Freshwater Fishes

Blue Salmon and Rainbow Trout from Lake Coleridge – A Genetic Mutation

Blue Salmon and Rainbow Trout

By Allan Burgess

What are the chances of you catching a blue rainbow trout or salmon from Lake Coleridge?  Well, they a not very good. There are many anglers who have fished Lake Coleridge all their lives and have never caught one or even seen any of these blueback fish! I have caught just one when fishing at the “picket fence” at the head of the lake about twenty years ago. Though I have photographed several more at Fish and Game Council fishing competition weigh-ins held at Lake Coleridge. 

Blueback trout are the result of a genetic mutation. According to a report by a Pennsylvania Fish and Boat Commission trout hatchery manager, it is estimated that blue trout occur only 30 or so times in 4 million rainbow trout egg hatchings. You can read more about that here.

Landlocked Quinnat Salmon – Oncorhynchus tshawytscha caught in Lake Coleridge. Photograph, Allan Burgess.

Mutations in the animal kingdom, such as albinism, are generally considered a disadvantage in the battle for survival. Most mutations result in the fish, or other animals,  not surviving to adulthood. However, some genetic mutations actually allow for a better chance of survival in localised populations. Lake Coleridge is a turquoise blue lake. This striking water colouration is caused by glacial flour from melting snow. 

A rainbow trout with a blue back would definitely have a camouflage advantage in that it would be less obvious to airborne predators like fish eagles and falcons. Sure, we don’t have such birds of prey in New Zealand but the rainbow trout don’t know that I’m guessing. It is hard to see that a blue-backed rainbow trout in Lake Coleridge would be at any sort of disadvantage.

Genetic variations and adaptations occurring in both wild and hatchery-reared trout are not all that unusual. Some of the trout, both rainbows and browns, caught in the Twizel Canals can look very strange. I’m not just talking about the enormous specimens either.        

Blue Quinnat Salmon

Although I have seen references to brown trout that are blue (particularly in small stocked lakes in England), I have not found any examples of blue coloured land-locked Quinnat salmon on the internet. I am sure that the two fish photographed in the plastic bin below are landlocked salmon from Lake Coleridge. These two fish have photographed me at the Lake Coleridge Fish & Game Fishing Competition on Opening Day 2011. Could it be that blue Quinnat landlocked salmon are very rare fish?

Landlocked salmon in Lakes Coleridge, Hawea, and Wakatipu are always underweight fish for their length because there is an insufficient natural food for them in these lakes.  As we have seen in the Twizel Canals salmonids grow very quickly,  and to a large size, if they have ready access to an abundant food source. Hence the reason these landlocked salmon are smaller and skinnier than their majestic sea-run cousins even though they are the exact same species. 

It was thought for many years that the landlocked Quinnat salmon in Lake Coleridge didn’t breed, so the lake was stocked regularly with hatchery-reared salmon. You can read more about this here Landlocked Quinnat Salmon – Oncorhynchus tshawytscha – Updated in July 2021.

Rainbow trout with blue back from Lake Coleridge (No.1). Note the shorter anal fin with long rays.
Quinnat salmon with blue back from Lake Coleridge (No.2). Note the wider anal fin with short rays.

Perhaps it is possible that a strain of blue Quinnat salmon is breeding naturally in Lake Coleridge?   

A friend of mine Dick Marquand reports catching blue rainbow trout in Lake Hawea but never in Lake Dunstan.

If you have caught one of these rare blue rainbow trout or salmon, please send us a photograph for inclusion on this page. Please send your photograph either to my email address: allan @ (no spaces) or to our Facebook page.


  1. Rainbow trout comes up blue in rare Lake Superior catch. Ed Eisch, Fish Production Program Manager for the Michigan Department of Natural Resources.
  2. Have you ever seen a blue trout? They aren’t one in a million, but they are darn rare.
  3. Reel Life February 2021.
Initially, it was thought that this trout, caught near Tekapo, may have been a brook trout, but it is in fact a brown trout with quite unusual markings. The condition factor looks to be very high. it measured 60cm and weighed in at 9.5 pounds. Many thanks to David van Rooyen for sharing his pictures with us.
Here is the same brown trout again pictured at the bottom. Above it, and caught in the same area, is a monstrous and also somewhat unusual looking rainbow which weighed in at a massive 22 pounds.

This post was last modified on 11/03/2022 10:44 pm

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