I have no idea how late I am with this info, but anyway- My goldies do get egg white as part of the homemade food I give them- this is very high protein.
You could also boil it and give them only the white ( NOT the yellow- thats FAT !!), also peas, soybean- again, boil/ steam/ microwave it, or whatever.., you can also try lentils, depending on how picky your fish are. Mine eat some kinds, I dont know the names

Hope this helps