Osmorespiration of marble goby (Oxyeleotris marmorata) juveniles under different background colours

This study examined the oxygen consumption and ammonia excretion rates of fed marble goby (Oxyeleotris marmorata) juveniles (mean [± standard deviation] body weight 25.5 ± 0.5 g) acclimatised for 2 h or 24 h under different background colours (dark grey, light grey, black, red, white, deep green, blue and transparent). Two-way permutational multivariate analysis of variance (PERMANOVA) analysis revealed that oxygen consumption rate was significantly affected by acclimatisation duration but not by background colour. However, a significant interaction was observed between acclimatisation period and background colour, indicating that the influence of background colour on oxygen consumption requires further confirmation. In contrast, ammonia excretion rate was significantly influenced by both acclimatisation duration and background colour, while no interaction between these factors was detected. Postprandial ammonia excretion was notably higher under black, dark-grey and light-grey backgrounds, which likely provided a dim environment conducive to the active metabolic mode of this nocturnal species, supporting specific dynamic action. Conversely, under blue, transparent and deep-green backgrounds, ammonia excretion remained relatively stable between 2 and 24 h, suggesting that these background colours may suppress or alter the fish’s specific dynamic action.