Observation: Couple of local residents were out and about fishing for trout in early February. While fishing, a Dolly Varden was caught and pulled in, we could visibly see that the trout had a deformity. What is the reason for the deformity?
ADF&G Fish Pathology Lab Consult: Jayde Ferguson writes: "The deformed fish could be also be a char, but it’s difficult to tell from the photograph. There are a number of different potential causes for a spinal deformity in fish, which would include genetic factors, infectious agents (e.g., Flavobacterium), traumatic injuries, neoplasia, dietary imbalances, and environmental (e.g., pollution) factors. Given that the fish has been frozen, this limits the type of testing and interpretation that can be performed. However, I would point out that if only 1 or 2 fish have been observed with these condition, then it is probably not a widespread issues caused by an environmental factor like pollution."
LEO says: Both of these conditions can be related to exposure to warm water temperatures during development. Is it possible that climate change and warmer summer water temperatures in the Goodnews River could be factor contributing to these disease? We put this question to the experts at the ADFG Fish Pathology Lab.
ADF&G Fish Pathology Lab Consul (2): Dr. Ted Meyers writes: "Probably unlikely that water temperatures during incubation is a cause. Eggs incubate in the winter when water temperatures are low. The high temperatures we’ve been experiencing have been in the summer. The range of water temperatures in the winter are probably within the range for adequate incubation. Fish will also seek out refugia for the best locations. Also, if this was the cause then more fish would be affected."
Resource:
Alaska Department of Fish & Game – "The Dolly Varden is one of the most widely-distributed salmonids in Alaska. Freshwater habitats of Dolly Varden range from the smallest headwater stream (often less than 3 feet wide) to large deep lakes. Saltwater habitats range from brackish estuaries to fully-marine shoreline environments, and occasionally the open ocean. Entire populations of freshwater-resident Dolly Varden may spend their entire life cycle within a single stream, and during the winter, the entire population may reside at a single springs." Read more: Species Profile - Dolly Varden (Salvelinus malma) ADF&G
- ADF&G Education Resources: Dolly Varden — Wildlife Notebook Series, (PDF 47 kB) "Two forms or sub-species of Dolly Varden (Salvelinus mama Walbaum) occupy most of the coastal waters of Alaska. The distribution and range of each form has changed in recent years with knowledge gained from genetic analysis, but there is no absolute distinction in life histories between the two forms."
Regional Aquatics Monitoring Program (RAMP) – Body Deformities: "The occurrence of odd shaped-fish can have many causes. It is normal to occasionally discover deformed individuals in any fish population. A physical injury or drastic change in water temperature (usually an increase) when the fish is in the egg stage can produce fish with characteristic “stumpy” or “truncate” appearance. These same conditions can cause scoliosis, which is easily recognized because the fish has a distinct curve in its spine." Source: RAMP Community Programs & What are fish adnormalities?
Observations From Members 