were not as dramatic as was observed with the move from white to black tanks. However, by
168h, the grade score had reduced from about 11 to about 7.5, indicating a similar magnitude change to that seen when background changes were made in the other direction.
These findings indicate that colour changed quite rapidly and is likely to result from the changes in the chromatophores as indicated above (Fig. 5). It would be expected that colour changes should occur quite rapidly as prawns need to adapt to different environments through a camouflage process (Fingerman, 1965). Light microscopy of dissected epidermal layers taken from the first abdominal segment of prawns indicated that indeed, gross morphological changes occurred within a short time of prawns being moved from one environment to another (Fig. 7). Investigation of the epidermal layer from prawns maintained in a white tank until time 0h (
Fig. 7 a) showed small, densely pigmented chromatophores. When similar epidermal layers
were viewed from prawns that had been moved to black tanks and left for 3h or 7 days (Fig. 7 c and e, respectively), there had been a dispersion of pigment throughout the chromatophores, such that by day 7, pigment was over the majority of the surface, located in stellate chromatophores.
The sequence in Fig. 7 (b, d and f) shows the reverse occurring when prawns were moved from black to white tanks. Dispersed pigment (fig. 7b) was slightly more concentrated at 3h (Fig. 7d) and tightly concentrated after 7 days (Fig. 7f). We have shown that the degree of esterification of astaxanthin appears to be dependent upon the background colour and it is possible that it is the changed chemical form that determines its location in the chromatophores.