Parasitism, space constraints, and gonad asymmetry in the pollan (Coregonus autumnalis)

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Abstract:

Both sexes of Lough Neagh pollan (Coregonus autumnalis) show directional asymmetry in gonad mass, the left being larger than the right in 70% of individuals. The frequency and degree of asymmetry are size independent in males but become progressively more marked in females of >120 g somatic mass. There is little evidence to support the hypothesis that the size of the body cavity constrains gonad size. Pollan are heavily and size-dependently infected by metacercariae of the trematode Ichthyocotylurus erraticus. Total gonad mass in both sexes of pollan is negatively correlated with infection intensity of this parasite. In females, mean egg size shows no trend but fecundity declines and the degree of asymmetry in ovary mass increases with infection intensity up to a threshold, beyond which it remains constant. While directional asymmetry in gonad size is strongly developmentally controlled in many fish species, variation in the degree of gonad asymmetry in pollan provides a potentially sensitive indicator of stress.

Les deux sexes du pollan (Coregonus autumnalis) au Lough Neagh présentent une asymétrie directionnelle de la masse de leurs gonades, la gauche étant plus grande que la droite chez 70 % des individus. La fréquence et l'importance de l'asymétrie sont indépendantes de la taille chez les mâles, mais elles deviennent progressivement plus marquées chez les femelles de masse somatique >120 g. Il y a peu d'indications pour appuyer l'hypothèse selon laquelle la dimension de la cavité corporelle restreint la taille des gonades. Les pollans sont fortement infectés par les métacercaires du trématode Ichthyocotylurus erraticus et l'infection varie en fonction de la taille. Il y a une corrélation négative entre la masse totale des gonades chez les pollans et l'intensité de l'infection par ce parasite. Chez les femelles, la taille moyenne des oeufs ne suit aucune tendance particulière; en revanche, la fécondité décline et l'importance de l'asymétrie de la masse ovarienne augmente en fonction de la gravité de l'infection jusqu'à une limite supérieure au-delà de laquelle elles demeurent constantes. Bien que l'asymétrie directionnelle de la taille des gonades soit fortement contrôlée par le développement chez plusieurs espèces de poissons, la variation de l'importance de l'asymétrie des gonades chez les pollans fournit un indicateur potentiellement sensible du stress.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: December 1, 2005

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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