Great Lake rainbow trout in excellent condition

Despite the low lake level at Great Lake rainbow trout arrived at the Liawenee fish trap in good numbers this year.

The fish were stripped of eggs and milt for grow out of the fertilised eggs at the IFS hatchery at New Norfolk. While this has been the practise for some time, this is the first year in recent times that eggs from wild rainbow trout have been treated at Liawenee to produce triploid fish.

Once fertilised, the eggs are treated in a pressure vessel to produce offspring that are sterile (triploid) in the sense that they do not produce gonads (sex organs). The consequence of this process is that the fish do not stop feeding in winter and do not put any energy into reproduction. The end result that the fish have the potential to grow larger in a shorter amount of time.

The IFS thanks Ron Morrison for assisting with the triploid process.

The resulting fingerlings once grown out will be stocked at fisheries that have minimal or no natural recruitment. This strategy will be used to reinstate the stocking of wild rainbow trout in Central Highland waters, particularly those that have populations of redfin perch.

Redfin perch predate heavily on fry that are migrating from nursery streams into lakes and lagoons. The aim of growing out these fish at IFS hatcheries is to get them to fingerling size where they will have an increased survival rate.

Not all of the eggs collected from Liawenee undergo triploidy as normal diploid stock is vital to the restocking of Great Lake. Other waters where redfin predation is not a problem are also stocked to boost natural recruitment of wild rainbow trout.

Continuing with the monitoring program that has been going for 40 years, a sample of 200 fish from the spawning run were weighed and measured. This year the average size of the fish increased in terms of weight, from 1289 grams last year to 1300 grams this year. With the fish decreasing in average length from 490 mm to 485 mm the condition of the rainbows for this year has increased overall. The rainbows have been holding or improving condition for last five years, something that anglers will definitely appreciate.

Inland waters stocking since August 2008

Courtesy of Inland Fisheries Service "Angler News'.