Join Date: Jan 2012
Location: Plattsmouth, NE
Goldfish make poor feeders--they are known for carrying internal parasites, which can be passed on to a reptile or carnivorous fish. I don't know about the fat content, but the primary nutritional danger is the fact that goldfish are very high in an enzyme called thiaminase. Thiaminase destroys thiamine, and interferes with the absorption of thiamine, so feeding goldfish will lead to a thiamine deficiency. (Rosy-Reds are also poor feeders, but guppies seem to be ok, and Tilapia fish are ok). Freezing destroys thiamine, and can increase thiaminase levels as well, so only feed fresh, never frozen, tilapia.
As for keeping turtles with fish--neither animal will be happy with that arrangement, and the turtles are likely to nip fins at any opportunity that presents itself.