Studies on the life history and development ofProteocephalus percae(Müller) (Cestoda: Proteocephalidea)

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Abstract
The life-cycle of the cestode Proteocephalus percae (Müller), a parasite of the perch Perca fluviatilis L., involves two hosts and was studied both experimentally and by field observations in Hanningfield Reservoir, Essex. The hexacanth embryo is bilaterally symmetrical, with three pairs of hooks and paired glands. The copepods Cyclops (Eucyclops) agilis, C. (Mesocyclops) leuckarti and C. (Acantftocyclops) viridis were infected experimentally with P. percae eggs. The egg hatches in the intestine, the embryo penetrates the intestinal wall by means of its hooks and possibly by secretions from its paired glands, and the larva develops within the haemocoel. Development took 3–4 weeks at 14°C in C. viridis, but the rate of development varied at different temperatures and copepod species differed in their suitability as hosts for P. percae larvae. The adult cestode showed a yearly cycle of occurrence and maturation in perch. Egg production occurred in the spring, after which adult worms were lost from the fish to be quickly replaced by juvenile worms of the succeeding generation. Increase in length of the adult cestode population occurred in two stages, a period of rapid initial growth commencing immediately after establishment in the perch, and a second stage closely associated with maturation of the worms.