In the past I’ve kept black spot, yellow spiny and tire track but this should apply. They seem to gravitate towards worms especially. Black, blood even earth worms I’d collect off the driveway in the rain. The only thing I’d feed that they’d accept with any amount of excitement was frozen salad shrimp. The smallest ones I could find in the grocery store. Once they were big enough to eat those they shot up in size! Girth too! That in combination with the frozen worm diet and some pellets on occasion has been really successful in the health and size of my eels.
Hope this helps!