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Trout on trout violence?

Maybe this is a product of having just a few fish in small tanks, but I wondered if trout sometimes attack similar size or slightly smaller fish that would be too large for them to eat. We harvested a couple of the largest fish from one tank and a couple days later two other fairly large fish appeared to have injuries around their tails and were barely swimming. Do trout get aggressive or territorial if there are only a few left in the tank?

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Permalink Reply by Mark on October 10, 2012 at 8:23pm

I had bought some large trout only about 6 at about 12" long and had them in a 100 gallon tank,one of the trout was so aggresive towards the other fish it killed two before I took him out. The tails on the dead fish where shreded. I now have some fingerlings that are about 3 to 5 inches long. They seem to be ok right now but I have noticed a few are getting a lot larger than the rest. I guess they are the more aggresive ones. I am not sure If I should seperate them or not they have not attacked any of the other smaller fish yet.

Permalink Reply by Jim Fisk on April 14, 2013 at 8:31am

I have suspected that some of my trout deaths have been the larger ones attacking the smaller ones and noticed tail damage as well. I also have noticed a large discrepancy in growth rate that I suspect is from bullying. They are a predatory fish after all so need more watching for sure. The bigger fish (all started out about the same) put on quite a display at feeding and I often give extra later if I don't see any food left over from feeding time to hopefully get some to the smaller ones once the larger ones are satisfied and over their grand display (and perhaps sleeping it off:-)

Permalink Reply by Tom OBrien on April 14, 2013 at 12:49pm

I found this article talking about aggressive behavior in trout. With a small tank like mine, I think the aggressive behavior they talk about in the article was the norm in my setup. I saw several instances where fish would chase or even ram other fish. I would guess that several of the fish deaths in my first batch of fish were caused by large fish attacking the smaller fish. Even if I had wanted to "grade" them and separate the larger ones from the smaller, I didn't have another tank to put them in. I'm going to try some Yellow Perch and hope they do better in my limited space.

http://www.benthamscience.com/open/tofishsj/articles/V004/62TOFISHS...

Permalink Reply by Jim Fisk on April 14, 2013 at 3:19pm

Thanks Tom, great article. I was just about to run that test here.

It sure is nice to have folks with that scientific approach so we don't have to. Pretty tricky to drop just one pellet at a time , on time, for a long time, every time and record the results. Great find.