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Immobilization Threshold and Fish Conductivity of Two Small Fishes
Author(s) -
Lutnesky Marvin M. F.,
Cradock Kenwyn R.,
Reynolds James B.
Publication year - 2019
Publication title -
north american journal of fisheries management
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.587
H-Index - 72
eISSN - 1548-8675
pISSN - 0275-5947
DOI - 10.1002/nafm.10319
Subject(s) - electrofishing , gambusia , mosquitofish , fish <actinopterygii> , range (aeronautics) , conductivity , poeciliidae , biology , fishery , zoology , physics , materials science , quantum mechanics , composite material
Power transfer theory (PTT), a useful paradigm in electrofishing, asserts that the threshold power density ( D t , μW/cm 3 ) transferred from water to fish for immobilization is dependent on the conductivity (μS/cm) of the water (σ w ) and of the fish (σ f ). Larger differences between the two conductivities require higher applied power densities and may make capture more difficult. Over a range of water conductivities, D t as a function of σ w will form a U‐shaped curve, and the minimum provides an estimate of σ f and D m (the lowest value of D t that occurs when σ w and σ f are equal). Studies have demonstrated a narrow range of σ f (56–160 μS/cm) relative to the conductivity of natural waters (10–5,000 μS/cm). However, these σ f values are for larger species. Electrofishing may also be directed at the capture of smaller species or diverse communities. In an experimental tank, we estimated D m and σ f for a small cyprinid, the Red Shiner Cyprinella lutrensis (TL = 35–64 mm) and a smaller poeciliid, the Western Mosquitofish Gambusia affinis (TL = 23–46 mm). We estimated D m and σ f to be 120 μW/cm 3 and 23 μS/cm, respectively, for Red Shiners ( n = 72) and 143 μW/cm 3 and 23 μS/cm, respectively, for Western Mosquitofish ( n = 23). These values for σ f are less than half the minimum of previously reported values, and our D m estimates are less than those that have been reported for game species of similar length (200–300 μW/cm 3 ). Our results serve to explain why smaller species require higher applied power densities and are more difficult to capture from an assemblage of various species and sizes.