Why won’t this Discus fish eat?

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Jeremy Gay tackles the question of a Discus not taking food.

Q: I have had a new group of six Discus for a week now. Five of them are 10-12cm; the other is smaller at 8cm or so. 

The bigger Discus have been eating since I added them and accept any food offered. But the small one has not eaten a thing and I’m starting to get worried. It’s swimming around happily, in full colour and I’m not noticing any issues with it, so I don’t understand why it won’t eat. I’ve tried different foods: dry, flake, granules, pellet, beef heart, frozen bloodworm and brine shrimp, but all to no avail. 

The temperature is 30°C, ammonia and nitrite are 0 and nitrate is at 10. It’s a well-established planted 400 l tank with a mix of other community fish. 

As the other fish come straight up top for the food, I’ve tried to feed them on one side of tank and then drop a little bit of food on the other side for the little one. Any advice would be much appreciated as I don’t want to see him waste away. 

ZAK HARRISON, VIA EMAIL

A: Jeremy says: Size matters in Discus communities and my guess is that your 8cm fish isn’t eating because it’s at the bottom of the pecking order. If you added some more 8cm Discus it may feel more emboldened — I have better results and less bullying with Discus kept in groups of ten or more, but even then they all need to be the same size. 

Is there anyone with a group of 8cm Discus that you could try it with, to see if it feeds with them? If it does, then hierarchy is the issue. If it still doesn’t feed, even with similar-sized fish, there is a possibility that it’s an older fish which is simply stunted and now slowly wasting away. 

I’d reach for the Discus wormer first and then try introducing it to other fish of the same size and type in another tank. If that’s not an option, introduce more three fish of the same size to your tank so that your little guy doesn’t feel singled out.