Thanks Ruben. I never feel 100% sure about most of my fishes identification to be honest. I've never counted dorsal spines or ventral rows of scales or anything like that. Looking around it seems that L182s can look like 183s, and I saw a post somewhere of someone getting 181s, though that wasn't really that close. Are there any other lookalikes you're aware to look out for?
All I've found is that L183s have bright white spots and the 182s don't, though off course shipping stress screws that. Planet catfish says
though I'm not sure how to check that, especially in a shop.
Matt as juvies L 183's are unmistakable. They have the bright white/bluish seams on the fins. As adults they lose their luster but still keep the white seams on the fins but not as intense as when they are younger. There are a few other Ancistrus that are finely spotted like the 183's but do not have the whitish seams on the fins. Most of these have some white on their tails as juvies but not as intense as the 183`s. Some that I can think of are L 100, L 180, L 181, L 182, and L 213. I am sure there are others.