Marine fish are weird. Here's a horse-shaped, armoured, uh, thing whose males get pregnant (Hippocampus sp.), a monogamous living pipette (Chelmon rostratus), a shark shaped like a snake with two legs (Hemiscyllius ocellatus), a fish that looks like a cross between a razor and a shrimp (Aeoliscus strigatus) and one that looks like a bad-tempered Picasso painting and apparently grunts like a pig (Rhinecanthus aculeatus).
I visited Sea Life, photographed some of the fish and used some of the photos as reference. Black marker and coloured pencils on brown recycled cardboard.