Yes, size matters…and that includes fish size when electrofishing. Large fish are immobilized with less field intensity or power density than are small fish. Large fish sustain a higher total dose of electrical energy than do small fish; this is sometimes referred to as whole body voltage. An excellent paper on this topic is Dolan, C.R. and L.E. Miranda. 2003. Immobilization thresholds of electrofishing relative to fish size. Transactions of the American Fisheries Society 132:969-976. This short blog provides results of a simple study with various sizes of alligator gar.
Dr. Alan Temple posted a blog on December 9, 2015 entitled “Setting Doses for Lab Experiments.” He suggested that I submit a blog on other aspects of lab studies in tanks. This blog covers the setup of tank studies for electrofishing research, and I plan to submit a companion blog on procedures for tank studies. Important aspects to consider for lab studies are the test tank, the electrodes, the power supply and the electrical field.
Experimental set-up for small fish. Picture by Dr. Jan Dean
Lab or tank experiments on fish have been around for decades, beginning with studies of fish behavior in electric fields. Presently, tank experiments are used for evaluating the effectiveness of candidate waveforms, estimating thresholds for various reactions that assist capture, guidance, and electrosedation, and determining probability of trauma. While insights gained by lab work, in combination with field trials, can and have improved fisheries sampling and provided insights for risk analysis, there are pitfalls that can sink the ship. A couple problems that often occur are the rationale for setting dose levels and the actual description of dose levels. These issues can lead to misinterpretations, inappropriate management decisions, and constrain application of experimental results. In fact, dose setting is becoming a big issue in electrofishing experimentation. I have seen studies lately that have used incredibly high doses, in fact extreme overdoses, preventing a connection from the lab to application in the field. I think the results of those studies are relatively meaningless. And, most of the disconnect is due to a poor understanding of electric fields generated by common sampling gears and typical exposure times while electrofishing.