Hey,
Does anyone know if I can put a puffer fish in with my goldfish? I would have to get a water heater of course, but I hear goldfish can live fine in heated water. But, do goldfish and puffer fish get along??
Does anyone know of any other cold-water fish I can add in with my goldfish if I can't put in the puffer?? Thank you!

im not sure about the puffer but goldfish do prefer cooler water though.

In my coldwater tank i have goldfish, zebra danios, white clouds and a coldwater platie. B)

Freshwater puffers are so cute but they are notorious fin biters. If put with goldfish (unless the goldfish were so big as to try to eat him causing other problems, like him puffing up), the puffer will nip at and rip the goldfish's fins off over time if not right away. Puffers not only like it warm while goldfish like it cool but puffers also need brackish water. While goldfish could technically be taught to survive in warmer brackish water, it's not really good for them.

As far as fish that can get along with goldfish, I've tried common plecos and panda cories who were good for about a year and then sucked on my goldfish. If the tank is large enough, rosy red minnows can work as long as they are healthy, and the goldfish aren't huge (in which case, they'll eat the minnows). How big is your tank? Goldfish should have at least 10 gallons each while middle-aged.

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Here is a list of goldy comaptible fish:

Zebra danios
Giant danios
Pearl danios
Blue danios
Leopard danios
White cloud minnows (sometimes)
Mosquitofish (sometimes)
Various North American native fish lke rosy red minnows
Small tench
Small rudd
Small gudgeon (very hard to keep)
Guppies (sometimes)
Ghost shrimp (not fish)
Platies, mollies and swordtails (sometimes)