My info on feeding live is pointed more towards certain species that sometimes won't take dead food or won't take the dead foods that are necessary for long term captive living. Some species also have shown very poor long term survival when fed a dead only diet.
In the case of eels, and especially fang tooth eels, it's usually not a good idea to feed live foods. Eels also mostly will accept a variety of of dead foods necessary to long term success. The most important aspects of a diet for eels is to limit thiaminese and include a fatty fish. Also do not feed too frequently. Feeding human grade seafood, bought fresh and frozen in small batches, and include native items that the species would have eaten in the wild. Check out Asian markets if you have one in your area, you may find human grade silversides which would be so much better than the lfs variety. If you do feed silversides, San Francisco Bay brand is the only true silverside that does not contain thiaminese. Thiaminese binds vit B1 and can be deadly to predatory fish. Wild salmon is abgoid source for a fatty fish. Some hobbyist may have access to options that others do not.