Clicking on the translation link activates a free translation service to convert the page to Spanish. As with any Internet translation, the conversion is not context-sensitive and may not translate the text to its original meaning. NC State Extension does not guarantee the accuracy of the translated text. Feeding trout is essential in recreational ponds which cannot naturally support large numbers of trout.
Without adequate feed, the health of the trout will decline. On the other hand, too much feed will add nutrients to the pond and could cause aquatic weed problems. Aquatic weeds like filamentous algae, pond weed, and other submersed underwater plants thrive when water temperatures are warm and nutrients are available. Most, if not all aquatic weeds are undesirable if the pond is being managed for fishing.
Floating feed is best for recreational ponds. This gives you an opportunity to observe the fish and their feeding behavior while they are eating. If their behavior is different than normal e. The problem would need to be corrected to avoid a fish kill. The recommended method for accurately feeding trout in ponds relies on using a feed chart such as the one below. The trout are fed a daily ration based on fish size and the water temperature.
These increases in demand for aquaculture products, food security considerations, and job creation have generated an increased need for skilled workers. Discover how you can be part of this rapidly expanding industry. Many countries were reporting rainbow trout farming production. Some of them have relatively insignificant output in comparison to the production from the larger systems that are located in the primary producing areas in Europe, North America, Chile, Japan and Australia.
The rainbow trout is a hardy fish that is easy to spawn, fast growing, tolerant of a wide range of environments and handling, and the large fry can be easily weaned on to an artificial diet usually feeding on zooplankton.
Capable of occupying many different habitats, ranging from an anadromous life history strain known as steelhead, living in the ocean but spawning in gravel-bottomed, fast-flowing, well-oxygenated rivers and streams to permanently inhabiting lakes.
The anadromous strain is known for its rapid growth, achieving kg within 3 years, whereas the freshwater strain can only attain 4. As a result, temperature and food availability influence growth and maturation, causing age at maturity to vary; though it is usually years.
Eggs are relatively large in diameter mm. Most fish only spawn once, in spring January-May , although selective breeding and photoperiod adjustment has developed hatchery strains that can mature earlier and spawn all year round.
Superior characteristic selection is also achieved by cross breeding, increasing growth rates, resistance to disease, and profligacy, and improving meat quality and taste. Trout will not spawn naturally in culture systems; thus juveniles must be obtained either by artificial spawning in a hatchery or by collecting eggs from wild stocks. Larvae are well developed at hatching. In the wild, adult trout feed on aquatic and terrestrial insects, molluscs, crustaceans, fish eggs, minnows and other small fishes, but the most important food is freshwater shrimp, containing the carotenoid pigments responsible for the orange-pink colour in the flesh.
In aquaculture, the inclusion of the synthetic pigments astaxanthin and canthaxanthin in aquafeeds causes this pink colouration to be produced where desired.
Monoculture is the most common practice in rainbow trout culture, and intensive systems are considered necessary in most situations to make the operation economically attractive. Ground water can be used where pumping is not required but aeration may be necessary in some cases. Supersaturated well water with dissolved nitrogen can cause gas bubbles to form in the blood of fish, preventing circulation, a condition known as gas-bubble disease. Alternatively, river water can be used but temperature and flow fluctuations alter production capacity.
Where these criteria are met, trout are generally on-grown in raceways or ponds supplied with flowing water, but some are produced in cages and recirculating systems. Trout will not spawn naturally in aquaculture systems, hence eggs are artificially spawned from high quality brood fish when fully mature ripe ; although two-year-old trout start spawning, females are seldom used for propagation before they are three or four years old.
The number of broodstock required is dependent on the number of fry or fingerlings required to meet the production schedule of the farm. The number can be back-calculated based on survival rates at the different life stages and the fecundity of the broodstock females.
Generally, one male to three females is deemed a satisfactory sex ratio for broodstock. Males and females are generally kept separate.
Broodstock are selected for fast growth and early maturation usually after 2 years. One frequently used management tool is the use of sex-reversed, all-female broodstock to produce all-female progeny that grow faster. Functional males are produced by oral administration of the male hormone methyl testosterone through starter feeds at the fry stage. The reproduction of rainbow trout is well understood and the techniques are well-developed. The dry method of fertilisation without admixture of water is the most common approach.
Eggs are removed manually from females under anaesthetics by applying pressure from the pelvic fins to the vent area or by air spawning, causing the fish less stress and producing cleaner, healthier eggs. Insertion of a hypodermic needle about 10 mm into the body cavity near the pelvic fins and air pressure 2 psi expels the eggs. The air is removed from the body cavity by massaging the sides of the fish. Males are stripped in the same way as females, collecting milt in a bowl, avoiding water and urine contamination.
Milt from more than one male ensures good fertilisation is mixed with the eggs. It is recommended that milt from three or four males is mixed prior to fertilisation to reduce inbreeding. Water is added to activate the sperm and cause the eggs to increase in size by about 20 percent by filling the perivitelline space between the shell and yoke; a process known as "water-hardening".
Fertilised eggs can be transported after 20 minutes, and up to 48 hours after fertilisation, but then not until the eyed stage eyes are visible through the shell. Direct exposure to light should be avoided during all development stages, as it will kill embryos. A technique that has been developed to improve production output is the use of monosex culture of females, or triploids.
Triploidy is induced by exposing the eggs to pressure or heat whilst monosex are produced by fertilising normal female eggs XX chromosomes with milt from sex-reversed, masculinised females XXX chromosomes. The mature testes of sex-reversed fish are large and rounded but have no vent. The testes are removed from the abdomen and lacerated to drain the milt into containers. An equal volume of extension fluid is added to make the sperm motile, and ready for fertilising normal ova.
One advantage of this technique is that only the broodstock is sex-reversed, and they can be grown separately, while the marketed fish are not exposed to hormonal treatment. Eggs are incubated undisturbed until the eyed stage is reached, in hatching troughs, vertical flow incubators or hatching jars. Hatching and rearing troughs are cm wide, 20 cm deep, and up to about 4 m in length. As the eggs hatch weeks the fry drop through the mesh to a bottom trough.
The alternative is vertical flow incubators Heath incubators that stack up to 16 trays on top of each other. Sac fry can remain in trays until swim-up at about 10 to 14 days after hatching. Time taken for hatching varies depending on water temperature, taking days at 3. Hatching jars, available commercially or constructed from a 40 L drum and PVC pipe, introduce water from the bottom and flow from the top. In all the above methods dead eggs are removed regularly to limit fungal infection.
Fungal infections can be controlled using formalin 37 percent solution of formaldehyde in the inflow water at dilution for 15 minutes daily, but not within 24 hours of hatching. Upon reaching the eyed stage addling dropping eggs 40 cm removes weak and undeveloped eggs. Trout hatch typically 95 percent with a reserve of food in a yolk sac which lasts for weeks , hence are referred to as yolk-sac fry, or alevins.
Hatching of the batch of eggs usually takes days, during which time all eggshells are regularly removed, as well as dead and deformed fry. Eggs incubated separately from rearing troughs are transferred to rearing troughs after hatching. After hatching, the trays are removed and trough water depth is kept shallow cm with a reduced flow until fry reach "swim-up" stage, the yolk sac is absorbed, and active food searching begins.
Fry are traditionally reared in fibreglass or concrete tanks, preferably circular in shape, to maintain a regular current and uniform distribution of the fry, but square tanks are also found. Tanks are usually 2 m in diameter or 2 x 2 m square, with depths of cm. Water is delivered to the side of the tank using an elbow pipe or a spray bar to create a circulation of water.
The drain is in the centre of the tank and is protected by a mesh screen. 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.
At this temperature and below, appetites are suppressed, digestive systems operate very slowly, and trout require only a maintenance diet 0. Feeding more than this wastes feed.
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. 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. 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.
0コメント