 In fish such as the herring which live in shallower water , the mirrors must reflect a mixture of wavelengths , and the fish accordingly has crystal stacks with a range of different spacings . A further complication for fish with bodies that are rounded in cross @-@ section is that the mirrors would be ineffective if laid flat on the skin , as they would fail to reflect horizontally . The overall mirror effect is achieved with many small reflectors , all oriented vertically . Silvering is found in other marine animals as well as fish . The cephalopods , including squid , octopus and cuttlefish , have multi @-@ layer mirrors made of protein rather than guanine . 
