White cloud minnow being bullied

[Nmoverley]

I have a planted 72 gallon aquarium with 2 snails, 2 bristlenose Plecos and 13 white cloud minnows. I checked and all the pH, ammonia and nitrate levels and fine. The temperature is at 24oC. We have had the minnows for about 2 weeks and 12 of the have grew considerably and are looking strong and healthy. Today we noticed one of the minnows wasn't eating with the rest of them and started to look closer. This minnow is underweight and not even trying to eat. When we watched the tank for about 10 minutes we saw every couple of minutes one of the healthy minnows would dart at him and nip at his side. They aren't hurting his fins they are going right for the main body. Each time it is a different minnow attacking him. They are all hanging up on him. I know minnows are schooling fish and like groups of 6 or more but in the attempt to save him I isolated him by himself for the night with some food hoping he will eat something without being attacked. Has anyone experienced this before? Is there anything we can do to stop it? The poor little guy is dying? I was thinking if we could get him to eat over the next day we will get a separate 10 gallon tank and some new baby minnows his size that won't bully him?

[Dodofish]

Does the bullying always happen during feeding times?

previously I have kept school of fishes such as tetras and clouds minnows. One thing I noticed, the terrestrial behavior from fishes may comes from excessive feeding. And it usually happens during feeding time because they need to compete for food. Irregardless how much you feed, the poor isolated fish is not going to be able to eat during feeding time because the rest of the fishes has probably outgrown him and needed more food.

If you feed less however, you will realized less of such problems. At the same time, there is little need to cope with ammonia or nitrite issues.

I maybe wrong but ever since I change my feeding cycles. I realized I have less of such problems.

Just my two cents worth.

[Neptune, the Mystic]

Is your tank size really 72 gallons? That's over 270 litre and there is no reason or little chance for friction amongst the occupants given that tank capacity.

The hapless fish could be sick. My hypotheses is that a sick fish releases chemical hormone that alerts others to stay clear. However, for the healthy minnows to mount a concerted attack is something rather unusual. This happens only to land animals of unrelated species, e.g. a stray animal that wanders into a different herd of animals may killed to stop his cries from attracting predators.

It is not clear whether overfeeding or underfeeding influences fish behaviour to each other because it can argued both ways. Are they less likely to fight when fully-satiated or more likely to fight when not under-fed. What is certain is that live food brings out the aggression in some species that are not-so-friendly to begin with.