Swimming behaviour of Daphnia galeata x hyalina as a response to algal substances and to opaque colours

Directional swimming of Daphnia galeata x hyalina was studied using a container 36 cm long, with tracks as in a swimming pool, and a small chamber separated by a mobile door at one end of each track. In one experiment, extracts or filtrates of Cryptomonas erosa and Fragilaria crotonensis cultures were placed in the chambers; in a second one, coloured cardboards were inserted at the tracks ends instead of the mobile doors. Illumination was from above; the animals were placed in the middle of the tracks at the start, and their position recorded after a certain time. The results indicate a tremendous attraction of Daphnia galeata x hyalina by the diffusing algal substances, and an equally strong attraction by the blue, compared to the green, yellow and red colours. The importance of colour vision in Daphnia is underlined.