Atrazine Influence on Northern Pike Sperm Motility and Viability in Minnesota

Concern has been noted by fish hatchery biologists with the Department of Natural Resources that southern Minnesota northern pike Esox lucius populations have exhibited reduced hatching rates, a trend not occurring with northern Minnesota pike populations. The chemical atrazine is a frequently used herbicide in Minnesota and has been found to cause gonadal dysgenesis and reproductive development issues in amphibians and fish. Sperm, length, and age data were collected from northern pike in four Minnesota lakes. Water samples were obtained from two of the lakes to test for atrazine. Test results indicated atrazine concentrations 0.10 and r < 0.06 for all regressions). Sperm motility reductions in northern pike could be related to declining populations and warrants further research. Introduction Northern pike Esox lucius populations in southern Minnesota have declined over the past few decades. A concern noted by hatchery staff is an observed low hatching percentage among southern Minnesota pike populations from 1991 to 2011, where the average hatch rate was 43.2% an observation not noted in northern Minnesota lakes where hatch rates are consistently much higher (Bruce Pittman, personal communications MN DNR). Northern pike are an important game species and declines are a concern of anglers. In addition, the species provides predatory balance to many lake ecosystems. Studies have shown that atrazine causes gonadal development problems in leopard frogs Rana pipiens. Frogs exposed to atrazine commonly experienced gonadal dysgenesis and sex reversal (Hayes et al. 2003). Atrazine can also reduce reproduction and cause tissue abnormalities in fathead minnows Pimephales promelas (Tillet et al. 2010). Atrazine is a frequently detected herbicide in agricultural area streams (Tillet et al. 2010) and can impact fish gamete health (Hayes et al. 2003). 1 Stevens and Pallardy: Atrazine Influence on Northern Pike Sperm Motility and Viability Published by Cornerstone: A Collection of Scholarly and Creative Works for Minnesota State University, Mankato, 2012 Southern Minnesota has higher concentrations of atrazine in its streams than northern Minnesota (Figure 1); however, little is known about atrazine impacts in surface waters. Atrazine is almost nonvolatile and its half-life in neutral condition is about 200 days but varies from 4-57 weeks, depending on various environmental factors like pH, moisture content, temperature and microbial activity (Ghosh 2006). At 25 deg C, a 5 mg/l solution of fulvic acid (naturally occurs in soils and most surface waters) resulted in half-lives of 34, 174, 398 and 742 days at pHs of 2.9, 4.5, 6.0 and 7.0, respectively (Spectrum Labs). Southern Minnesota surface waters tend to be pH neutral or slightly basic; therefore, atrazine should persist longer and have the potential to cause greater impacts (e.g., lower pike reproduction rates) due to extended exposure. The objectives of this project were to 1) assess sperm motility and density between atrazine-exposed and atrazine-free northern pike populations and 2) review sperm traits as a function of northern pike length and age. To achieve our objectives, we attempted to determine if northern pike sperm concentrations and motility were different among several potentially atrazine-impaired populations. We anticipated that sperm concentration and motility would decrease with increasing atrazine levels. We also evaluated if pike sperm concentrations and motility were influenced by male age or length, as bigger and older fish may have been exposed to atrazine for longer time periods. Figure 1. An estimated 21-day moving-average concentration of atrazine (μg/L) in Minnesota streams. Red markers indicate the four lakes at which pike samples were taken. The model statistically relates atrazine concentrations in streams to watershed characteristics determined from data sources with national coverage. The model was developed using standard statistical techniques. Work is currently underway to extend the WARP model approach to other pesticides (USGS 2007). 2 Journal of Undergraduate Research at Minnesota State University, Mankato, Vol. 12 [2012], Art. 12 http://cornerstone.lib. mnsu.edu/jur/vol12/iss1/12