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Age and Growth of the Australian Freshwater Fish Murray Cod, Maccullochella peelii peelii Stuart J. Rowland NSW Fisheries, Inland Fisheries Research Station, Narrandera NSW 2700; present address, Grafton Research Centre, PMB 3, Grafton NSW 2460 Rowland, S.J. (1998). Age and growth of the Australian freshwater fish Murray cod, Maccullochella peelii peelii. Proceedings of the Linnean Society of New South Wales 120, 163-180. Murray cod, Maccullochella peelii peelii, were sampled over the period 1975-1984 from six tributaries and two impoundments of the Murray-Darling river system in NSW; the Murray, Edward, Wakool, Murrumbidgee, Darling and Gwydir rivers, and Lake Mulwala and Lake Burrinjuck. Age determination techniques have been validated by: analysis of seasonal changes on the margins of opercular bones and whole otoliths; by close agreement between observed and back-calculated mean lengths-at-age; and by examination of known-age fish. The sharp transition from narrow, translucent zones to broad, white zones on opercular bones, and the white, opaque zones on whole otoliths have been determined to be annuli formed each spring. Opercular bones are superior for ageing cod, particularly those older than 8 years (> 800 mm). Murray cod is a large, relarively long-lived fish; the oldest cod was estimated to be 34 years. There was no significant difference between the growth or length-weight relation-ships of males and females, or cod from different rivers, but cod from the impoundment. Lake Mulwala, were significantly larger than same-aged cod from rivers. The growth in length (L) of Murray cod in rivers is described by a von Bertalanffy curve, represented by the equafion: Lt = 1369.05 { l-exp[-0.060(t -i-5.209)]). Although overall growth in length is slow (K = 0.060), there was no asymptote in the age-weight relationship for cod up to 30 years, indicating that Murray cod grow predominantly by weight increases after about 10 years of age. The length-weight reladonship for cod in rivers is described by the equation: W = 3.240 X 10""^ L^ -^^-, where W is whole weight in kg and L is total length in mm. Manuscript received 12 October 1998, accepted for publication 18 November 1998. KEYWORDS: Australian percichthyid, ageing, growth rates, opercular bone, otolith, Maccullochella, Murray cod. INTRODUCTION The Murray cod, Maccullochella peelii peelii (Mitchell), is an Australian native, warmwater, percichthyid fish found naturally in the vast Murray-Darling river system (Fig. 1). It is Australia's largest, wholly-freshwater fish (growing to a maximum recorded size of 113.6 kg) and is highly valued by recreational and commercial fishers for its size and excellent edible qualities (Rowland 1989). There has been a dramatic decline in the abundance and a reduction in the distribution of Murray cod, particularly since the 1950s, and it is now relatively uncommon in many areas (Lake 1971; Cadwallader and Backhouse 1983; Rowland 1985, 1989). Initial studies (Llewellyn 1966; Lake 1967; Jones 1974; Langtry, in Cadwallader 1977) used scales or otoliths to age Murray cod, but sample sizes were small, few age-classes were included, and the techniques used were not described or validated. More recently, Gooley (1992) and Anderson et al. (1992) used sectioned otoliths to age Murray cod from Lake Charlegrark (Victoria) and the Lower Murray-Darling basin. In both these studies ageing techniques were validated. Rowland (1985) conducted a major research project into aspects of the biology of Murray cod, to provide essential data for the formulation of management policies for the Prog. Linn. Soc. n.s.w., 120. 1998

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Age and growth of the Australian freshwater fish Murray cod, Maccullochella peelii peelii

S J Rowland
Proceedings of The Linnean Society of New South Wales 120: 163-180 (1998)

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