Question
I have an outdoor pond that has 6 large (10+ inch nose to tail) goldfish in it. These are fish that were originally bought as pet store feeder-type fish, so they're nothing special. I have a webcam on the pond, and have observed that several of the fish keep chasing, crowding, and trying to bump into one of the other fish (which is distinctly colored, so I know it's the one that's being consistently targeted).
I am suspecting that this is a breeding behavior where the targeted one is likely female and is ready to lay eggs and the others are males, trying to squeeze eggs out of her by pushing against her in order to fertilize them. But this is just a guess, as I'm not a goldfish behavior expert. :-) We did have some in-pond births last year with these same fish, so I know that there are both males and females in the pond.
So is this expected breeding behavior, or should I be concerned about something else going on?
Answer
This is classic mating behaviour in goldfish and other fish in the carp family like koi.
The mating behaviour will most often happen in the evening as the sun sets,it can be a danger to the fish as sometimes the fish jump/get pushed out of the pond so if possible you should have an elevated barrier around the edge of your pond.
If you want to keep the eggs/fry you can put a tiny pine tree in the water so your fish have a place to spawn and to protect the eggs or they will get eaten by the other fish.
After the spawning you can then move the tiny pine tree to a separate tank/pond for hatching of the eggs,they will hatch in about a week and the fry will start to eat after the egg sack is consumed after 2-3 days.
If you do not want a gazillion of fry swimming in your pond you do nothing and let nature do it`s thing and let the eggs and fry get eaten(you might still get a few extra goldfish during the summer).
Answered By - trond hansen