We’ve all lost new fish as a result of the stresses of shipping and of aclimating them to their new environments. Lee Harper points out that the factors contributing most to the loss of new fish are sudden changes of osmotic pressure in the water (especially a sudden drop), and the results of sudden fright, when the fish literally may knock themselves out against hard objects.
Lee suggests implementation of the following procedures, which have proven effective in reducing new fish losses in his fishroom to nearly zero.
1. Always add salt (one teaspoon per gallon) to the water you plan to use for new fish, to prevent a sudden drop of osmotic pressure, which can severely damage the fish’s gills.
2. Slowly and gradually add this new waterto that the fish come in, over the period of at least an hour or so.
3. Always provide cover and security for the new fish, in the form of plants or hiding places. Java moss is excellent for this purpose, since it both provides security and acts as a soft “cushion” if the fish do erupt into a panicked dash. Keeping the tank partially darkened or the sides and back covered may help, too.
— G.C.K.A. N ewsletter, February 1998