Bacelo, J., Engelmann, J., Hollman, M., Von Der Emde, G., & Grant, K. (2008). Functional foveae in en electrosensory system. Journal of Comparative Neurology, 511, 342-359.

Bacelo et al. (2008) investigated the distribution of different electroreceptor types and their central nervous system representations in Gnathoneumus petersii. This weakly electric fish is a member of the mormyrids with a pulse-type electric field. G. petersii has three types of electroreceptor organs: 1) mormyromast system, which is used for prey detection and identification, 2) knollenorgan system, which is involved in electro-communication, and 3) ampullary system, used to detect and identify prey. The authors hypothesized that the elongated chin appendage of G. petersii represented an electric fovea that would be magnified in the electrosensory lateral line lobe (ELL) in the brain.

The authors used biocytin and biotinylated dextran amines to trace the projection from the electrosensory organs all over the body to the central nervous system. They also determined the total number and surface area of electroreceptors of each type along the body of the fish. Then, several ratios could be calculated: 1) the ratio between the peripheral sensory surface area and the projections in the ELL, and 2) the ratio of the total number of each type of electroreceptors to the size of their representation in the central nervous system.

Results revealed a strong central magnification of mormyromast and ampullary receptors in the chin appendage and nasal region, implying that these two areas of G. petersii could be considered as foveae of the mormyromast and ampullary systems. There was a very high electroreceptor density on the chin appendage and a slightly less but still high density on the nasal region.

This article applies to our lecture on electroreception. The paper discusses a weakly electric fish that emits electrical pulses. In lecture, we learned that pulse fish produce very short duration EODs with variable rates and low maximal rates. This paper focuses on electroreception of G. petersii. Our textbook refers to one type of electroreceptor organ found in this fish: the ampullary receptors. These receptors are the most common type of electroreceptive organ among fish, and consists of a tube opening to the fish’s skin. This tube extends to a small cavity lined with receptor cells. These ampullary organs detect DC or low-frequency electric fields of low amplitude. In the article, ampullary receptors are said to be used by the fish to detect and identify living prey, which is consistent with those types of electrical fields.

Our textbook also discusses tuberous electroreceptors, which are used for conspecific communication. The knollenorgan system described in this paper consists of tuberous electroreceptors; the knollenorgan system is tuned to the higher frequencies of the fish’s species-specific EOD. Both the textbook and the article describe these electroreceptors as being covered by an epithelial plug. The textbook briefly mentions the third type of electroreception organ, or the mormyromasts, which are dedicated to electrolocation functions. Howeber, our textbook does not mention the possibility of a fovea in this electroreception system.