Does phosphate cause stunting?

[slipknottin]

Phosphate is well known to prevent calcification when phosphate levels are quite high. Stunting is often said to limit the external/observable features of fish, yet the internals continue to grow, resulting in decreased lifespan.
And Im sure most of us know that stunting is most likely to occur in overstocked tanks without frequent water changes.

So is there a correlation bewteen the two?

[happychem]

So, is the question: Does the phosphate cause the stunting, or is it adverse conditions, such as overstocking, that causes stunting with a concomitant increase in phosphate?

[mogurnda]

Vertebrates are pretty good at regulating their internal milieu (any points for fancy words?). If I were to hazard a guess, I'd say the phosphate inside a fish does not reflect the phosphate outside.

Since phosphate is highly charged, it won't easily pass through membranes, so it would be relatively easy to keep out of the body. It would have to be transported into the fish actively in the gills.

If I remember, I'll have a look in my fish physiology book at home tonight.

[happychem]

True, but, if I recall correctly, many cells use the electrical potential difference between the inside and outside of the cell as the driving force for many active transport systems, or would that be passive transport since no ATP is required?

Excess negative charges outside the cell would alter this potential, changing the effectiveness of the transport mechanism. Just a shot in the dark here, btw. If the cells were less effective, or had to resort to energy requiring pumps, then perhaps the extra energy required for cell homeostasis would result in less energy devoted to growth.

This could also be the case in cells regulating their internal PO4 content, with a steeper up-concentration gradient to work against.

But again, PO4 could simply be a measurable proxy for other organics more prevalent in overstocked tanks that could cause unhealthy conditions, reducing growth rates...

Molecular Biology aside, it seems reasonable that the Ca++ & PO4-- interactions would increase with PO4 concs. With Ca more difficult to obtain for bone development, nerve and muscle control, this too could reduce growth, I think.

Man it's been a long time since my last bio class...

[slipknottin]

Originally posted by happychem

Molecular Biology aside, it seems reasonable that the Ca++ & PO4-- interactions would increase with PO4 concs. With Ca more difficult to obtain for bone development, nerve and muscle control, this too could reduce growth, I think.


This is what I had in mind. I call tell you from observation that corals grow many times slower when there is alot of phosphate in the water.

And your right, the question is if phosphate is the prime contributor to stunting, or if its just common in the tank setups that lead to stunting. IE- tanks with higher levels of hormones or other things that the fish emit.

[mogurnda]

I think my initial post was unclear. I don't think the phosphate will get into the fish. It has to get past the gill membranes first, and won't do that easily as a highly charged molecule.

Coral cells can't control the solutions their cells are in, fish can.

If Ca levels were to change from their usual 10[-4] M outside and 10[-7] M inside cells, it wouldn't just stunt the fishes' growth. It would kill them outright.

[slipknottin]

accumulated phosphate has been shown to impede calcification in many animals, including cats, birds, reptiles, and humans.

[mogurnda]

I'd like to hear more.

Where is it accumulating? At what levels?

[slipknottin]

I dont really have any sources, I cant find much of anything online. Ive already posted pretty much everything Ive read on the subject.

Im sure there are links out there somewhere, but I cant find them. Maybe happychem has more info.

Ill keep looking in the meantime.

[happychem]

Hey don't look at me, I was just applying knowledge to a question. Mogurnda's the biology expert here. But I will check it out in some of the biochem texts I've got at home.

Maybe I'll run it by some people in the fiance or some people in her biochem lab. I doubt I'll find the answer, they're all gene people, but there are some smart cookies so you never know...

[Sensei_the_dojo]

Originally posted by happychem
. . .Maybe I'll run it by some people in the fiance . . .:confused: There aren't actually people in your fiance, are there happychem?!? I mean, I thought the rest of this thread was confusing enough, but . . . wow! :D

[happychem]

Hehe, I guess I was a little out of it when I edited that post.:rolleyes: :D

[mogurnda]

So, I have looked up ionic regulation in my really old fish physiology book, and found a lot about Na, K and HCO3, and a little about SO4, but nothing about PO4.

I still think it won't be readily absorbed (remember the difference between NH3 and NH4+, one of which is toxic because it is uncharged and is easily absorbed via the gills).

Nonetheless, there's another important point. What are the normal plasma and intracellular concentrations of PO4 in FW fish? If PO4 is normally higher in the blood than in a polluted tank, then it's not likely to make much of a difference. On the other hand, if the plasma concentrations are a lot lower, then the fish may struggle to PO4 out.

I found one ref on google for 4-8 mM, but I'm not convinced that it's reliable. Now I want to go back to work and get on a decent database, but it will have to wait.

[happychem]

Hey, then all we have to do is convert combursome ppm to useful mM, or rather, vice versa!

Keep us posted, this is interesting...:)

[mogurnda]

Hey, then all we have to do is convert combursome ppm to useful mM, or rather, vice versa! Hey, I thought you were the chemist :laugh:

[mogurnda]

Allright, I have combed through the lit, as much as keeping my job will allow. Here's what I learned:

In aquaculture, getting enough phosphate into the fish is more of a problem than keeping it out.

The vast majority of phosphate is absorbed actively in the intestine. It is stored in the bones, where it can be released for metabolism as needed. Output is regulated by the kidneys. Once it gets over a certain level, the kidneys let loose and excrete it at a high rate.

The plasma level I mentioned earlier (about 5-8 mmol/l) seems fairly common.

I really hate ppm, but I'll try to make the conversion. The molecular weight of PO4 is 95. So, a 1 M solution would be 95 ppt, right? 1mM = 95 ppm, so 5 mM would be 475 ppm. If my calculations are right, then this is a whole lot higher than even the most polluted aquarium.

[happychem]

Looks right to me, the calculation that is.

So I guess that that means that high PO4 in an aquarium is just a proxy for unhealthy conditions caused by overstocking.


Hey, I thought you were the chemist

Hey, I can do the conversion, I can convert inches to cm if need be too, doesn't mean I won't gripe about people using outdated, non-base 10, systems;)

[mogurnda]

Just giving you a hard time. :D

Living in the states can lead to some interesting recipes. My weekly kalkwasser mix is as follows:
2.5 gallons RO water
100 ml white vinegar
7 tsp kalkwasser.

If I could add a third system of units, I would do it.

[happychem]

Why not? How many stone does it weight?:D

[slipknottin]

does a higher level of phosphate in the water prevent the fish from absorbing calcium from the water possibly?

[happychem]

Aha! I think we've been looking at it all wrong! Good point slip!

[mogurnda]

Hmmm. Had to think about that for a bit. I would guess that there wouldn't be much interference between the two, because they use separate cellular transport systems. Plus, Ca is largely absorbed from the food in the gut. Since FW fish don't drink, there wouldn't be water from the tank coming into the gut.

I am reminded as I poke around the literature that freshwater is a lousy source of electrolytes. Almost everything has to come from food.

[happychem]

Yes, but, the increased concentration of PO4 may bind Ca, decreasing available Ca for absorption, or making uptake more difficult. Maybe, anyway. I don't know how strong the CaPO4 bond would be. My instincts tell me that it wouldn't be very strong and that the uptake of free Ca would tend to pull the equilibrium back to the free ionic form. But, you never know. Perhaps the binding makes it kinetically more difficult, even though thermodynamically it all comes out in the wash?

[mogurnda]

Calcium Phosphate is insoluble at normal pH. It's one reason that the addtion of Ca(OH)2 (kalkwasser) to marine tanks reduces phosphate. It precipitates out as CaHPO4.

But it will be more soluble in the acidic environment of the gut.

After a little more hunting, I found that I was wrong about Ca intake. Most FW fish take it up through the gills from the water, using specialized cells called "chloride cells." The mechanisms for pumping Ca into the blood are quite interesting, and different from how the same transport happens in the gut.

Under circumstances of low external Ca, they will take it in via the food, though.

So, if PO4 rises high enough to precipitate the available Ca, then the fish will be forced to rely on Ca in the food. Is there a metabolic cost to this, I have no idea. There is probably an answer in the aquaculture literature, but I don't have time to pursue it right now.