The Fate of 14C Labeled Food Ingested by Underyearling Sockeye Salmon, Oncorhynchus nerka, in Relation to Temperature and Ration

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Abstract
Underyearling sockeye salmon (Oncorhynchus nerka) provided rations likely available in nature grow more rapidly when held under cyclic than under constant temperature. The basis of this enhancement was investigated by following the short-term fate of labeled food in young sockeye fed low (3.4% dry body wt/d) and moderate (6.4% dry body wt/d) rations and maintained under constant and cyclic temperatures. These experiments, corrected for low 14C measured rates of respiration, indicated that growth potential of young sockeye is greater under cyclic temperatures because of the higher respiration rates at constant high temperatures and the greater rates of defecation and excretion at low temperatures. The difficulties in estimating respiration rates from 14CO2 measurements are emphasized.Key words: sockeye salmon, 14C-labeled feeding, incorporation, respiration, excretion, defecation, diel vertical migration, diel cyclic temperature, constant temperature, ration size
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