Hypersalinity

[Reef_Geek]

Once took a semester long course on ichthyology, a long long time ago in a galaxy far far away.

Fish living in freshwater have a challenge where their blood have a higher concentration of solutes than water in its external environment. Bodily processes of freshwater fish are thus always countering osmosis since water has a natural osmotic tendency to enter their bodies while salts have a natural tendency to exit their bodies. In general, freshwater fish physiologically osmoregulate by retaining as much salts as possible at exchange sites (gills, gastrointestinal tract, urine, skin) and expelling water. Freshwater fish are basically always peeing water to maintain homeostasis. This is why adding a bit of salt for FRESHWATER fish eases their energy expenditure and helps when they are under stress.

In contrast, saltwater fish have a lower concentration of solutes in their blood than natural seawater. Water thus has a natural osmotic tendency to leave the fishes' bodies while salts have a natural osmotic tendency to enter their bodies. Saltwater fish are basically always drinking water and peeing fluids with high solutes concentrations, and expelling salts through their gills. This is why lowering salinity for SALTWATER fish helps when they are stressed, as it eases their energy expenditure in maintaining homeostasis. This does not apply to Elasmobranchs (sharks, rays, ratfishes)... their blood have higher solutes concentrations than seawater.

So if you go HYPERsalinity, it's going to energetically tax the fish more so than their natural environment.

[Reef_Geek]

from wikipedia on "Osmoregulation"

Freshwater fish: always peeing diluted urine. Adding salt would help by reducing osmotic differential.



Saltwater fish: always drinking water and peeing out concentrated urine. Reducing salinity would help by reducing the osmotic differential.

[reefwars]

Originally Posted by Reef_Geek

from wikipedia on "Osmoregulation"

Freshwater fish: always peeing diluted urine. Adding salt would help by reducing osmotic differential.



Saltwater fish: always drinking water and peeing out concentrated urine. Reducing salinity would help by reducing the osmotic differential.

are they sure the direction of food is that way??



does anyone else find salty concentrated urine offending??

[reefwars]

and how come the second fish does not eat food im confused

[gregzz4]

Originally Posted by reefwars

and how come the second fish does not eat food im confused

I think they take turns

[Reef_Geek]

Originally Posted by reefwars

and how come the second fish does not eat food im confused

I think that picture is a new species of jacks... I think it's a Chatty Jack. Can't talk and eat at the same time.

[windcoast reefs]

I'm pretty sure the Red Sea has a salinity of 1.028-1.029 (or higher in some areas). I know someone in town that runs there tank at 1.028, seems to have good results so far. Seems the corals like it more than anything

I think the fish need to be adapted to that environment to do well, I would think it would be very stressful on a fish if it was a rapid change.

[Reef_Geek]

Originally Posted by windcoast reefs

I'm pretty sure the Red Sea has a salinity of 1.028-1.029 (or higher in some areas).

I think the fish need to be adapted to that environment to do well, I would think it would be very stressful on a fish if it was a rapid change.

That's neat! I did not know about the Red Sea salinity. Wiki says 41 ppt at the north end farthest away from Gulf of Aden, and 36 ppt at the end near Gulf of Aden.

That's a good point to add--whether lowering or raising salinity, the fish need exposure to gradual implementation. For example, ion exchange rates in gill and gastrointestinal cells are expelling salts at a steady rate and need time to adjust, so if you suddenly dropped salinity... ions continue to be steadily expelled while the body's expectation of natural influx of ions isn't there... the fish's salt balance goes out of whack for sodium, potassium etc... both will really screw up bodily functions. (Sodium and Potassium ions play major roles in muscle contractions).