Rainbow Trout Culture II

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Rainbow Trout Culture II
Notes modified from Dr. Doug Holland, Aquaculture, Brunswick Community College.

Feeds and Feeding
Many companies manufacture high quality trout feeds. Feeds in all particle sizes are available, beginning with crumbles #00, 0, 1, 2, 3, 4 which are best suited for fry and small fingerlings. Advanced fingerlings, larger fish and broodstock should be fed floating or sinking pellets 1/16", 1/8", 3/16", etc.

Homemade diets should be avoided, especially unsterilized trash fish. The risk of disease combined with a diet that is usually nutritionally unbalanced, may result in a variety of nutritional disorders.

Feed utilization by the fish is of utmost importance.
Feed should be distributed in a manner that all fish get something to eat. To do so reduces variations in growth rate genetically inherent in fish. Such genetic predisposition are made worse by uneven distribution of feed and aggressive feeding instinct among individual fish.

Feeding can be made less efficient and/or wasted because:
1. Low temperatures
2. Excessive flow-through rates
3. Excessive water turbidity (trout feed by sight)

Automatic feeders may reduce labor costs, but also may result in poor feed conversion and/or uneven feed distribution, which contributes to higher feed cost. The cost of feed is generally higher than labor costs, therefore automatic feeders may represent a "false economy".

The best way to keep track of feed conversion is to keep accurate records of daily consumption rates and frequent sampling of fish for average size and weight. Fish sampling should be done preferably every two weeks but at least once per month.

Grow-Out Techniques
"The least-cost producer wins"
To develop a production strategy with any culture, available markets should be investigated first, then "working backwards" to determine a workable production strategy. By knowing the particular requirements of any market, the producer can develop methods to produce at the lowest unit cost.

Most consumers want an even supply of food-size fish throughout the year. Fluctuations in demand occur during certain times throughout the year:
- Thanksgiving and Christmas. Less people eat fish and seafood during the Holiday season.
- During Lent many people give up meat for religious reasons. Lent begins on Ash Wednesday the day following "Mardi Gras" and ends at Easter. The demand for fish and seafood increase during this time of year.

Fertilized eggs/embryos of trout, called "eyed trout eggs" are available from various parts of the world during most of the year.

For grow-out to market size fish, differential growth rates in fingerlings make stocking almost any size during most of the year possible. Differential growth rates during grow-out to market size further contributes to overall size variability, making market-size fish available throughout the year.

Growth rates of fish may be controlled by any combination of:
1. Genes. Natural variability exists between different strains and individuals within strains.
2. Feeding rates
3. Temperature which is not under the control of the farmer, but may be anticipated and utilized in overall production strategy.
4. Current/flow rate - swimming against rapid currents requires more energy which reduces growth rate at a constant feeding rate.
5. Grading. While it is best to have every fish growing at an optimum rate, naturally the rate will differ from individual to individual and from strain to strain. This can be used to ensure that market size fish are available at any and all times of the year.

Grading the fish
Grading should be done on a regular basis, but if done too frequently it risks increased stress and reduction in production levels.
A variety of grading methods are available. Producers should choose carefully to ensure the greatest grading efficiency with the least stress on the fish as possible.

Effluent Management
Types and amounts of allowable effluents from trout farms are governed by state and federal regulations. The most important of these is the NPDES permit, National Pollutant Discharge Elimination System. An NPDES permit is required of trout farms that produce more than 30,000 lbs annually.

Trout streams and other coldwater receiving waters are likely to be more profoundly affected by effluents than warmer waters, due to the low natural nutrient levels of most coldwater streams.

Suspended solids are the most serious effluent problem:
1. Contribute to Biochemical Oxygen Demand (BOD).
2. Can completely cover the bottom of receiving streams.

Settleable Solids = Suspended solids that settle out of standing water in one hour.

0.3 lb. of settleable solids are produced for every lb of feed offered to the fish in trout raceways.

Settleable solids are typically removed from effluents through the use of sedimentation basins.

Total pollutants in trout farm effluents come from many sources, but most originate from feed offered to the fish.

Levels of effluent pollutants due to feed can be calculated using the equation:

Average ppm pollutant = Pollutant Factor x Lbs Feed
Water Flow (gpm)

Pollutant factors for this equation:

Total ammonia 2.67
Nitrate 7.25
Phosphate 0.417
Settleable solids 25.0
BOD 28.3

Example
250 lbs of feed are offered each day in a hatchery with 1,000 gpm of water flow. What is the concentration in ppm of settleable solids in the effluent?

25.0 x 250
------------- = 6.25 ppm
1,000


An example of a sedimentation basin design from arizona.edu on Filtration and Biofiltration
Sedimentation basin design: Wide inlet (to reduce velocity), a surface area of .7 to 1.4 sq. ft. of basin per gpm flow (for feces with a specific gravity of 1.01 or greater), wide outlet weir (never a stand pipe), no baffles (which increase velocities) and a simple waste drain. A depth of just a few inches is enough for most designs.
Source: University of Arizona
Sedimentation Basins
These are usually tanks, ponds, lagoons, etc. which serve the purpose of slowing velocity of the water, and allow suspended solids to settle to the bottom.

Four factors taken into account for design of sedimentation basins:
1. Retention time
2. Density of waste solids
3. Water velocity and flow distribution
4. Water depth

Retention time = average period that a unit of water remains in the basin.

Retention time ranges from 15 minutes to 2 hours. For a given rate of flow, retention time increases with area and depth of the basin.

If not carefully engineered, a sedimentation basin will have an area of rapid flow down the middle, with backwater "dead zones" where water stagnates and is replaced very slowly. A system of baffles should be incorporated into the design to ensure even flow through the basin.

The basin should be about 1.5 feet deep. A shallower basin promotes scouring of the bottom, keeping solids suspended throughout the basin. There may not be enough time for solids to settle out completely in a deeper basin.

There are several types of sedimentation basins:

1. Linear clarifier - a modified concrete raceway.

Water should enter the raceway through a series of screens to distribute flow and reduce turbulence.

2. Lagoons - usually a shallow earthen pond.

The larger the pond, the more effluent it can accommodate.

3. Commercial Settling Systems

There are many types and designs of these systems available. They all generally incorporate baffles and settling tubes. This type requires less space and retention time than linear clarifiers or lagoons. They are expensive, and usually impractical in commercial aquaculture.

Solid Waste Disposal
Over half of all nutrients released by trout farms are in the form of settleable solids. The sludge from sedimentation basins is a high quality organic fertilizer. It may be composted and made available to organic farmers, gardeners, etc. It may be possible to market such material to help offset costs of waste management.

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Rainbow Trout Culture

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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)

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

Where:

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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