LABORATORY EXPERIMENTS ON BEHAVIOR AND MOVEMENT OF A FRESH-WATER MUSSEL, LIMNOPERNA-FORTUNEI (DUNKER)

Experiments on the movement and behaviour of a freshwater mussel Limno perna fortunei (Dunker) were conducted in the laboratory. Small mussel s of 5-12 mm shell lengths moved over 100 cm during a day within plast ic containers, with a maximum distance of 300 cm. However, their movem ent was concentrated during the first five hours of the experiments. T he distance moved decreased with increasing shell length, and mussels larger than 27 mm moved less than 20 cm. Both small (< 15 mm) and larg e (greater than or equal to 15 mm) mussels showed negative phototaxis and positive geotaxis under the light, but positive geotaxis of small mussels tended to be weak in darkness or under the shade. Small mussel s had strong thigmotaxis with a preference for settling in the angled crevices between the vertical walls and the flat bottoms of the contai ners. Small mussels tended to aggregate after movement, and the presen ce of large mussels facilitated secretion of byssal threads by the sma ll mussels. The possible adaptive significance of these behaviours and movement are discussed in relation to response to predation and dislo dgement by waves or water current.