Dogfish are a type of shark, and they are so named because they hunt in packs, like dogs do. It has nothing to do with their appearance, which is entirely fishlike and not canine at all.
Dogfish price in Growtopia: sells for about 3 DL 11 WL (median of 1 offers from community Discords, past 30 days). Live price chart and the latest buy and sell offers.