Does goldfish give off chemicals that hurt other freshwater fish?

Yes, goldfish produce chemicals that can harm other freshwater fish. Goldfish produce a chemical called 'goldfish slime', which is a type of mucus that they secrete from their skin. This slime can be toxic to other fish, as it contains a number of compounds that can cause irritation and damage to the gills and skin of other fish. Additionally, goldfish also produce a hormone called 'gonadotropin-releasing hormone' (GnRH), which can interfere with the reproductive cycles of other fish. GnRH is a hormone that is produced by the pituitary gland in goldfish, and it is involved in the regulation of reproduction. In other fish, exposure to GnRH can disrupt their normal reproductive cycles and cause them to produce fewer offspring.