New Freshwater Crayfish

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Aquarium Advice Newbie
Jul 11, 2023
Hi, I've just bought my first freshwater tank (60x30x30 54 Litre) and have done a pretty good job (Filter, Heater, Sand, Slate structure, Backdrop, Tank ornaments and Plants). I conditioned my water and half filled it with some slate sticking out of the water. I have now introduced two freshwater Blue Crayfish (Ron & Reggie but I can't tell the difference yet). They seem happy enough and spend most of the time in the many hidey holes I've provided. My concerns are feeding. I know they will eat about anything but I have two questions.

1. Other sources tell me to put food in the tank and then take away any they haven't finished in Ten minutes. They never come out to feed so I've tried leaving the food and it disappears overnight. Is this normal?

2. Why should I take the food out after Ten minutes. I'm told that they eat anything including carrion and decaying vegetation so why do I have to remove old food?

Thanks in anticipation of a reply.


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Hi and welcome to the forum :)

You want the tank as full as possible without being too full. Crayfish can climb out if the water quality goes off or if they start fighting. But the more water in the tank, the cleaner it will be.

You remove uneaten food after 5-10 minutes so it doesn't rot in the water and cause ammonia problems that will kill the crayfish.

I'm not sure of the plants are real but if they are plastic, you won't need the light on except to view them. If the plants are real, they will need around 8-12 hours of light per day. However, crayfish will eat live plants so see what happens.

Crayfish are nocturnal and won't come out when the light is on.

Did you cycle the tank and filter before adding the crayfish?
Cycling a tank/ filter is where you add a source of ammonia and allow beneficial filter bacteria to develop. this normally takes around 4-6 weeks. If you didn't cycle the tank beforehand, you are doing what's called a Fish in Cycle. this simply means there are creatures (crayfish) in the tank while the filter develops good bacteria that eats ammonia and converts it in nitrite and then nitrate. During this time you should only feed the 2-3 times a week and do a 75% water change and gravel clean the substrate 4-8 hours after feeding. you should also monitor the ammonia and nitrite levels in the water and do a 75% water change any day you have a reading above 0ppm.

Make sure any new water is free of chlorine chloramine before it's added to the tank.
Thanks for the advice Colin but the amount of water in my tank is plenty good enough for Ron and Reggie to live in. I didn't cycle the tank for weeks before I added them. I used untreated tap water and ran my pump for two days before adding them. All the plants are live except for one ornament so if I don't give them enough food they will eat the plants. The ph in my tank is 7 so I'll not be changing water until it starts to deteriorate. As I said in my question I have problems understanding why Crayfish eat rotting vegetation and dead animals but you have to take out uneaten food after ten minutes
Fish food (or anything that breaks down/ decomposes in water) needs to be removed from an aquarium after 5-10 minutes because it produces ammonia as it breaks down. Ammonia is extremely toxic to all aquatic organisms and if there is an ammonia reading in the water, it can kill the crayfish.

In the wild there is usually a lot more water for each crayfish and there is usually plenty of aerobic bacteria living in and on the mud that can convert any ammonia produced by the rotting leaves. And most leaves or food in a creek or river will be eaten within a short space of time (usually 30 minutes or less).


There are plenty of things in the water besides pH that can affect the crayfish. If the water has a high KH (carbonate hardness), the pH is unlikely to change.

Ammonia, nitrite and nitrate can build up in water and if you don't keep the levels at 0ppm, the crayfish can and probably will die, especially if there's ammonia or nitrite. If you don't want to test the water for these things, that is fine. But you should increase the water level in the tank so any ammonia that builds up will take longer to get to a toxic level, and you should do a big (75%) water change at least once a week, or preferably 3-4 times a week for the first month. Then do it once a week after that.

Any new water should be free of chlorine/ chloramine before it's added to the tank so it doesn't burn the crayfish's gills.
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