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Monday, January 25 • 2:20pm - 2:40pm
The Shoaling Behavior of Invasive Bigheaded Carps Suggest These Species Can Be Targeted Using Judas Fish

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AUTHORS: Ratna Ghosal*, University of Minnesota; Peter Xiong, University of Minnesota; Peter W. Sorensen, University of Minnesota

ABSTRACT: Shoaling, or the tendency of fish to aggregate and swim together, serves many purposes in teleost fish including facilitating finding food and predators. Further, if fish shoal, that makes them easier to locate using individual fish with attached transponders as these fish can then be remotely tracked by biologists as they locate shoal mates. This approach, also known as “Judas fish technique” has been used successfully to locate and remove invasive common carp Cyprinus carpio in lakes in Australia and Minnesota and would seem to have potential for bigheaded carps (Hypophthalmichthys sp.). As a first step to test the utility of this approach, we tested the tendency of silver (H. molitrix) and bighead carp (H. nobilis) to shoal in the laboratory. We examined the roles of species identity and fish density on shoaling behavior. Trials were conducted using juvenile bighead and silver carp in 2-meter circular tanks with low-light cameras. To determine the role of density on shoaling we tested groups of 4, 8, 12 and 20 fish. To investigate the effects of species identity, we conducted trials only for group size 8, in two species groups with equal number of silver, bighead, or common carp. Nearest neighborhood distance (NND) was measured and used to calculate the number of shoals formed and their average size. Data analysis revealed that both bighead and silver carp shoal (P0.05). Further, when tested as mixed-species groups of 8 fish, bighead and silver carp preferred to shoal with each other than with the common carp. The two bigheaded carp formed very tight mixed species groups. How they discern species identity is not known but pheromones are suspected. In conclusion, bigheaded carp shoal and the Judas fish technique could potentially be applied to find and perhaps count or remove them. (Funded by the Minnesota Environmental and Natural Resources Trust Fund)

Monday January 25, 2016 2:20pm - 2:40pm EST