Raising Rainbow Trout  For Beginners
                     Raising Rainbow Trout
In trout farming, the amount and suitability of feed used determines the profitability of production. 
Trout and other salmonids can efficiently digest foods that contain primarily protein (mostly from 
fish), and can obtain some of their energy from fats and, to a lesser extent, from carbohydrates.
Fry and fingerling trout require a higher protein and energy content in their diets than larger fish. 
Fry and fingerling feed should contain approximately 50 percent protein and 15 to 20 percent fat. 
Feeds for larger fish typically contain 38 to 45 percent protein and 10 to 18 percent fat. The switch 
to lower protein formulations usually occurs at the transition from a crumble feed to a pelleted 
ration, called a growout or production diet. High energy diets may contain 45 to 50 percent protein 
and 18 to 24 percent fat.
Several brands of high quality commercial trout diets are available, and although a farm could 
produce its own fish food, it is not usually economical to do so.
Feed quality
Trout feeds have been greatly improved in the past decade. Fish meal is still the primary source of 
protein, but protein digestibility has been improved and ash content has been reduced by using fish 
meal processed at lower temperatures (low-temp fish meal). Also, diets now have higher energy 
levels that help fish use protein more efficiently.
Increasing the energy level in the diet limits the fishs use of protein as an energy source. Trout are 
being grown efficiently with dietary fat levels (mostly from fish oils) as high as 18 to 28 percent, 
provided the ratio of digestible protein to energy remains in the correct range. This ratio is 
expressed as grams digestible protein per megajoule of digestible energy.
Ask your feed manufacturer to tell you the ratio of protein to energy in your fish feed, especially if 
you plan to use high energy diets. For typical high energy diets the ratio should be about 20:1. 
Feeds with ratios significantly higher than 20 may contain excess protein or large amounts of 
protein that trout can not digest easily. Feeds with lower ratios may contain excess fat, and could 
affect flesh quality and dress-out percentages. However, specific diet formulations may vary 
considerably from this ratio and still be highly efficient if properly formulated.
Feeding practices
Trout producers usually try to grow the fish as quickly and efficiently as possible while maintaining 
uniformity of growth and degrading water quality as little as possible. To accomplish these goals it 
is important to feed the correct amount. The amount of feed trout require depends on water 
temperature and fish size. 
Smaller fish have faster metabolic rates and need more feed relative to their body weight than do 
larger fish. Because fish are poikilothermic (cold-blooded), their body temperatures and metabolic 
rates vary with water temperature. Fish in warmer water need more feed than fish in cooler water.
The minimum temperature for growth in trout is about 38°F. At this temperature and below, 
appetites are suppressed, digestive systems operate very slowly, and trout require only a 
maintenance diet (0.5 to 1.8 percent of body weight per day, depending upon fish size). Feeding 
more than this wastes feed. In warm water (above 68°F), a trouts digestive system does not use 
nutrients well and more of the consumed feed is only partially digested before being eliminated.
This nutrient loading of the water, coupled with the generally lower oxygen levels in warm water, 
can easily lead to respiratory distress. 
In warm water, feeding rates should be reduced enough to maintain good water quality and avoid 
wasting feed. The optimum temperatures for growing trout are 55 F to 65o F. At this temperature 
range feeding rates should be at maximum levels (1.5 to 6.0+ percent of body weight per day).
The best way to determine the correct amount and size of feed for trout production is to use a 
published feeding chart, usually provided by the feed manufacturer. 
These charts are useful guides, but you may need to make adjustments to fit specific conditions on 
your farm. Under most circumstances, fish need to be fed less than they will eat. Overfeeding will 
cause the fish to use the feed less efficiently and will not increase growth rates significantly.
To determine the appropriate amount of feed, know the number and size of the fish on your farm. At 
water temperatures above 55o F, make a sample count of the fish at least monthly and adjust 
feeding percentages accordingly. 
In cooler waters, a sample count every 1 to 2 months usually is adequate. Good growth records for 
trout on your farm will help you predict seasonal growth rates. Do not overfeed. Once feed settles to 
the bottom of the tank, small trout will ignore it. Excess feed reduces water quality and promotes 
disease. Remove any excess feed promptly.
How to feed trout
Once a high quality feed has been selected and the correct amount of feed determined, the next 
consideration is how to feed the fish. The best method depends on the size of the fish. Trout will 
begin to consume prepared diets within 7 to 10 days after hatching. At first, fry should be fed a 
small amount by hand eight to ten times per day until all the fish are actively feeding.
A large kitchen strainer makes an excellent tool for distributing the finely ground starter feeds used 
for trout. After the initial feed training, an automatic feeder is most practical, with two or three hand 
feedings daily so that you can observe the fish. As the fry grow, the frequency of feeding can be 
gradually decreased to about five times per day. 
When fed nearly to satiation, trout will consume roughly 1 to 2 percent of their body weight in dry 
feed at each feeding. The feeding frequency should be adjusted to obtain the desired feeding 
percentage. Fry gain weight rapidly and should be sample counted weekly for the first 4 to 6 weeks. 
The daily feed ration should be adjusted according to their weight. Feed should be distributed over 
at least twothirds of the water surface when fry are less than 2 inches long.
This gives them easy access to the feed and helps to keep a uniform size within the population. 
After fingerlings are moved out to tanks or earthen ponds, there are several feeding alternatives. 
Hand feeding each day until the fishes appetites are suppressed usually produces the best 
combination of feed conversion efficiency and growth rate. However, hand feeding is labor 
intensive and may not be practical on a large commercial farm. Hand feeding is the best way to 
train fish to use demand feeders or to administer medicated feed to sick fish.
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