When you picture your ideal fish tank or koi pond in your mind, you see it teaming with life. So thick with fish and colors, but hold on. Did you ever consider that your fish might need a lot more room than you are considering? Sure, it may look great, but you will be sacrificing fish health over aesthetics.
Consider a fish’s natural environment out in a lake or the ocean. Compare that vast space to a confined structure like a pond or tank. You lose considerable water volume and potentially acres of natural filtration. When we confine fish to a tank or a pond, you can only hold as many as your filtration allows. If you have a lot of filtration, you can have a lot of fish, but your fish may still not like it. If they feel overcrowded, it will cause stress and secondary disease. It will depend on the species of fish you have and your filtration capabilities to determine how many fish your system can handle. When in doubt, always err towards the side of fewer fish rather than more.
But what about that 1” of fish per gallon rule? Well, I challenge you with the three following species:
All three live in very similar environments, but have very different body shapes. You could pack 10 little tetras into 1” of goldfish, and the same goes that you could pack 10 goldfish into 1” of koi! And this rule assumes that your filtration is well established, receiving regular maintenance and all the fish get along!
So I’m going to throw out the rule that sets any guidelines whatsoever. The best thing to do is start with a few fish and slowly increase your numbers. Get the opinion of an expert in the field or whatever species you are interested in keeping. Read books on which species get along with each other and know if they will want their own territory or need buddies nearby. Watch your water quality and fish health. If your ammonia starts to go up with an established tank, you are past capacity. If your fish all show vague clinical signs or one gets picked on by its counterparts, see if some more room will settle everyone down.
Remember, less fish can lead to better fish health, but make sure you know your species well. For example, koi like friends. We have one hospital tub that everyone acts normally when there are 7+ fish in the tank. 7 or less, everyone stops eating and just sits on the bottom. Add some new fish and everyone is back to normal.
Don’t forget to plan ahead! Let’s take our three example species again:
Neon Tetra: Starts around 0.5” and can get up to 2”
Goldfish (variety dependent): Starts around 2” and can get up to 12”
Koi (variety dependent): Starts around 6” and can get up to 24”-28”
If you plan on keeping your fish for their entire lives, you better make sure you have room or can upgrade their tank when the time comes. Think you’ll run out of room? Get rid of fish sooner rather than later. It is much easier to find homes for smaller fish than big fish. Ask your local fish organization if they can help you find a new home for your pet before you run out of room and filtration.
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