well with Osmosis if fish are acclimated to a certain amount of solids in the water, and then are suddenly placed into a new environment with a drastic change in solids, it puts pressure on their osmosis system.
Things like aquarium salt will add solids to the water, and give a boost in electrolytes by flooding the osmosis system with solids..
however, fish that do not enjoy lots of solids in their water will be put under a large amount of pressure and can eventually die from it..
larger fish are more greatly effected.. some species depending on collection locality may differ from others.. some 'rare' species might be 'rare' because they have a high DOA rate from improper acclimation and lack of osmosis understanding..
When I imported soft-water fish from Peru, i saw this red blood streak issue alot.. I always thought it was ammonia damage from shipping, which can cause long lasting effects.. such as Hyperplasia, which will permanently damage the gills and make osmoregulation very difficult.. etc..
So basically I found out through talking to other importers about acclimation is that an increase in solid will put pressure on the osmosis system over a long period of time and eventually they will get those bloody red streaks, gasp for air, and die..
I had some healthy blue canero 'whale' catfish.. they need cooler water and high o2.. they were great in the import tank for a long time, then I put one in a community tank with 5 degrees warmer water, resulting in less o2, and it was harder than the import tanks.. It got bloody red streaks and died a slow death over a 20 minute period once introduced to the tank.
It's very common in south american dragon gobies because they are a brackish fish that needs alot of solids, then put into fresh water.. there osmosis system works super hard and they eventually die. I see the red blood streaks on them at work quite often.
just my 2 cents
