The colour of prawns decreased in response to black substrates, but the effect of time was not significant until 2 h after exposure (Table 2). R and G values of animals fed either 50 or 100 mg/kg Axn were significantly lower after 2 h exposure compared with pre-exposure values(Table 2). This worked in combination with the effects of diet, where after 120 min exposure to black substrates the R, G and B values were all significantly lower in 100 mg/kg fed animals than those fed 0 mg/kg (Table 2). After exposure to black substrates, results indicated that animals on high carotenoid diets became significantly darker than those on low carotenoid diets