The Research of Dr. Harold Zakon
ur lab studies a number of questions using weakly electric fish as our model organism. These fish live in murky waters and are nocturnally active. They generate weak electric fields around themselves from a specialized electric organ and sense these electric fields, with specialized sensory receptors, called electroreceptors. They sense the distortions caused in their own electric fields to locate nearby objects, and the electric fields of other fish as communication signals.
Weakly Electric Fish
Weakly electric fish have evolved twice. One group, the mormyriformes, live in Africa, the other group, the gymnotiformes, live in South America.
Electric organs (EOs) have evolved independently in at least six different groups of fish including two groups of elasmobranchs (Torpedo rays and the skates), and four groups of teleosts (gymnotiforms, mormyriformes, stargazers, catfish). In some groups EOs generate strong discharges (such as the Torpedo ray) and in others, weak discharges (such as the knifefish we study). In all but one case, they derive from muscle (the exception is the family Apteronotidae in which the axons of the EMNs form the electric organ). How the electric organ comes from muscle evolutionarily and developmentally is one question that we have been pursuing in our laboratory. The morphology of the electrocytes varies greatly between species and these variations are intimately bound up in the generation of species-specific electric organ discharge (EOD) waveforms. However, they operate on fundamental features of excitable membranes and current flow. Mainly, electric organs are composed of columns of electrocytes oriented in the same axis and ensheathed in high resistance connective tissue. The connective tissue channels the flow of current along the axis of the organ, out into the water, and back into the other end of the electric organ. Species such as Torpedo rays or electric eels, which have many stacks of flattened electrocytes, are capable of generating discharges of hundreds of volts. Weakly electric fish, such as the ones we study, make modest discharges of only hundreds of millivolts to a few volts.
(Picture by J. Oestreich)