Producing Wild Triploid Trout

The Service recently purchased a hydrostatic pressure chamber from France for use in its hatchery in order to produce triploid trout. These fish are sterile; they do not produce reproductive organs. This makes them more desirable than normal diploid fish for stocking in certain waters and for particular purposes.

Although triploids look and taste like normal fish, they tend to grow bigger faster because they convert more food into body mass rather than expending energy in producing eggs and sperm. Also, they don’t suffer the same stress that diploids do at spawning time, particularly if they become egg bound in waters where there are no natural spawning creeks. They are the preferred stock for commercial aquaculture and also in ‘put and take’ recreational fisheries around the world.

Although small numbers of triploid fish occur naturally in most populations, researchers have 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 timing after fertilisation and the actual pressure are critical to the process, and they vary depending on the species. The 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.

The Service’s new purchase – the hydrostatic pressure chamber, Mega Pascal – has been specially designed and manufactured in France to treat trout eggs for triploid fish. It weighs approximately 440 kg and includes a 10 l hyperbaric chamber and jack set, and includes a hydraulic pump. The equipment has been mounted on a moving, jointed galvanised stainless steel frame with retractable wheels, which is important for operating the chamber and getting it in position.

The vessel arrived at New Norfolk on 9 August 2010 and after an initial inspection and trial, it was loaded by forklift onto a vehicle and taken to Huon Aquaculture’s Springfield Hatcheries to undergo definitive trials on domestic rainbow trout ova. The vessel is the ‘state of the art’ in aquaculture and its purchase by the Service is of particular interest to commercial hatcheries such as Springfield. It is a vast improvement on existing models, including the vessel owned by Springfield and loaned to the Service in the past.

During the initial trial, Springfield Hatcheries reported that a lot more eggs could be treated in a lot less time, and that 100,000 eggs had been processed and stored in incubators with pleasing results. Springfield plans to treat more ova with the Service’s vessel, and hatch and on-grow the majority of this progeny for the Service to stock out next year.

The vessel will be transferred to Liawenee in mid September in time for the rainbow trout spawning so that the Service can use it in triploiding eggs collected from wild rainbows.

The collaboration and assistance provided by Springfield Hatcheries in developing the Service’s triploiding program is greatly appreciated by the IFS. The exchange of information and resources is a benefit to all but ultimately, it is anglers who will receive the real benefits – more bigger better fish to catch in the State’s inland waters!