New Zealand Journal of Marine and Freshwater Research abstracts

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Seasonal profiles in growth, energy reserves, gonad development, and plasma steroids in age 1+ cultured Chinook salmon (Oncorhynchus tshawytscha) females

M. J. Unwin¹
C. W. Poortenaar²
D. K. Rowe³
N. C. Boustead¹
M. J. R. Porter⁴,*

¹National Institute of Water and Atmospheric
 Research Limited
P.O. Box 8602
Christchurch, New Zealand
email: m.unwin@niwa.co.nz

²National Institute of Water and Atmospheric
 Research Limited
Private Bag 109 695
Auckland, New Zealand

³National Institute of Water and Atmospheric
 Research Limited
P.O. Box 11 115
Hamilton, New Zealand

⁴Institute of Aquaculture
University of Stirling
Stirling, FK9 4LA
United Kingdom

*Present address: Tasmanian Aquaculture & Fisheries Institute,
GPO Box 252 49, Hobart, Tas 7001, Australia.

Abstract  Sexual maturation in 2-year-old female Chinook salmon (Oncorhynchus tshawytscha) is unknown within their native range, but occurs in up to 20% of farmed stocks in New Zealand. To characterise the seasonal timing of oogenesis and subsequent ovarian development, we measured levels of plasma 17β-estradiol and testosterone, condition factor, and gonadosomatic and hepatosomatic index, for freshwater-reared female Chinook at 2-4-week intervals during their second year of life (May 2001-April 2002). These comprised two treatment groups under additional 24 h illumination from September to January, and two ambient controls. Macroscopic ovarian development first occurred in mid September (8 months before spawning), coinciding with detectable increases (≥0.3 ng ml^-1) in both plasma steroids. Vitellogenesis was first observed in November and coincided with an increase in hepatosomatic index, possibly indicating the liver’s role in transferring lipids to the developing ova. Neither mean weight nor the percentage of maturating fish (mean 6.9%) differed between the treatment and control groups at the end of the experiment, but ovarian development in the treatment group was advanced by 13 days relative to the controls. Reduced dark phase plasma melatonin levels confirmed that the additional light was sufficiently intense to produce a physiological response in the artificially illuminated fish.

Keywords  Chinook salmon; Oncorhynchus tshawytscha; female; maturation; vitellogenesis; plasma steroids

M03040; Online publication date 15 March 2004; Received 17 July 2003; accepted 8 December 2003
New Zealand Journal of Marine and Freshwater Research, 2004, Vol. 38: 29-41
0028-8330/04/3801-0029 © The Royal Society of New Zealand 2004

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