Summary

The market value of Australian snapper is strongly dictated by the appearance of the fish. Farmed snapper are generally darker and less red than wild snapper and previous research has found that they can alter the degree of skin lightness or darkness to blend in with the colour of their surroundings and can gain red pigmentation when fed diets containing a pigment called astaxanthin. One approach by farmers may be to feed astaxanthin to snapper in sea cages to increase skin redness and then transfer fish to white tanks before sale to increase skin lightness. Before this can be done in a commercial situation, it is important to determine the time taken to produce a suitable change in skin colour and if this will cause stress on the fish.

In this study, snapper were held in black or white tanks and fed a diet containing astaxanthin. After 49 days, snapper were transferred from black tanks to white cages or white tanks to black cages and monitored over seven days. Fish rapidly became lighter when transferred to white cages and darker when transferred to black cages with maximum change taking place within one day. However, the redness of snapper transferred to white cages continued to decrease during the seven days. There was no difference displayed in levels of the stress indicator plasma cortisol between cage colours. In conclusion, transferring dark coloured snapper to white cages for one day is sufficient to provide the greatest benefit in terms of producing light coloured fish while minimising the reduction in favourable red skin colouration.