I was speaking to a guy once and he reckoned that a fingerling would take about 3 years to reach 25cm. I never thought it would take that long, but maybe he is right as they do live in cold water and I suppose that they would be slow growing. I also understand that a trout living in a lake or damn will grow much faster that one living in a creek or stream.
I'd be interested to know in both situations how long it takes for them to grow. In Victoria after the drought some of the trout were over a kilo. As the others said depends on the environment and fish numbers lots of fish little food equals slow growth rates less fish lots of food quicker growth rate on average asides fuss with ideal conditions could be between 15 and 20cm in its first year. Cheers for the replys. The main thing that got me wondering was hearing about some planned releases in damns and then wondering how long it would take them to reach legal size.
I've read about a fourteen year old brownie in a hatchery,having said that seven years would be an good age for a wild fish. For rainbows three years is a mature fish and they might be lucky enougth to live another year or two, I 'd expect a 5kg rainbow to be five years old.
The general consensus from American sites is around 6 years for Rainbows, although you'd expect the odd fish to go on to reach This explains why the general size of Rainbows in comparison to Browns is smaller as they simply don't live long enough. It also explains why stocking levels need to be higher along with a certain lack of natural recruitment.
At the end of the day having done a lot of trout fishing in nz and fishing with some gun fishers and talking to doc hatchery guys a 45cn fish I a high growth rate protein rich source such as Taupo is about 3lb and 2 - 3 years old saying that I've seen a 18lb bow in a river they do get big!
Browns in the other hand can get in excess of 40lb and 12 yrs old in paces like Patagonia. You need to be a member in order to leave a comment. Sign up for a new account in our community. Trout fisheries are maintained, or culture practised, in the upland catchments of many tropical and sub-tropical countries of Asia, East Africa and South America. As a result, several local domesticated strains have developed eg Shasta and Kamloops , while others have arisen through mass selection and cross-breeding for improved cultural qualities.
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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. Breeding season is generally winter and early spring, but spawning is known to occur in some Victorian streams as early as May and as late as October.
Females produce about 1, eggs per kg of body weight. Eggs are laid in gravel substrate in flowing water having relatively high dissolved oxygen levels. Hatching occurs in 3 to 12 weeks depending on water temperature. Growth rate varies considerably depending on water type and conditions and food supply.
Three-year-old fish of g have been found in some Victorian streams due to fish numbers exceeding available food, while fish of the same age in some Victorian lakes have weighed 2. The rainbow trout fishery in Victoria is roughly divided into two parts.
The eastern half of Victoria has mainly self-supporting populations which exist where suitable habitat is available, while most suitable waters in the western half of the State depend on stocking with hatchery-produced fish - in most cases stocked waters are lakes or reservoirs. Native to the western coastal drainages of North America from Mexico to Alaska. Introduced to Australia in Where rainbow trout and brown trout occur together, the brown trout usually dominates.
Faster growing fish than brown trout in most circumstances, but growth rate varies according to habitat and food supply. Lake Purrumbete in south-western Victoria once held the World record for growth, yearling fish reaching 1. These growth rates were exceptional and no longer occur partly because of the highly competitive and increasingly abundant redfin population in the lake direct competition for food and space ; partly because the very fast-growing populations were produced from stocking rates much lower than are now released; and partly because the productivity of the lake has declined markedly in the last 30 years and galaxiids which were the staple diet of rainbow trout in the lake no longer occur in as large numbers as formerly.
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