Effects of water conductivity on electrocommunication in the weak-electric fish Brienomyrus niger (Mormyriformes) (original) (raw)

A characteristic electric organ discharge display in social encounters between mormyrid fish is a temporary discharge cessation. Using this response, we have investigated the useful range of electrocommunication under different water conductivity conditions in the mormyrid Brienomyrus niger. An individual fish was confined to a porous ceramic shelter tube and moved from a starting distance of 380 cm toward a similarly confined conspecific until discharge cessation occurred. The moved fish was subsequently returned to its original position. Water conductivity affects the peak-to-peak source voltage of the electric organ and the sensitivity of the fish's electroreceptors. Within a range of t0 to 36 000 gS/cm, the peak-to-peak amplitude of the electric organ discharge declined as a power function. At 120 pS/cm, the amplitude was 50%, and at 300 gS/cm, 30 ~ of the 10 pS/cm value. The interfish distance at which discharge cessation occurred and the associated electric field gradients were dependent on water conductivity and upon the spatial orientation of the two fish (end-to-end or parallel orientations of their shelter tubes). The respective ranges were from 135 cm and 0.02 mV/cm at 52 gS/cm (parallel orientation) to 22 cm and 0.36 mV/cm at 678 gS/cm (end-to-end orientation). When the data for both tube orientations were combined, the relationship between water conductivity (x) and the distance at which discharge cessation occurred (y) could be expressed by a power function, y = K. x" (with K = 10z.97 and a =-0.56). When an electrically 'silent' fish was moved away from its conspecific, a discharge resumption in the form of a high-frequency rebound occasionally effected changes in the other fish's discharge activity at distances up to 157 cm (with an associated electric field gradient of 0.01 mV/cm under the lowest conductivity condition).