Dinosaur eel. I.e. one of four fish:
Violet Goby, Goboides broussonetti. Check it out at:
http://www.aquariumfish.net/catalog_pages/wild/dragon_fish.htm#top2
Or Polypterus senegalus meridionalis. Check it out at:
http://www.aquajapan.com/encyc/ancient/polypteridae/polypterus/senegalusmeridionalis_e.html
Or Polypterus senegalus. Check it out at:
http://www.aquariacentral.com/species/db2.cgi?db=fresh&uid=default&ID=0409&picture3_page_view=1
Or Polypterus palmas. Check it out at:
http://www.thetropicaltank.co.uk/Fishindx/poly-pal.htm
I'd really take my advice on this issue, though usually I'd refer you to a more senior member... Here's the deal.
If it's a violet goby, you're good to go. They will get to about 10 inches, but it's a cool fish if you have room for it, and it won't eat your other fish. It likes small meals of tubifex, brine shrimp etc.
If it is a Polypterus senegalus meridionalis (brown uniform colored body and cream underbelly), get rid of it right now! Unless you want a 2.5 foot fish on your hands in a year and a bit, and unless you're willing to buy a 200-gallon aquarium to house him (if so, good on you!).
If it is a Polypterus senegalus (grayer body and cream underbelly, otherwise identical to the meridionalis subspecies), you are looking at housing a 1.75 foot fish in a year or two.
If, however, it's a Polypterus palmas (look for the mottled lateral striping or blotches on the body), enjoy! It will only grow to a foot, but make sure you have a big enough aquarium, i.e. 90 gallons+.
Take care when you look at the websites I've posted here, and make sure you know exactly which fish you have (there is a big difference between the fish, though it is not immediately a visible difference). A lot of stores sell the Polypt. seneg. merid. as a Polypterus palmas, and most who do sell either species are unaware of how large and powerful the fish get (they are extremely strong, and very quick to jump out of the aquarium if you're transferring them to another container/tank.
If you're at all unsure, personal message me, and I will give you more info, help you to identify your specimen. It's really important you return the fish if you don't think you're going to be able to house it in a year, especially if it is a Polypterus senegalis meridionalis (most likely).
One question: did you buy the fish at Petco or Petsmart? I almost bought one at Petco (ended up buying at an
LFS, and returning it (they mislabled it as a palmas)? If so, Petco seeems to sell these fish and not warn buyers of the size the fish achieves. Reprehensible behaviour on their part!
Good luck identifying, and if you feel up to housing a large fish, good luck with that! You're a better person than I am.
