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> Here's one of the weirder ones I've heard, speaking of whales. My buddy is > working on hydroelectric dams up in the northwest. Right now, they have adult > salmon coming upstream around the dams and kid salmon going downstream. To aid > the fingerlings, they blow water over or through the dam to wash them > downstream. Now this is coming about 4th hand, filtered through a few > non-technical but reliable people, but they say that the turbulence of that > extra water going over the dam puts a lot of air in the water, and the adult > salmon coming upstream get skin bends. My friend was told to watch for fish > with visible skin bubbles, often around the mouth and fins, large enough to > remove scales. Not sure I believe this. Could be parasites, but they are > studying these fish, and I'm sure somebody would have cut one open and know > the truth. Generally, fish don't get what we call bends (trust me, it's my business to bring 'em up alive from great depths). The dissolved gas partial pressures in their tissues are equal to or less than those in the surrounding water (except in the rete mirable, in the vicinity of the swim-bladder, but that's another story...). In the ocean, the dissolved gas partial pressures in the water are equal to (or less than) the partial pressures in the atmosphere at sea-level (by Henry's Law). Hence, fish never have elevated dissolved gas partial pressures in their tissues, and don't get bent when brought straight to the surface (their swim-bladders inflate like a balloon and crush their other organs, but again, that's another story...) The case of the salmon sounds interesting, however. If in the structure or flow patterns of the dam, air is trapped it great depths, theoretically the dissolved partial pressures in the water might increase to the point where they could cause bends in fishes exposed to them. For example, tap-water is usually super-saturated with dissolved gas (presumably because air is trapped in the pipes somewhere, and the system is pressurized to ~60 psi). This can be demonstrated by filling a glass with tap water and watching small bubbles form along the sides over the course of the next several hours. If you place a fish immediately into this super-saturated tap water, the elevated dissolved gas partial pressues will get into their tissues (via the gills), and as the bubbles grow in the water, analagous bubbles may form within the tissues of the fish. These fish get "bent", and it is usually manifested by small bubbles in the eyes and on the fins (and sometimes between the scales). If the salmon are exposed to super-saturated water for long enough periods of time, it's conceivable that their tissues might absorb enough gas that they will eventually get bent. I seriously doubt this is actually what's going on, though, because the constant water flow through the dam should be constantly flushing in unsaturated water from upstream. I suspect that the turbulance causes a profusion of micro-bubbles in the water which are somehow absorbed or ingested by the fish. These bubbles, if they reach it to the circulatory system, could cause the symptoms you describe. It's important to know whether the observed bubbles are actually INSIDE the tissues of the eyes, etc, or if they are simply adhered to the outside. A fish swimming through high-turbulance with zillions of tiny bubbles will get small bubbles stuck to their mucous all over their bodies. This, of course, would not be bends. Aloha, Rich
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