Is my goldfish stressed?

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Jeremy Gay offers his advice to a reader that is worried her goldfish is stressed.

Q) I’ve just rescued two goldfish, one Common and one Fantail, from a previous housemate who left them behind. I bought them a new, larger 125 l tank, kitted out with a good internal filter so that there’s good surface water movement, sand and real plants. The water is of good quality and I’ve been testing regularly.

I introduced the fish three days ago and they seemed fine: they ate and explored and seemed quite content, but now the Common goldfish just frantically swims along the same route constantly, up against the glass, over and over again.

I’m a new fish owner and my knowledge is limited but it seems like he’s stressed. The Fantail is fine and very chilled — his behaviour has not changed — but that of his tankmate seems frantic and erratic. There are no physical signs of illness and their colours are still bright. Any advice would be much appreciated.

KAYLEIGH MALLON, VIA EMAIL

A) JEREMY GAY SAYS: If you’ve taken them from a small, cramped tank, the Common goldfish may just be enjoying the extra space and taking full advantage of the exercise, which is a good thing. It may be swimming against the current too, which again isn’t a bad thing for a Common goldfish, although make sure that water flow isn’t too strong for the Fantail, and that his chilled out behaviour isn’t due to exhaustion.

Temperature can increase goldfish activity, as can pheromones from female goldfish, which will cause males to swim and chase for days.

If water quality is good and the Common goldfish isn’t gasping at the surface or shimmying on the spot, I wouldn’t be too concerned, but in the long term I would consider housing this fish with others of its own kind, in larger accommodation. As you’re probably aware, Common goldfish grow to over 30cm long, and really need very large tanks long term, in the region of 450 l or more, or — better still — a pond. Also be wary of the common goldfish out-competing your fantail for food or just stressing it out with constant activity.