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RECA: Fish Processing and Food Habits

ABL Home
Recruitment, Energetics, & Coastal Assessment
Recruitment Energetics:
Fish Processing and Food Habits
Proximate Composition
Coastal Assessment
Division Activities:
Data Sets
NOAA Scientists at work in the lab
NOAA Scientists at work in the lab

Recruitment Energetics and Coastal Assessment staff provides fish processing services to several Auke Bay Laboratories. The goal is to better understand recruitment mechanisms and processes that describe growth and survival of these populations relative to their prey, predators, and potential competitors. Sample processing in our labs focuses on measurements of fish size, energy density, and diet and feeding success of juvenile salmon and associated fishes, as well as the abundance and composition of their zooplankton prey fields.

Fish Identification and Measurements are common activities in our lab. Length and weight data provide important information on annual and seasonal growth rates and condition. For salmon, Otoliths and coded-wire tags (CWTs) are removed from fish which will us their age and what specific stock they belong to. Otoliths are thermally-marked with unique bar code-like patterns induced during the hatchery rearing process, whereas CWTs are implanted in fish snouts. Many fish processed in our lab are from the long term Southeast Coastal Monitoring project that targets all five species of salmon.

Diet by Stomach Content Analysis
Fish diet studies require detailed examination of stomach contents, a particular area of expertise of our staff. Stomachs are excised and weighed, and the food bolus is teased apart under the microscope to count and identify a wide range of prey using taxonomic keys and qualitative indices. The digested prey is often only 1-2 mm in size and in pieces, making them more difficult to identify than fresh zooplankton. Diet studies are also critical in determining the consumption of zooplankton stocks by juvenile salmon.

Energy Density Determination by Calorimetry. Calorimetry is used to determine the energy content of fish per gram of body weight. This precise measure of condition is determined with a highly sensitive electronic instrument, a micro-bomb calorimeter. Fish are dried to a constant weight and pulverized to a homogeneous powder. A subsample of the powder is formed into a pellet which is combusted in the calorimeter oxygen “bomb” unit. The temperature change measured in the water bath surrounding the “bomb” is then converted to energy units or calories per gram.

Related Links
Southeast Coastal Monitoring (SECM) project
Coded-wire tags (CWTs)

Emily Fergusson
Auke Bay Laboratories
Alaska Fisheries Science Center, NOAA Fisheries

Ted Stevens Marine Research Institute
17109 Pt Lena Loop Rd
Juneau, AK 99801

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