Midwest Fish & Wildlife Conference 2019

AUTHORS. Amy E. George, Benjamin H. Stahlschmidt, Cayla L. Carlson – U.S. Geological Survey; Rafael O. Tinoco, Andres F. Prada – University of Illinois; Duane C. Chapman, U.S. Geological Survey

ABSTRACT. Sensory input and systems are critical for organisms to respond to their environment, allowing movement to suitable habitat and potential escape from predators.  While many aspects of grass carp ontogeny have been described, neurosensory development remains unclear.  Previous studies have shown that phototaxis occurs in larval grass carp, which was a basis for the successful deployment of light traps as a collection gear for larval carp.  However, other cues, such as chemotaxis, rheotaxis, and phonotaxis have not been studied for grass carp larvae, and it remains unclear when a response would begin to occur.  Using behavioral tests, we looked at phonotaxis and chemotaxis from initial gas bladder inflation to the development of the second gas bladder chamber (the period where larvae leave the mainstem river and move into nursery areas). Rheotaxis was examined from hatch through gas bladder inflation by quantifying orientation in a laboratory flume.  Grass carp larvae showed no preference for any chemosensory stimulus tested, and auditory stimuli elicited very little reaction except at frequencies above 1000hz and volumes up to 30 decibels higher than ambient noise.  Larvae showed a consistent orientation facing into the flow at most developmental stages, suggesting that rheotaxis may be the earliest developing sense and most critical for navigation. By knowing how and when different sensory systems develop in grass carp larvae, control measures may be developed that attract or deter larvae from specific areas.