Hopkins Marine Station Student Paper

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(full paper is archived in the Miller Library)

Title: New techniques for low-stress blood sampling in yellowfin tuna (Thunnus albacares)
Student Author(s): Fletcher, Simon
Faculty Advisor(s): Block, Barbara
Pages: 26
Location: Final Papers Biology 175H
Date: June 1997
Abstract: Blood samples are used in many organisms as an indication of health and physiological state. In yellowfin tuna, blood analysis is complicated by stress responses to handling. These responses include changes in serum osmolarity, blood metabolites, and release of red blood cells from the spleen leading to increased hematocrit. Samples from stressed fish therefore do not accurately represent the resting health and physiology of an individual. This study presents a new method developed to minimize stress levels during blood sampling. Blood is drawn from the bulbus arteriosis of captive yellowfin tuna while the fish are still in the tank. Twenty-seven samples were taken from 18 individuals over the course of seven weeks. Hematocrit, hemoglobin, red blood cell counts, ions, and metabolites were measured and compared to values obtained from fish sampled using other common techniques. Hematocrit and hemoglobin values were similar to those measured in chronically cannulated tuna, and lower than for fish sampled using a common practice of capture in a net (hematocrit 31.6%±0.8 vs.44.1%±8.5; hemoglobin 11.1 g/d1±0.3 vs. 17.0 g/d1±2.0). Creatine phosphokinase, potassium, and creatinine (all related to stress and/or increased muscle activity) significantly increased in net-sampled fish. Therefore, fish sampled using a bulbus puncture appear to be less stressed. Using this sampling technique, an experiment was run in which diet in one tank was changed from a normal 1% fat diet to a high 8% fat diet. Blood samples were taken before and after the 8% diet treatment. Serum free fatty acid concentrations doubled (0.25 mmol/L±0.03 vs. 0.524 mmol/L ±0.03) in the 8% fat fed fish that were sampled. The results of the experiments demonstrate an ability to measure changes in blood chemistry using the new sampling techniques. This study will help determine what is physiologically "normal" in yellowfin tuna blood.