Sarre and Potter; Variation in age compositions and growth rates of Acanthopagrus butchen 



793 



Swan River, Moore River or Wellstead estuaries (Table 3). 

 Furthermore, although these two growth parameters did 

 differ significantly between the two sexes in the Norna- 

 lup Walpole Estuary, the probability levels in both cases 

 were close to 0.05. However, the asymptotic length (L ) for 

 female fish was significantly greater than that of male fish 

 in each estuary except that of the Moore River (Table 3). 



The values for k and L for each sex differed signifi- 

 cantly among the populations of A. butchen in the four 

 estuaries and between those of males in each of these 



estuaries and Lake Clifton (P<0.001 or 0.01). Further- 

 more, the values for ?„ for each sex almost invariably 

 differed significantly (P<0.001 or <0.05) among the popu- 

 lations in the four estuaries and between those of males 

 in each of these estuaries and Lake Clifton. Because the 

 three von Bertalanffy parameters for both sexes were each 

 shown almost invariably to differ significantly among 

 the different populations, no attempt was made to test 

 whether there was a common pattern of growth for each 

 sex in each system. 



