Hi there,
It appears that you just purchased a
Mastecembelus armatus, commonly known as a tyre track eel (although the name "Anaconda" eel might suit this animal justly
)
Given proper conditions, a tyre track can gain up to an inch per month, usually reaching/slightly exceeding 3 ft in length when fully grown. Tyre tracks are probably the most predatory of the spiny eels- although very peaceful they will prey upon smaller fish when given the opportunity.
Even when small, they should be housed in as large a tank as possible, eventually requiring 180+ gallons (oh, and it's not easy catching these guys either).
I have had my tyre track for 8 months, he was five inches when I got him and is now nearly a foot. He eats blackworm, chopped earthworm, the occasional mealworm (w/heads cut off, of course), frozen bloodworm (sometimes), molly fry, and guppies. This does not include the $$some of fish that were not intended for his meals, nor the failed attempts at expensive dinners too big for him to swallow
.
Tyre tracks can be fantastic fish to keep if you have the tank space. Good luck.