Density-dependent growth of Sea Lamprey larvae:: evidence for chemical interference

1. Density can influence growth through exploitation competition and behavioural or chemical interference. Negative effects of population density on the growth rate of Sea Lamprey larvae have been reported in several field and laboratory studies, but the mechanisms involved are poorly understood. 2. In this study the role of population density and waterborne-mediated interference on the growth rate of Sea Lamprey larvae was assessed in two laboratory experiments. The effects of these factors were evaluated by comparing growth of larvae reared at three different densities (27, 75 and 128 individuals m(-2)) or in preconditioned water (i.e. containing Sea Lamprey larvae at the same three densities). 3. Larval density had a negative effect on growth rates. Water conditioning had a negative but weaker effect on growth. Larvae reared in water preconditioned at the two higher densities showed a lower mass increase than those growing in water preconditioned at the lowest density. 4. The results are consistent with the existence of some chemical or biological agent released into the surrounding water and influencing growth in larval Sea Lampreys. However, chemical interference is not the only factor influencing density-dependent growth.