Body colour adjustment of the freshwater shrimp Macrobrachium jelskii (Miers 1877) in different background colours

Abstract

The body colour variation in response to different background colours is associated with camouflage, increasing efficiency against predation. In our study, we investigated the body colour variation of the freshwater shrimp Macrobrachium jelskii in response to different background colours. For this, we collected specimens of M. jelskii in the Thomás Osterne Reservoir, Municipality of Crato, State of Ceará, Brazil. For the experiment, we used six aquariums divided into three treatment groups: white background; black background; red background; with two replicates for each group. Before the experiment, we photographed 30 specimens of M. jelskii in dorsal view. Then, we distributed five shrimps in each aquarium, totalling 10 shrimps per treatment. After 30 days, we obtained new images of the shrimps, under the same settings used before the experiment. We used ImageJ software to obtain the RGB values (Red, Green, Blue) of the dorsal region of the first abdominal somite of the shrimps. Before the experiment, the body pigmentation of M. jelskii was homogeneous, with overlap between the groups. After the experiment, the RGB of M. jelskii varied according to each background colour, differing between the white and black, between the white and red, and not differing between the black and red. Our results show that M. jelskii adjusted its pigmentation to different background colours, evidencing a mechanism that may favour the camouflage of the species in different habitats and provide more chances of survival against visual predators.