Lepeophtheirus pectoralis copepodid stage, during which the copepod attaches itself to the fish. Stages IV, V, VI and VII are the chalimus stages, and are followed by the pre-adult and adult stages, when differentiation of males and females is possible. Lepeophtheirus pectoralis Lepeophtheirus pectoralis is a species of parasitic copepod. It is a parasite of flatfish, the most frequent hosts being the European flounder ("Platichthys flesus"), the plaice ("Pleuronectes platessa"), and the dab ("Limanda limanda"). It feeds on the mucus, skin and blood of the fish, with oviferous females being found in the pectoral and pelvic fins of the host, while immature
European flounder eyes usually migrate to the right side of the fish and what appears to be its upper surface is in reality its right side. In about thirty percent of individuals, its eyes move to the left and the left side becomes uppermost. The fish has a small mouth at the end of its bluntly pointed snout. The upper surface is fawn, olive green or pale brown with spots and larger patches of darker brown and some irregular reddish spots. The under surface is opaque pearly-white giving the fish its common name of "white fluke". The lateral line is nearly straight