DISCUSSION: "SW Inch per Gallon"....

[Tommy Gun]

Hello fellow fish addicts!

Please let me preface the following by saying that I am NOT a big supporter, nor advocate, of any "per gallon" type rule/guideline even though I realize their true, and mostly positive, intention. With that being said, I have noticed that there is always a large difference between the freshwater version of "One inch of fish per gallon of water" and the saltwater version of "One inch of fish per every 2,3,4, or 5 gallons of water" (depending on who you ask, of course). So, I thought it might be somewhat insightful to discuss the reasons, or probable reasons for this difference - which I also feel equates into the statement of "saltwater fish are more sensitive to water quality than freshwater fish" (agree?).

In short, based upon some more recent research, I feel as though a large reason for this is probably due to the difference between the osmotic regulation "goals" of FW and SW fish. For example, this is what I found, with SM Jay's help, through research and subsequent posting of the "Role of Osmosis" article:

Freshwater Osmotic Goals
With the understanding that electrolytes are vital to maintaining life and that salt, when dissolved in water is an electrolyte, it becomes apparent why our freshwater fish continually work towards collecting and retaining salt from the water they live in. In fact, this also means that freshwater fish are often more salty than their watery environment, which creates an imbalance in osmotic pressure between cell walls and the water. Because of this, freshwater fish are continually ?drinking? water and rely on efficient kidney function to absorb salts and then transport the abundance of water and other wastes out of the body.

Saltwater Osmotic Goals

The exact same electrolyte principles apply to the marine environment as well; however, in this case there is an overabundance of dissolved salts which creates the need for saltwater fish to not only limit salt content, but also retain the equally important aspect of hydration ? water. Because of this situation, marine fish must also drink a lot of water, however, unlike their freshwater counterparts, these animals utilize modified kidneys which limit the removal of water from their blood, but remove wastes and some forms of salt; where as other forms of salt ? such as Sodium Chloride ? are removed via specialized gills and other functions.

However, as SM Jay forwarded to me, by many accounts, both freshwater and saltwater fish 'drink' or otherwise ingest quite a bit of the water they live in on a regular basis; meaning they both must be subjected to all of the water's solutes, yet we are always (or almost always) advised that we should stock lightly in a marine aquarium with little to no exception being placed on tanks which hold no sessile or motile inverts. Anyone have more insight into why this is the case?

[Rychek]

Wow, that is a great abstract. It not only filled in a few memory gaps about osmosis, but shed new light on how it applies to the hobby. It also affirmed some of my thoughts/beliefs concerning water parameters in the aquarium versus the wild (more so for FW than SW though).

I'm very curious as to the logic behind the gallon/inch "rules" for SW and FW. At the present, I haven't heard any real reasons why SW fish "need" more gallons/inch than FW. I'll have to give it more thought myself as well.

[chadf]

Saltwater fish need more water volume because they are more sensitive to water params changing and nitrates, nitrites, and ammonia in the water. Thus if something were to come up and you missed a few water changes, your power went out, or whatever you would have more room for error. An overstocked tank isn't going to last very long in a power outage or lack of routine mainence. That's my theory on the issue.

[Rychek]

Thanks for the explaination chad. So, basically, you're saying marine fish should be more lightly stocked so in the event of an emergency/fault in maintenance, they have a better chance of survival? I agree with that, in principle.

I also agree that marine fish are more sensitive to water parms than FW fish due to osmotic influences. However, I don't agree that there is a hard and fast rule about gallons/inch that govern such a subjective topic as stocking levels. I'm not advocating overstocking by any means either. I'm simply trying to learn what others think in order to make a more informed/educated decision for my own fish keeping.

[Tommy Gun]

Please don't get me wrong here....I am not posing this question(s) because I already know the answer since I really don't, but have been able to shed a lot of doubt on some of the more popular explanations due to the large amount of research I have already done on the subject. For example...

they are more sensitive to water params changing and nitrates, nitrites, and ammonia in the water

....I read many many many accounts where the information and/or opinions state that it would take a very large amount of nitrAtes to kill a fish (including SW types) - in fact, one of them stated that a fish wouldn't really die until nitrate levels reached 400 ppm (which is not to imply that I agree but just passing that along). However, I realize that nitrates are more problematic for invertebrates - perhaps even more so for coral and anemones - so the 'stock lightly' advice makes perfect sense when those items are involved....yet I haven't noticed anyone stating that we can have 'one inch of fish per gallon of water" if the tank is truly a fish-only variety and that is what has peaked my curiosity more than anything else.

[Rychek]

It seems to me that when it comes to our hobby, we as hobbiests (and I am just as guilty of this as anyone else) tend to pass along the things we've been told as all encompassing fact (not that in many instances, they aren't). I don't know why there isn't more distinction between FO, FOWL and Reef, but in my opinion, there should be quite a bit of differentiation.

Tommy, Could you possibly provide a few links from your research or point me in the right direction to find them? I would like to read up a bit more on the subject so as to overcome "lfs syndrome" which is the sharing of information whose veracity is of a dubious or incomplete nature.

[knorsk]

In a few of the books I have read ;Saltwater aquariums a great hobby, aquariums, and a few others the biggest difference that the books make reference to is the size of marine species compared to freshwater species. So if you have a 55 gallon you could have four four inch fish at max adult length. So roughly 3.5 gallons for every inch of fish. If you had a bad ass system you could probably bend the rules but then it would be SW money per gallon.

[Rychek]

That's a new one to me. Do your books say why a 55 gal tank should only house a maximum length fish of 4"? Does it have to do with swimming space requirements? Is the tank too narrow? I guess I'm looking for reasons other than "so-and-so said so."

[Tommy Gun]

It seems to me that when it comes to our hobby, we as hobbiests (and I am just as guilty of this as anyone else) tend to pass along the things we've been told as all encompassing fact

This has always been my thinking as well....and why I try to explain the "why" behind most of my replies, suggestions, or answers (and to annoy some people with long posts, but oh well). I figure if I know why I am supposed to do something, then I will be more apt to do it...if I can't figure out why I should be doing it, then I become a skeptic.

Tommy, Could you possibly provide a few links from your research or point me in the right direction to find them? I would like to read up a bit more on the subject so as to overcome "lfs syndrome" which is the sharing of information whose veracity is of a dubious or incomplete nature.

Sure! Like I said, I have been focusing on osmosis as the answer to this question and perhaps one of the better, more easy-to-understand explanations of the differences between FW and SW osmotic regulation:

http://academics.smcvt.edu/dfacey/an...ystemplate.htm

A good description of the four main methods of approaching hydration...which requires both water and salt:

http://www.madsci.org/posts/archives...5291.Zo.r.html

And while I realize that wikipedia is less than what it seems...and this article is certainly a farce...but I stumbled upon a mention of this compound and will be looking deeper into it today since it might actually create a level playing field between SW and FW:

http://en.wikipedia.org/wiki/Trimethylamine_oxide

biggest difference that the books make reference to is the size of marine species compared to freshwater species.

I also can't really agree with that notion...it is probably easier to find a SW fish with a max size of one inch than the same in a FW version. The same rule regarding tank dimensions would apply to longer or larger FW fish or SW fish equally.

If you had a bad ass system you could probably bend the rules but then it would be SW money per gallon.

I can tell you right now, I don't have a very expensive or overly technical system and I have well over one inch of fish per every 3.5 gallons of water. In fact, I am thinking about adding one more fish which would eventually result in me having one inch of fish per gallon of water...in a reef tank.

[Rychek]

Thanks for the links Tommy! Hopefully I'll have time to read them today.

I am of the opinion that size requirements between SW and FW fish are very similar. Hopefully I will soon learn if I am right or wrong. Either way, I want to know the facts. I've been told too many contradicting things by too many people readily accept anything they say without a little research and thought of my own.

Thanks to all who have participated so far, and, please, keep the discussion going so we all can benefit together.