Aspects of the reproductive biology of torrentfish, Cheimarrichthys fosteri, in two braided rivers of Canterbury, New Zealand

Abstract

The reproductive biology of torrentfish, Cheimarrichthys fosteri Haast, was investigated in the braided Rakaia and Ashley Rivers, South Island, New Zealand. Fish matured in their second year (1+) with males exceeding 63 mm and females 65 mm in fork length (FL). Few fish lived for more than 3 years. Spawning is thought to take place in the lower reaches of rivers and occurred in both rivers from January to April. Gonosomatic index (GI) values for females were lowest from April to August, inclusive, in fish from both rivers; they peaked in October in the Rakaia and in January in the Ashley River. Male GI values were lowest during April‐July and highest in October and March in the Rakaia and Ashley Rivers, respectively. Fecundity varied from 2769 to 55100 eggs and was linearly related to fish length. Juveniles (0+), 23–30 mm FL, entered the Rakaia lagoon primarily from April to September. Females dispersed up stream, up to 90 km from the sea, whereas males were most abundant in the lower reaches. The absence of juveniles in upstream localities suggests that early rearing is marine, and juveniles move up from the lower reaches of the river as they grow.

Key words:

• Cheimarrichthys fosteri
• gonad maturation
• sexual maturity
• egg diameter
• fecundity
• fish migrations
• braided river

Notes

Present address: Department of Biological Sciences, University of Calgary, 2500 University Drive, N.W., Calgary, Alberta, Canada T2N 1N4.

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