- Joined
- Sep 11, 2015
- Messages
- 246
- Reaction score
- 114
In this thread, I'll share my thoughts on tank sizes for marine fish. Coming from a math background, I'll have to include some math in here - but I promise it's simple!
There are many factors to "tank size". There's volume, which the opens up to the volume of your system. Then you've got distance measurements, the most common being length. However, there is definitely merit to working with width and height when determining an appropriate aquarium size for a fish. Another distance measurement that I think is often overlooked in fishkeeping is the maximum swimming distance - that is, how far can your fish swim in a straight line without being interrupted? Sometimes this is the length of the aquarium, but it can be longer or shorter based on your aquascape.
So, how would you go about deciding on a tank size for any given fish?
Simply put, there isn't a "do-it-all" formula for this.
The first step in determining a tank size - is determining the size of your fish.
Many fish will NOT reach their maximum size in captivity, for any number of reasons. Stunting is usually what comes to mind first - that is, the fish had some kind of environmental issue that didn't allow it to grow to its full potential - but it is my belief that simple genetics are often the cause of this. Think about it - the tallest human ever was about 9 feet tall, and the heaviest was about 1400 lbs. How many people do you know that are even close to 9'/1400 lbs? The average human is nowhere near the size of the maximum human - not because of any growth issues, but simply because their genetics don't allow them to grow that tall.
So if a fish isn't going to reach its maximum size, how big is it going to get? Again, there's no answer that is universal - but my experience, and many others', has been that fish in an aquarium will reach an average of 65-75% of their maximum size. (Note: if you prefer fractions, this is equal to about 2/3 to 3/4 the maximum size.)
For instance - yellow tangs reach a maximum size of about 8 inches. So using our formula, we can see that the average yellow tang in an aquarium will reach about 5-6 inches long.
Now, of course, there are exceptions to this rule - and you should research this based on the individual fish you want to keep. But on average, fish will reach 65-75% of their maximum length in your aquarium.
Now that we've defined how big our fish is likely to get - we will need to classify it based on its swimming patterns. For this, we can define three patterns - sedentary, hovering, and darting.
Now, if you're experienced with fish - you'll often know which category a fish falls into. But if you aren't, there is a way to determine it, that does take some time. In order to do it "scientifically", observe multiple specimens of the given fish often - 20-30 times, and even more is better. On each observation, note what the fish is doing - is it sitting still, is it "hovering" around the rock, or is it darting across the tank? Assign a value to each - sitting still is a "1", hovering is a "2", and darting is a "3". At the end of your observations (again, at least 20 would be preferable, with more being better), add up all the values you have recorded, and divide it by the number of observations - in other words, take the average of the values. This value, which will likely be a decimal number, should represent the average swimming pattern of the fish. If it is in the range of 1-1.3, it is safe to say the fish is often sedentary. If it is in the range of 1.4-1.6, you are in sort of a "grey area", where I feel it is best to classify the fish as a hovering species. From 1.7-2.3, you are safely in the range of a hovering species. Again from 2.4-2.6, you are in another "grey area", and I feel it is better to classify the fish as a darting species - and of course from 2.7 to 3, the fish would be classified as a darting species.
A much simpler and less scientific way to do this, is to simply ask the knowledgeable members on this forum how they'd classify the fish
For reference, here are some rough classifications for different types of fish:
So you've determined how big your fish is going to get, and how it's going to swim - that's great! You've gotten two of the most important parts out of the way. Now, we can discuss tank sizes.
This is a topic of great debate, and what I'm posting is sure to spark some debate in the comments below - but these are what I feel to be proper formulas in determining the minimum tank size for most saltwater fish.
A note before I show the formulas - I believe that the maximum straight shot distance is equally important as the length and width of the tank. I don't think length is as important, I don't think width is as important - but I do think that added together, they are equally important. So, I will be including the maximum swimming distance and the combined length and width of the tank. This isn't meant to scare anyone off with the math - just to help create an ecosystem properly sized to a given fish!
For sedentary fish, that tend to sit still most of the time - aim for a maximum swimming distance of at least 4 times the length of the fish and a length and width of the tank that combine to be at least 6 times the length of the fish.
For hovering fish, that tend to hover around the rockwork, or fish that tend to equally mix their time between actively swimming and sitting still - aim for a maximum swimming distance of at least 5 times the length of the fish and a length and width of the tank that combine to be at least 8 times the length of the fish.
For darting fish, that are more often than not observed darting across the tank - aim for a maximum swimming distance of at least 8 times the length of the fish and a length and width of the tank that combine to be at least 12 times the length of the fish.
These formulas may seem to recommend very large tanks for some fish - and they are, if you're going on the maximum wild length of the fish. But when you use the maximum expected length of the fish, it is perfectly reasonable. For example, let's use a yellow tang that we expect to be up to 6" long in our tank. This would be a darting fish, so we want a maximum swimming distance (bit more on that later) of at least 48 inches, and a combined length and width adding up to 72 inches.
This means that in standard rectangular tanks, a tank 5 feet long and 1 foot wide is fine for the average yellow tang - which, in my opinion, is a perfect size tank for a yellow tang.
But for those wanting a square or cube tank - can they get away with a smaller tank? With proper aquascaping, yes.
This is where the maximum swimming distance comes into play. In square and cube tanks, where a fish can swim from one corner to the other - there is a great ratio of tank length to maximum swimming length (the best you can get, mathematically speaking). Since we said that a yellow tang needs an average uninterrupted space of 48 inches to swim - that means that we can keep a straight path from one corner of the tank to the other, and if it is 48 inches, we are in good shape. Using triangles (specifically the Pythagorean Theorem, a^2+b^2=c^2), we will find that a tank that is 36x36" around will give us 48 inches of uninterrupted swimming space. And since adding up 36 and 36 will give us 72, we also have a sizeable perimeter available for the fish - meaning the average yellow tang can live in a 36x36" aquarium, or a 60x12" aquarium - a statement I think few would disagree with.
Personally, I think height has limited merit. As long as your fish isn't out of the water when it's swimming vertically, you're in good shape. The decision of height comes more down to corals and aquascaping plans, rather than fish choices - IMO.
And of course, we can apply this logic to nearly any species of fish we come across in the hobby.
To conclude this post, I will say this:
In a rapidly transforming hobby, where all shapes and sizes of tanks are popular, from pico tanks of less than a gallon, to mega tanks over 20,000 gallons, and tanks ranging in shapes from cubes to cylinders to outstretched rectangles 16 feet long yet only a foot wide, fish choices become more and more difficult. What fish can live in these specialized tanks? "Is [insert option here] a good choice for my tank?" is a question often heard around the forums, and rightfully so - typical "tank size recommendation" threads only focus on typical rectangular tanks, leaving out cubical tanks, circular tanks, extra-long tanks, extra-wide tanks, and so on and so forth. So, when deciding on fish for these innovative new systems, we must take into account that the gallonage and even the length of the tank are not the only factors playing into the fish selection process.
And of course, don't shoot for the minimum. Minimum is a guideline, if you can go bigger - do it! You certainly won't regret it, especially in this hobby
I hope this post will help some people out - both people making their own decisions on fish, and people giving advice on fish and their needs. I encourage any discussion below, I know not everyone will agree with me and I'd love to hear your input!
Drew
There are many factors to "tank size". There's volume, which the opens up to the volume of your system. Then you've got distance measurements, the most common being length. However, there is definitely merit to working with width and height when determining an appropriate aquarium size for a fish. Another distance measurement that I think is often overlooked in fishkeeping is the maximum swimming distance - that is, how far can your fish swim in a straight line without being interrupted? Sometimes this is the length of the aquarium, but it can be longer or shorter based on your aquascape.
So, how would you go about deciding on a tank size for any given fish?
Simply put, there isn't a "do-it-all" formula for this.
The first step in determining a tank size - is determining the size of your fish.
Many fish will NOT reach their maximum size in captivity, for any number of reasons. Stunting is usually what comes to mind first - that is, the fish had some kind of environmental issue that didn't allow it to grow to its full potential - but it is my belief that simple genetics are often the cause of this. Think about it - the tallest human ever was about 9 feet tall, and the heaviest was about 1400 lbs. How many people do you know that are even close to 9'/1400 lbs? The average human is nowhere near the size of the maximum human - not because of any growth issues, but simply because their genetics don't allow them to grow that tall.
So if a fish isn't going to reach its maximum size, how big is it going to get? Again, there's no answer that is universal - but my experience, and many others', has been that fish in an aquarium will reach an average of 65-75% of their maximum size. (Note: if you prefer fractions, this is equal to about 2/3 to 3/4 the maximum size.)
For instance - yellow tangs reach a maximum size of about 8 inches. So using our formula, we can see that the average yellow tang in an aquarium will reach about 5-6 inches long.
Now, of course, there are exceptions to this rule - and you should research this based on the individual fish you want to keep. But on average, fish will reach 65-75% of their maximum length in your aquarium.
Now that we've defined how big our fish is likely to get - we will need to classify it based on its swimming patterns. For this, we can define three patterns - sedentary, hovering, and darting.
Now, if you're experienced with fish - you'll often know which category a fish falls into. But if you aren't, there is a way to determine it, that does take some time. In order to do it "scientifically", observe multiple specimens of the given fish often - 20-30 times, and even more is better. On each observation, note what the fish is doing - is it sitting still, is it "hovering" around the rock, or is it darting across the tank? Assign a value to each - sitting still is a "1", hovering is a "2", and darting is a "3". At the end of your observations (again, at least 20 would be preferable, with more being better), add up all the values you have recorded, and divide it by the number of observations - in other words, take the average of the values. This value, which will likely be a decimal number, should represent the average swimming pattern of the fish. If it is in the range of 1-1.3, it is safe to say the fish is often sedentary. If it is in the range of 1.4-1.6, you are in sort of a "grey area", where I feel it is best to classify the fish as a hovering species. From 1.7-2.3, you are safely in the range of a hovering species. Again from 2.4-2.6, you are in another "grey area", and I feel it is better to classify the fish as a darting species - and of course from 2.7 to 3, the fish would be classified as a darting species.
A much simpler and less scientific way to do this, is to simply ask the knowledgeable members on this forum how they'd classify the fish
For reference, here are some rough classifications for different types of fish:
- Anglerfish/scorpionfish, lionfish, and gobies can be classified as sedentary
- Eels can also be included in this category - but in determining a tank size, using their full predicted length is overkill - taking 30-35% or 1/3 of their predicted length is okay
- For seahorses, which can also fit into this category, taking 50% of 1/2 of the fish's predicted height is okay
- Anthias, clownfish/damselfish, butterflyfish/angelfish, and triggerfish can be classified as hovering
- Tangs, most wrasses, and moorish idols can be classified as darting
So you've determined how big your fish is going to get, and how it's going to swim - that's great! You've gotten two of the most important parts out of the way. Now, we can discuss tank sizes.
This is a topic of great debate, and what I'm posting is sure to spark some debate in the comments below - but these are what I feel to be proper formulas in determining the minimum tank size for most saltwater fish.
A note before I show the formulas - I believe that the maximum straight shot distance is equally important as the length and width of the tank. I don't think length is as important, I don't think width is as important - but I do think that added together, they are equally important. So, I will be including the maximum swimming distance and the combined length and width of the tank. This isn't meant to scare anyone off with the math - just to help create an ecosystem properly sized to a given fish!
For sedentary fish, that tend to sit still most of the time - aim for a maximum swimming distance of at least 4 times the length of the fish and a length and width of the tank that combine to be at least 6 times the length of the fish.
For hovering fish, that tend to hover around the rockwork, or fish that tend to equally mix their time between actively swimming and sitting still - aim for a maximum swimming distance of at least 5 times the length of the fish and a length and width of the tank that combine to be at least 8 times the length of the fish.
For darting fish, that are more often than not observed darting across the tank - aim for a maximum swimming distance of at least 8 times the length of the fish and a length and width of the tank that combine to be at least 12 times the length of the fish.
These formulas may seem to recommend very large tanks for some fish - and they are, if you're going on the maximum wild length of the fish. But when you use the maximum expected length of the fish, it is perfectly reasonable. For example, let's use a yellow tang that we expect to be up to 6" long in our tank. This would be a darting fish, so we want a maximum swimming distance (bit more on that later) of at least 48 inches, and a combined length and width adding up to 72 inches.
This means that in standard rectangular tanks, a tank 5 feet long and 1 foot wide is fine for the average yellow tang - which, in my opinion, is a perfect size tank for a yellow tang.
But for those wanting a square or cube tank - can they get away with a smaller tank? With proper aquascaping, yes.
This is where the maximum swimming distance comes into play. In square and cube tanks, where a fish can swim from one corner to the other - there is a great ratio of tank length to maximum swimming length (the best you can get, mathematically speaking). Since we said that a yellow tang needs an average uninterrupted space of 48 inches to swim - that means that we can keep a straight path from one corner of the tank to the other, and if it is 48 inches, we are in good shape. Using triangles (specifically the Pythagorean Theorem, a^2+b^2=c^2), we will find that a tank that is 36x36" around will give us 48 inches of uninterrupted swimming space. And since adding up 36 and 36 will give us 72, we also have a sizeable perimeter available for the fish - meaning the average yellow tang can live in a 36x36" aquarium, or a 60x12" aquarium - a statement I think few would disagree with.
Personally, I think height has limited merit. As long as your fish isn't out of the water when it's swimming vertically, you're in good shape. The decision of height comes more down to corals and aquascaping plans, rather than fish choices - IMO.
And of course, we can apply this logic to nearly any species of fish we come across in the hobby.
To conclude this post, I will say this:
In a rapidly transforming hobby, where all shapes and sizes of tanks are popular, from pico tanks of less than a gallon, to mega tanks over 20,000 gallons, and tanks ranging in shapes from cubes to cylinders to outstretched rectangles 16 feet long yet only a foot wide, fish choices become more and more difficult. What fish can live in these specialized tanks? "Is [insert option here] a good choice for my tank?" is a question often heard around the forums, and rightfully so - typical "tank size recommendation" threads only focus on typical rectangular tanks, leaving out cubical tanks, circular tanks, extra-long tanks, extra-wide tanks, and so on and so forth. So, when deciding on fish for these innovative new systems, we must take into account that the gallonage and even the length of the tank are not the only factors playing into the fish selection process.
And of course, don't shoot for the minimum. Minimum is a guideline, if you can go bigger - do it! You certainly won't regret it, especially in this hobby
I hope this post will help some people out - both people making their own decisions on fish, and people giving advice on fish and their needs. I encourage any discussion below, I know not everyone will agree with me and I'd love to hear your input!
Drew
