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Rainbows and spawning

Forum for discussing fisheries conservation and other environmental issues related to fish, wildlife, watersheds, and aquatic ecosystems.

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VGB
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Re: Rainbows and spawning

#11

Post by VGB » Tue Dec 21, 2021 8:24 pm

Based upon observational evidence James is right, foxes and dingoes are more selective at reproduction than French bulldogs. I’ve never seen foxes or dingoes hump legs or furry toys, French bulldogs are at them morning till night, no wonder their eyes stick out.
“The difference between science and madness is correcting your explanation when it doesn’t map on to the world.”

Wavy but not quite wavy enough

Thomas
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Re: Rainbows and spawning

#12

Post by Thomas » Wed Dec 22, 2021 6:14 am

VGB wrote:
Tue Dec 21, 2021 8:24 pm
Based upon observational evidence James is right, foxes and dingoes are more selective at reproduction than French bulldogs. I’ve never seen foxes or dingoes hump legs or furry toys, French bulldogs are at them morning till night, no wonder their eyes stick out.
:D :D :D :D :D

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whinging pom
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Location: Oundle uk

Re: Rainbows and spawning

#13

Post by whinging pom » Wed Dec 22, 2021 12:03 pm

From my pretty limited understanding of the situation,I have a few thoughts.

It's not only the Derbyshire Wye but also the Don in Sheffield that have breeding populations, the source of the Don it seems were stocked in holding reservoirs that occasionally were released into the main flows when extra levels were needed.
Rainbows prefer to breed in crystal clear mountain waters, and in lower flow rates than our Native browns.
Rainbows over winter then go to redds when the Temp is rising again to I think around 10c which is a very long winter in some parts of the UK to be stalled with low metabolism and hanging onto face the rigours of spawning.
Rainbows go to the redds at 12 months old, Browns are older and more conditioned before going to the redds.

When we stocked rainbows in our typical little English club water, had any of the overwintering Rainbows attempted to breed, in the areas with the suitable flow rates I suspect they would have been choked in silt before hatching. As I think it is with most low-lying English waters where rainbows have been stocked.

( -as it is the farmed rainbows we stocked had unrealistic conditions and demands with what the stream could supply to maintain that weight and had no predator awareness, and few if any got past winter).

The Wye, Lathkill and Don are all suitable high freestone crystal clear waters, high on the Derbyshire and Yorkshire Dales, and though there are similar conditions in parts of the lake district and Wales, I suspect most upland streams there are more turbulent and I don't think there was much need for stocking Rainbows in those areas in Victorian days.

Another thing that I think needs to be taken into account is the source of the original fish.
Rainbows breed from Mexico up to Alaska and I'm sure with them so widespread that there are populations with regional variations in timing, temp tolerance and robustness of strain.

Maybe the original stocks brought over were selected for robustness, whereas later stocks were chosen or bred for speed of growth and commercial considerations?.
Just like when we English started moving Browns around the globe, I think it was first tried with Test or Itchen trout with the best growth rates but it was discovered that the Loch Leven strain was the most robust to survive the passage, and thus made its way to populate the Himalayas, Australia and New Zealand.

I don't think it's just to one aspect and answer to this puzzle. I suspect if more upland areas had been stocked when the original prodigy was being shipped over the Atlantic we'd probably have a few more streams and rivers with breeding populations, and I would love to see some definitive research on the matter. As I'm sure someone must have studied it.
all best
WP

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Paul Arden
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Re: Rainbows and spawning

#14

Post by Paul Arden » Wed Dec 22, 2021 2:20 pm

I think it raises the question, where have rainbows been successfully introduced? Chile I know. NZ largely too. However I also gather that Taupo is very much reinforced with hatchery fish. SI certainly has a surviving population of wild rainbows, but is better known for its brown trout. I don’t know the situation in South Africa, apart from that they have both?

Browns have obviously fared much better.

I think it, originally at least, comes down to suitable spawning. Incidentally as I understand it, the successful strain of rainbows that were introduced to NZ were from steelhead ova.

Cheers, Paul
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andrewparkeruk
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Location: near North Wales, UK

Re: Rainbows and spawning

#15

Post by andrewparkeruk » Wed Dec 22, 2021 11:26 pm

The story of the wild Rainbow Trout population on the Derbyshire R Wye, UK. The story recounted by a friend, Warren Slaney, who was river keeper at Haddon Estate for many years
In the 1890’s a small shipment of rainbow trout was received and placed into an inline dam on the Wye. After four years a flood caused some fish to escape downstream. The Wye was almost an exact copy of their home river. They were first generation fish bred from wild stock so they spawned and multiplied. They now complement our fishery in large numbers and provide a sporting chance to the fly during the bright summer daytime while our native browns and grayling rise well either side of noon. You will only find these superb fish in the Derbyshire Wye.
The Derbyshire R Wye supports extremely healthy populations of wild Brown Trout, Grayling, and wild Rainbow Trout. They spawn at different times; they appear to favour different parts of the river.

I’m pretty sure Warren thought that because these fish were essentially wild, rather than domesticated, they survived and thrived. Pretty much the same story as Loch Leven Brown Trout “transplanted” to New Zealand

ska1911
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Re: Rainbows and spawning

#16

Post by ska1911 » Wed Jan 19, 2022 1:12 pm

Hi!
Thats a really interesting question i have discussed a lot in the past. Here in Austria we have some rivers where there are self-sustaining rainbow populations, as far as i know all of them are in the alpine region, there is no reproduction in the lower land rivers. In my region (not alpine) there are lots of rivers where rainbows are stocked but never managed to reproduce successfully. One hypothesis was that water chemistry may has something to do with it. I saw rainbows spawning in my home river so my first thought was that the eggs don`t develop as they should...my hypothesis was debunked when we started a cocooning project with rainbow eggs. They just developed fine and the project resulted in a good population of rainbows. Another hypothesis is tat the timing of the spawning may be an important factor. We did the cocooning project with the rainbow eggs simultaneously with a brown trout cocooning project. We put the eggs in the water in january, and both browns and rainbows hatched at the same time (approx 300 day-degrees). I often read that rainbows generally spawn later, so maybe there may be some unknown factor at this later timepoint that interferes with the development of the eggs (runoff for example). But there may also be some kind of rivalry for the spawning places with the more aggressive browns. I think there might be some studies from an austrian university on this topic, i will look them up...
Cheers
Stefan

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