fish keeping - below 35ppt - beneficial?

[Coffeeinbed]

Hi all,

Q) Is it still considered "less stressful" to keep reef fish below 35ppt in a FO tank?


For some years it was considered beneficial to keep reef fish (not all reef fish some fair poorly at less than 35ppt) from 1.019 SG to 1.021(2). It was thought it was easier for fish to maintain osmolarity with lower salt content.

Is this still true?

The hobby evolves all the time, now even skimmers , a MUST have for reef tanks - is considered optional for some. Things change.



thanks

 

[ThRoewer]

In the past I kept all my fish tanks at around 1.018 and my fish did fine. I even bred clownfish at that salinity and it worked actually better than at normal salinity.

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[OrionN]

The total dissolved solid in the fish (almost all the animals, human included) is about ~9ppt. NSW is at 35ppt. The animal must maintain this by prevent water loss through exposed surface, mainly the gills. It is though that by lowering the salinity, the fish would have easier time at this.
There were some study in the past on hypo-salinity all the way down to 9ppt. In that study they check cortisol level in the fish, one hormone that would indicated stress on the fish as a whole, and find that the cortisol level is normal with hyposalinity. The fish did fine essentially indefinitely (for long period anyway). I don't think they get them to breeding or anything like that.
That was why hypo-salinity was recommended. For me, I would just try to match the natural level for the fish. Million years of evolution is not something that I feel I should mess with. We know that they will do well with 35 ppt, why change it. Salt cost isn't that much.

 

[Coffeeinbed]

Thanks guys.

Sounds nothing has changed over the years - or it's still not considered harmful.

good to know... and thanks again

 

[j_mazzy]

The total dissolved solid in the fish (almost all the animals, human included) is about ~9ppt. NSW is at 35ppt. The animal must maintain this by prevent water loss through exposed surface, mainly the gills. It is though that by lowering the salinity, the fish would have easier time at this.
There were some study in the past on hypo-salinity all the way down to 9ppt. In that study they check cortisol level in the fish, one hormone that would indicated stress on the fish as a whole, and find that the cortisol level is normal with hyposalinity. The fish did fine essentially indefinitely (for long period anyway). I don't think they get them to breeding or anything like that.
That was why hypo-salinity was recommended. For me, I would just try to match the natural level for the fish. Million years of evolution is not something that I feel I should mess with. We know that they will do well with 35 ppt, why change it. Salt cost isn't that much.

Well there are many fish that move from seawater into brackish water during high feeding opportunity times and sharks that move into freshwater with no ill effects.

 

[ThRoewer]

... Million years of evolution is not something that I feel I should mess with. We know that they will do well with 35 ppt, why change it. Salt cost isn't that much.

Over millions of years the salinity of the oceans has gone up and the fish in the oceans have learned to cope with that. But that doesn't mean it is ideal for them.

In my experience fish are actually doing fine at lower salinities, as long as it isn't so low that it damagest their kidneys from inactivity.
24 ppt (1.018) is perfectly ok for fish. They even breed at that salinity and the larva not only develop fine, but actually faster than at 35 ppt. Also they are larger at hatch which make feeding them easier.