tats and other vampire tetras are difficult to notice stomach bulges, and the only ones i've seen to eat like pigs so you can see easily are the H. Armatus, not really H. tat ... i would say not to panic, but i would continue to feed frequently ... see what the prior owner was feeding and try that, otherwise live fish to get him eating, and watch very closely, even feed extra so there are a couple feeder fish swimming freely in the tank, and i would try feeding as soon as you turn the lights off to help trigger an automatic response .... when they eat it happens fast, so watch ... also, as i've experienced with my old tats, they are finicky and fragile, current in the tank is a must, since their skin and slime coat is very sensitive and needs current to maintain a balance, so they dont have a slime build up, is the best way to describe it .... i'd also say a larger tank wouldnt be a bad thing very soon
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