Why do the fins on my oscar model keep curling off the bed?

I've printed a few of those fish models on my Adventurer setup and the fin scarring is just how supports work on PLA unless you tune them. The two things that made the biggest difference for me were the support Z distance and the tip shape. Bump the top Z distance up to about 0.25 or 0.3mm in your slicer so the support doesn't fuse to the fin surface, and use tree supports if your slicer has them. Tree supports touch the model in fewer, smaller spots than the default grid style, so instead of a big scarred patch you get a few tiny dots that sand off in seconds.

Also worth doing is adding a support interface, sometimes called a support roof or interface layer. It puts a flat sacrificial cap between the support column and the fin so the actual support material never touches the print directly. On PLA that peels away with a pair of tweezers and leaves the texture underneath pretty much untouched.

Another trick that helped with the scale details on the flanks: rotate the model. If the fish is lying flat on its side, one flank is facing down and every bit of that texture is either buried against the bed or littered with supports. Tilt it a few degrees so the bad side points mostly up, or print it belly down with the fins angled outward. Fewer contact points on the flanks means less cleanup on the part you care about. Last thing, in most slicers you can right click and add supports manually instead of letting the slicer auto-place them. Thin fins ussually only need a support right at the thickest joint where it connects to the body, not along the whole span. The fin tips will bridge or droop slightly and honestly it reads as natural on a fish. Cleaning up one spot at the base beats scars running the whole length of the fin.

Gotta push back on the Z distance advice. Bumping it to 0.25 or 0.3 on thin fin overhangs is asking for trouble on a stock machine. I tried something similar on a dragon wing print and the supports barely stuck, so half of them broke loose halfway up and got dragged around by the nozzle. Then the fin sagged into the gap anyway. A small bump helps, sure, but if you go that far you need better cooling and slower overhangs to make up for it, which a stock setup may not give you. I'd rather keep Z distance snug and rely on the interface layer idea, that part I agree with completly.

I ran into the same scarring thing on a little turtle print and my fix was just patience with removal. I used to yank the supports off by hand right away and it always tore a chunk of the surface with it. Now I let the print sit overnight first and peel them slowly with my thumbnail, twisting instead of pulling. Way less damage. The guy above mentioned sanding off the leftover dots though, and I have no idea what to use for that. What kind of sandpaper do you grab for something that small?

Kind of a related thing, I printed an axolotl model a while back and the little gill fronds got chewed up the same way. What helped me after the fact was hitting the rough spots with a hairdryer for a few seconds, the PLA softens just enough that you can press the texture back with a fingernail. Not perfect but way better than sanding on a textured part like scales. Total beginner question though, does the same trick apply before printing, like would a slightly lower layer height make those scale details less fragile to begin with? I'm still on defaults for everything.