Sunday, January 13, 2013

Dead Giveaway.

      I often get comments from anglers that caught large rainbows in the Colorado or Blue and they wonder if it is one of the whirling-disease resistant fish that we have been slowly getting established.  I started stocking large numbers of very small WD-resistant rainbows (a strain that we call HXC's) into the Colorado and other rivers starting in 2010. Those fish have been growing 5-7" annually. The 2010 year class in the Colorado is now in the neighborhood of 14" and I'm hopeful that we may see wild recruitment in 2013 for the first time in decades. So, if the fish in question is is larger than 16", chances are very good that it was stocked privately. There are a handful of private landowners along some of the rivers that do stock fish into their reaches of river. We see these privately stocked fish show up in far-flung locations, both upstream and down. The other source of "non-wild" rainbows into the rivers is if one of the large reservoirs where we stock 10" catchable rainbow trout happens to dump some of those fish as it is spilling.
    We're trying to manage the genetics and usher in a new golden era, if you will, of wild, self-sustaining rainbow trout in our rivers. This takes time and patience but I am confident that we are on the verge of seeing this effort pay off, big time. When highly domesticated fish move into these areas and mix with the HXC's, it may hinder this process if they manage to inject their genetics into the mix. So if a large number of these fish turn up in our sampling reaches, it presents a bit of a concern.
     There are some other ways to tell if the fish you caught is not wild. Often the stocked fish are skinnier and have less color, such as the example below.

     Now, take a look at this dorsal fin:

     This is the dead giveaway that this fish was raised to a large size in a hatchery. Wild fish (or fish stocked at a very small size, therefore virtually wild) have a normal dorsal fin with straight fin rays and it's obvious when you lift the fin.

    Once you get in the habit of looking closely at the dorsal fin on the fish that you catch, it becomes very instructive.

   Here's an example of a one-year-old HXC. This fish was photographed in September of 2012, and was stocked at 1.5" in July of 2011. This year class averaged 9" in September and there are a good number of them out there. I caught a few of these on rod and reel myself this year and these fish make themselves known as soon as they are hooked. Even at 9" they'll take a little line off your reel. I can't wait to see how it will be to catch one twice that size. Look at the difference in color. I don't have a picture of me holding up the dorsal fin on one of these, but the fin rays are perfectly straight and not distorted.


  1. As you said this is a perfectly legal opportunity. Given the large stocked trout are not WD resistent how is the world could their offspring theory they would not survive as well because they don't have the "special" genitics and eventuually be selected out of the population. Next, that big stocked trout sure looks in poor shape. I would doubt it would even have the energy to spawn this spring. I like your posts and certainly appreciate it but the science on this article is a little shaky.

  2. Frank,
    If that large stocked fish is a male, than it is likely it would be able to outcompete the smaller HxC males to spawn with an HxC female. The offspring would have a lower chance of being resistant to whirling disease because only one parent would have the requisite genetics for WD resistance. Therefore, that large stocked fish may be able to "contaminate" one generation of rainbows that will not survive. Multiply that scenario by 100s or 1000s and it slows the potential for recovery of wild rainbows.

  3. John,

    Assuming you continue to see some success with the stocking of the HxC fingerlings, is the stocking program to be continued in the same fashion as it has been over the past few seasons? That is, will you continue to stock the fingerlings from the raft at the same point in the year as you have for the last couple of years?

    1. Yes, that's the plan. The ultimate goal is to cease stocking once natural reproduction takes over. So hopefully I won't continue doing it forever. We check on fry densities every summer, and when we start seeing good numbers of baby rainbows BEFORE stocking the fish in a given year, we'll probably stop.

    2. How many years does it take the stocked fingerlings to reach sexual maturity? I'm thinking you probably need a couple of sexually mature year classes of the offspring from the initial HxC stocked fingerlings before you can reasonably expect the population to be self sustaining. So, by summer 2016, a clearer picture of whether the population is or will be self-sustaining should be coming into focus.

      Also, are any other regions implementing a similar strategy with stocking HxC fingerlings? Or are they waiting to see results before getting on board?

  4. Dan,

    I am currently stocking HxCs in the Poudre River. Additionally, we have some ongoing experiments on the Poudre and Laramie Rivers to evaluate some other stocking methods. In my sampling this year we did pick up wild rainbow reproduction and are doing genetic testing on these young of the year to evaluate the strain/s that may be successful. I am aware of similar fingerling HxC stocking on the South Platte as well.

    Kurt Davies

    1. Thanks Kurt. I know that there has also been some good success with these on the lower Gunnison as well.