Scale stocking checks to differentiate between hatchery-reared and wild mulloway Argyrosomus japonicus M. D. TAYLOR & R. F. PIOLA Ecology and Evolution Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Australia Abstract Scales from hatchery-reared, stocked and wild mulloway Argyrosomus japonicus (Temminck and Schlegel) captured in the Georges River, and a library of mulloway scales from coastal New South Wales, were examined for the presence of scale checks. Checks specific for hatchery-reared fish were present in 100% of recaptured hatchery-reared mulloway; the origin of which was confirmed by the presence of a chemical mark in the otolith or fin spine. Up to 7% of wild mulloway were incorrectly classified as hatchery-reared on the basis of these checks. An abrupt reduction in salinity from 35 to 5 and 6 days starvation successfully induced checks in the scales of hatchery-reared mulloway. The marking efficiency for stocking checks was comparable to that obtained using oxytetracycline hydrochloride, and supports the short-term use of scale stocking checks to evaluate mulloway stock enhancement programmes in Australia. KEYWORDS: mulloway, re-stocking, scale increment, stock enhancement, stocking checks. Introduction Current fish culture techniques allow the rearing of large numbers of fish for release to supplement or enhance existing wild fish stocks (Munro & Bell 1997; Taylor, Palmer, Fielder & Suthers 2005b). Responsible enhancement projects include robust monitoring programmes and adaptive management to facilitate ongoing improvements in success, but these rely on suitable methods to identify hatchery-reared finger- lings on recapture (Blankenship & Leber 1995). Whilst coded wire tagging and genetic marking represent the ideal marking techniques for stock enhancement pro- jects (Bartley, Kent & Drawbridge 1995; Brennan, Leber, Blankenship, Ransier & DeBruler 2005), both methods are expensive to set up through either large capital investment in tagging apparatus or characteri- sation of selectively neutral polymorphic loci. At the pilot stage, enhancement studies may be financially constrained, so other methods of marking are required to evaluate initial enhancement efforts. Such methods include otolith marking with chemical stains, and circuli patterns on scales (Barlow & Gregg 1991). Mulloway Argyrosomus japonicus (Sciaenidae; Tem- minck and Schlegel) is an apex predator common across the Pacific and Indian Oceans, including South Africa (Griffiths 1996), China and the southern coast of Australia (Taylor, Laffan, Fielder & Suthers 2006b). The species is fast growing and heavily targeted by both commercial and recreational fishers in Australia. Consequently, mulloway is subject to declining catches in most southern Australian states (Silberschneider & Gray 2005; Taylor et al. 2005b), and is now the subject of pilot stock enhancement research along the mid-northern coast of New South Wales, Australia. Scale increments may be deposited on a daily basis (Kingsford & Atkinson 1994), but ageing of sub- yearling fish using scales may be confounded by incongruent rates of circuli deposition. Scale formation does not usually commence at hatch in sciaenids (Bridges 1971), and the lack of a regular relationship between numbers of sub-yearly increments and time has prevented use of scale circuli for back calculation of size-at-age for age-0+ a fish (Szedlmayer & Able 1992). Circuli deposition on ctenoid teleost scales is thought to Correspondence: Matt Taylor, Ecology and Evolution Research Centre, School of Biological, Earth and Environmental Science, University of New South Wales, 2052, Australia (e-mail: mattytaylor@unsw.edu.au) Fisheries Management and Ecology, 2008, 15, 211–216 Ó 2008 The Authors. Journal compilation Ó 2008 Blackwell Publishing Ltd. doi: 10.1111/j.1365-2400.2008.00602.x Fisheries Management and Ecology