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If the only remains found in a squid's stomach are fish scales, is there any way to determine what kind of fish the squid was eating? Do the scales of various fish have unique characteristics? (What is that, dumb question #103?)
Yes you can, up to a point, but it's not easy. Yes to the second question too, though again it's not easy. At the very least you would need a reference collection of scales from identified fish species, to compare your scales with. Also the morphology of fish scales is not uniform; scales from the head are not the same as scales from other parts of the fish.