Tyre track eels (Mastacembelus armatus) are probably the easiest of the commonly available freshwater eels to keep and feed, the other species Fire eels (Mastacembelus erythrotaenia) and peacock eels (Macrognathus aculateus and siamensis) can be extreemly fussy and often starve to death. Trye tracks can reach around 3 feet in length but 2 feet is more likely in captivity so a 100 gallon tank would be the minimum recomended size, they will take a variety of meaty frozen and live foods such as mussels, cockles, prawns, live shrimp and earthworms.
Avoid eels labled as swamp or tulip eels (Synbranchus, Monopterus and Ophisternon species) which easily reach 3 feet and will attack even much larger fish causing serious injuries with their strong jaws. Also avoid any of the freshwater moray eels which are not freshwater at all requiring brackish to marine conditions and will quickly fade away and die in freshwater.