Dorsal deformation and hatchery steelhead?

Discussion in 'Steelhead' started by Klickrolf, Mar 13, 2013.

  1. I've noticed dorsal fin ray deformation in hatchery steelhead but haven't paid close enough attention. I don't know if it's ubiquitous among hatchery strains. It's easy to see if you're looking, the dorsal will not stand up nice & straight. Trouble is I haven't always looked...wdfw trained me to look at the adipose instead. Hoping to get ideas on whether it's genetic or a result of the hatchery environment. I'm interested in any research that has delved into this.

    Hoping maybe some WFF resident biologists can push me in the right direction.
  2. Fins on fish can be deformed from other fish nipping at them when there are in over crowded pens, rubbing on the cement race ways etc. I have worked on fish traps and fish from different hatcheries have different degree of deformation. In my experience the steelhead we received from the Grande Ronde from Lyons Ferry Hatchery looked almost identical to the native fish (minus fin clip) but other fish (from places unnamed) looked like swimming hot dogs with caudal fins.... Its not necessarily a genetic thing, if raised in ideal conditions they should look like their native counter parts.

  3. Fish Biologists out there? Do you suppose that steelhead are similar in this way to Orcas? I have seen pictures and read descriptions of Orcas that are in captivity or have been, having dorsals that do not stand up straight as in the wild orcas. I wonder if there is a distant relationship?
  4. Deformed dorsal fins on hatchery steelhead appears to be the result of fish nipping at each other in hatchery raceways. Fish reared in larger ponds or in net pens tend to have a lower incidence of deformed dorsals. Before the universal ad clipping of hatchery fish dorsal fins, the deformity was a primary way of identifying hatchery steelhead if one could not get scale samples. Seems like about 85% of hatchery fish have the deformed dorsal fin, but it varies according to the rearing vessel.

  5. The rate and degree of deformed dorsal fins in hatchery steelhead is often a function of the density at which the fish are reared. Those reared in natural ponds have less severe deformations than those reared in the more crowd conditions found in raceways.

    In the worst cases the entire fin can be missing in other cases the fin can be stubbed (shorter than normal), in others the fin's ray will have bend look resulting from the fins growing out after being released. In other cases the fin looks "normal" with nice straight fin rays and a nice high fin but there can be one or more missing rays on the posterior edge of the fin. If you look closely at the where the back edge of the dorsal fin enters the fish's back that insertion will be clean and straight. On hatchery fish there often is small bump left from the missing fin ray giving the posterior point of insertion a slight rounded look.

    A decade before mass marking of hatchery steelhead became common I was limiting my harvest of steelhead to those that clearly had deformed dorsal fins.

  6. I hooked a buck on the Noochy last month that had a funny looking dorsal. It didn't appear scarded just not formed right. In the picture you may be able to see the fin. I've clipped coho at the Humptulips hatchery and those poor little guys 008.JPG are lucky to swim away with any fins. LOL Some of those guys were lucky to escapt alive at all.
  7. I never took you for a Stones fan, Befishin, but at least that brim has some bend to it. Nice grin!
    That is a swanky lookin' boot you're gripping, too.:D
  8. Crowded cement raceways are the culprit here. Some newer circular recirculating tanks at hatcheries have much better results with fin erosion.
  9. I suspect the dorssals are not the only thing that is deformed in these fish...
    Derek Young likes this.

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