Fish are friends

For our independent project, my group chose to study the effects of rice agriculture on fish health. Rice production requires extensive irrigation and produces a lot of runoff, which contains a cocktail of agrochemicals. We wanted to see if fish collected form rice fields and exposed to this runoff had reduced predator avoidance behavior when compared to fish collected from the protected marsh at Palo Verde National Park. We decided to use fish from the genus Gambusia in our research.

We collected fish from two different sites in the drainage canals of the Bagatzi agricultural fields. Catching the fish using hand nets seemed impossible at fist, but we managed to get better at by the end of the project (though it was often interspersed with a good deal of flailing, splashing, cursing, and the occasional fall in the mud).

We collected fish from Palo Verde at the end of the boardwalk near the station and at marsh we referred to as crocodile marsh, because the first time went, there was a crocodile in the middle of the road. Catching fish was also difficult, and at had the additional bonus of mosquitoes.

After we captured the fish, we tested the fish one by one in a plastic tubs. We measured the distance they initially darted away from a tongue depressor that placed directly behind them. We then chased the fish around the arena with the tongue depressor and recorded how long it took the fish to cease fleeing. We recorded whether or not the fish jumped during the trial. Finally we measured the each fish’s length.

Fish from the rice fields were shorter than fish from the protected marsh, and they stopped fleeing the stick sooner than marsh fish. Fish exposed to agricultural landscapes may have access to fewer nutrients, or may have stunted growth from agrochemical exposure. They could cease swimming sooner because the have reduced metabolism and gill function, or an impaired antipredator response that reduces their flight behavior. Agrochemical exposure has been shown to cause both of these changes in other species of fish. Longer fish darted further upon initial agitation, and jumped more than smaller fish. Since rice field fish tended to be smaller, agricultural exposure may exert indirect effects on sprint ability in fish. Clearly conventional agricultural landscapes influenced Gambusia, just as they influence many other species both in documented ways and in ways we have yet to fully understand.

Rose Hinson

Duke University