Sunday, March 13, 2016

One Fish, Two Fish, Red Fish, True Fish




We began last week with fish but no question. We had managed to miraculously get almost a dozen fish to leap into my net and they had survived the bumpy journey back to the station. Then we were faced with the question of what were we going to do with these fish? What question could we ask? We decided to ask: Do agricultural landscapes impact fish health and behavior? After some research, we learned that we can use carotenoids to assess fish health. Carotenoids are red, yellow, and orange pigments that are required for immunological functions and ornamentation. Only the healthiest individuals, who have excess carotenoids can allocate them for ornamentation. This tradeoff maintains the honesty of carotenoids as a signal. We were then plagued with the question of how do we assess carotenoids. After some more research and a lunch with Erika we determined that we could photograph the fish and then analyze the images. By looking at the percent of red pixels in the images we could assess carotenoid levels. Our next question was about behavior—What did we want to make the fish do and how could we possibly get them to comply? We consulted the literature and our trusty advisor Erika and determined that agrochemicals have been shown to impact predator avoidance behavior. We designed a protocol and built a testing arena comprised of plastic tubs with a plastic plate taped to the top of one side to create shade and a condiment cup and a couple predator (bird) models. 
The next day we were standing in the canals at the Bagatz√≠ Agricultural Projects and the Palo Verde Marsh trying to catch fish. We didn’t have quite as much luck as we had had the first day but we were still able to catch more than 10 fish from each site (which met our daily goal). We brought them back to the station in plastic bags that leaked all the way back. Wet but happy we began to test our fish. We placed them into testing arenas one at a time and timed how long it took each fish to cross in front of the "predator", as well as several other measurements to help us assess boldness. After the fish completed its test, it was taken out of the water for a photo.
By the time we had tested and photographed all of our fish it was just about sunset. We took our marsh fish and headed for the boardwalk. We returned the fish we had collected from the marsh back into it and we watched the sunset. Then we began analyzing our fish photos, looking for observable carotenoids in each fish. However, we discovered a small problem. The pictures showed that our fish were not all Gambusia affinis as we expected - but there appeared to be different species.  We consulted Gil, the fish expert, who told us that we had three fish species and none of them were Gambusia affinis!! The majority of our fish were Poecilia gillii, so we used only the photos of those fish for our analyses. 
We discovered that there was a significant difference in carotenoid levels between the agricultural sites and the Palo Verde marsh! The fish from the marsh had many more carotenoids indicating that they were significantly healthier than the fish from the agricultural sites.
With respect to fish behavior, we did not find a difference between agricultural landscapes and natural landscapes.  Perhaps there are differences in the predator environments surrounding each of our collection sites.
Almost as challenging as catching fish and getting them to cooperate in our experiment was the challenge of preparing a presentation and paper analyzing our experiment and results in fewer than three days! Engaging in this full scientific process in under a week was challenging but exciting at the same time!


Andriana Miljanic
Emory University

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