Question about fish size and tank size...?

Question

Ok, so I'm a little confused here. I've heard a lot of people say that you need 1 gallon of water per inch of fish. Then I've heard don't put this fish in this tank cause they will get too big for the tank. But, I've also heard that a fish won't outgrow the tank. They will only grow to the size the tank will allow. So, what is actually right? Or are all these statements true? If so, using a pleco as an example, then why couldn't you put a small pleco in a ten gallon tank? He won't get too big for the tank, right? I'm not trying to be flippant or argumentative. Just trying to figure out how this all works.

Answer 1

I never will say use one inch of fish per gallon rule. It doesn't work. What this doesn't account for is waste production and fish mass in the water. Even with a good filter to counter the waste, you then have to account for oxygen and physical space for a fish to grow. Ok some fish take longer to grow then others, so you can sort of cheat this guideline of what you should keep in what sized tank, by having a larger enviroment readily available. Of course in my case I have that, so by size, I've put some of my plecos in my 15 and 20 gallon tanks, but by the same token, I have a 75 and 180 gallon set up I can move them too. If you don't have the long term living space or can't afford it, or just don't have the room, it then makes no sense to buy that fish in the first place.

The problem on size is this. Let's use your example of a pleco in a 20 gallon tank. That tank has a length of like 18 inches lets say, by 18 inches high. Just an estimate. Those plecos tend to get to about 24 inches in lenght. Sure, when someone says fish grow to the size of the enviroment, it's true, to a certain extent. Just as with people, men are say an average 5'11", but yet you see basketball players at 7' +. What does that mean to us in fish? Guidelines about what you can expect a fish to grow to are put out, but there are always exceptions. You should plan for your fish to grow out to what they say adult sizes reach. By putting a pleco in a 20 gallon tank, that fish may stop growing because there's no room to allow it to grow, IN LENGHT, however, that does not stop the internal organs from trying to grow, and thus you develope deformaties and eventually death because there isn't adequate space for that fish to grow in the enviroment you have them in. This is why people say not to put a pleco in such a small tank. The vast majority of hobbists aren't like myself and have massive long term habitats for them. If you can't provide the proper enviroment, for the fish's best interest, and your budgets, don't buy that fish.

JV

Answer 2

Its a matter of opinion. In general 1" of fish per gallon is fine if your dealing with fish that grow to 1" after that it's wrong.

For arguments sake we're dealing with two types of fish one has evolved in rivers and one in still waters.

the one in still waters can secrete a vitiman in the water, this is then measured by a glands if the said vitimin/chemical is too strong the glands telss the fish to stop growing and the fish in the lake all become stunted.

In a river what function would this serve? none the water flows through taking the vitimin/chemical away, Which is why some river species that a put in still waters can attain some amazing sizes.

So as you say you put you pleco in the tank and guess what it continues to grow and grow, its a river fish which can be seen by the torpedo like shape it has it hugs the bottom head into the stream.

If however you put a large lake fish in it releases its chemical and you come along and do a partial water change in fact every 2 weeks or more you do this so said chemical/vitimin has not real effect and the fish grows and grows.

Water can contain only a finite amount of oxygen, so if that being the case what would you think was the key to how much fish you can put in an exclosed system, and what is the importance of surface area.

Some would argue that you can put oxygenating plants into that system to create oxygen however, you should carry through that arguement in the fact that plants actually take in oxygen when they can't photosynthesis, so the benefit is minimal if effective at all, and most people with planted aquariums stock fish lightly.

So the guide to stocking an aquarium is not so easy as shops certainly would have you believe, as a guide in most literature they will point you towards 1" of fish per 12sq" of surface area, this is a guide as a gold fish will require at least twice that amount, where as a neon tetra half of it.

The fact that fish eat, process and dump waste into the tank gives you some idea of what your water can cope with as in the above example.

The fact that some fish have short body length and tall body's like the Angel fish should indicate that you can't rely on just that.

In the end you add you fish and test, then add another and test after a few years you tend to have a knack of knowing whether thats it or not.

AJ

Answer 3

The 1" per gallon is a rule of thumb used to explain things to beginners. This is meant for the type of fish that beginners are more likely to be getting which are small, thin lined, tropical community fish, the largest usually being a molly. This rule of thumb is used to help prevent the beginner from overstocking their tank. Once you have had a little experience, you start to realize that there is more to it (as you have shown by your question) and that it's not such a clean cut question/answer.

When selecting fish or the tank size, you need to consider:
1 - What size will this/these fish be as adult(s)
2 - What is the body shape, narrow or wide? Wide fish will produce more waste because they are larger fish.
3 - Are your fish likely to reproduce? If so, is there room for more population in the tank or will you supply another option for offspring.
4 - How much work will I be putting into the tank? Tank maintenance is the most important part of owning a tank and the more work you are willing to do, the more you can "get away with". But if you are lax in your cleanings, you need to stock significantly less.

There are actually some fish that will stop growing until they are in a large enough environment but usually that's not the case. Once you have stumped the growth, the damage is usually done.

******
In response to an earlier poster - The Chinese Algae Eater can easily grow to 10" or larger in the right conditions. The small ones you are used to seeing are only babies or stunted by being kept in an improper enviornment.

Answer 4

The one inch of fish rule is not really a good "tool" to use, however, I think it's ok to use for smaller tropical/community type fish. And, it's 1 inch of ADULT size fish per gallon. That little 1 inch molly will grow to about 3 inches and that needs to be taken into account. Take neons for example-they grow to about an inch.
Putting 10 neons in a 10 gallon tank, they're small, don't put out much bioload, then compare a 10 inch oscar(though they grow over 12 inches) and put him in that 10 gallon tank. Not only isn't there enough room for the oscar, but they put out much more waste then the neons. That's why it's not good to use that rule for fish other then community fish.

As for them only growing to the size of their tanks, somewhat true for some fish. There's a hormone in the fish that tells it to stop growing. But their insides and guts continue to grow, causing them to take on a roundish appearance. This is called stunting. It stresses them, and shortens their life considerably, amongst a host of other problems you'll most likely encounter with it. I had a good photo of a goldfish, pleco, and an oscar that were stunted, but it's not working. But it was really disgusting to look at. It was obvious looking at them they were messed up really bad too.

Answer 5

Ok, generally speaking one gallon per inch of total fish size is true. Keep in mind that a fat fish counts as more than just his length, think surface area. So for example 10 fish that are 1 inch long may be "more" than one 10 inch fish. Also keep in mind swimming space. For example that same 10 inch fish will NOT be happy in a 10 gallon tank because it is only 10 inches wide and 20 inches long he couldn't even turn around or swim very far without having to turn around. Also keep in mind that goldfish and cichlid family fish are generally big eaters and therefore big poopers, you will need more space or a bigger filter.

Fish will only grow to size of tank: THIS IS A MYTH!!! if anybody tells you this they're wrong, it's not true. Here's what happens a fish grows and loses swim space and speed. He doesn't get enough exercise or clean water circulation so his diet decreases and he gets sick and stressed. He eats less so his growth slows. IF he survives long he will eventually grow causing the same problem to cycle, eventually his growth is stunted, he gets sick and dies. Then people think he died of old age "but he never outgrew the tank" DUH. Once again it is a MYTH. You cannot override nature with glass walls, it does not work that way.

If your tank is 15 gallons or less stick with tetras, mollies guppies, OR some fantail goldfish won't get very big, ask the guy at a real fish store.

Hope this helps

Answer 6

2 foot pleco in a 15 gallon tank? i find that hard to believe.

the basic rule is 1 inch of full grown fish needs 1 gallon of water.
however, i would never follow this rule. lets take a dwarf livebearer, which grows to 1 inch. that would mean a 1 gallon tank would suffice. i would NEVER keep any species of fish in a 1 gallon tank, its inhumane. now if we take a red bellied pacu, which gets to 40 inches. one would require a 40 gallon tank. i find that extremely inhumane. to keep a fish in a tank where he cannot even turn around without bumping into the wall is horrible. its like a person living in a closet their entire life.

when fish are in too-small of a tank they stop growing...thats partially correct. their body stops growing, but their internal organs continue to grow. this is called stunting, and leads to a slow and painful death.

when people say that a fish will outgrow a tank, they mean that the fish is only in a smaller tank until he is large enough to compete with other larger fish in a bigger tank. the smaller tank is the grow-out tank. if the fish is kept in the small tank, he will become stunted and eventually die before his time.

so yes, all of those statements are true. however, its up to you to decide which one you want to follow.

Answer 7

I say 55 is a nice community tank size and more and smaller tanks are for smaller fish like a specialty tank,

Answer 8

it is usually true about 1 in per gallon , giving allowance for the specific fishes size cap , say you read a book or inf sheet on the fish you choose , if it says its largest adult size is 3 in , make allowance for 3in even if the fish is only presently 1 in , some fish althougfh do not have growth caps , pleco's catfish , carp ect. goldfish do not have growth caps and will keep getting bigger and bigger over time , i have had a 1 in pleco that has over years grown to over a foot long. Try an algae eater that has a growth cap , like the chinese algae eater technically called the "sucking loach" it has a maybe 1 -1 1/2 in length and is generally small

Answer 9

basically, all i do is put fish in. dont put like huge fish in a tiny tank cause they WILL outgrow it. plecos can get big, but if you start out with a small one, itll be awhile b4 it gets 2 big and ull no wen its 2 big caouse your filters wont b able 2 keep up with your tank and youll have to clean it al the time. basicaly, when the tank is always really dirty and you have a filter, you probably have too many fish. you need to either get a bigger tank or sell some fish at that point

Answer 10

i was told this weekend at the "aquatic critter" that fish will grow to their natural size. the one inch per gallon is to not overcrowd them. like one oscar needs to be in a 30+gallon tank even if it is only 1 inch now. so you would need 60+ gallons for 2 of them.
some fish stay smaller and some are "disposable" meaning they wont live long anyway so it doesn't matter to crowd them good luck