MSI: 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.
Energy data from the FEDZ lab is used in both process and monitoring studies. Energy density of juvenile chum salmon starved in the laboratory (Figure at right) declined by approximately 40% in 6 weeks with very few mortalities; this experiment simulated the effects that might occur when natural prey fields are depleted. Such process studies help us understand differences observed in fish between stocks, years, or regions.
The FEDZ lab also uses calorimetry to monitor the condition of juvenile salmon stocks. The figure below shows the relatively high energetic condition of chum salmon released from the three principal hatcheries in Southeast Alaska (SSRAA, Ketchikan; NSRAA, eastern Baranof Island; and DIPAC, Juneau) compared to wild fry from the Taku River estuary in April and May. Both hatchery and wild juvenile chum salmon are later caught in SECM trawls in Icy Strait, June-August. Wild fish gain and hatchery fish lose energetic condition over time; by late July, energy values converge and the groups are virtually indistinguishable.
Contact:
Molly Sturdevant or Emily Fergusson
Auke Bay Laboratories
Alaska Fisheries Science Center, NOAA Fisheries
Ted Stevens Marine Research Institute
17109 Pt Lena Loop Rd
Juneau, AK 99801
Molly.Sturdevant@noaa.gov
Emily.Fergusson@noaa.gov
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