Fish louse. Coloured scanning electron micrograph (SEM) of the underside of a fish louse (Argulus sp.) This freshwater crustacean is usually found on carp. The head (bottom right) has two reduced antennae (spiked) above the eyes (stalk-like). Two suckers (round, pink) are modification of the maxillae. Below these are arm-like mouthparts. The louse attaches itself to a fish's gill covering and feeds on mucus, scales and blood. Magnification: x10 when printed at 10 centimetres wide.