Fin Clip regrowth

[Mike]

Fins may or may not grow back after having been clipped. Clips that are meant to be permanent involve clipping the fin off as close to the base as is possible. If such clipped fins grow back anyway, they are usually substantially deformed (curled sometimes, narrower sometimes). Other clips are meant to be temporary. In those cases just a portion of the fin is removed. Regrowth usually is complete in a matter of months, but it is true that in some more aggressive clips of this type, particularly in streams where trout are growing slowly anyway, full regrowth may take more than a year. Also, in the cases of temporary clips, one can usually spot a previous clip by holding the fish up to the sunlight to examine the fin, which will show what is often referred to as a scar. It is illegal in Pa for anglers to apply either form of fin clip to a fish yet evidence shows that it is still being done by some trout anglers.

 

[Maurice]

Mike,

Could you describe the characteristics used by biologists to determine the difference between stocked trout vs. wild trout.

Thanks

Maurice

 

[Stone_Fly]

Explain to me then why during surveys PFBC finds fish with clipped fins that were last surveyed 3 years earlier?

 

[Wulff-Man]

Because the PFBC intentionally clipped them close to permanently "tag" them?

 

[vcregular]

I like the word regenerate when describing fin grow back. I have no doubts fins grow and fill in to some degree, and if you really look closely you can almost certainly tell. Pics of all fish help. :-o

The fish below came from the Lehigh near Walnutport. Probably a stockie and if you look at the tail it looks like it has regenerated - lighter new-growth along the edge. At first glance it may appear wild....but where is that damn blue halo at :-D

 

[Mike]

We have a few simple characteristics that we check in the field. Bear in mind that while an angler has a lot of time to check a fish, we have seconds because there are usually a large number of fish waiting to be processed. First, I would say context is important before we even start looking at the fish. In my mind I am already thinking about how long it has been since the stream received its last stocking and how long it has been since it received its preseason stocking (or if it is not stocked, is it a trib to a stocked stream?). I am also thinking about whether or not it receives cooperative nursery stockings and what species are typically stocked. With fish in hand, I am first checking for color that is more washed out than typical (but not always) wild trout color. I am next checking for fin wear. Next, I am checking for fin regrowth. Finally, if I am really, really curious, I take a scale sample. The scale samples from hatchery trout are almost 100 percent regenerated scales ( requires a microscope) while the wild trout have a much lower percentage of regenerated scales.

 

[troutbert]

Re: "Finally, if I am really, really curious, I take a scale sample. The scale samples from hatchery trout are almost 100 percent regenerated scales ( requires a microscope) while the wild trout have a much lower percentage of regenerated scales."

Very interesting stuff. Mike, if you have time, could you please explain this some more?
What does regenerated scales mean?
Why do hatchery fish have almost 100 percent regeneraated scales and wild trout a much lower percentage?
(And where can I get a good buy on a microscope? )

 

[Mike]

In the wild or in a hatchery when scales are forcibly removed from a fish the fish grows replacement scales. Unlike the circuli pattern on the original scale, which would have been a series of concentric rings surrounding the focus, the new scale picks up where the old one left off with respect to the placement of circuli. All previous circuli are gone from the new scale and in their place is an enlarged focus where the original circuli used to be. In effect, you have a "blank" scale that tells you nothing about the fish's growth or age prior to the scale having been lost and replaced. Hatchery trout have a large number of regenerated or "blank" scales, as I have called them for the purposes of this explanation, most likely because of the crowded conditions, collisions when feeding in a raceway, a history of handling with nets and while grading, and other abrasions. While wild trout have regenerated scales as well, their occurrence is very, very much reduced in comparison to hatchery trout. I have tried to look at scales from hatchery trout in the past and have had very little success in finding scales that were not regenerated. at least with respect to scales from browns and rainbows. I am not saying that is not possible to find a perfect scale on a hatchery trout from the region of the fish where we normally take the scales (adjacent to dorsal fin), but I am saying that they are uncommon in my experience. Thus, the high frequency of regenerated scales would be helpful in detecting hatchery fish.