Salinity Of Loaches

[prk22]

Does anyone know the salinity tolerance of loaches...in particular clown loaches?

 

[loachman]

Generally said to be poor.

 

[prk22]

does anyone know for sure, either from research or experience?

 

[kj23502]

Here's some info I found doing research for you:

"Clown loaches are not really brackish fish but they can tolerate very little salt."

From all I've read for you, it sounds like its not the best environment for the loach. How big's the tank? Clowns get bigger than a foot long!!

 

[Lateral Line]

Loaches are freshwater fish. Salt is a pollutant in freshwater. Some fish tolerate it better then others, but it interferes with the fishes osmoregulation system and particularly the kidney has to work harder, it burns out earlier then normal killing the fish prematurely. Loaches tolerate salt worse then many other fish types. Being scaleless, the skin is semi-permeable allowing the salt into the body.

 

[mikev]

What LL said.

The only situation where salt may be considered is as a temporary measure to deal with a disease (Ich) or a nitrite poisoning.

 

[andywg]

Loaches are freshwater fish. Salt is a pollutant in freshwater. Some fish tolerate it better then others, but it interferes with the fishes osmoregulation system and particularly the kidney has to work harder, it burns out earlier then normal killing the fish prematurely. Loaches tolerate salt worse then many other fish types.

However, as nmonks found when discussing clown loaches with Bob Fenner, it would appear that clown loaches have been found in brackish water in the wild. The level of salinity in that area is unknown, as too is the length of time they spend there and how natural behaviour it was (after all, natural events may temporarily move the fish out of where it wants to be) - from this topic.

Bottom line, brackish water is not best for clown loaches, and considering how almost every other post by prk22 is about whether different animals can be kept in an already running marine tank, I think it is best to put very clearly here that clown loaches should not be kept in marine conditions

Being scaleless, the skin is semi-permeable allowing the salt into the body.

I am not a fan of the belief that scales (or a lack thereof) has some issue with osmregulatory capabilities.

My moray eels are scaleless (or more correctly their scales are embedded under the skin), yet they do fine with salt in their water. The coral catfish (Plotosus lineatus) is scaleless, yet lives on reefs.

Now, the dermal biology of a fish will play a part in preventing water coming in through the general skin. To quote from Biology of Fishes by Professor Carl Bond (I have not corrected American spelling):

Scales and other armor in bony fishes aid in retarding water uptake, as armor must have done with the extinct relatives of the lampreys. The eel, Anguilla, is often singled out as having a nearly impervious skin. Eeel skin is reported to be so thick that it equals about 10 percent of the body weight.

So, while scales will help prevent an interaction between the fish's internal salt levels and that of the water, those fish that do not have scales would appear to have a modified skin level to afford them protection (in the case of the above eel, potentially greater than that afforded by scales).

Let us not also forget that freshwater has an osmotic concentration of 1-10 mOsm/kg (compared to 1,000 mOsm/L in seawater - mOsm/kg). The osmotic concentration of freshwater fish blood is in the range of 265 to 325 mOsm/kg. This means a freshwater fish (such as a clown loach) is hyperosmotic to its surroundings. If a clown loach (due to being without scales) was so much more susceptible to salt entering the body at its skin, it would also be losing far more salts at its skin in freshwater. This would put any osmoregulatory function under increased strain.

If this were really the case one would expect to see far fewer scaleless fish than scaled fish in areas that do not have high salt contents. Considering how successful catfish are throughout the mineral poor waters of South America I do not believe this is the case (though fully accept there may be research to disagree). Similarly, scaleless fish in marine conditions would be losing large amounts of water and as such one would not expect to see a scaleless fish (such as moray eels) to be so successful in the wild.

Finally the evidence is that most of the water absorbed in FW fish is through the gills (due to them being open to the water and having a large supply of blood going across them). However, this means that water is still entering the fish through other areas. Diagrams in Ichthyology texts will state that water is absorbed through the gills and the skin. So even scaled fishes will experience some disruption to internal salt levels through the skin.

As a result of all of the above I am far from convinced that fish without scales are in such a worse condition with regards to changing salinity levels and maintaining osmoregulation.

 

[Lateral Line]

Scaleless fish evolved in harsh ionic conditions would have naturally selected for, and thus evolved tougher kidneys. Fish evolved in freshwater have a kidney evolved for maintaining electrolytes.

Would your moray survive long in freshwater? Why?

 

[andywg]

Would your moray survive long in freshwater? Why?

It would not survive long because it doesn't have the osmoregulatory system to deal with living in a hyposmotic water. Similarly, my Tang which does have scales would also perish quickly for the same reason, the internal omsoregulatory functions. From all the reading I have done, the presence or absence of scales is nowhere near a deciding factor in the ability of a fish to deal with differing levels of salinity.

You yourself have resolved to discussing whether a fish has the kidneys to deal with differing salinities. And that is the key here, not the presence or not of scales, and that is the point I made, that whether a clown loach has scales or not is not the relevant point, but rather whether it has the internals to osmoregulate in the water with increased salinity. It was your statement that because a fish was scaleless its skin became semi-permeable and thus was more at risk I was talking over.

 

[Fella]

http/www.fishbase.org/Summary/speciesSum...=choirorhynchos

Horsefaced loach is found in brackish water in the wild.