PREMATURE SCHOOLING OF LARVAL HERRING IN THE PRESENCE OF MORE ADVANCED CONSPECIFICS

The availability of food to fish larvae influences the mean and varian ce of the growth rate in a cohort. At higher food densities, slower de veloping herring, Clupea harengus, larvae in the pre-metamorphic stage may co-occur with more developed, post-metamorphic individuals. The d evelopment of schooling in herring is closely associated with metamorp hosis. To assess whether the presence of schooling conspecifics encour aged the premature development of schooling in larvae, laboratory rear ed larvae (length 29-31 mm) were exposed to wild-caught schooling juve niles (length 55 mm) for the duration of the experiment. Observations of larvae from the experimental group were carried out for 37 days and the behaviour of the fish was recorded on video for subsequent analys is. These larvae were observed in the presence and absence of schoolin g juveniles with no food in the observation tank, and a few minutes an d Ih after food was added. The behaviour of these two groups (juvenile s present and juveniles absent) was compared with that of two addition al groups (different rearing densities), where the larvae had not been exposed to schooling herring. The exposure to schooling conspecifics did not affect the degree of interaction among herring larvae unless t he juveniles were present in the observation tank. Consequently, in th e presence of a school the larvae seemed to opt for the increased prot ection of the school, regardless of associated disadvantages, such as greater competition for food. These findings are discussed in relation to larval vulnerability to predators. (C) 1995 The Association for th e Study of Animal Behaviour