Colour preference and colour vision of the larvae of the giant freshwater prawn Macrobrachium rosenbergii

• The larval innate colour preference and vision were examined based on their response to coloured beads.
• The larvae have preference for blue colour.
• They discriminated colours by chromaticity.

This paper reports on the innate colour preference and colour vision in the hatchery-reared larvae (10–16 days old, stages IV–VIII) of the giant freshwater prawn Macrobrachium rosenbergii (De Man) based on their response to coloured beads in a grey-walled tank under natural illumination. Plastic beads (4.1 mm in diameter) of different colours (dark blue, light blue, light green, yellow, red, white, black, and grey) in various combinations were suspended in the water 5 cm from the water surface and 12–20 cm from the tank walls where the larvae rested in the absence of aeration. The larvae swam head first straight toward the beads and gathered around them. The number of larvae was highest around the dark blue, light blue, and white beads; lowest around the black, red, and light green beads; and moderate around the yellow bead. Tests with different colours in combination with three shades of grey indicated that the larvae of M. rosenbergii discriminated colours by chromaticity. The preference for blue seemed to be an innate rather than a learned ability since the larvae did not prefer the yellow and red beads that were more similar to the colours of the egg custard and the Artemia nauplii on which they had been reared.