Do Fish Drink? Osmoregulation in Fish
Carlrs
Osmosis in fish;
Their cells must always be bathed in a solution having the same
osmotic strength as their cytoplasm. This is one of the reasons why fish
and other animals have kidneys. The exact amount of water and salt
removed from their blood by the fish kidneys. The process of regulating
the amounts of water and mineral salts in the blood is called
osmoregulation. Fish which live in the sea (remember the sea is full of
salt and other elements), but fish which live in freshwater have the
opposite problem; they must get rid of excess water as fast as it gets
into their bodies by osmosis. Osmosis is an important topic in biology
because it provides the primary means by which water is transported into
and out of cells.
Osmosis is also important in the treatment of many aquarium diseases in
both freshwater and saltwater. A general breakdown in osmoregulation due
to disease, poor water quality (especially the lack of essential
mineral electrolytes such as Calcium, magnesium, and Sodium) is often
responsible for the bloated condition that results from excess water
accumulation in tissues. This lack of proper osmoregulation can not only
result in bloating, it can cause issues with disease resistance,
curvature of the spine, and the ability of the fish to stabilize itself
in the water.
It is common for Fish in this condition often rapidly succumb due to
loss of homeostasis (the constant internal environment), essential to
carrying out metabolism and other life activities. This tends to be more
common among FW fish in my experience, in part due to the lack of
understanding of the role that many essential minerals play in essential
life processes of fish.
Generally salts (trace elements), not just sodium chloride can affect
osmosis. Magnesium can also play a major role too. Calcium can affect
and just as importantly BE affected by proper osmotic function.
Sulfates have been shown effective in improving nutrient absorption and toxin elimination.
Magnesium plays a role in the activity of more than 325 enzymes and aids in the proper assimilation of Calcium.
Often many aquarists understand how salt (sodium chloride) affects
osmoregulation and the popular question of “Do fish drink?” however this
is a dangerous over simplification as although sodium chloride (as
often represented as sodium and chloride) are important, the lack of
OTHER ESSENTIAL ELEMENTS including Calcium in fish can lose/leak
substantial quantities of other minerals/salts into the water.
Here is an over simplification I read recently that is not necessarily
wrong, but in misleading in that it implies salt is the only essential
mineral:
“They (freshwater fish) absorb water through
their skin and have effective ways of excreting excess liquid to
maintain the salt they need”.
The implication is that the fish basically just needs to maintain salt
and/or this or other minerals somehow take care of themselves.
The FACTS are that without Calcium (as tested via GH), the fish CANNOT properly osmoregulate.
For much more information about the importance of Calcium and other
electrolytes, please read this article (in particular the section about
Calcium):
CALCIUM, KH, AND MAGNESIUM IN AQUARIUMS; Why Calcium and Electrolytes are Important.
FRESHWATER FISH
In freshwater, a higher electrolyte level (particularly of sodium chloride, calcium and magnesium) will help pull fluids through the body which also stimulates the natural mucous coat on fish so as to resist parasites, bacteria, and fungus.Also by pulling fluids through the body this can help with bloat, swim bladder problems, intestinal problems, and even dropsy (which I have had few problems with in clean tanks with good electrolyte/ trace element levels).
This process results in the loss of many electrolytes. Some of these trace elements can be replaced by ions contained in food but by far the most common method is through the movement of a substance against an osmotic gradient through the use of energy.
This usually involves the exchange of one substance for another. In the case of freshwater fish, Na+ (sodium) ions are taken from the water and ammonia ions are taken from the fish and they are exchanged.
This effectively rids the fish of ammonia. Chloride ions are exchanged for carbonate ions which help in maintaining the pH of the body fluids.
This is one more important reason for adequate Calcium, carbonate (KH), & electrolyte levels
Opportunistic diseases such as Columnaris, Saprolegnia (often known as fish fungus), and Aeromonas (often the cause of Septicemia are more easily prevented when osmoregulation is functioning properly in fish via adequate mineral levels.
Information on:
Columnaris, Saprolegnia
Aeromonas