All-females and Triploids
Trout farmers seek maximum efficiency to convert fish feed into saleable meat. Sexual maturation prior to harvesting can reduce the production efficiency and quality of the product. During sexual maturation, the nutrients in the feed are diverted away from the production of muscle (meat) towards the development of reproductive organs. Physiological changes during sexual maturation will also affect the quality of the meat by softening the flesh.
Most strains of rainbow trout spawn naturally on a 2-year cycle. However, the faster-growing males in a population can develop reproductive organs precociously and be ready for spawning in the first year. In culture conditions, precocious males can become a significant portion of the stock, with the resultant loss in production volume and value. Female trout rarely mature precociously. For these reasons, Troutlodge has specialized in the production of all-female rainbow trout eggs as our standard product. All-female eggs are preferred by trout farmers around the world for a variety of benefits, such as:
Excellent overall fish quality at harvest.
Firmer and tastier flesh (meat).
Healthier fish due to the absence of males.
Better feed conversion.
No unmarketable, precocious males.
Availability of roe from all-females as an additional marketable product.
Troutlodge offers both diploid (2N) and triploid (3N) trout eggs. The difference between diploid and triploid trout is the number of chromosome sets contained in the nucleus of each cell. Within each cell of an organism is a nucleus, which houses the DNA packaged in units called chromosomes. During normal reproduction, offspring receive one set of chromosomes from the mother and one from the father resulting in a diploid organism with 2 complete sets of chromosomes. This is the normal state of being and results in fully viable offspring that can reproduce.
In contrast, triploid organisms have 3 complete sets of chromosomes, 2 from the mother and 1 from the father. Prior to fertilization, an egg contains 2 sets of chromosomes, one of which is called a polar body. Under normal conditions, the polar body is expelled shortly after fertilization, leaving only 2 chromosome sets and creating a diploid organism. However, if a fertilized egg is exposed to either increased atmospheric pressure, or increased temperature, the polar body is not expelled and is retained in the nucleus. Thus, each cell of the organism has 3 chromosome sets and is referred to as triploid. Due to the extra chromosome set, triploid animals cannot produce functional gonads and are reproductively sterile.
For trout production above 3 kg, Troutlodge recommends the use of sterile, triploid (3N) ova. Some trout farmers believe that 3N ova are better than diploids (2N) even for smaller harvest weights, since gonad development is avoided resulting in a better SGR. However, this is not always realized in terms of better meat yield and meat quality for <3Kg harvest weight. Since triploid fish will not mature, they enable a more efficient and productive use of hatchery facilities by avoiding the removal of maturing fish.
Triploid eggs are the perfect solution for producers needing a sterile trout for:
There are several scientific studies of relevance regarding triploidy in rainbow trout. Here you can find some research with Troutlodge genetics regarding this topic in these links:
Effect of sexual maturation on growth, fillet composition, and texture of female rainbow trout (Oncorhynchus mykiss) on a high nutritional plane (USDA Agricultural Research Service)
In Trout, onset of puberty is recognized by clear secondary sexual characteristics prior to spawning. Currently, there is much research in progress on puberty control, e.g. by photoperiod treatments, as many factors are still not completely understood.
Alterations of environmental cues, such as the photoperiod, induce changes of activity of the brain-pituitary-gonad axis that in turn regulates the timing of sexual maturation, spawning, sex steroids and thyroid hormone profiles. Photoperiod is considered as the most important environmental cue determining the timing of puberty and reproduction in fish living in temperate waters.
Photoperiod manipulation is used by fish farmers and researchers, to control puberty in farmed fish to prevent or delay unwanted gonadal maturation. Photoperiod can easily be controlled even in outdoor enclosures and under cage culture conditions.
Continuous 24h light photoperiodic manipulation inhibits or modulates the activation of the endocrine cascade from the brain-pituitary-gonad axis, which initiates puberty. It can also affect growth performance directly, by preventing reallocation of energy resources towards gonadal development. Under this light regime, endogenous rhythms controlling reproduction may enter a delayed free-running rhythm or block the onset of gametogenesis altogether (e.g. if applied during autumn after the exposure to natural photoperiod conditions). In this last case, it is highly effective in inhibiting the appearance of precocious males.
Photoperiod manipulation is a realistic therapy on a commercial scale for Trout reared in sea cages or tanks.
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