# Osmoregulation In Fish



## b3w4r3 (Dec 14, 2012)

Epsom salt treatment by adding it to the water doesn't do much. At best it would slow the intake of water through the skin which would just mean the fish would urinate less. But really the reduction would be very low. The epsom salts won't move through the skin, only water does, and freshwater fish don't drink water so how it is going to act as a laxative is beyond me.


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## GTZ (Apr 21, 2010)

b3w4r3 said:


> Epsom salt treatment by adding it to the water doesn't do much. At best it would slow the intake of water through the skin which would just mean the fish would urinate less. But really the reduction would be very low. The epsom salts won't move through the skin, only water does, and freshwater fish don't drink water so how it is going to act as a laxative is beyond me.





> In freshwater, a higher electrolyte level (particularly of sodium chloride, calcium and magnesium) will help pull fluids through the body...by pulling fluids through the body this can help with bloat, swim bladder problems, intestinal problems, and even dropsy


- http://www.aquarium-pond-answers.com/20 ... freshwater



> Magnesium is important for proper osmotic functions in fish and invertebrates...Epsom salts that contain magnesium sulfate, are best used for therapeutic reasons such as to aid in flushing the system as it aids in and speeds osmotic function, and helps to move fluids out of the body. Sulfates, one of the major components of Epsom Salt, have been shown effective in improving nutrient absorption and toxin elimination.


- http://www.americanaquariumproducts.com ... #magnesium


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## b3w4r3 (Dec 14, 2012)

I'm still fuzzy on how exactly increased magnesium in the water causes a fish to take on more fluids. Generally raising GH (which is what epsom salt does) will lower the rate at which water is absorbed through the skin.

http://www.simplydiscus.com/library/bio ... osis.shtml


> Osmosis is the process where water moves through a semi-permeable membrane (fish skin or gill membrane) from a lower concentration of minerals (aquarium water) to a higher concentration of minerals (fish's body). The semi-permeable membrane (fish skin or gill membrane) only allows water to pass through it, in and out, not the minerals. This is how freshwater fish stay hydrated. Saltwater fish have to drink lots of water and retain water through their kidneys, excreting minerals, to stay hydrated


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## dreday (Oct 12, 2007)

i thought the fish would absorb it through the gills, i thought they absorbed trace elements that way.

When you do a salt dip with sodium chloride they take it in somehow, i wait until they roll over then back into fresh water. Through osmosis they should pull in the salt and then expel it in fresh water. Salt water fish have to drink the water to maintain their osmotic pressure.

And i do believe freshwater fish absorb water through their skin as well. The more soluble the item the easier the fish gets it. that holds true for other salt type medications like metro and levamisole.


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## DJRansome (Oct 29, 2005)

I can't tell you how it works, but I do believe epsom salts act as a laxative. This is even an ingredient in human laxative medications.


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## GTZ (Apr 21, 2010)

Some information I've dug up over the past couple of days...

Branchial Magnesium Transport


> In freshwater environments, the gills are an important route for active uptake of ions such as Na+, Ca2+ and Cl- (Evans,1980; Flik et al. 1985). Some evidence suggests that Mg2+ may also be absorbed via the gills. In fish fed a low-magnesium diet, the deposition of magnesium in the body can exceed the dietary magnesium intake (Shearer, 1989; Dabrowska et al. 1991; Bijvelds et al. 1996a), indicating that the food cannot be the only source of magnesium and that, consequently, Mg2+ may be obtained directly from the water. Assuming that water ingestion is negligible in freshwater fish (to prevent water loading), these observations implicate the integument as an alternative route for Mg2+ uptake. In Mozambique tilapia, when dietary Mg2+ intake is reduced by providing a low magnesium diet, the extra-intestinal (presumably branchial) Mg2+ uptake contributes significantly (approximately 30 %) to the total amount of magnesium accumulated (Bijvelds et al. 1996a). Moreover, when access to water-borne magnesium is also reduced, a marked depletion of the magnesium stores of the body occurs (Shearer and Asgard, 1992; Bijvelds et al. 1996a). Thus, it is reasonable to conclude that it must be branchial Mg2+ uptake that enables the Mozambique tilapia to maintain a positive magnesium balance (a net magnesium accumulation) when the dietary magnesium intake is restricted. In fresh water, a slightly negative transepithelial potential (approximately -5 mV) is maintained across the branchial epithelium, which would not support passive Mg2+ uptake (Dharmamba et al. 1975; Perry and Flik, 1988; Young et al. 1988). Therefore, although such a mechanism has not hitherto been demonstrated, we predict that an active transcellular Mg2+ transport mechanism is present in the branchial epithelium.1[/super]


Branchial magnesium uptake does occur.

In the same study, he goes on to describe the effects of high water magnesium concentrations:


> A high water magnesium concentration (up to 50 mmol l-1) lowers the integumental permeability to water and ions, and this elicits a compensatory hormonal response (involving a decrease in prolactin activity) in stickleback Gasterosteus aculeatus (Wendelaar Bonga, 1978) and in Mozambique tilapia (Wendelaar Bonga et al. 1983). Only relatively small changes in plasma Ca2+ and Mg2+ levels occurred, and a high external magnesium concentration had no apparent deleterious effects in stickleback (Wendelaar Bonga, 1978), Mozambique tilapia (Wendelaar Bonga et al. 1983) or goldfish Carassius auratus (Olivereau et al. 1987). Whether this is because freshwater fish can restrict their integumental magnesium influx and/or, like sea water species, eliminate excess magnesium through renal pathways is not known. Certainly, it has been shown that some euryhaline species maintain the capacity for rapid and effective renal Mg2+ excretion in fresh and brackish waters when challenged by a large magnesium dose administered directly to the body (Natochin and Gusev, 1970; Hirano, 1979; Oikari and Rankin, 1985). Apparently, the secretory mechanism present, albeit normally silent, can be activated instantaneously, probably triggered by an increase in plasma magnesium concentration. As far as we know, no comparable studies have been conducted with stenohaline freshwater fish. Therefore, it is not known whether the renal magnesium secretion mechanism found in some euryhaline species is also present in species restricted to freshwater habitats.[super]1[/super]


It's possible, although unproven, that in freshwater fish, an increased magnesium content in the surrounding water will increase the rate of renal excretion.



> If divalent ion intake from food is less than branchial/renal loss, then branchial active uptake must balance the net loss; for example, branchial uptake of Mg2+ may account for 30% of uptake in freshwater tilapia fed a low Mg2+ diet. Unfortunately, studies on the mechanisms of Mg2+ uptake have not been published.[super]2[/super]


Unfortunately, specific studies covering magnesium sulfate specifically do not exist, or at least I haven't been able to find them. Studies involving magnesium, calcium, sodium chloride and their effects on osmoregulation were the most prevalent and are listed below.

Additional:

Uptake of Drugs In Relation To Route of Exposure


> 4. The relative importance of drug uptake across the gastrointestinal versus respiratory versus epidermal epithelium in fish is unknown (Shepherd 1993 ). Indeed, for many drugs, the relationship between concentration in the water and systemic levels has not been determined and dosage levels are based on empirical data. 5. When drugs are added to the water, their half - life within the environment must be considered in addition to their half - life within the fish. The chemical activity and rate of uptake may be influenced by pH, temperature, light, water hardness, and many other factors (Lunestad 1992).
> 6. The water is the life-support system of aquatic species and adding any substance to it must be done with full consideration made to the potential consequences of that chemical on environmental quality. For example, formalin, commonly used as a parasiticide, is a strong reducing agent and will rapidly reduce oxygen levels if adequate aeration is not provided. Other drugs, such as methylene blue and certain antibiotics, inhibit the ability of nitrifying bacteria to detoxify nitrogenous wastes, resulting in the accumulation of these toxic metabolites.[super]3


1.	MAGNESIUM TRANSPORT IN FRESHWATER TELEOSTS
- http://jeb.biologists.org/content/201/13/1981.full.pdf
2.	Osmotic And Ionic Regulation: Cells and Animals 
- http://books.google.ca/books?id=1zP4bYD ... sh&f=false
3. Fish Disease Diagnosis and Treatment 2nd Edition, Edward J. Noga

http://www.basny.org/Documents/Aquatica ... -COLOR.pdf
- Water Chemistry: Osmoregulation, Ionic Imbalance & pH
http://www.fishyportal.com/cgi-bin/pub/diag?c=v&id=55
http://www.earthlife.net/fish/oregulate.html
http://www.fishtanksandponds.co.uk/aqua ... ation.html
http://yarbroughlaw.com/Patent%20Projec ... 0wrong.htm
http://www.raingarden.us/osmoregulation.htm
http://www.angelsplus.com/ArticleOsmosis.htm
http://people.biology.ufl.edu/devans/DHEJEZ.pdf
- Ionic Transport in the Fish Gill Epithelium
http://www.aquarium-pond-answers.com/20 ... drink.html
http://www.americanaquariumproducts.com ... #magnesium


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## b3w4r3 (Dec 14, 2012)

Nice finds. I posted a thread in the biology section of the physics forum so I'll relay any info they give in response. There are a few biologists that post there so hopefully one of them can add to this.


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## GTZ (Apr 21, 2010)

Thanks. One thing I was very surprised at was the lack of information out there but maybe I wasn't searching effectively, idk. Another was the conflicting information. There is a lot of incorrect information out there, or information that has been proven incorrect but still exists, the latter being more likely, I hope.


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## dreday (Oct 12, 2007)

Ornamental fish do not become part of studies due to the low interest to the masses. Food fish have the most documented information. One has to try and relate that to ornamental. I think a lot of the information is understood to be true until disproved, kind of like gravity.

Thanks for the articles.


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