880 



Fishery Bulletin 98(4) 



leaving the prawns in the ponds for longer, then one of 

 the methods that test for relative changes in gi-owth rate 

 (method 4 or 5) would probably be more appropriate. 



The difference in parameter estimates, and hence growth 

 rates, may have important implications when researchers 

 are trying to compare growth between species or between 

 regions. Francis (1988) argued that length-at-age data do 

 not contain precise information on the expected growth 

 rate offish of a given length. He concluded that length-at- 

 age data and tagging data contain different information 

 on growth; therefore the parameters estimated from them 

 had different meanings and were not directly comparable. 



Our proposed tests for different methods, including the 

 overall test, aim to incorporate all the parameters and the 

 overall uncertainties and correlations between each other 

 Further research can be carried out to study the robustness 

 of the proposed test and to apply it to other growth models. 

 The method suggested for constructing tests to compare 

 growth rates could be easily modified to apply to other types 

 of growth equation besides the von Bertalanffy equation. 



Acknowledgments 



We thank David Die, Chris Francis, and Vivienne Mawson 

 for constructive comments on an earlier draft of our manu- 

 script. We are also grateful to four reviewers for insightful 

 comments that led to a much improved version. 



Literature cited 



Anderson, T. W. 



1971. An introduction to multivariate statistical analysis. 

 John Wiley & Sons, New York, NY, 284 p. 

 Francis, R. I. C. C. 



1988. Are gi'owth parameters estimated from tagging and 

 age-lengtli data comparable? Can. J. Fish. Aquat. Sci. 

 4.5:9.36-942. 

 1996. Do herring gi-ow faster than orange roughy? Fish. 

 Bull. 94:783-786. 

 Ivirkwood, G. P.. and I. F. Somers. 



1984. Growth of the two species of tiger prawn, Penaeus 

 esciilentus and Penaeus seniisulcatus. in the western Gulf of 

 Carpentaria. Aust. J. Mar Freshwater Res. 3.5:703-712. 

 Somers, I. F, and G. P. Kirkwood. 



1991. Population ecology of the grooved tiger pra-wn, Penaeus 

 semisulcatus, in the north-westei'n Gulf of Carpentaria, 

 Australia: growth, movement, age structure and infesta- 

 tion by the bopyrid parasite Epipenaeon ingens. Aust. J. 

 Mar. Freshwater Res. 42:349-467. 

 Wang, Y.-G. 



1998. An improved Fabens method for estimation of growth 

 parameters in the von Bertalanffy model with individual 

 asymptotes. Can. J. Fish. Aquat. Sci. 55:397-400. 

 Wang, Y. -G., and M. R. Thomas. 



1995. Accounting for the individual variability in the von 

 Bertalanffy growth model. Can. J. Fish. Aquat. Sci. 52: 

 1368-1375. 



