Labeling is always tricky. The bag I buy says jumbo shrimp, but it could be the same kind you buy for all I know. I buy the frozen, raw, gray colored kind. My eel is also close to 4 feet. I can only really guess at his size when I force him to swim around the tank to get the shrimp. My tank is 6 foot and he is easily longer than half of that. So you definitely don't want to feed yours the same as mine. But I still think every 3 days for one that is 18in would work well. Then again, the more you feed him the less likely he is to snap at tank mates.