Recipient Organization
CORNELL UNIVERSITY
(N/A)
ITHACA,NY 14853
Performing Department
Nutritional Sciences
Non Technical Summary
Freshwater fish and humans alike require long-chain omega-3 polyunsaturated fatty acids (n-3 PUFAs), including DHA, in their diets in order to survive, making these nutrients essential and an important metric of food quality. Fish are one of the most important sources of long-chain n-3 PUFAs for humans. It is well established that wild marine fish contain high amounts of long-chain n-3 PUFAs, the vast majority of which are ultimately produced by and obtained from marine algae. We will study where wild freshwater fish obtain their n-3 PUFAs in streams along an agricultural gradient in New York. Past research suggests that freshwater foods, such as algae, have more n-3 PUFAs than terrestrial foods and are therefore of higher quality. This research will provide New York citizens with information on whether freshwater fish are substantial sources of PUFAs as established for some marine fish species, and whether fish nutritional quality with respect to n-3 PUFAs differs along an agricultural land use gradient. It will provide insights for policy about how agricultural land use influences primary producers of n-3 PUFAs.
Animal Health Component
50%
Research Effort Categories
Basic
50%
Applied
50%
Developmental
0%
Goals / Objectives
The goals of this project are to understand if New York's freshwater fish, in particular fish from streams, can serve as important sources of long-chain n-3 PUFAs for human consumption like marine fish, and to understand the effect that agricultural land use has on the nutritional quality of wild freshwater fish for human consumption.We have four main goals:Goal 1. Determine how fatty acid composition varies among wild stream fish species by surveying stream fish of recreational value along an agricultural land use gradient and analyzing their fatty acid profiles. Determine which streams support fish that are richest in long-chain omega-3 polyunsaturated fatty acids.Goal 2. Determine how the quantity and quality (fatty acid composition) of food resources for wild stream fish varies along an agricultural land use gradient by surveying the availability of food resources for stream fish (e.g. periphyton, terrestrial detritus, invertebrates, and forage fish) and analyzing fatty acid profiles different food resources.Goal 3. Determine the relative contributions of freshwater and terrestrial-derived foods to stream fish diets and how this varies along an agricultural land use gradient using stable isotope analyses to reconstruct diets.Goal 4. Determine where within stream food webs fish obtain their long-chain omega-3 polyunsaturated fatty acids and how this varies along an agricultural land use gradient by using compound-specific stable isotopes to trace the pathway of individual fatty acids through food webs from aquatic or terrestrial primary producers (periphyton or terrestrial detritus) to fish.
Project Methods
General Methods: We will survey fish and stream food webs in ten streams in the Cayuga and Susquehanna Basins. We will survey five forested streams and five agricultural streams for a total of ten study sites along our agricultural gradient. We will classify each site along our gradient in terms of both whole watershed and riparian buffer area land use based on publicly available GIS data. Preliminary data collected by Alexander Flecker's lab on stream food webs along an agricultural land use gradient in the Cayuga and Susquehanna basins will inform our site selection. At each study site we will measure percent forest cover, riparian buffer width, stream temperature, dissolved oxygen, conductivity, pH, and will collect water samples to analyze nutrient concentrations.Methods for Goal 1: We will survey stream fish species of recreational value in each stream along our agricultural land use gradient to determine their fatty acid composition. We will collect fish from via electrofishing using a Smith-Root backpack electrofishing unit. After capture, fish will be identified to species and sacrificed in the field via MS-222 overdose. We will take tissue plugs from each fish of muscle, which is the most relevant tissue the standpoint of human consumption, for fatty acid composition analysis. The rest of the fish will be saved for stable isotope analyses in goals 3 and 4 (see below). Tissue plugs from fish will put on ice before being transported to a minus 80ºC freezer at Cornell. In the lab at Cornell, we will homogenize fish tissue plug samples prior to fatty acid extraction. We will extract fish fatty acid methyl esters following the one step method. Extracted samples will be stored at minus 80ºC until being analyzed. We will generate fatty acid chromatograms using a Varian Star 3400 GCMS with Varian Saturn 5.5.1 software and identify the peaks in each profile on an HP5890 series II GC-FID using the software PeakSimple. Finally, we will analyze all identified peaks in our chromatograms in PeakSimple to generate percent fatty acid composition data for each fish.We will share data on wild stream fish fatty acid composition with farmers, land owners, fishermen, and other local citizens on our project webpage and through dissemination of stream report cards that present relevant information on the health of the stream and the nutritional value of the fish in the stream.Evaluation for Goal 1: Relate data on stream fish fatty acid composition, in particular percent long-chain n-3 PUFAs, to land use. Survey the number of fishermen fishing in streams with high and low n-3 PUFA quality fish before and after the dissemination of stream report cards.Methods for Goal 2: We will survey the quantity and quality of food resources available to stream fish across our land use gradient. While collecting fish, we will assess the quantity of food resources in each stream for fish of recreational value by determining the abundance of periphyton (algae and cyanobacteria growing on rocks), terrestrial detritus, invertebrates, and small forage fish. We will assess periphyton abundance by scrubbing materials off of subsections of three rocks per stream. In the lab at Cornell, we will filter subsamples of slurry onto ashed (for ash free dry mass determination) and non-ashed filters, which we will freeze until analyzing. We will determine ash free dry mass (total amount of living and non-living organic matter) of periphyton samples. We will analyze chlorophyll a as a proxy for periphyton biomass via fluorometery. We will assess terrestrial detritus abundance by sampling terrestrial detritus in three 0.25m2 sections of three. We will put samples on ice in the field and then bring them back to the lab to be dried in a drying oven. We will then determine both dry mass and ash free dry mass of terrestrial detritus using the procedure described above. We will assess per area stream macroinvertebrate abundance using a standard Hess sampler. Macroinvertebrates will be preserved in 95% ethanol in the field and then brought back to the lab to be identified to genus under a dissecting microscope. After identification, we will determine dry mass and ash free dry mass of all invertebrates. We will collect forage fish via electrofishing as described in goal 1 while collecting fish of recreational value. We will determine forage fish species composition in the field and assess abundance based on catch per unit effort. Forage fish not needed for fatty acid analyses as described below will be released back into the stream after collection.We will also assess the quality of food resources by collecting samples of freshwater food resources to bring back to the lab for the fatty acid analyses. Samples of periphyton, terrestrial detritus, the three most abundant stream macroinvertebrate species, and the four individuals of the three most abundant forage fish species collected using the procedures described above (eg. rock scrubbing, electrofishing) will be placed on ice in the field before being transported to a minus 80ºC freezer at Cornell. We will analyze the fatty acid composition of food resource samples at Cornell following the same procedure as described in goal 1.Evaluation for Goal 2: Relate data on stream fish food resource quality, in particular percent long-chain n-3 PUFAs, and quantity to land use.Methods for Goal 3: We will determine the relative contributions of terrestrial and freshwater-derived foods in the diets of stream fish along an agricultural land use gradient using stable isotopes as diet source tracers and stable isotope mixing models. We will analyze nitrogen, carbon, and hydrogen (δ13C, δ15N, and δ2H) stable isotopes of whole fish and their potential food resources using samples collected in goals 1 and 2. Samples for deuterium analyses will equilibrate with the building for approximately six weeks prior to analysis. Frozen samples will be oven-dried and homogenized and then weighed out into aluminum (δ13C and δ15N) and silver (δ2H) capsules at Cornell. Samples will be analyzed on a Finnigan MAT Delta Plus IRMS with a Carlo Erba NC2500 elemental analyzer (δ13C and δ15N) and a Thermo Delta V Advantage IRMS with a temperature conversion elemental analyzer (δ2H) in the Cornell University Stable Isotope Lab. We will use the package SIAR in R to create Bayesian mixing models to estimate the contributions of potential food resources to macroinvertebrate prey items and stream fish.Evaluation for Goal 3: Relate data on stream fish reliance on terrestrial and freshwater foods to land use.Methods for Goal 4: We will perform compound-specific stable isotope analyses on three of the most important omega-3 PUFAs, ALA, EPA, and DHA, along an agricultural land use gradient to determine where stream fish obtain these specific fatty acids. In the lab at Cornell, we will analyze compound specific-stable isotopes of stream fish and food resource samples collected and extracted for fatty acid composition analyses in objectives 1 and 2. We will perform compound-specific stable isotope analyses of ALA δ13C, EPA δ13C, and DHA δ13C with an Agilent 6890 GC coupled to a Thermo Finnigan MAT 253 IRMS equipped with a Thermo Finnigan Conflo III for CO2 gas calibration introduction with ISODAT 3.0 software for data acquisition and analysis.Evaluation for Goal 4: Relate data on the sources of long-chain n-3 PUFAs for stream fish to land use.