INTRO
You want to know what is the appropriate sized display aquarium for a particular marine fish. You look it up. You find books; you find Forums; you find on-line marine fish sources; you ask your LFS; and you ask around. You get about a minimum of 3 and up to 10 different recommendations. Who is right? Are any of them right?
There is no doubt that ANY display tank (DT) is too small for our wild-caught marine fishes. They come from a relatively limitless area of space into the confines of a glass or plastic box. So there is no perfect space. For those of you who are purists and argue this point, I agree. But there is a rational way of determining what is appropriate space in a DT for a given fish.
In this post I’ll explore what goes into making this sort of decision. You may disagree or agree. That is your option. But avoid the simpleton’s response that all captive fishes are in the wrong space. It is not only tiresome but shows an unwillingness to consider the needs of these wonderful fishes.
This post is connected to the post on fish stocking limit: Fish Stocking Limit – for FO and FOWLR
PLEASE NOTE: The original date of this post. The information contained in this post regarding other posts, online store recommendations, etc., were all based upon information available at the time of this post. Things do change, although in short, I still believe that most online stores do not represent the properly needed tank space for the mature, adult size of the fishes they offer for sale.
MEET THE MEAT
Who’s on First
Any resource you use to gather information on this subject needs to answer your questions. The minimum questions you need to ask them are:
1. Did you keep this fish in captivity? How many? How long?
2. If “No” to the above, then where did you get the information you have provided?
3. If this is original information, then how did you determine what size DT is needed for this fish?
1. There are many marine aquarium books. They have sample fishes. There are many marine fish books. They have even more marine fish examples. There are online sites with hundreds of pictured marine fishes -- some for information; some for sale. They have recommended DT sizes. Do you think the authors of these publications have actually kept all those fishes? If so, how many of those fishes did the authors actually keep? and for how long? This is where the mis-information starts. The provided opinions are not based upon real knowledge or firsthand experience.
2. So if they don’t have first-hand information, where are they getting the recommendation from? Someone copying someone else’s recommendations without question is the second source of mis-information on this topic. Only, there are many different recommendations. So who do they copy? and why? Many of the sources of this information have no idea whose right or which recommendation to follow anymore than you, the person trying to get a reliable answer to, ‘Can I keep this fish in a X aquarium?’
3. This leaves the third possibility. You are getting information from an informed source who has, by some means, determined the correct DT for a particular fish. Is this an opinion? Yes. Does opinion make it wrong? No. If opinion is well founded and rationally sound it should be followed until shown flawed. How should this person give such advice? That is, what needs to be taken into account?
INFO NEEDED
There is some basic information needed to give this kind of advice on the DT needs of marine fish. In an ideal world the advising person would have and know the following:
a. Knowledge of the fish behavior in the wild AND in captivity (the two often differ);
b. Having kept the fish before in different sized DTs;
c. Having kept multiple specimens for a long time (5+ years);
d. Studied fish behavior in captivity in different DTs; and
e. Understands the bio-load and ultimate potential size of the fish
It is rightly argued that circumstances dictate the answer. So one reason why you might get different answers is because someone has a specific size of fish in mind. But take the recommendation for, let’s say four different fishes is the same = 30 gallon aquarium. Does that mean all four can still go into that 30 gallon aquarium? You see, this is one place where recommendations fail. If the hobbyist puts four fishes into a tank and then looks up the tank needed for their fourth fish and finds their tank ‘just fits’ the recommendation, can that fish go into there or should the DT be larger? The reader knows the answer. (It's "It depends. . .").
What is not part of determining what DT is needed is how much you want to buy or the other persons wants to sell the fish. Yes. There are people who sell things you shouldn’t own or are unable to provide for. In our society, the sale is often more important than the life and in this hobby, fishes are mostly considered commodities, not life. Motivating factors such as profit or desire are not a part of a good DT size recommendation.
WHAT IT TAKES
I use those five criteria for my recommendations. I don’t look up other people’s opinions. Mine is original and maybe that is why there are only a few who repeat what I offer. “He’s different” has not bothered me when I believe I am correct.
My recommendation takes into account what fishes are also present or what other fishes would be allowed for the bio-load capacity of the marine system. This leads into another consideration – the system. More volume in the system isn’t totally without some value, but fish that need space for swimming find this extra volume, unavailable to them, is without benefit.
Don’t underestimate the value of items a. and d. Some fishes need open space; others don’t. Some fish need to swim long distances (so tank length is of value). For this reason, we generally realize that open ocean fishes are not suitable for aquarium life. Other fish may just need to swim around and pick at things and need a certain space for that activity. Other fish are content to call a square foot of substrate home. All these kinds of behaviors are noted in the wild and in observation in captive fishes. These behaviors are what has a great weight in allotting DT space to them.
Is there a formula? No. You don’t get an easy rule to follow. You have to know those five items to get the best recommendation. Nothing replaces the experience. Knowledge goes a very long way, but doesn’t get you all you need. If you don’t have the experience but still want to make the recommendations, then you need to, as a minimum, get to several different public and private aquariums and observe the fish in captivity. Observation in the wild is not enough. With captive observation behind your opinion, you’re at least in some position to make a recommendation on a fish you haven’t kept before.
Lastly, my recommendation comes from the long term needs of the fish without any other consideration (your budget, your time, your care, what you want, what others have said, profit, etc.).
LESS THAN GOOD
EXAMPLES:
1. Humuhumu Triggerfish - largest size is about 12 inches
The Marine Center in Dallas says that the minimum tank size for a Humuhumu Triggerfish (a.k.a Humu Triggerfish (Rhinecanthus aculeatus)) is 20 gallons. This is an astounding recommendation without saying anything about the size of the fish or other fish inhabitants. Can you see a 12" fish in a 20 gallon container? I don't think it could turn around! Who would believe this? A person trying to justify getting one for the 30 gallon tank, that’s who! And who would repeat this? An LFS trying to sell this fish, that’s who. Think of e. above: Would you think that this size DT could handle the bio-load of such a fish? They sell 2-3" sized fishes, but do they believe the fish will or should remain this size in the 20? Is the 20 even the correct size for the 3" fish?
Drs. Foster & Smith says the minimum tank size is 70 gallons. Where did this come from? If they are thinking this fish belongs in that aquarium, then what size is the fish? And does the fish live there its entire life even when 12+ inches long?
Terry B. kept one of these in a 135-gal tank for 14 years. He recommends a minimum tank size of 100 gallons for this particular species.
The book Marine Fishes by Scott W. Michael says this fish is suitable for a 55 gallon DT.
Who to believe? Are any of them accurate? Here is my take:
The fish has been found in the wild up to 1 foot in length. We know that this is the observed maximum fish size. I know however that marine fishes don’t stop growing. So the foot length is not a true maximum, but at least something we can work with at this point in time, for this consideration. Sometimes though, this number reported to the reader is just totally wrong, too.
The fish swims quite a bit in captivity. Not too surprising since the fish is a hunter by nature. It isn't a fish that waits for food to come to it, like an Angler -- it seeks its prey. It ‘paces’ in a small aquariums, I have observed. ‘Pacing’ is a potential sign of space stress. The ones I kept in 100g or smaller were pacers. I’ve owned 6 of them in the last 40 years and seen 30+ others in captivity in other DTs and aquariums. What else do I know of this fish? It swims in the coral reefs in a fairly large area. It is a predator that either chases down its prey or catches it off guard from the open waters and the substrate. It covers a lot of territory in life (relative to its size).
Pulling what I know together -- the fish needs for captivity:
Swimming space; length of tank to get up to speed; a big bio-load capacity system; similar attitude tank mates.
How will it fit into a hobbyist's DT? Will the hobbyist keep this fish alone - by itself? Not likely. I assume the hobbyist wants to keep this fish with others, maybe putting together an aggressive or semi-aggressive tank setup. I anticipate it being in a (limited and specialized) community tank.
My recommendation: The fish lends itself to different sized DTs depending upon its size and bio-load needs. That is, this fish can be in a smaller place when the fish itself is small. Then the fish would be transferred to larger DTs as its size or maturity warrants. This is what I've called "tank hopping." The fish is suitable for a community tank of no less than 55 gallons when the fish is below 2". When 2" to 4" it should be in a 125+ gallon aquarium (at least a 6 foot length). When above 4" it needs to be in a 240 or longer aquarium. The aquarium needs to be open and with a lot of swimming space.
Are you seeing how the answer isn’t always just one number? Do you see how those five points are being taken into account? I hope you also note that these are opinions. But you have the right and should exercise it, to ask and understand where and how the opinion was derived.
2. The Maroon Anemonefish
Another example is the Maroon Anemonefish (Premnas biaculeatus). I’m not a fan of Damselfishes, let alone the Anemonefishes. I’ve had thousands (yes, that is not a typo) in my life. My favorite of the entire group is the Maroon, however.
I leave it to you the reader to look up places that recommend a DT size for this fish. You’ll find differences just like for the Humuhumu Triggerfish.
The recommendation should be different for a single fish than that for a mated pair. In a mated pair the female will get to over 6 inches in size! That’s one big Anemonefish when you think about it! So a single fish below 1" is okay in a 25 gallon; or for its full life in a 29+ gallon. In the wild, we know that a mated pair will take up to 12 cubic feet of space and call it their own. They will dive off competitors or suspicious marine lifeforms to that boundary.
In the confines of the DT, the mated pair must be in no less than a 45 gallon for the size of the female and the territory the mated pair will need.
There is no one answer to the DT size for this fish without additional information. Yet in almost all the references you’ve found, you will get just one number. Does this mean that two can be put into that same sized DT? It doesn’t make sense to me when I understand and have experience with these fishes. In the 45, I’m assuming the pair is mated and with only one other fish (or two small) which will have little or zero interaction with the pair (so as to not stress them even more then their mating behavior stresses them!). The aquarium doesn’t need a lot of swimming space, but aquascaped with some hiding places and a location suitable for a mated pair. It should be a system with a sump, skimmer, mechanical filter, carbon, and of total volume of no less than 45 gallons of water.
If a larger community is desired, begin by assigning 40 gallons and that space to the Maroon pair and then add DT size for other fishes.
3. A Tang
I know a 12" Tang living in 6" (depth) of water. The tank is a coral grow out tank and is shallow for the corals. The dimensions of the tank is 10 feet long and 4 feet wide. This way, the person/owner/operator can reach all places in the tank with gloved hands. If you do the math, the DT could hold a bit less than 150 gallons (but closer to 130 since it isn’t full). With sump comes to about 155 gallons in the system. I think this fish is in as close to ‘captive heaven’ as it can be!
SO. . .
When I post that I don’t agree with the tank size of a particular fish, I am referring to the way I determine appropriate DT size, noted above. It is different for almost every Genus of fish and sometimes even different species.
Is it always accurate? No. There is one more factor I can’t always account for – the personality of a particular fish. I’ve had a few dozen Powder Blue Tangs [PBT] (Acanthurus leucosternon) in my time and have two now. For the first time in my life, one of my PBT (in a 180) is pacing, showing signs of space stress. This is unusual from my experience. That is one reason I suggest that before you take anyone’s opinion, they have experience with multiple fish in that species. One is not always representative.
This is the background that goes into my reply to posts that tank size is not appropriate. It forms the foundation of when I’m asked to explain why a particular fish needs a certain size of aquarium. I’m happy to explain the particulars, but unless you read this post and understand the background, my answer(s) may seem unfounded.
What you do not want
You don’t want advice from someone with just one experience to determine what is right for the majority of those fish. You don't want advice from those without experience with this fish -- preferably multiple experiences. You don’t want advice from a third party quoting another person’s advice. You don’t want advice from those that haven’t got at least 4 out of the above 5 requirements. You don’t want to take advice from those selling you fish without being skeptical. And you don't want to take advice from a person who only sells the fish from stock tanks.
Disclaimer: The online references were accurate at the original time of this writing. It would be great if they actually rethought those recommendations and made changes.
You want to know what is the appropriate sized display aquarium for a particular marine fish. You look it up. You find books; you find Forums; you find on-line marine fish sources; you ask your LFS; and you ask around. You get about a minimum of 3 and up to 10 different recommendations. Who is right? Are any of them right?
There is no doubt that ANY display tank (DT) is too small for our wild-caught marine fishes. They come from a relatively limitless area of space into the confines of a glass or plastic box. So there is no perfect space. For those of you who are purists and argue this point, I agree. But there is a rational way of determining what is appropriate space in a DT for a given fish.
In this post I’ll explore what goes into making this sort of decision. You may disagree or agree. That is your option. But avoid the simpleton’s response that all captive fishes are in the wrong space. It is not only tiresome but shows an unwillingness to consider the needs of these wonderful fishes.
This post is connected to the post on fish stocking limit: Fish Stocking Limit – for FO and FOWLR
PLEASE NOTE: The original date of this post. The information contained in this post regarding other posts, online store recommendations, etc., were all based upon information available at the time of this post. Things do change, although in short, I still believe that most online stores do not represent the properly needed tank space for the mature, adult size of the fishes they offer for sale.
MEET THE MEAT
Who’s on First
Any resource you use to gather information on this subject needs to answer your questions. The minimum questions you need to ask them are:
1. Did you keep this fish in captivity? How many? How long?
2. If “No” to the above, then where did you get the information you have provided?
3. If this is original information, then how did you determine what size DT is needed for this fish?
1. There are many marine aquarium books. They have sample fishes. There are many marine fish books. They have even more marine fish examples. There are online sites with hundreds of pictured marine fishes -- some for information; some for sale. They have recommended DT sizes. Do you think the authors of these publications have actually kept all those fishes? If so, how many of those fishes did the authors actually keep? and for how long? This is where the mis-information starts. The provided opinions are not based upon real knowledge or firsthand experience.
2. So if they don’t have first-hand information, where are they getting the recommendation from? Someone copying someone else’s recommendations without question is the second source of mis-information on this topic. Only, there are many different recommendations. So who do they copy? and why? Many of the sources of this information have no idea whose right or which recommendation to follow anymore than you, the person trying to get a reliable answer to, ‘Can I keep this fish in a X aquarium?’
3. This leaves the third possibility. You are getting information from an informed source who has, by some means, determined the correct DT for a particular fish. Is this an opinion? Yes. Does opinion make it wrong? No. If opinion is well founded and rationally sound it should be followed until shown flawed. How should this person give such advice? That is, what needs to be taken into account?
INFO NEEDED
There is some basic information needed to give this kind of advice on the DT needs of marine fish. In an ideal world the advising person would have and know the following:
a. Knowledge of the fish behavior in the wild AND in captivity (the two often differ);
b. Having kept the fish before in different sized DTs;
c. Having kept multiple specimens for a long time (5+ years);
d. Studied fish behavior in captivity in different DTs; and
e. Understands the bio-load and ultimate potential size of the fish
It is rightly argued that circumstances dictate the answer. So one reason why you might get different answers is because someone has a specific size of fish in mind. But take the recommendation for, let’s say four different fishes is the same = 30 gallon aquarium. Does that mean all four can still go into that 30 gallon aquarium? You see, this is one place where recommendations fail. If the hobbyist puts four fishes into a tank and then looks up the tank needed for their fourth fish and finds their tank ‘just fits’ the recommendation, can that fish go into there or should the DT be larger? The reader knows the answer. (It's "It depends. . .").
What is not part of determining what DT is needed is how much you want to buy or the other persons wants to sell the fish. Yes. There are people who sell things you shouldn’t own or are unable to provide for. In our society, the sale is often more important than the life and in this hobby, fishes are mostly considered commodities, not life. Motivating factors such as profit or desire are not a part of a good DT size recommendation.
WHAT IT TAKES
I use those five criteria for my recommendations. I don’t look up other people’s opinions. Mine is original and maybe that is why there are only a few who repeat what I offer. “He’s different” has not bothered me when I believe I am correct.
My recommendation takes into account what fishes are also present or what other fishes would be allowed for the bio-load capacity of the marine system. This leads into another consideration – the system. More volume in the system isn’t totally without some value, but fish that need space for swimming find this extra volume, unavailable to them, is without benefit.
Don’t underestimate the value of items a. and d. Some fishes need open space; others don’t. Some fish need to swim long distances (so tank length is of value). For this reason, we generally realize that open ocean fishes are not suitable for aquarium life. Other fish may just need to swim around and pick at things and need a certain space for that activity. Other fish are content to call a square foot of substrate home. All these kinds of behaviors are noted in the wild and in observation in captive fishes. These behaviors are what has a great weight in allotting DT space to them.
Is there a formula? No. You don’t get an easy rule to follow. You have to know those five items to get the best recommendation. Nothing replaces the experience. Knowledge goes a very long way, but doesn’t get you all you need. If you don’t have the experience but still want to make the recommendations, then you need to, as a minimum, get to several different public and private aquariums and observe the fish in captivity. Observation in the wild is not enough. With captive observation behind your opinion, you’re at least in some position to make a recommendation on a fish you haven’t kept before.
Lastly, my recommendation comes from the long term needs of the fish without any other consideration (your budget, your time, your care, what you want, what others have said, profit, etc.).
LESS THAN GOOD
EXAMPLES:
1. Humuhumu Triggerfish - largest size is about 12 inches
The Marine Center in Dallas says that the minimum tank size for a Humuhumu Triggerfish (a.k.a Humu Triggerfish (Rhinecanthus aculeatus)) is 20 gallons. This is an astounding recommendation without saying anything about the size of the fish or other fish inhabitants. Can you see a 12" fish in a 20 gallon container? I don't think it could turn around! Who would believe this? A person trying to justify getting one for the 30 gallon tank, that’s who! And who would repeat this? An LFS trying to sell this fish, that’s who. Think of e. above: Would you think that this size DT could handle the bio-load of such a fish? They sell 2-3" sized fishes, but do they believe the fish will or should remain this size in the 20? Is the 20 even the correct size for the 3" fish?
Drs. Foster & Smith says the minimum tank size is 70 gallons. Where did this come from? If they are thinking this fish belongs in that aquarium, then what size is the fish? And does the fish live there its entire life even when 12+ inches long?
Terry B. kept one of these in a 135-gal tank for 14 years. He recommends a minimum tank size of 100 gallons for this particular species.
The book Marine Fishes by Scott W. Michael says this fish is suitable for a 55 gallon DT.
Who to believe? Are any of them accurate? Here is my take:
The fish has been found in the wild up to 1 foot in length. We know that this is the observed maximum fish size. I know however that marine fishes don’t stop growing. So the foot length is not a true maximum, but at least something we can work with at this point in time, for this consideration. Sometimes though, this number reported to the reader is just totally wrong, too.
The fish swims quite a bit in captivity. Not too surprising since the fish is a hunter by nature. It isn't a fish that waits for food to come to it, like an Angler -- it seeks its prey. It ‘paces’ in a small aquariums, I have observed. ‘Pacing’ is a potential sign of space stress. The ones I kept in 100g or smaller were pacers. I’ve owned 6 of them in the last 40 years and seen 30+ others in captivity in other DTs and aquariums. What else do I know of this fish? It swims in the coral reefs in a fairly large area. It is a predator that either chases down its prey or catches it off guard from the open waters and the substrate. It covers a lot of territory in life (relative to its size).
Pulling what I know together -- the fish needs for captivity:
Swimming space; length of tank to get up to speed; a big bio-load capacity system; similar attitude tank mates.
How will it fit into a hobbyist's DT? Will the hobbyist keep this fish alone - by itself? Not likely. I assume the hobbyist wants to keep this fish with others, maybe putting together an aggressive or semi-aggressive tank setup. I anticipate it being in a (limited and specialized) community tank.
My recommendation: The fish lends itself to different sized DTs depending upon its size and bio-load needs. That is, this fish can be in a smaller place when the fish itself is small. Then the fish would be transferred to larger DTs as its size or maturity warrants. This is what I've called "tank hopping." The fish is suitable for a community tank of no less than 55 gallons when the fish is below 2". When 2" to 4" it should be in a 125+ gallon aquarium (at least a 6 foot length). When above 4" it needs to be in a 240 or longer aquarium. The aquarium needs to be open and with a lot of swimming space.
Are you seeing how the answer isn’t always just one number? Do you see how those five points are being taken into account? I hope you also note that these are opinions. But you have the right and should exercise it, to ask and understand where and how the opinion was derived.
2. The Maroon Anemonefish
Another example is the Maroon Anemonefish (Premnas biaculeatus). I’m not a fan of Damselfishes, let alone the Anemonefishes. I’ve had thousands (yes, that is not a typo) in my life. My favorite of the entire group is the Maroon, however.
I leave it to you the reader to look up places that recommend a DT size for this fish. You’ll find differences just like for the Humuhumu Triggerfish.
The recommendation should be different for a single fish than that for a mated pair. In a mated pair the female will get to over 6 inches in size! That’s one big Anemonefish when you think about it! So a single fish below 1" is okay in a 25 gallon; or for its full life in a 29+ gallon. In the wild, we know that a mated pair will take up to 12 cubic feet of space and call it their own. They will dive off competitors or suspicious marine lifeforms to that boundary.
In the confines of the DT, the mated pair must be in no less than a 45 gallon for the size of the female and the territory the mated pair will need.
There is no one answer to the DT size for this fish without additional information. Yet in almost all the references you’ve found, you will get just one number. Does this mean that two can be put into that same sized DT? It doesn’t make sense to me when I understand and have experience with these fishes. In the 45, I’m assuming the pair is mated and with only one other fish (or two small) which will have little or zero interaction with the pair (so as to not stress them even more then their mating behavior stresses them!). The aquarium doesn’t need a lot of swimming space, but aquascaped with some hiding places and a location suitable for a mated pair. It should be a system with a sump, skimmer, mechanical filter, carbon, and of total volume of no less than 45 gallons of water.
If a larger community is desired, begin by assigning 40 gallons and that space to the Maroon pair and then add DT size for other fishes.
3. A Tang
I know a 12" Tang living in 6" (depth) of water. The tank is a coral grow out tank and is shallow for the corals. The dimensions of the tank is 10 feet long and 4 feet wide. This way, the person/owner/operator can reach all places in the tank with gloved hands. If you do the math, the DT could hold a bit less than 150 gallons (but closer to 130 since it isn’t full). With sump comes to about 155 gallons in the system. I think this fish is in as close to ‘captive heaven’ as it can be!
SO. . .
When I post that I don’t agree with the tank size of a particular fish, I am referring to the way I determine appropriate DT size, noted above. It is different for almost every Genus of fish and sometimes even different species.
Is it always accurate? No. There is one more factor I can’t always account for – the personality of a particular fish. I’ve had a few dozen Powder Blue Tangs [PBT] (Acanthurus leucosternon) in my time and have two now. For the first time in my life, one of my PBT (in a 180) is pacing, showing signs of space stress. This is unusual from my experience. That is one reason I suggest that before you take anyone’s opinion, they have experience with multiple fish in that species. One is not always representative.
This is the background that goes into my reply to posts that tank size is not appropriate. It forms the foundation of when I’m asked to explain why a particular fish needs a certain size of aquarium. I’m happy to explain the particulars, but unless you read this post and understand the background, my answer(s) may seem unfounded.
What you do not want
You don’t want advice from someone with just one experience to determine what is right for the majority of those fish. You don't want advice from those without experience with this fish -- preferably multiple experiences. You don’t want advice from a third party quoting another person’s advice. You don’t want advice from those that haven’t got at least 4 out of the above 5 requirements. You don’t want to take advice from those selling you fish without being skeptical. And you don't want to take advice from a person who only sells the fish from stock tanks.
Disclaimer: The online references were accurate at the original time of this writing. It would be great if they actually rethought those recommendations and made changes.
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