Influence of Bottom Substrate, Bottom Depth and Day/Night on In Situ Coloration Variability of Pomatoschistus minutus (Pallas, 1770) (Actinopterygii: Oxudercidae)

Individuals of sand goby, Pomatoschistus minutus (Pallas, 1770), were photographed underwater in their natural habitat at Breivika, Norway, from October 2022 to January 2023. Of the 67 individuals collected, 58 were subsequently confirmed in the laboratory as P. minutus. Quantified coloration profiles were generated and statistically tested for the influence of substrate type, depth, time of day (daylight vs. night-time), and the sex and developmental stage of the individuals on the in situ coloration variability of P. minutus. Lateral body coloration showed a significant difference across bottom substrates but no significant difference for the factors of sex, developmental stage, time of day, or depth. Dorsal body coloration showed no significant difference across substrates, sex, or developmental stage; however, a significant difference was found for depth and time of day. This study provides the first detailed description of the live coloration patterns of P. minutus in its natural habitat, including a documented analysis of its qualitative variability in relation to background substrate. The found coloration plasticity highlights a sophisticated and rapid adaptation for crypsis. The ability to adjust coloration to both substrate and light conditions likely represents a significant survival strategy for this small, benthic fish against visual predators.