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Swimming ping-pong balls, that's what I've seen.
Is anyone out there familiar with Alaska blackfish (Dallia pectoralis), adaptations to low oxygen environments, or extreme subcutaneous edema in fishes? Here's a puzzle for you.
Blackfish are small (about 10 cm) fish of northern and interior Alaska and Chukotka (eastern "Siberia"). They have an incredible ability to survive low oxygen under the ice. According to one source, they are one of two fishes in the world able to absorb significant oxygen through their esophogus. When oxygen is low, they constantly swim to the surface (if there is an unfrozen surface), gulp air, and submerge with a mouthful of air. During winter they sometimes find cracks in the ice to breath through, and there can be so many of them swirling around to get oxygen that they keep the water open; or, as I have observed, can even melt the ice from beneath, thinning it with their constant movement and the transport of warmer water from deeper in the water column, I believe. A hole I cut through 14 inches of ice (in November, a very warm year here), size about 50 by 80 cm, became as thin as a few centimeters for an area a half meter to a meter in radius around the original hole. After first cutting the hole I had covered the hole with sticks and snow to keep from freezing too fast, but none-the-less a peculiar happening.
So, this winter I have been chopping holes in the ice in a pond near where I live (Fairbanks, Alaska), catching blackfish in minnow traps (hey, I'm a layed-off fish tech; you can't keep a Labrador from fetching sticks, can ya'?). Oxygen is low. The highest DO measurement in the water column three weeks ago was 0.45 ppm (near the surface) and the water stank like sulfer.
Anyway, out from this rank water came fish. Many had so much clear fluid just under the skin that some were as wide as they are long, rotund as ping-pong balls. Several of these "fat" ones were brought inside and placed in a container in a refrigerator, prior to being sent to a fish pathology lab to check for parasites. The swelling went down to nothing within a couple of weeks and the fish looked healthy. Incidently, there were no obvious parasites. Another small gallon container with three fish (approx. 7 to 10 cm length) was left at room temperature in my house. One of the fish was a "fat" one and the swelling did not go down after 3 weeks. I put them in the refrigerator and the swelling went down. Maybe having the fish at room temperature kept oxygen stress high enough that the swelling did not go down (granted, can't tell anything from a sample of 1, but still interesting). However, like I said these fish can effectively "breath" air.
So, does anyone know about edema and stress in fishes? Is it common with certain other kinds of stress, or just low oxygen? Maybe this is an adaptation, increasing surface area for gas exchange through the skin. The bellies of the fish from low oxygen situations are cherry red, as are the pectoral fins, no doubt for gaseous exchange. Maybe the fluid under the skin is just a place to isolate poisonous byproducts of anaerobic respiration. Incidently, these fish can be frozen, and will at least temporarily "come back to life" after thawing out. Maybe this is a way to jettison interstitial fluid before the likely onset of freezing?
Any insight as to why this swelling would occur, or good books/articles that might provide a lead would be greatly appreciated.
Thanks, Ted Lambert (new subscriber).
PS: anyone want some blackfish?
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