Comparisons between the growth of Acanthopagrus butcheri cultured from broodstock from two estuarine populations that are reproductively isolated and differ markedly in growth rate

The populations of black bream, Acanthopagrus butcheri, in the Swan and Moore River estuaries are reproductively isolated and their juveniles grow at very different rates. Adult A. butcheri from these two estuaries were used as broodstock for culturing juveniles, whose growth was then recorded. Schnute growth curves, fitted to the lengths at age of the larvae and juveniles derived from these separate broodstocks, were very similar during their first 267 days of life. Thus, extrapolations from the two curves yielded a maximum difference in length of only 6% for fish in the two groups at any age after 100 days of age and the predicted lengths at the end of the experiment differed by only 0.6 mm. Furthermore, the mean lengths of the two groups at the end of the experiment were not significantly different. The evidence suggests that the marked differences between the growth of juveniles in natural populations of black bream in the Swan and Moore River estuaries reflect the marked differences in conditions in those estuaries, such as in the quality and/or amount of food available and fish densities, rather than any potential genetic differences. The implications of the results for aquaculture and translocation are discussed. (C) 2004 Elsevier B.V. All rights reserved.