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 Bagatzí 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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