freshwater sole

[OraLacerta]

Ok, I used too strong of a word, but we recommend on this forum that people bring them up to at least 1.018 because of the reasons you listed, and based on the recorded success of keeping them in those conditions. I haven't read any long-term studies on GSPs successfully being kept in lower salinity, but there may be something out there. If so, enlighten me!

Either way, 1.005 won't cut it long-term.

Any idea what specific gravity is best for a Trinectes maculatus to be kept in? Everything I have found is unclear, saying they are found in full fresh to full marine. Mine has been in 1.005-8 for about a year and doubled in size, but I wonder what range is best. Mine seems to be thriving in his current conditions.

[nmonks]

Both Ebert and Schaefer, authors of the Aqualog books on Pufferfish and Brackish Water Fishes respectively consider mid-salinity brackish to be just as good as full marine conditions. The London Aquarium has kept GSPs for many years in a brackish water tank alongside things like green chromides and scats. Aquarists I trust have kept them in brackish conditions without problems, and in my book I recommend SG 1.010 upwards. I have no personal experience of GSPs, but I have kept monos and scats for long periods, and while many people say they need marine conditions, they don't, and do fine at 50%-ish brackish water conditions provided water quality and water chemistry are otherwise good.

People who think brackish water fish need steadily increasing salinity with age are simply failing to understand how brackish water fish work. By definition, a brackish water fish will adapt to a range of salinities. Anadromous and catadromous fishes (like salmon and eels) are completely different, and do indeed need different conditions for specific phases of their life cycle.

It's also worth noting that Ebert mentions that the GSP he kept in freshwater didn't die prematurely, it merely stayed smaller than the ones he keeps in brackish or marine conditions for the same length of time. So while I agree than SG 1.005 is probably too low, the reasons are perhaps not quite what they might appear. I'd wager than the buffering capacity of the water and the elevated levels of hardness and pH are perhaps just as important as the salinity, if not more so. Once the fish is at SG 1.010, it probably doesn't make any difference whether you raise the salinity further or not, provided the water quality remains good.

I've yet to see any evidence at all that GSPs inhabit marine conditions in the wild.

Cheers, Neale

[OraLacerta]

Ok, I stand corrected. Thanks for the info; I wasn't aware they could thrive into adulthood at 1.010. Your reasoning certainly helps explain why:

I'd wager than the buffering capacity of the water and the elevated levels of hardness and pH are perhaps just as important as the salinity, if not more so. Once the fish is at SG 1.010, it probably doesn't make any difference whether you raise the salinity further or not, provided the water quality remains good.

RTR mentioned the same thing about Figure Eights and how they may just thrive in freshwater if properly buffered (ie. with an aragonite substrate).

I've yet to see any evidence at all that GSPs inhabit marine conditions in the wild.

I don't contest that, everything I was referring to in my former post was on GSPs in home aquaria. I have heard the theory that they spawn in freshwater and move to the ocean with maturity, but I didn't catch any sources so I question the credibility of the theory. There is so much controversy on the wild habitat of all the brackish puffers. It would be wonderful to travel to their natural habitats and do a several year study. If only I had no obligations here in the States!

Thanks for the info Neale.

[Nick]

I had thought they were surely at slightly less than marine conditions when mature in the wild, but it was easier to maintain water quality at an SG where a protein skimmer and LR works, and does not harm the fish, so it's a good option for keeping them in aquaria.