Mebbid
Aquarium Advice Addict
Osmotic shock is a real thing and a lot of fish end up dying from it. If the fish is from a LFS that's truly local and uses the same water source I wouldn't really worry about it. However, if the water isn't the same as yours then by far the best practice is to acclimate the fish to the new water slowly.
Blurb about osmotic shock:
From: Aquarium tropical fish disease diagnostics. Fish treatment. Sick fish, ill fish, cure fish.
Osmotic shock
A sudden change in salt concentration (for example, if fish are transferred without gradual acclimatization from the water with a different mineral level). This causes death within 2-3 days and is a common reason for high mortality rates among newly introduced fish. High-concentration salt baths (used to treat, for example, external parasites) can also cause osmotic shock. All fish that show adverse reactions to such baths should be immediately returned into fresh water.
In less dangerous cases, when the difference in water conductivity is small, mucous membranes will flake away, which causes secondary infections. When the difference in is big, cartilaginous parts of fins can snap under high osmotic pressure. Large pieces of fins begin to fall off and the resulting wounds can be infected with fungi and bacteria, which happens because fish are weakened. Ammonia can also have an adverse effect on osmoregulation.
Prevention:
Osmotic shock can be avoided by gradually (sometimes within several days) balancing osmotic gradients between the fish’s present and new habitat by means of water change. Under no circumstances should be fish exposed to sudden changes in the chemical composition of water.
Note that: Salts is in reference to mineral salts and not just aquarium salt. This refers to Potassium, calcium, phosphate, magnesium, etc.
Why spend an obscene amount of money and risk losing a fish when you could just spend 30 minutes acclimating the properly. If it could potentially save you from losing a $60 fish wouldn't that be worth it?
