Growth, metamorphosis and feeding behaviour of Rana catesbeiana Shaw 1802 tadpoles at different rearing densities

An experiment was carried out to investigate the effects of rearing density on growth, metamorphosis and behavioural patterns of feeding in bullfrog, Rana catesbeiana Shaw, tadpoles. Stage 25 (Gosner) tadpoles from a single cohort were stocked at 0.5, 1.0, 2.0, 4.0 and 8.0 L-1 in 6-L plastic containers. A combination of phytoplankton and supplementary feed was used. There was an inverse relationship between rearing density and growth and metamorphosis above two organisms L-1. Tadpoles reared at 0.5 and 1.0 L-1 reached the metamorphic climax in 135 and 120 days, respectively, whereas more than 80% of all tadpoles reared at 4 and 8 L-1 did not metamorphose at all. Intraspecific competition appeared to be consistent among the cultured organisms regardless of the rearing density. Smaller tadpoles were displaced to sites distant from feeding points during supplementary feed addition, while no displacement was observed during phytoplankton addition. It is concluded that bullfrog tadpoles grow well at up to two organisms L-1 and that intraspecific competition is present within cultured tadpoles regardless of stocking density and may result from intrinsic genetic variability.