation and for that used to flush out waste materials. In contrast, many raceway systems used to grow trout are termed "open" or "flow through" systems because all the water makes only one pass through the tank and then is discarded.

Fish grown in RAS must be supplied with all the conditions necessary to remain healthy and grow. They need a continuous supply of clean water at a temperature and dissolved oxygen content that is optimum for growth. A filtering (biofilter) system is necessary to purify the water and remove or detoxify harmful waste products and uneaten feed. The fish must be fed a nutritionally-complete feed on a daily basis to encourage fast growth and high survival.

BENEFITS OF RAS
RAS offer fish producers a variety of important advantages over open pond culture. These include a method to maximize production on a limited supply of water and land, nearly complete environmental control to maximize fish growth year-round, the flexibility to locate production facilities near large markets, complete and convenient harvesting, and quick and effective disease control.
+Intensive Production
+Water and Land Conserved
+Location Flexibility
+Species and Harvest Flexibility :RAS afford growers the opportunity to manipulate production to meet demand throughout the year and to harvest at the most profitable times during the year.

DISADVANTAGES OF RAS
+ They are relatively expensive systems to develop (building, tanks, plumbing, biofilters) and to operate (pumping, aerating, heating, lighting).
+ Moreover, they are complex systems and require skilled technical assistance to manage successfully.
+ Constant supervision and skilled technical support are required to manage and maintain the relatively complex circulation, aeration, and biofilter systems, and to conduct water quality analysis.
+ The danger of mechanical or electrical power failure and resulting fish loss is always a major concern when rearing fish in high densities in small water volumes.

THE RAS DESIGN
(1) growing tank,
(2) sump of particulate removal device,
(3) biofilter,
(4) oxygen injection with U-tube aeration,
(5) water circulation pump.

Depending on the water temperature and fish species selected, a water heating system may be necessary.

Ozone and ultraviolet sterilization also may be advantageous to reduce organic and bacteria loads.

WATER SUPPLY
A good supply of water, adequate in both quantity and quality, is essential to a successful fish farming enterprise, RAS or otherwise. Ground water obtained from deep wells or springs is the best source of water for fish culture. It generally is free of pollutants and has relatively high hardness levels, which are beneficial under some circumstances.

Municipal water supplies also can be used after chlorine, floride, and other chemicals are removed. Other sources of water, particularly surface waters from streams, rivers, ponds, and lakes, are not recommended for fish culture. Surface waters may contain fish diseases, parasites, pesticides, and other pollutants that can kill or slow the growth of fish. Testing the quantity and quality of the available water supply is one of the first steps for a prospective fish farmer to take to insure an adequate supply of high quality water.

BIOFILTER MEDIA
The ideal biofilter media has
(1) high surface area for dense bacterial growth,
(2) sufficient pore spaces for water movement,
(3) clog resistance,
(4) easy cleaning and maintenance characteristics.

We use and recommend plastic because it's lightweight, flexible, and easy to clean, but it can be expensive.

Most fish production recirculation systems are designed to provide at least one complete turnover per hour (24 cycles per day). Increasing the number of turnovers per day would provide increased biofiltration, greater nitrification (bacterial contact), and reduced ammonia levels.

FEEDS AND FEEDING
A complete feed, containing all the essential minerals and vitamins for healthy fish growth, and formulated specifically for the fish species being reared, is necessary for fish production in RAS. Do not substitute other animal feed for fish feed. Even different fish species have different nutritional requirements, particularly the quality and quantity of
protein needed, that must be met to optimize growth.

We recommend feeding a commercial feed of dry, floating pellets so that the feeding activity and health of the fish can be easily observed at the water surface. The size of the pellet should correspond with the size of the fish. Feed the largest pellet that the fish will readily swallow in order to maximize consumption and minimize waste. To keep feed fresh, order only a limited supply and store it in a cool, dry area, free of insects and rodents. In case of a liability problem with contaminated feed, it's a good idea to freeze small samples of each new batch of feed purchased for subsequent analysis if necessary.

If fish suddenly stop feeding, immediately check for high ammonia levels, low oxygen concentrations, diseases, or other problems. Reduced feeding rates occur at very high and low water temperatures. To maximize growth, feed on a regular schedule at the same time each day. More frequent feedings several times per day) have resulted in better growth rates and feed conversion efficiencies than a single daily feeding.

MARKET OPPORTUNITIES
A wide variety of freshwater fish can be farmed in RAS for a diverse number of purposes. Many species are commonly grown as food fish for marketing as live or processed products to wholesalers or retailers and directly to supermarkets and restaurants.