Rainbow Trout Culture

Feed and fingerlings make up greater than 70% of the total cost of raising trout. Assuming a sales price of $1.10 per pound, and total cost of production of $0.76, the farm nets $21,452 per year on 60,480 pounds harvested.
-NC Dept. Agriculture and Consumer Services
Modified from notes by Dr. Doug Holland, Aquaculture, Brunswick Community College on Rainbow Trout Culture I

North Carolina is the second largest producer of rainbow trout in the United States, following Idaho in production.

Aquaculture is the fastest growing segment of U.S. agriculture. The farm valueof the U.S. aquaculture industry is estimated at nearly $1 billion. Trout food fish production accounts for about 10% of the total value, and catfish for about 50% of the value. Trout farming is the oldest form of commercial fish production in the U.S.; trout have been grown in culture systems for over 150 years. Rainbow trout is the predominant species raised. Trout are cultured in earthen or concrete raceways (rectangular tanks) supplied with flowing water. In 2000, an estimated 447 trout operations harvested and sold 59 million pounds of trout valued at $64 million. Idaho produces 58% of the total dollar production. North Carolina is the second largest producer, with about 7% of the production value. In 2000, U.S. trout farmers sold 70% of their harvest to processors, 18% through recreational fee fishing operations, 5% directly to restaurants and retailers, and the remainder to other outlets. Production in the U.S. trout industry has remained stable over the last decade. Three reasons for limited expansion are: lack of suitable sites for new facilities; increasing costs associated with fish waste management; and difficulty in competingwith the retail prices of imported trout orother seafood products.
(see http://www.ncagr.com/Aquacult/Trout01.pdf)

Trout Producers in North Carolina

There are about 89 farms in NC, and most of these are west of Asheville in southwestern North Carolina. The largest concentration is in Transylvania, Graham, Macon and adjacent counties.

The annual production of rainbow trout in NC varies, but lately has averaged around 7.1 million lbs, worth 1.10 per lb on average. It is obvious when looking at these figures that most of the farms in NC are small-scale family operations, each producing less than 100,000 lbs of trout each year. There are several large farms, however, and some of these are quite profitable.

Environmental Requirements
Rainbow trout is a coldwater species and requires water temps less than 68°F year-round for optimum growth. They may survive at somewhat higher temps, but with little or no growth and high stress levels.

Culture of rainbow trout in raceways requires large amounts of flow-through water. A farm with a holding capacity of 100,000 lbs of fish would require a minimum flow of 5000 gpm (gallons per minute) during the driest part of the year, assuming that it has oxygen-injection technology and a highly experienced manager. Few places have this much high-quality, cold water available year-round, even in the NC mountains. Most of the best sites in southwestern NC are already taken.

Tank and Pond Design

Major types of culture structures:
1. Ponds
2. Raceways
3. Tanks

Earthen ponds are still utilized on older farms, but are less than optimum for grow-out of food fish, though useful for fee-fishing operations. The irregular flow in current create "dead areas" which inhibit circulation of water. Difficulties in grading and sorting fish are created by slope in the side of ponds. Higher maintenance than raceways or tanks is required due to accumulation of organic matter and weed problems, etc., which are relatively economical to build, though to conserve on unit/volume, often constructed larger than they should be.

The larger the pond, the more difficult to manage. Using small, straight-sided earthen "raceways" has proven a better method and make for easier management than small round ponds. They can be lined with butyl liners to make management even easier.

"Unless your ground is a thick impervious clay, it is important to line your pond with a waterproof layer. There are several types of material on the market which you could try but most experts agree that the final choice is between relaxing beside a deluxe, butyl rubber lined pond or continuously repairing the holes in a pond lined with one of the cheaper alternatives. To protect the liner from stones you can use a layer of old carpet or sand under the butyl sheet.

If a layer of geotextile under the butyl helps protect it against stones, then another layer of geotextile, this time on top of the butyl, helps the soil to adhere to the sloping edges."
From Building a Pond - Butyl Liners

Raceways are the most widely established culture system for Rainbow Trout in both the United States and Europe. Comparing advantages with disadvantages, the disadvantages are generally outweighed.

The advantages are large densities of fish can be maintained, with few "dead" areas. Compared to ponds, differentiation in growth rate is reduced. Crowding fish for grading and harvest is much easier. A raceway can have a built in system for crowders and bar graders that are easily moved up and down the raceways, without physically removing them from the water or transferring them. Raceways may be partitioned, where several size classes of graded fish may be held simultaneously.

The disadvantages are a lack of utilization of the full water volume and abrasion. Fish tend to "school" together in 1/3 to 1/2 total volume of the raceway. Raceways are usually either poured concrete or concrete block construction. When fish are crowded to feed or grading/harvest, repeated contact with concrete walls may open them up to bacterial and fungal infections.

Round or semi-round tanks are being used by many newer farms. An advantage of round tanks is the self-cleaning aspect which takes place due to centripetal forces by the circulating water. Uneaten feed and fecal wastes are moved to the center of the tank as water moves around in circular motion. Once collected these materials are removed using a "double-drain" type system. This system reduces need for maintenance and labor costs.

Almost any tank can be used, though important it is durable, weatherproof and UV-resistant for outdoor use. It should be round or semi-round (above). This is also important in establishing a current against which the fish will swim, as is the habit of Rainbow Trout. It is important as well to obtain a tank that is already assembled or be easily assembled, and economical in cost. Tanks which are more convenient to set up and use may create an added expense, compared to cheaper tanks which will be durable though requiring more time and labor. The costs of labor and management must be compared with the cost of tanks.

Round tanks are preferred by many trout producers because the entire life cycle of the trout may be carried out in a variety of tank sizes, from broodstock to growout. There are some systems which now provide tanks that allow for fertilized eggs to be placed on top, and fry to pass through to an underlying container when hatched, which may then be removed, allowing fry to grow to fingerlings or even to market size. A major disadvantage of tank systems is the high cost, a higher initial investment is required compared to raceway systems, and comparatively, raceway systems are much more expensive to build and maintain than ponds.

Strains of Rainbow Trout
Once the culturing system has been constructed, the strain of trout must be determined.
Different strains have different characteristics that affect production and marketing:
1. DO tolerance
2. Temperature range/tolerance
3. Optimum culture densities
4. pH range/tolerance
5. Water hardness requirement
6. Growth rates under various temperature regimes.

Choosing a strain best suited to individual environmental conditions for each farm is important.

Optimum Production Level
Optimum production level for a particular system/farm may be determined by the equation:

OP = T + F + O + C


OP = optimum production level

T = ideal temperature for optimum feed conversion

F = correct amount and size of food

O = dissolved oxygen level needed to metabolize food

C = ideal flow rate for optimum exercise (swimming against the current).

Increase in temperature within the optimum range for trout production will result in increased metabolic rate, therefore feeding rate. Feeding rates should be adjusted with changes in temperature. These increases due to an increase in temperature are accompanied by an increased demand for oxygen. DO (dissolved oxygen) saturation level decreases with any increase in temperature. Due to these factors, supplemental sources of oxygen to keep DO at optimum levels, at or near saturation, are required. Aeration devices or oxygen injection may accomplish this. Oxygen injection, using pure bottled oxygen is expensive, but in many cases is economically feasible, even desirable.
Producers must be on guard not to become dependant on a pure oxygen injection system because it creates an artificially high level of production, which is unsustainable over long periods of time. Besides a risk of mechanical failure, it also creates stress to the fish due to crowding which may reduce feeding, growth rates and even potential risk of disease. An outbreak would spread rapidly and cause high mortality rate. Producers must compare risks with profit when dealing in such highly intensive production. While an oxygen injection system may look good theoretically, losing all your fish at once due to a system failure could put you out of business.

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