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Latitudinal variation in the growth and maturation of masu salmon (Oncorhynchus masou) parr

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We examined latitudinal variation in riverine growth and parr maturation of an endemic Asian salmonid, masu salmon (Oncorhynchus masou), in 12 rivers located between 36.6°N and 45.4°N. Masu salmon parr showed considerable variation in growth and maturation patterns among populations. Body sizes were generally larger, and parr maturation was common at southern latitudes. Male parr matured at smaller sizes at more southern latitudes. Latitudinal variation in riverine growth and maturation of masu salmon parr was largely attributed to latitudinal changes in temperature and population density. Parr size at age increased with increasing temperature and decreased with population density. Riverine growth conditions were an important environmental factor determining parr maturation for both males and females; however, the occurrence of mature female parr required extremely favorable growth conditions. Water temperature in May, approximately four months before maturation, was the most important environmental factor affecting the maturation of male parr. Our study supports the hypothesis that freshwater residency was promoted by favorable growth conditions at southern latitudes.

Nous examinons la variation latitudinale de la croissance en rivière et de la maturation des tacons du saumon masou (Oncorhynchus masou), un salmonidé asiatique endémique, dans 12 rivières situées entre 36,6°N et 45,4°N. Les tacons du masou montrent une importante variation dans leurs patrons de croissance et de maturation entre les populations. Les tailles corporelles sont généralement supérieures et la maturation des tacons fréquente aux latitudes inférieures. Les tacons mâles atteignent la maturité à des tailles inférieures aux latitudes plus basses. La variation latitudinale de la croissance et de la maturation en rivière des tacons du masou est en grande partie attribuée aux changements latitudinaux de température et de densité de population. La taille des tacons en fonction de l’âge augmente avec une augmentation de la température et diminue en fonction de la densité de la population. Les conditions de croissance en rivière sont un important facteur du milieu dans la détermination de la maturation des tacons, tant chez les mâles que chez les femelles; cependant, la présence de tacons femelles matures nécessite des conditions de croissance extrêmement favorables. La température de l’eau en mai, environ quatre mois avant la maturation, est le facteur du milieu le plus important qui affecte la maturation des tacons mâles. Notre étude appuie l’hypothèse qui veut que la résidence en eau douce soit favorisée aux latitudes inférieures par des conditions propices de croissance.

Document Type: Research Article

Publication date: 2010-06-01

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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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