Rapid fluctuation in infection levels of Neoheterobothrium hirame (Monogenea) in Japanese flounder Paralichthys olivaceus in the Joban area, Japan

摘要

Neoheterobothrium hirame a haematophagous monogenean parasite on Japanese flounder Paralichthys olivaceus occurred at high prevalences (>70%) from 1999 to 2002 but thereafter declined and remained low (<20%) from 2003 to 2005 in the Joban area, Japan. In 2006, N. hirame became abundant again reaching a prevalence of 63%. Generalized linear models explained these rapid fluctuations in infection in relation to inshore water temperature, which affected the reproductive success of the parasite, and also the encounter rate between host and parasite through changes in their respective population densities. Severely anaemic fish were few, 2.4% even in 1999-2002 and 2006, suggesting that the effect of N. hirame infection on the P. olivaceus population was small in this area.