A. Migliaro, A.A. Caputi, R. Budelli. (2005) Theoretical analysis of pre-receptor image conditioning in weakly electric fish. PLoS Comp Biol 1(2): e16

As we discussed in class, electroreceptive fish detect nearby objects by processing the information contained in the pattern of electric currents through the skin. If object is more conductive than the water, the electric current will be shunted through the object because it represents a path of lower resistance, and gives rise to “electrical bright spot” on the skin. On the other hand, if the object is less conductive than the water, electric current will be shunted around the object, and gives an “electrical shadow” on the skin. These processes are known as electrolocation. Therefore, electric images are constructed by the brain through the distribution of voltage or current on the sensory surface of the fish’s skin.

This experiment calculated the electric image of a metal object on a simulated fish (G. petersii) and found out the different magnitudes of conductance for internal tissues and skin. The high conductivity of the fish body enhances the electric image. The authors generalized two concepts for how fish recognizes objects: object perturbed field (change in the basal field generated by the presence of an object), and imprimence (equivalent sources produced at the location of an object). The study involved the investigation of the effect of changing internal conductivity while maintaining a high skin conductance. Though the conductivity cannot be too low, or else the currents produced by the electric organs (EO) are negligible since the current short-circuits inside the fish because it cannot flow through the skin.

Therefore, high conductance of internal tissues is critical for enhancing the local electric organ discharges (EOD) field as well as for generating the centre-surround opposition pattern that characterizes electric images and that is coded by primary afferents.

This study relates to what we have discussed in class in lecture when we consider how electroreception evolved independently in several fish families. They produce EOD, which is very important; it gives a strong influence on the overall pattern of current flow. For example, fishes choose to stay in confined spaces that are frequently its preference in the natural habitat, or in the tube-shaped shelter commonly used in captivity.