Sharks can sense bioelectric fields of prey and other animals in seawater using an extraordinary system of sense organs (ampullae of Lorenzini) [R.D. Fields, The shark's electric sense. Sci. Am. 297 (2007) 74-81]. A recent study reported that these sense organs also enable sharks to locate prey-rich thermal fronts using a novel mode of temperature reception without ion channels. The study reported that gel extracted from the organs operates as a thermoelectric semiconductor, generating electricity when it is heated or cooled [B.R. Brown, Neurophysiology: sensing temperature without ion channels, Nature 421 (2003) 495]. Here we report biophysical studies that call into question this mechanism of sensory transduction. Our experiments indicate that the material exhibits no unusual thermoelectric or electromechanical properties, and that the thermoelectric response is an artifact caused by temperature effects on the measurement electrodes. No response is seen when non-metallic electrodes (carbon or salt bridges) are used, and ordinary seawater produces the same effect as shark organ gel when silver wire electrodes are used. These data are consistent with the voltages arising from electrochemical electrode potentials rather generated intrinsically within the sample. This new evidence, together with the anatomy of the organs and behavioral studies in the literature, best support the conclusion that the biological function of these sense organs is to detect electric fields.

Zebrafish are ideal for experimental studies in the classroom because, in contrast to chicks or mammals, fish embryos are relatively easy and inexpensive to maintain, and embryonic development can be observed with common classroom equipment. The eight student-developed laboratory exercises described here have been used by students in Neuroscience Research at Sidwell Friends School. This course uses zebrafish as a vertebrate model to study genetics, development, behavior, neurobiology, regeneration, learning, and memory. The students develop protocols through collaboration with the teacher and scientists in specific fields. Through individual research, students develop and perform their own experiments, formulate and test hypotheses, learn basic laboratory and microscopy techniques, collect and analyze data, read original scientific literature, and collaborate with prominent zebrafish researchers.

No abstract

Lara D. Hutson: We're here with Melanie Fields, who has done extensive work with zebrafish among secondary-school students. I'd just like to briefly introduce myself. I'm an assistant professor at Williams College in Williamstown, Massachusetts. I study zebrafish neural development, although it turns out that the gene family on which I work is involved in the human degenerative disease known as Charcot-Marie-Tooth disease. It's a neuromuscular disease and involves the degeneration of motor axons. We're making zebrafish models of it to examine the nongenetic factors that contribute to progression of the disease. Melanie, can you tell us a bit about yourself? Melanie Fields: I teach at the Sidwell Friends School in Washington, DC, which is a Quaker school. Lara D. Hutson: Do you have any children of your own? Melanie Fields: I have three children, ages 26, 21, and 17. My 26-year-old is partly responsible for my interest in zebrafish, because he went to the University of Oregon. I took a sabbatical that gave me a chance to visit with him and learn about zebrafish. Lara D. Hutson: Do you have any hobbies? Melanie Fields: I have quite a few hobbies. Our whole family-myself, my children, and my husband-loves to go rock climbing and backpacking, canoeing, and kayaking. Every year, during spring break at Sidwell, we take some students with us to the West Coast and other locales to go climbing and backpacking. Lara D. Hutson: Can you tell us a bit about the school, and what you teach and at what grade level? Melanie Fields: Sidwell Friends is a Quaker school, which means that it does things according to processes established by the Quakers, who are known formally as the Society of Friends. Its grades run from pre-K through 12, and it has about 1100 students. In the upper school, which is where I teach, there are about 460 students, and I teach what I call ''all flavors of biology.'' That includes honors classes; introductory biology for 9th-and 10th-grade students; advanced placement (AP) biology for 11th-and 12th-grade students; a neuroscience research course, where we work on zebrafish and other organisms; and a marine biology course, which I teach for 11th-and 12th-graders.