Fellow Fish Squeezers:
Several weeks ago, I sent a query concerning the use of fin erosion as
a diagnostic characteristic to distinguish wild and hatchery salmonids.
The responses follow. My sincere thanks to all who responded.
It is my repeated, but anecdotal, observation that fin erosion is an
unreliable mark to differentiate hatchery from wild fish. Several state
agency biologists with whom my students and I interact have suggested that
they can separate stocked from wild fish by their fins (erosion - not a
clip), but this is a very subjective trait, especially after stocked fish
have spent some time in the wild. In that case, the fins often have some
amount of curvature in their shape and rays - an even more subjective trait
that requires a keen imagination. These are my observations from stocked
and wild salmonids in tailwaters of the White River in Arkansas and
Missouri, and the situation may be different in other systems.
I would be very surprised (and skeptical of the work) if your post
results in a published account that uses this trait, but please let me (or
the list) know if you find one.
... ....... passed an e-mail along to me about fin erosion being used to
differentiate between hatchery and wild fish. I operated a hatchery in the
Kodiak area for many years and we had one year where we had a considerable
amount of pectoral fin erosion in coho smolt. We ran a few samples and
estimated that 60% of the fish had some fin erosion. We released these fish
and upon their return we certainly were able to tell where the hatchery coho
were being caught in the commercial fishery from all the reports of coho
missing fins. We did not use these fish for estimating hatchery production
as we only had an estimate of the number of eroded fins and we did not know
how much erosion would be required for the fin to not regenerate. At any
rate, it was rather interesting as an induced mark, purely accidental, but
it did give us a very good idea of where these fish were harvested.
North Carolina Wildlife Commission personnel have used this fin erosion technique
for many years (1970s at least) to differentiate between stocked and
The state field biologists in Connecticut routinely use overall condition,
including fin erosion, color, epidermal texture, etc., as a qualitative
indicator of wild versus hatchery origin trout. In addition, the Connecticut Stream
Survey Team collected and viewed scales and otoliths from hatchery reared trout
taken from the raceways, suspected hatchery reared trout captured in the field, and
suspected native trout captured in the field. These were qualitatively compared to
confirm casual field observations and native versus hatchery origin classifications
based on overall trout condition (most notably fin erosion). They found that fin
erosion and overall condition was a good indicator of origin in Connecticut.
Unfortunately, these data were never reported in the literature (peer reviewed or
I don't know any particular paper on that topic but I can tell you
for sure that we quite regularily catch or see sturgeon Acipenser baeri in
the field in France where this species normaly exist only for aquaculture
purpose. Almost all the fish caught showed fin erosion or fin abnormally
shaped. They also showed on the tip of the snout a sort of ball caused by
the farming condition. Only for 3 specimen that were in the river for more
than 3 years and that didn't showed any particular features of farming,
every other Acipenser baeri caught were easy to determine.
Thats all the 5 cents contribution I can tell you.
I'm not aware of published studies but I can tell you from our own
experience that it could be used. We census residual steelhead and
cutthroat in the Elochoman River, Washington. Although all these fish
have adipose fins removed, it is very clear that the dorsal fins could be
equally used to differentiate the hatchery fish from the natural fish. It is
very obvious underwater, as long as the fish remains stationary (which
they usually do) for several seconds, and the water clarity is sufficient
I received your query regarding fin erosion. I have done some research on
fin erosion and have a number of papers on the subject. I am not aware of
any that deal with that particular topic per se. Idaho did a study that
was published on the survival of stocked hatchery fish that had poor fin
condition that you may want to find:
Heimer et al. 1985, N. Am. J. Fish. Management 5:21-25.
The problem with using fin erosion as an identifier of hatchery fish is
that it is inconsistent. We have problems with it at our hatchery here,
but some fish in the raceway will have good fins. These percentages are
low, but are there. Maybe these could be sorted out or the numbers of
"marked" fish adjusted.
In Norway fin erosion is commonly used to identify farmed from wild
Atlantic salmon in the field. See:
Lund, R.A., Hansen, L.P. and Jarvi, T. 1989. Identification of reared and
wild salmon by external morphology, size of fins and scale
characteristics. NINA Forskningsrapport 1: 1-54. (In Norwegian with
Fleming, I.A., Jonsson, B. and Gross, M.R. 1994. Phenotypic divergence of
sea-ranched, farmed, and wild salmon. Can. J. Fish. Aquat. Sci. 51:
For comparisons of hatchery (sea-ranched) and wild fish see:
Boskowski, T. and Wagner, E.J. 1994. Assessment of fin erosion by
comparison of relative fin length of hatchery and wild trout in Utah.
CJFAS 51: 636-641.
Also: Fleming et al. 1994 above, which includes comparisons of
hatchery/sea-ranched Atlantic salmon and coho salmon with wild
While we have not done any type of "study" on this issue, we do use fin
condition to separate out wild fish from stocked fish. We feel
reasonably comfortable with this technique when looking at durations of
1 year or less, particularly when looking at catchable sized fish (>225
mm). In most cases, wild brook and rainbow trout above this size are
not common and therefore just the size of the fish serves to distinguish
hatchery fish. When you look at smaller fish the erosion is not usually
as severe and fin regeneration makes it difficult to distinguish between
them and wild fish.
I think if you look at the converse issue - what do studies of fin clips
as marks show as short, medium and long term identifiers - you should be
able to make some conclusions about how fin erosion would serve as a
I know from my own experience clipping fingerling brown trout (125-175
mm) that if the clip is not done correctly, that you can have difficulty
identifying marked fish in less than a year.
That's all folks!
Montana Cooperative Fishery Research Unit
Montana State University
Bozeman, MT 59717