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[RalphH]

In BC, hatchery steelhead, trout and most coho have the adipose fin clipped before release to distinguish them from their wild counter parts.

https://midcurrent.com/science/fish-science-the-fatty-little-fin/

Long assumed to have little or no useful purpose it now appears the adipose fin plays a role in balance and swimming efficiency and possibly in reproductive behaviour in some species of salmonids. :

The fin’s role in swimming has also become clearer in recent years. One research group had a look at whether fin clipped juvenile steelhead were at a disadvantage when swimming. The biologists measured tail beat frequency and amplitude at different flow speeds and having established what the steelhead did with their adipose intact the researchers then snipped off the fin and put the fish through their paces again. In all but the smallest fish tail beat amplitude increased by about 8%, not a lot but a significant change to the beat amplitude recorded prior to adipose removal. The fin then has a role to play in increasing the efficiency of sustained swimming. The researchers also thought they saw some small nerves running to the base of the fin and in a subsequent study demonstrated that these nerves were indeed present – the first time this had categorically been shown. Their presence strongly supports their initial idea that the fin is a ‘precaudal flow sensor’ especially useful when the fish has to maneuver in turbulent water. Fish with their adipose fin removed are likely to have higher energy expenditure than those retaining the fin, a costly loss in a dynamic aquatic environment.

[CohoJake]

I wonder if this has anything to do with the claims I've heard from many anglers (and sometimes I think I observed as well), that hatchery coho tend to not fight as hard as wild fish.  It is interesting to me how much the size of the adipose can vary in unclipped fish, and the truly huge ones are found on big males like the chinook in my profile pic (I remember it was nearly as big as the palm of my hand!).

[RalphH]

I'd agree there is a difference overall, between hatchery clipped and wild fish for steelhead, coho and cutthroat.Hatchery fish often seem to be smaller and at least for cutthroat look a bit less 'fit' than wild fish. I've also wondered if there may be a connection between higher mortality for hatchery smolts and wild related to the clip. I think the expectation is/was the smolts would quickly adapt to the lack of the fin but who knows? Another question that needs to answer and likely no money for funding research, at least in Canada.

[Dave]

It is interesting to me how much the size of the adipose can vary in unclipped fish, and the truly huge ones are found on big males like the chinook in my profile pic (I remember it was nearly as big as the palm of my hand!).

Interesting subject. I remember when buck and I were counting steelhead in the upper Chilliwack river area and the times we were close to fish, say within 20', the adipose fins were easy to see.  The males appeared to use the fin almost as antlers, showing it off it seemed. And you're right about the size, big males had huge adiposes ... when chasing females the fin was erect, much like a phallus.

[RalphH]

that's discussed in the article.

[Rodney]

So that's how you're supposed to chase females.... 💡 Don't even need to buy dinner.

[Fish Assassin]

So that's how you're supposed to chase females.... 💡 Don't even need to buy dinner.

Don't go there Rodney

[CohoJake]

that's discussed in the article.

That made me go back and more carefully read the article.  I would say overall it is well written, but I am disappointed by the lack of citations, mostly because I would like to do further reading on the topic.

[GordJ]

That made me go back and more carefully read the article.  I would say overall it is well written, but I am disappointed by the lack of citations, mostly because I would like to do further reading on the topic.

The author did leave his contact info sim.blanford@gmail.com

[CohoJake]

The author did leave his contact info sim.blanford@gmail.com

Thanks, I emailed him, and I'll share any response I get here.

[CohoJake]

The author sent me PDFs of 13 scientific articles - I can share them with anyone who PM's me an email address.

[Dave]

The author sent me PDFs of 13 scientific articles - I can share them with anyone who PM's me an email address.

pm sent

[CohoJake]

pm sent

Email sent.  Check your spam box if you don't see it.

[dennisK]

In BC, hatchery steelhead, trout and most coho have the adipose fin clipped before release to distinguish them from their wild counter parts.

https://midcurrent.com/science/fish-science-the-fatty-little-fin/

Long assumed to have little or no useful purpose it now appears the adipose fin plays a role in balance and swimming efficiency and possibly in reproductive behaviour in some species of salmonids. :

its like circumcision.

best to be au natural instead of artificially modified/snipped.

besides.

chicks dig convertibles.

[Dave]

Post of the month!