9318065 Dickson In addition to being the focus of important commercial fisheries throughout the world, tunas are of particular interest to biologists because they are the only bony fishes known to maintain muscle temperatures(Tm) elevated significantly above the temperature of their environment by using metabolically derived heat; i.e., they are endothermic. To do so, tunas need a source of heat (provided by contraction of red muscle during continuous swimming) and a mechanism to retain the heat within the muscle during activity (blood vessels arranged as counter-current heat exchangers). The goal of this research project is to test the hypothesis that maintenance of high muscle temperatures in tunas results in increased swimming performance. A computerized, temperature-controlled, variable speed, swimming-tunnel respirometer system will be used to measure the maximal sustainable/aerobic swimming speed versus fish size and the cost of swimming versus fish size relationships for juvenile black skipjack tunas ranging in fork length (FL) from ~100mm to ~250mm. These sizes are above and below the minimum size for endothermy of 207 mm FL postulated in a recent publication by the Principal Investigator. Comparisons will be made with a similar size range of closely related fishes that cannot elevate Tm significantly at any size to "control" for the effects of fish size. Also, if swimming mode changes with fish size, the maximal speed and/or cost of swimming may change independent of Tm. Therefore, swimming mode, as well as tail beat frequencies and amplitudes, will be determined from high-speed videotape recordings of each fish swimming at speeds up to its maximum, using a computerized video motion analysis system. In addition, Tm in a size range of juvenile black skipjack tuna will be measured as they swim in laboratory aquaria and in the respirometer: these data, combined with microscopic examination of heat exchanger blood vessel morphology and red muscle amou nt in the same fish, will allows the PI to test the hypothesis that the minimum size for endothermy in black skip jacks is 207 mm FL. These studies will contribute a great deal to our understanding of the evolution of endothermy and the advantages it confers. The results will have implications for the ecology, energetics, and both short- and long-range movements of tunas. In addition, estimates of the cost of swimming obtained in the proposal study can be used in models of tuna energetics and population dynamics that are used to regulate the fishery aspects of these species. ***
