Yes, please don't starve the poor fish. And give it a more suitable diet, please. I know that this isn't what you want to hear, but my advice is to take it back before it's too late. I did the same with a black pacu when I first started out in fishkeeping, and I have been able to keep him-- but now I'm setting up a 2,000 gallon aquarium to keep up with his growth. Normally, I would've given him away quite a few years ago, but he's very personable, and now I've ended up building a 2,000 gallon set up. We all make mistakes with fishkeeping, so my advice is, once again, take it back to the shop that sold it to you, or sell it, and don't worry about it. Go buy a nice rainbow wolffish, or some of the smaller bichirs. Sometimes, fish shops give out faulty information, so you should always research fish before purchasing them. Just today I was at one of the lfs around here, and one of the fish-department staff told a buyer that the 1' long nurse shark that the fish shop was trying to sell only grew to 2', when they grow to 14'. I quickly notified the buyer of that, and they ended not getting the nurse shark, which they were going to cramp into their 55 gallon.