How Much Space Does a Fish Need?

[leebca]

Much debated; often argued; everyone has advice; and who knows?

Regarding how much aquarium space a particular marine fish needs (gallons of a tank, tank dimensions, filtration size, etc.) do you follow the advice of:
1. An LFS owner;
2. An LFS employee;
3. A diver;
4. A fish collector;
5. A veterinarian (specialized in marine fishes);
6. An online fish seller;
7. An online data base;
8. A book author;
9. A friend/hobbyist;
10. An experienced aquarist;
11. A professional aquarist;
12. A wholesaler;
13. An exporter; or
14. "Other"

How do you know the person knows? How do you know if that the person is just trying to sell a fish? or encourages overstocking for material gains? or is just plain guessing? (i.e., really doesn't know)?

Does our desire to keep more fish, a type of 'greed,' create lies to support our desire? Do we overstock because we want more fish? or choose to listen to the person(s) who says we can add one more fish?

Does a fish that covers 25 miles of ocean on a daily basis belong in a 55, 100, 180, 300, 500 gallon or larger aquarium? What is suitable? Does a 3" fish that burrows into the substrate and calls the hole its home need to live in a 180 gallon aquarium?

Is it okay for a small fish to be in a small aquarium? a large fish in a large aquarium? regardless of behavior or kind of fish?

When we see a crowded fish-only aquarium do we say, 'See, it can be done.' Or are we more likely to say, 'I wonder if that is right?' and 'Are the fish living their full, healthy lives like that?'

How much aquarium space does a captive mated fish pair need when in the wild that same pair stakes out an ocean claim of 9 cubic feet they call their 'own?'

Or do you measure the capacity of the aquarium not by the habits, behavior, or kind of fish, but how much bio-load the fish puts on the biological system? Is it inches per gallon, filled to the brim? Should the aquarium be stocked full so long as the aquarium will hold them? Where's the line?

Will the aquarist be able to tell if the aquarium is overstocked? How? Can the aquarist tell the fish died early because of space stress? or was ill or unhealthy because of space stress?

Every aquarist has answered these types of questions, whether or not they've been asked them or have consciously thought about them. The reader marine fish aquarist has an opinion about stocking limits and space requirements, whether expressed or implied, by the fact that you have put fish in an aquarium.

Who has a good answer?

[JimmyM]

I'm not an expert on saltwater fish keeping yet, but I am very good with philosophical questions.

Nobody has a good answer, but if you're going to ask those philosophical questions, then maybe we're all wrong for trying to keep fish in tanks and we shouldn't even participate in the hobby. After all, there's no tank on earth that duplicates conditions in the wild. But since we all keep fish in tanks, then we're going to have to accept the fact that there is a level of cruelty going on and we're all guilty of it. So to ask the questions you ask means that we should all reconsider the hobby and sell off our aquariums for which we paid thousands of dollars. But who do you sell them to? Do we really want to propogate this cruelty by selling our tanks to someone who will do the exact same thing we've been doing? Might as well take everything to the dump to be safe.

But that ain't gonna happen. We'll keep fish and try to be as responsible as possible, and we'll all make a few mistakes from time to time as we learn the hobby, and yes a few fish may suffer for it as we make mistakes, but at the end of the day, they're fish, a living organism that we catch, kill and eat regularly.

[CSeaSee]

As another point of view to JimmyM's response, if we are able to breed a fish in captivity, then I contend that captive reproduction is a good measure of necessary tank size- if a fish is able to overcome the stress of a captive environment to reproduce, I believe that the fish's environment is sufficiently large and well-suited. Not to anthropomorphize our fish here, but if the fish feel confident enough to reproduce and bring fry into their captive environment, they probably feel low levels of stress. Other ideas?

[leebca]

Like some questions that appear to be philosophical in nature, this one isn't. The answer can be rationally determined by objective information.

All of the numbered 14 sources of determining tank size for any given fish can have the correct recommendation. The 'catch' is that the 'adviser' have to take into account a few 'aspects' about the fish and aquarium:

1. Fish territory in the wild
2. Fish behavior
3. Aquarium system bio-load ability
4. Fish 'size' (when 'grown up')
5. Minimum sized aqarium to use

Anyone of the persons on that list of 14 can certainly have insights into one or more of these aspects. But to provide reasonable recommendations, the person has to have knowledge of all the aspects in order to piece the best advice together.

1. Fish territory in the wild
Where does the fish get food? Hunting? or does food come to it? What space does it need to get its food? What other species is its competitor? Does the fish stake out a space/territory in the wild? If so, what is it? Etc.

2. Fish behavior
Does the fish swim great distances for food or any other reason? or does the fish burrow into the ground and remain in one spot most of its life. What species of fish is it compatible with; not compatible with? Where does the fish swim and stay (top, middle, or bottom)? Etc.

3. Aquarium system bio-load ability
How much (fish + other) waste can the aquarium system handle? Will there be enough gas exchange of sufficient speed? Are the tank dimensions suitable? Tank water volume suitable? Substrate suitable? Any additional biological filtration? (e.g., live rock, cannister filter, deep sand bed, etc.). If there is a lot of live rock, how much swimming and/or water space is left? Etc.

4. Fish size (when grown up)
What bio-load will the fish be putting on the system in the near future? Will it outgrow its aquarium? Etc.

Minimum sized aquarium to use
What are the minimum dimensions and volume aquarium to reasonably not place undue space stress upon the fish? Will the decorations, live rock, substrate take up swimming space and volume? How much? Etc.

Example:
Powder Blue Tang - Sub adult size
1. Sub-adult fish swims about 15 miles a day foraging for algae food along the reef. Travels in groups.

2. Grazer (like cow). Moves around a lot going to areas of suitable greens. Swims along areas that grow algae. May have issues with conspecific species and its own species confined in an aquarium. Relatively shy until it knows its area. Usually stays and swims near the bottom, but goes to surface of rocks growing near the surface. Lenth of aquarium and width will be of importance.

3. Currently, it is a FOWLR aquarium. Bio-load ability will be proportionate to the size with no extra/external biological filtration in system. The live rock at about 2lbs per gallon. Thin substrate of 1-2mm sand. Experience has shown that this fish swims a lot even in the captive environment and may start 'pacing' the tank when the space is limited.

4. Sub-adult is about 3+ inches long. Will continue to grow in the aquarium up to 8 inches. Not a thin fish like some Butterflyfishes, but not a 'thick' fish like some wrasses. However, being a grazing herbivore this fish produces a lot of food wastes -- it eats and deficates a lot. Its bioload will be on the high end of the scale for its mass.

5. Live rock will take up about one third to half the swimming space of the aquarium. Dimensions of at least 6 feet long are needed. The dimensions and size of the 180 standard aquarium fits these needs. The tank has some width to allow the fish to either swim in the open or be reclusive (in the back of the tank). The depth does not have to be as much and with the similar length and width dimensions, the tank could be shortened to hold as little as 135 gallons with 250 pounds of live rock (less than the full amount recommended). Give this fish about 1/6th of the aquarium bio-load ability now and 1/4th later when it grows.

The final recommendation is a 180 gallon aquarium with no more than 5 other fish of the same bio-load in with it. Its companions should preferably not be other tangs. If the fish grows to 5+ inches, the bio-load usage needs to shift to where the fish is taking a larger share and the numbers of the other similar fishes should be reduced, or the fish is moved to a larger aquarium.