If you are feeding your eels dead food with tongs, etc; whether it be fish, he will not relate that to his tank mates. Fang tooth eels eat fish, it would be good to include fish in their diet. I feed salmon because that's in my diet. I found the inclusion of fresh fatty fish to beneficial. They also need the minerals among other nutrients from shell and bone. Fresh shrimp, or preferably prawns, with shells are also good. I literally ask for 3-5 fresh shrimp, cut them up and freeze what I don't use for a couple of weeks.
Feeding endless frozen foods are mostly dead of nutrients and supplementation can be useless or even risky. Just as with humans, fat soluble vitamins can become toxic. And you never know how much they are getting either way. I know people who are religious about supplementation, I am finding they are still having limited long term success with predators.
