Olfaction and Vision in Fish Schooling

Abstract

1. The behaviour of individual roach was observed in a horizontal linear gradient of species odour. No attempt was made to analyse the odour involved. 2. The behaviour of roach, grey mullet and Chromis was studied in the presence of (a) a mirror, or (b) a second fish behind a clear plastic sheet. 3. Roach showed nearly as strong a response to attractant species odour as to the repellent ‘Schreckstoff’. The relative strengths of responses to directional visual images and non-directional odour gradients were compared. 4. Short-term and long-term declines in the strength of the response to odour occurred. 5. Observation of a ‘two-fish school’ suggested that a system of exploratory, returning and following tendencies co-ordinated schooling behaviour. 6. Isolation of roach for a period of 20-25 weeks caused enhancement of the olfactory reaction but completely disrupted the visual response. 7. It is suggested that school structure is maintained by balanced attractive and repulsive ‘forces’; the attraction modalities involved are vision by day and olfaction by night, and the repulsion modality is the lateral line sense.