PCB intake and the growth of waterfowl: multivariate analyses based on a reparameterized Richards sigmoid model.

Multivariate analyses of the parameters of a modified Richards growth model were used to determine the effects of sex and varying levels of dietary intake of PCB's (0-50 ppm), on the asymptotic size (W infinity), total growing time (T) and shape (m) of the growth curves of game farm mallards (Anas platyrhynchos) and wild wood ducks (Aix sponsa) raised under laboratory conditions. Level of PCB intake did not affect any of the growth parameters of the wood ducks, while sex affected both m and W infinity, with males of this species growing to greater body weights and showing slightly lower shape parameters than females. Growth characteristics of the mallards on the other hand, did not differ between the sexes. PCB intake however, had a significant effect on the shape of the mallard growth curve, but did not affect either W infinity or T. All interactions between sex and PCB treatment level were non-significant in both species. The growth responses of game-farm mallards to PCB intake cannot be assumed to typify that of other wild waterfowl species without additional evidence from comparative studies.