Wednesday August 8, 2018

The overwhelming majority of fish that we handle in the field look how you would expect them to – more or less a typical fish of their species. Every once in a while, however, we encounter a fish out of the ordinary – sometimes with eye-catching deformities. Most skeletal deformities are so debilitating to the affected individual that they reduce their ability to survive. While deformities are relatively common in larval and juvenile fish, nature tends to make quick work of sorting out individuals with abnormalities, so disfigured adult fish are especially rare. However, we do occasionally catch a fish that has beaten the odds, such as the bass above with a misshapen head, or the steelhead below with an odd droopy lip.
Droopy lipped steelhead
Deformities can happen for a number of reasons. During development, genetic effects, exposure to toxins or radiation, temperature fluctuations, or nutrient deficiencies can lead to abnormal skeletal formation. After hatching, bacteria and viruses, parasites, or injuries can cause deformities that make individual fish stand out from the crowd. Regardless of the cause or nature of their condition, the lucky survivors we sometimes observe in the field are a reminder that sometimes irregular fish can defy the odds.

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