Salmon diets are skin deep

Health clues may be revealed in what fish are eating

Scientists at the Oregon Hatchery Research Center look for clues to what salmon eat in an unlikely place: the mucus that fish produce on their skin. In this video, David Noakes, professor in the OSU Department of Fisheries and Wildlife and Senior Scientist, Oregon Hatchery Research Center; and Robbins Church, an Environmental Research Scientist with the U.S. Environmental Protection Agency, describe their research. See “Once and Future King,” a story about salmon science in the Pacific Northwest.

Transcript

Robbins Church
My name is Robbins Church. I am an environmental research scientist with the Western Ecology Division of the National Health and Environmental Effects Research Laboratory of the U.S. Environmental Protection Agency’s Office of Research and Development.

David Noakes
My name is David Noakes. I am a professor of Fisheries and Wildlife at Oregon State University and a senior scientist at the Oregon Hatchery Research Center.

Robbins Church
We are working at analyzing the mucus of coho salmon and steelhead trout for the purpose of understanding how they may switch their diets in the wild. This work has previously been done using muscle tissue of fish for the purpose of studying the influence of returning salmon spawning runs and the dead salmon on the ecology and health of the fish that are still in the stream. When using muscle tissue there is a long lag time involved waiting for the muscle tissue to change in its isotopic composition. This lag is so long that it really gives us a difficult time in making the determination of whether the in-stream fish are using the salmon carcasses.

So we started research to investigate the use of a tissue that might change faster than muscle tissue in order that we could understand the influence of these returning salmon and their carcasses on the fresh water stream ecology. The search for a faster responding tissue led us to consider the use of mucus, the slime that occurs on the outside of fish that they use to protect themselves from various parasites and diseases and also to aid in their swimming. Isotopic analysis of fish mucus has never been done before, and we were the first to do it.

We originally did our work at looking at changes in the isotopic composition of fish mucus in the West Fork of the Smith River in the Oregon Coast Range. In order to understand the dynamics of that situation, however, we had to do controlled experimental work. This work needed to be done with diets of different isotopic composition, and this lead us to work with the Oregon Hatchery Research Center.

David Noakes
At the Oregon Hatchery Research Center, we have an experimental laboratory in a natural environment. One of the main parts of our mission is to look at differences that might exist between hatchery fish and wild fish. We can hold fish and rear fish and study fish under a variety of conditions. This study is particularly important for us, because it helps us to understand the basis for the feeding ecology of these animals, whether they come from a hatchery origin or a wild origin, to help us better understand the relationships of animals in nature.

It’s particularly important because there is a lot of concern, as people well know, about the production or lack of production of salmon and steelhead from freshwater systems. It is believed that diets, early diets and change in diets can be quite critical for these fish, and so this collaboration, which involves different agencies (the EPA, OSU, the OHRC and in fact people in different states) is what the OHRC does best. It brings people together, allows us each of us to contribute our particular expertise to solve a much bigger problem that any one of us could not deal with individually.

The way we conduct our part of the study in collaboration with Robbins and his people is that we hold the fish in very carefully controlled conditions. These are animals that we rear from hatching, and so we know their history. We rear them on controlled diets at controlled feeding rates. We then sample the fish at specific times, basically by washing the fish. It’s a remarkably simple procedure. We wash the fish, take the mucus from them and capture that mucus in the sealed plastic bags that then go through the procedures at the EPA laboratory.

So for us, it is part of a much bigger study that we are involved in looking at early life history and development of salmon and trout. Understanding what it is they feed on and how they feed and then how we can use that information to better manage populations of wild and hatchery fish.

Robbins Church
Once we receive the samples of mucus in plastic bags from the Oregon Hatchery Research Center, that mucus is frozen in the plastic bags and brought to the laboratory. It is then washed out of the plastic bags with just distilled water. That water is then filtered to remove debris and extraneous materials. The sample is refrozen until the time when it can be freeze-dried in the freeze-dryer, which is behind me operating right now. The water is removed from the sample by freeze-drying procedure, which takes two days.  The resulting material is just a biologic material – just dried mucus. That mucus is then weighed out in very tiny amounts and then analyzed in the mass spectrometer. The mass spectrometer provides us with the data that we need to do our analyses and to write research papers reporting our results.

We have just published our first research paper on the results of experiments at the Oregon Hatchery Research Center, and this work has now, in January 2009, been published in the Canadian Journal of Fisheries and Aquatic Sciences. This paper was published as a rapid communications paper of high interest to the journal, and its publication is featured prominently on the journal’s Web pages.

There are additional benefits of our research, mainly that we can take samples non-lethally from threatened and endangered fish species. This research is part of our laboratory work in support of the Clean Water Act.
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Video produced by Craig Anderson, OSU Media Services

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