Might the interspecies interaction between fish and shrimps change the pattern of their avoidance response to contamination?

Contamination seems to exert a crucial role in the spatial distribution of some organisms, such as shrimps and fish. Both, especially the freshwater fish Danio rerio and the shrimp Atyaephyra desmarestii, have been tested experimentally for their avoidance response and have showed the ability to escape from toxic effects. As the behavior of avoiding or not the contamination might be altered in the presence of other factors, the aim of the current study was to verify whether the avoidance response of both species, when exposed jointly (multispecies tests), to a copper gradient is different from the avoidance response observed in monospecies tests. The avoidance was assessed in a multi-compartmented exposure system, in which a copper gradient was simulated. Organisms were tested individually and together. Both species avoided potentially toxic copper concentrations; however, shrimps were slightly more sensitive in the monospecies tests: AC(50) (avoidance concentration for 50% of the population) of 60 (53-68) mu g/L for the zebrafish and 50 (45-56) mu g/L for the shrimp. In the multispecies tests, the sensitivity pattern changed: the avoidance response by the fish [AC(50): 30 (14-46) mu g/L] was greater than by the shrimps [AC(50): 70 (22-141) mu g/L]. Although the AC(50) values are in the same order of magnitude, a slight trend to change the avoidance pattern was observed in the shrimps during multispecies test: the avoidance was lower and time-delayed. This behavioral change could be linked to the stress caused by the zebrafish sharing the space with the shrimps, perhaps increasing the territorialism of the fish, or a delay in the shrimps detecting the risk of contamination.