|Langston University Aquaculture|
CAGE CULTURE OF RAINBOW TROUT
by Marley Beem and Glen Gebhart
RAINBOW TROUT ARE cold water fish which can not survive when the water temperature rises above 70 degrees Fahrenheit for an extended period of time. Consequently, rainbow trout can only live in most Oklahoma waters from late October to early May. Rainbow trout can he grown in cages from a large fingerling size to a harvestable fish during this time period in many suitable Oklahoma farm ponds.
The reason for growing the trout in cages is to allow for the complete harvest of fish in the spring when the water temperature rises above their tolerance level. Most ponds and lakes can not be drained or completely seined to insure a total harvest of the trout. Rainbow trout survive and grow well in a caged fish culture system since they adapt well to crowded conditions and readily eat a processed feed.
A system of growing channel catfish in the summer and rainbow trout in the winter works well since the approximate growing season for channel catfish is May through October. Therefore, rainbow trout can be stocked into the cages in late October when the channel catfish are harvested and the trout can be harvested in late April when it is time to stock channel catfish back in the cages. This double cropping system increases the economic potential of caged fish culture by allowing double the use of the pond, cages, and other fish culture equipment.
Any pond over I acre in size and deeper than 8 feet will probably be suitable for winter production of rainbow trout unless it is very muddy or contains a large amount of organic matter such as cattle waste or aquatic vegetation which can decay and use up the dissolved oxygen in the water. Any pond that has had a fish kill in the past should probably not be used for trout culture.
Cages may be made or purchased from commercial sup- pliers. Cage construction is discussed extensively in the booklet, "Small-Scale Caged Fish Culture in Oklahoma Farm Ponds," available from Langston University. The free flow of water through the cage is vital to the health and growth of the fish. Occasionally algae ("moss") may build up on the cage and restrict water flow. If this occurs, a quick cleaning with a push broom should correct the situation.
The closest suppliers of rainbow trout for most places in the state are located in southwest Missouri, northeastern Arkansas, or southern Kansas. If a group of fish farmers is able to combine orders, it is usually more convenient and economical to have the fish delivered. Prices vary considerably between suppliers so it is wise to shop around for the overall best buy and delivery price. A partial list of rainbow trout suppliers is included at the end of this fact sheet.
FISH STOCKING SIZE
It is best to stock about seven inch fingerlings weighing about three ounces each in order to obtain nice harvestable size fish weighing from one-half to three-quarters of a pound at spring harvest time. These fish will cost from about 35 to 45 cents per fish including delivery. Smaller fish can be purchased at a cheaper rate if a smaller harvest sized trout is acceptable to you or your customers.
There are two limits on the number of fish that can be raised in a cage culture system. The upper cage limit for trout is generally considered to be a maximum of 15 fish per cubic foot which is 405 fish per cubic yard or 523 fish per cubic meter. The maximum safe pond limit is about 1,200 fish per acre. It is a good idea to stay conservative on your first venture into fish culture, especially if you are working with a small pond which is more likely to have dissolved oxygen problems. With experience you may be able to exceed the recommended number of fish per acre, especially in a larger pond over five acres or in a pond that has a constant flow of water through it.
STOCKING AND HARVEST DATES
Rainbow trout grow best in the water temperature range from 55 ' to 68 ' F, but can not survive prolonged periods of temperatures above 70' F. Consequently, it is best to stock the trout shortly after the water temperature drops below 70 F to take advantage of the warm fall temperatures when growth will be rapid.
It is best to monitor the water temperature regularly before this period in order to determine the pattern for water temperature in your pond. Small ponds warm and cool more rapidly than large ponds or lakes. Obviously, you do not want to stock the trout when the temperature is fluctuating around 70 F or when the possibility exists for the temperature to rise above 70 F for a prolonged period.
Harvest should then take place before the temperature rises above 70 F in the spring. The approximate stocking date for Oklahoma is usually around late October with the approximate harvest date around late April.
HANDLING AND HAULING
Rainbow trout require more care in handling than do channel catfish. They should be kept in water as much as possible when transfering them from the hauling tank to the cage. Hauling trout over any distance will require some sort of aeration device in the tank. Your supplier should be able to assist you in choosing the best method of transporting your fish.
Specially made fish feeds are available for trout from many feed stores. Rainbow trout demand a higher quality feed than channel catfish. A minimum of 36 percent protein is required for rainbow trout. Trout feed is more expensive than other types of feed, but it is highly recommended for best results. Floating feed is essential in a cage culture system in order to minimize waste. Feed should be stored in a dry, cool place and held for less than three months.
The feeding rate will vary depending upon the size of the trout and the water temperature. The feeding rate can be set on the basis of a percentage of the total body weight of fish being fed and adjusted for the size of fish and the water temperature (Table 1). To feed by this method it is necessary to know the approximate average weight and total number of fish in a cage. The average weight can be obtained by weighing a small sample of fish from the cage. A cut off milk jug makes a good holding basket for weighing trout which are too active to lay still on a scale. The average weight can be estimated from the total length of the fish (Table 1). The total weight is then obtained by multiplying the average weight by the number of fish in the cage.
For example, if you have 350 trout weighing four ounces each in a cage then the total body weight would be 1,400 ounces or 87.5 pounds. If the water temperature was 50 F then you would multiply 1,400 by 0.015 to get 21 ounces as the suggested feeding rate per day.
A simpler way to set the feeding rate is to feed all that the fish will eat in a set time period. The optimum time period appears to be about 10 minutes at the warmer temperatures increasing to about 30 minutes feeding time at the colder temperatures. It is convenient to keep a cup, jar, or small can in your feed sack which will let you feed exact amounts.
The feeding rate also depends somewhat upon your individual goals for the trout culture program. If you want the biggest fish you can grow regardless of cost, then you should feed at the maximum recommended rate on a daily basis. If you want the most economical growth rate in terms of food conversion efficiency, then you should feed at a slightly lower rate. One feed company recommends feeding at a rate about 0.4 percent less than the values listed in Table 1. Never feed more than the fish will consume since this is both a waste of money and the uneaten food will decay and use up dissolved oxygen in the pond. The feeding rate should be adjusted about once a week.
Rainbow trout feeding guide. (Click thumbnail to enlarge)
Rainbow trout will learn to operate a demand feeder where they bump a trigger device to release a small quantity of feed. We obtained adequate growth of rainbow trout in a cage with a demand feeder mounted on top of the cage. There are also battery operated automatic feeders available from commercial suppliers.
DISEASE AND WATER QUALITY
An in-depth discussion of diseases and cures is complex and beyond the scope of this fact sheet. Disease is usually not a problem unless the fish are stressed by poor water quality,
overcrowded, underfed, or fed a low quality feed. Always stock disease-free fish that are in good condition. Never allow the cage to rest on the bottom where waste buildup leads to poor water quality.
The biggest danger in winter production of fish is called "winter-kill" and occurs when ice freezes solid on the surface of the pond and then a large snow fall accumulates on top of the ice. The ice layer stops the transfer of oxygen from the air to the water by wind mixing and the snow cover stops the penetration of sunlight. Sunlight produces oxygen through a process called photosynthesis where plants and microscopic algae (phytoplankton) in the water give off oxygen. At night or during times of low sunlight the plants reverse the process and use by oxygen. Consequently, if there is a lot of organic matter such as cattle waste in the pond decaying and using up oxygen at the same time as a heavy snow cover, then the pond can run low on oxygen and the fish will die.
Any pond that has a history of winter-kill should not be used for trout culture. The dissolved oxygen level in the pond should remain above 5 mg/l for trout culture.
HARVESTING AND MARKETING
Trout are easily harvested from the cage with a long handled dip net. It is usually necessary to pull the cage up on shore for complete harvest. Rainbow trout are generally harvested from one-half pound on up to whatever size is desired.
The small-scale fish culturist can make a modest return on his investment by selling the fish direct to the public (Table 2). Fresh fish generally command a higher price than frozen fish found in supermarkets. An aquatic culture license from the Oklahoma Department of Wildlife Conservation is required to grow fish for sale. An inspection by the local health authorities is required in order to sell dressed fish to the public.
Table 2. Enterprise Budget
Production Expenses $ 140.00
Rainbow Trout Fingerlings
400 a $0.35/fish
Transport of Fingerlings
200 miles @ $0.20/mile 40.00
Fish Feed 325 lbs. @ $0.35/lb.* 113.75
Cage (home-built) $40.00 amortized
over 5 years 8.00
Misc. equip., license, cage maintenance 10.00
Interest Foregone 10% simple interest per annum 15.59
for a 6 month period
Total Cost'* $ 327.34
Cost per lb. of Fish $ 1.31
Net Return if sold a $2.00/lb. live weight $ 172.66
* assumed feed conversion of 2.0 and final average wt. of 0.625 lb.
** cost of labor not included
RAINBOW TROUT SUPPLIERS
Crystal Lake Fisheries, Rt. 2, Box 272, Ava, MO 65608. (417) . 683-2301.
Crystal Springs Trout Farm, Rt. 3, Cassville, MO 65625. (417) 847-2174
Hartley Fish Farm, Box 1, Kingman KS 67068. (316) 532-3093
Mountain Spring Trout Farm, Rt. 1, Box 248, Highland- ville, MO 65669. (417) 587-3400
Osage Spring Farms, Inc., Rt. 8, Box 591, Rogers, AR 72756. (501) 636-2301
Spring River Trout Farm, Box 145, Verona, MO 65769. (417) 498-6622
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