Silver tip shark

You're going to have to acclimate it slowly. What SG are the puffers in? I'm assuming they're GSPs? How large is the tank?
 
If you don't want to give him brackish water then I would return him. They are native to brackish waters and this should be duplicated in captivity. Puffers on the other hand SHOULD be kept in brackish (esp. Fig 8's and Spot) but they can be kept in freshwater and saltwater. If they are kept in freshwater they require a high pH of at least 7.6. Figs and Spots can be kept in freshwater, brackish, and saltwater but you will see best colors, health, etc in brackish. Why don't you want a brackish tank? Nothing personal just wondering. Brackish has some of the most amazing and oddball fish. Can you find an Anablep Anablep (4-eyed fish) in freshwater or saltwater? Nope! Can you find an Archer that can spit water in order to knock insects off a branch above the water in freshwater or saltwater? Nope! Also can you find a Mudskipper anywhere else other than Brackish? Nope! Just thought I would point out some of the highlights of brackish.
 
So how much longer will the 5" silver tip sharks last in freshwater? I have 2 that are 4" and seem to be doing just fine in freshwater.
 
The question should not have to be asked about longevity of a fish in less-than-optimal conditions. If you are planning to keep it in such conditions, return the fish and get something else which you would be willing to maintain!
 
The only answer I can give you is that it certainly won't live nearly as long as it's life expetancy could be. It's immune system will eventually be compromised & disease will set in. Please take into consideration that these are living beings! These are wild-caught fish, that could have lived a long & happy life in nature. Man has scooped these fish out of their natural environment to sell to us, & it is our responsibility to give them the best care possible, in the most natural environment, for the fish to live a long & healthy life. Do you know that goldfish can live 70 years? Most folks consider them "throw away" fish! Please don't throw away yours!
 
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