What Mentat said

In addition to parasite issues, goldfish contain an enzyme called Thiaminase that can be very harmful to reptiles and amphibians (a lot of fish do. the best safe fish are the frozen/thawed silversides you can by at petco). Individual animals have different sensitivities to this enzyme, so it's really kind of like playing Russian roulette when you feed goldfish. It can cause some serious neurological issues and even be fatal.