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The population age structure and reproductive biology of Gyrodactylus salaris Malmberg (Monogenea)

Published online by Cambridge University Press:  06 April 2009

P. D. Harris ,
P. A. Jansen  and
T. A. Bakke
P. D. Harris
Affiliation:
Department of Adult Education, University of Nottingham, Nottingham NG7 2RD
P. A. Jansen
Affiliation:
Zoological Museum, University of Oslo, Sars gt. 1, N-0562 Oslo 5, Norway
T. A. Bakke
Affiliation:
Zoological Museum, University of Oslo, Sars gt. 1, N-0562 Oslo 5, Norway
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Summary

Gyrodactylus salaris has recently become a major pathogen of Atlantic Salmon (Salmo salar) in Norway. The survivorship, population age structure and pattern of insemination of G. salaris were studied to determine the extent to which this species reproduces sexually. The age-specific mortality schedule of G. salaris could be described by an exponential model but day to day variations were large, with an increase in mortality after each birth. Modelling population growth using the best fit mortality schedule indicated that, at stable age structure, 35% of the population would consist of newborn and pre-1st birth flukes. Using testis, penis and embryo development, pre-1st birth and immediately post-1st birth flukes could be unambiguously identified, and established infections were found to contain 35% pre-1st birth flukes, as predicted. The proportion of pre-1st birth flukes in newly established infections was significantly smaller, probably because of differences in the rate of transmission between newborn and older flukes. Gyrodactylus salaris is relatively long-lived, and more than 40% of the population may survive to give birth for the third time. As gyrodactylids are protogynous, and the first daughter is probably produced asexually, this long-lived strategy ensures that a large part of the G. salaris population possesses a functional male system, and that the asexually derived flukes are a smaller component of the total population in this species. Flukes with whorls of inseminated spermatozoa within the seminal receptacle were found in all age groups possessing a functional male system, and were interpreted as having been cross-inseminated. G. salaris on susceptible Norwegian salmon appears to regularly reproduce sexually, possibly accounting for its morphological variability and wide range of potential salmonid hosts.

Keywords

Gyrodactylus salarisage-specific mortalitysexual reproduction
Type
Research Article
Information
Parasitology , Volume 108 , Issue 2 , February 1994 , pp. 167 - 173
Copyright
Copyright © Cambridge University Press 1994

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