Rainbow Trout Triploid Processing

Rainbow Trout Triploid Processing

Rainbow trout spawners have been trapped in Liawenee Canal over the past month in preparation for egg harvesting. Several batches of eggs totally approximately 360,000 were collected from these wild fish in early October for on growing as diploid fish.

On Thursday 28 October, the remaining rainbow spawners were stripped of eggs and milt and approximately 250,000 fertilised eggs were then processed to produce triploid fish. This process was undertaken using the Service’s new the hydrostatic pressure chamber, Mega Pascal (triploiding vessel), which the Service imported from France in May this year. The processed eggs were then brought to the IFS hatchery and placed in the incubator troughs to await hatching before transfer to the grow tanks.

The hydrostatic pressure chamber is designed to produce triploid fish which are sterile and do not produce reproductive organs. Triploids are known to grow bigger because they convert more food into body mass rather than expending energy in producing eggs and sperm, and they tend to hold their condition all year round. This makes them ideal for recreational fishing, particularly for stocking in ‘put and take’ fisheries and in waters where there are no spawning creeks. They are also the preferred stock for commercial aquaculture production.

Although small numbers of triploid fish occur naturally in most populations, researchers discovered that they can produce high numbers of triploid offspring by treating newly fertilised eggs. This treatment involves a physical shock, such as applying a very high pressure on the eggs just after fertilisation and during cell division. The triploiding vessel from France has been specially designed to produce triploid trout by ensuring the exact timing after fertilisation of the pressure shock on the eggs. This treatment process must be controlled exactly to achieve success; too little pressure or exposure time and nothing will happen, too much and the delicate egg membranes will be destroyed.

Prior to the triploiding of wild rainbow eggs, the Service commissioned Springfield Hatcheries to trial the new triploiding vessel on eggs destined for commercial use.  Under the initial testing, Springfield Hatchery reported that a lot more eggs could be treated in a lot less time, with higher success rates.

The triploid rainbow eggs now resident at the New Norfolk hatchery will hatch and grow over the next six months. The young fish should be ready for stocking as fry in March, fingerling from around May and yearlings by September next year.