I starved it only for a day, it was so hungry it basically tracked the rat visually while I had it outside the tank. That's why I believe these fish have better eye sight then thought, but that's just my opinion. I don't use them as a staple in their diet, just fed as a treat once in awhile. BTW TO ALL, PINKY RATS HAVE MORE PROTIEN THAN PINKY MICE. Just letting you all know, in case you wanted to feed em one, rat is the way to go!