The observed differences in the levels of blood pco2 and pH may have been due to an increased aerobic activity in white-adapted carp compared to that in black- and green-adapted fish.
This increased aerobic activity may indicate an increase in oxygen consumption, although it was not measured in the present study.
Besides, a possible increase in oxygen consumption by the white-adapte carp could be related to the highest SGR that they exhibited.
Carter and Brafield (1992) have found significant positive correlations between oxygen consumption and SGR in grass carp Ctenopharyngodon idella. Furthermore, Fanta (1995) observed that Oreochromis niloticus on white background exhibited higher respiratory frequencies than on black, blue,green, yellow and red backgrounds.