Transparent, Semi-transparent, or Translucent?

Reeder

Reeder

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In the recent brook trout thread this statement was made:
TB, I can't say that I've EVER seen transparent pectoral, pelvic, or anal fins on brook trout. After seeing your post I went back and looked through a bunch of pictures of more typical 4-8" brookies, and same deal. No, none are transparent. None of them. I then went to google images and googled "wild brook trout", and again, no transparent pectoral, pelvic, or anal fins.Browns and bows, yes. Not brookies. Though many of the tail (caudal) fins are semi-transparent

This got me thinking. I do not think I have ever seen truly transparent fins on any trout, not just brook trout. Transparent would allow all light to pass through forming a clear image on the other side, opaque would allow none, and translucent would allow some with a distorted image on the other side. To me, anything between opaque and transparent would seem to be translucent. Semi-transparent and translucent are the same in my book. I tried a quick search on any discussions or questions on this topic as it relates to trout fins and found nothing. Any transparent fin photos out there?

Here is the semi transparent brook trout fin for Pcray.
 

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I'm no biologist but I believe that it's accepted that wild steelhead leaving the salt and entering fresh water have translucent fins.

Could fin coloration/translucency vary throughout the year on the humble brook trout?
 
Yes, translucent or semi-transparent would be a better term than transparent.

The photo in the OP is what I'm talking about, for fin appearance of wild trout. The fins, particularly the thin edges and tips, look like that on wild trout. You can easily see the person's finger through the edge of the fin.

Look through the other brookie thread and note the large brookies with very milky, chalky, opaque looking pectoral fins. This is the opposite condition, and I consider that an indicator that it is a hatchery trout.

But I'm interested in other opinions about that indicator, and other indicators, used to distinguish wild from stocked trout.

And especially I'd like to hear from Mike and other fisheries professionals, grad students, etc. about this. When fisheries professionals are doing electrofishing surveys, they must use certain criteria to distinguish wild from stocked trout. What are those criteria?
 
Google research seems to lead to several places saying brook trout do not have transparent fins. Looking through my pictures I only found the one I originally put up disproving that theory, but realized there weren't many shots where something was behind the fin to tell the difference. I went out and did a little stream side research this afternoon to try and get more definitive proof. Here is a wild brookie with a small tape measure under the fin. One of the most "transparent" fins I've seen. Case closed on that part of the issue. As far as that being an indicator of wild or stocked, I am not really sure. Stocked rainbows have translucent fins too.
 

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Here's a good example of semi-transparent, you can see some dirt on my finger through the pectoral fin on this native.
 

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I've never heard of the "fact" that brook trout have opaque fins. Like with all trout (brown, bow brook) I've always used used translucent fins as a strong indicator of being wild or stocked.

Good pics to debunk that "fact"...thanks

 
wildtrout2 wrote:
Here's a good example of semi-transparent, you can see some dirt on my finger through the pectoral fin on this native.

Yes, that's a good example of a wild brookie, with a translucent pectoral fin. Notice also how the fin rays are distinct and run parallel to each other.

 
At this link there's a post by Frank Nale. Not far down in the post is a photo of a brook trout just shy of 13 inches long.

Look at the fins, particularly the pectoral fin.

http://www.huntingpa.com/forums/ubbthreads.php?ubb=showflat&Number=3685960&page=#Post3686049

 
Ok, I meant translucent, not transparent.

It's very common, almost universal on wild browns and a pretty dang good indicator of wild vs. stocked. Though even there it's not as good on large fish, which are more opaque. (more, not completely, I think they're maybe just thicker fins, and a thicker translucent thing passes less light).

On brookies, it's not as apparent, though yes with a perfect pic there's some light coming through. Most pics where you're not purposely staging the fin I don't really see it. The color is what makes it tougher to see. Wildtrout2s pic is a good example. Without a white finger behind it I'd never call that translucent, and even with it, the piece of dirt is required for me to be convinced that you are in fact seeing through it.

Color is a decent, albeit not perfect indicator. With wild fish tending to have far more orange/red in their fins and less white/gray/black, aside from the leading edge of course. This holds even on fish where the belly doesn't have much orange/red. Again, like wildtrout2s.

I still think the white/black edges, on the pectoral and anal fins, is a better indicator. It's typically a sharp, well defined straight line on wild fish, with absolutely pure white and black, no bleeding into each other. The OP pic is about as bad as it gets on a wild fish, and would still be abnormally sharp on a wild one. Wildtrout2s is again, near perfect.

As with all wild trout indicators, none are universal. But there are several of them that are 90% accurate. If all are pointing in one direction or the other it's easy. But there are always a few where its tougher to tell.
 
I heard a talk by Ed Van Put, fisheries technician for the Catskill region for 40 years, on identifying wild trout. His view was that wild trout have long thin fins with a straight leading edge. Stocked trout, even with full fins, will not have the straight smooth leading edge of a wild fish.
 
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