Acclimating these puffers to a different salinity is easy; the tricky bit is doing the filter bacteria.
Remember, these euryhaline, brackish water fish naturally swim between high and low salinity several times per day. The idea they need days or weeks to acclimatise is a myth. If it were true, every time the tide changed, estuary-dwelling fish would die!
In practical terms, I've been able to move, for example, black mollies from marine to fresh water in 2 or 3 hours. Schaefer, in the Aqualog brackish book, even says you can take scats from freshwater and dump them straight into marine!
The one thing that rarely works is taking fish adapted to marine water down to pure freshwater very quickly; mollies are okay, but scats, monos, etc., usually take exception. But going in the other direction, from fresh to salt can usually be done as fast as you want. Similarly, switching the salinity rapidly between marine and, say, 25% seawater (SG 1.005) can be done quickly, as well.
The simplest thing to do would be to set up the aquarium at some moderate salinity, e.g. SG 1.010. Then buy your puffer, and place it in a large bucket with an airstone. Over the course of the next 2 or 3 hours, replace some of the water in the bucket with water from the aquarium, at a rate of, say, 10% every quarter hour or so. Keep an eye out for stress, and keep the bucket covered so the fish cannot jump out.
If this is too scary for you, then set up the tank at a low salinity, SG 1.005. The puffer should be able to adapt to that at once, and simply floating the bag in the tank with a few holes cut into it (the bag that is, not the fish) should do the trick. I know lots of people object to mixing fish shop water with aquarium water, and they do have a point, so if you prefer, put the puffer in a bucket again and dribble in some fish tank water over the next half hour or so.
The downside to this approach is that as you raise the salinity in the tank, the filter bacteria are going to die, and you're going to have a few weeks while the puffer is exposed to high nitrites.
Cheers,
Neale
) a GSP from freshwater to the correct salinity ( I don't have one yet lol), and what is the best salinity to keep them at?
