Swimming performance of the Barrens topminnow

(Fundulus julisia) and western mosquitofish (Gambusia affinis):

Implications for barrier design and topminnow conservation

Paul D. Benton and Hayden T. Mattingly

Department of Biology, Box 5063

Tennessee Technological University

Cookeville, Tennessee 38505

pdbenton21@tntech.edu

Abstract.  Introduced mosquitofish often have a negative affect on native organisms and may be a major contributing cause of declining Barrens topminnow populations.  Thus, topminnow population viability would likely be improved in mosquitofish-free habitats.  The barriers at the type locale and the Vervilla site may provide for mosquitofish-free habitats, but they do not represent a comprehensive, long-term management approach because topminnows may need to seek refuge downstream during periods of drought and subsequently recolonize after droughts.  A potential solution is to place a barrier in a spring run that alters natural flows to exceed the swimming ability of mosquitofish.  Thus, there are two objectives of this study: (1) to determine the swimming performance of topminnows and mosquitofish in a flume using a fixed velocity test; and (2) to use these results to construct and test a barrier in a controlled laboratory setting.

  Many factors affect fish swimming performance including fish length, temperature, photoperiod, acclimation period, stress, motivation, and conditioning.  These variables will be controlled for and set at levels that result in maximum swimming performance for mosquitofish since it will be important to determine their maximum abilities.  Endurance times from the fixed velocity test will be used to predict passable water velocities flowing through barriers of various lengths based on the equation originally reported by Peake et al. (1997): V_f = V_s - (L/E_vs); where V_f is the maximum passable water velocity (cm/s), V_s is a test velocity (cm/s), L is a proposed length of a barrier (cm) (i.e., distance), and E_vs is the endurance (s) at V_s. 

In the barrier study, channel lengths of 50, 100, and 200 cm will be tested, and three velocity treatments will be used for each length based on mosquitofish data from the flume study.  Velocity treatment A will be set at the velocity corresponding to 50% of the maximum passable velocity and will be the control.  Treatment B will be set at the maximum passable velocity and treatment C will be set at 10% greater than B.  The channel barriers will be fitted between two troughs and fish movement will be monitored for a 72-hour period.  Predictions from the flume study will be supported if no mosquitofish move into the upper trough at treatment level C.  Furthermore, the study can suggest a practical field application for topminnow conservation if topminnows move into the upper trough at treatment level C. 

A pilot flume study was conducted to determine if the current flume setup is adequate for testing fish as well as to obtain test velocities.  Mosquitofish outperformed topminnows in the pilot study.  Use of captive-raised topminnows along with stress and motivation factors may have resulted in the lower swimming abilities of topminnows.