Depressed pleco

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New Member
Jun 7, 2023
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Fall River, MA 02723
I have had a tank with a common pleco and 2 fancy goldfish (55gal). They have been together for 2 yrs with no issues. All of a sudden my pleco is becoming aggressive toward the goldfish. They are well fed-get frozen and veggies daily, water parameters and temp normal limits. I was told in the beginning that the pleco and goldfish would be fine together, but now I find out that is not true. I removed the goldfish so now the pleco has the tank all to himself. It has been 3 days and he seems "depressed". Does this happen? What should I do for him? Thank you.
Well, part of it might be the low temperature: fish simply get lazier when their metabolisms are slowed, and it’s possible that now that he doesn’t have to defend his territory from the goldfish, he’s relaxing and sees no need to expend energy. Plecos are also nocturnal fish (as you probably know), so it’s entirely possible the goldfish were keeping him up and he’s now saving his energy for the night. You should also test your water, just to make sure he’s not being poisoned.

In my experience, depression in fish is usually rare. I did see it once, when I had to separate a apistogramma pair because of sickness, but it seems more relegated to things like cichlids. It’s more likely your pleco is just relaxing now that the goldies have stopped bothering him.
I believe fish can get depressed. Even though fighting with the goldfish is likely a negative reaction, the pleco now has no other denizens it can interact with, so its environment is not as interesting/interactive from what it used to be. With no external stimuli life is not quite as interesting. I doubt they view it like we do but there is likely some comfort in having other fish in with him. Consider the role that dither fish provide. Is putting the gold fish back in a good plan, that I don't know.

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