Hi Paul.Paulanderson wrote:Hi Will the hybrid Murray/Trout Cod you mentioned - would that likely have been stocked that way or does that mean the Murray and Trout Cod are actually inter-breeding in the river where you were fishing?
Where the two cod species naturally occur together low levels of hybridisation appear to have always existed - the old timers talked about it - and were recorded fairly early on when they began to naturally recover in the Murray River from the mid 1970s onwards. The translocation population in Cataract Reservoir is dominated by hybrids so it has been speculated that reproductive isolating mechanisms between the two species break down more readily under marginal conditions.
Until recently only F1 hybrids have been found in the wild so it was assumed they were sterile. That changed recently with the discovery of F2 hybrids in the upper Murrumbidgee, an avoidable man made mess. The historical evidence is that upstream of the gorge at Tharwa trout cod were the prevalent cod species with Murray cod being scarce (computer models based on the Murray River say otherwise!). Trout cod became extinct up there during the 1980s and from the mid 1990s a fair number have been stocked - without much success. That was quite predictable as the river is badly silted and the river deprived of flow by Tantangara Reservoir - the factors that exterminated them in the first place. Anyhow, NSW Fisheries a few years ago stocked Murray cod into the sub-alpine streams flowing into the area for angling. I argued against it, suggesting trout cod be stocked as that was within their former range and outside that of Murray cod at least in any numbers. They ignored that for the usual trout cod are endangered blah blah blah reasons. Obviously there were trout cod in the bidgee and swamped with the Murray cod moving downstream combined with a shortage of mates they have crossed and the hybrids appear to be fertile.
Another mess is in the upper Murray River above Lake Hume. This received a few small trout cod stockings in the late 1980s and established a small breeding population - I confirmed that as I had one angler send in data about his captures and you could see the small recruits coming through as cohorts. Then about fifteen years ago a Murray cod stocking program started up there. They ignored the idea of stocking trout cod there for angling and did not even consider a 1:1 stocking of the two species. The population there is going extinct as the trout cod have been swamped by the Murray cod with the result that most of the juvenile 'trout cod' are now hybrids. The response of the experts is the trout cod are primarily a lowland fish and were never really common up that way. They bang on about not allowing the stocking of trout cod for angling because they are endangered but are happy to let a population go extinct when it doesn't fit in with their narrative.
Best Wishes
Truedogz
