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UBC Theses and Dissertations

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UBC Theses and Dissertations

Effects of parasitic copepod, Salmincola californiensis (Dana, 1852) on juvenile sockeye salmon, Oncorhynchus nerka (Walbaum) Pawaputanon, Kamonporn

Abstract

Sockeye salmon parasitized with Salmincola californiensis were compared experimentally with unparasitized fish of the same age to determine: (1) its effects on growth; (2) effects on parasitized fish under some environmental stresses and (3) hematological effects of this parasite on its fish host. It was found that average infection levels of 31.25 parasites per fish can reduce the weight of the fish host by almost 34 % within a period of 112 DPI. The rate of increase in length of the infected fish group was slower than that of the non-infected fish group though no statistically significant difference developed during the experimental period. The parasitized fish were found to develop anemia, expressed by the reduction in red cell counts, hemoglobin concentrations and hematocrit values. This anemic condition is attributed to hemodilution of the blood, resulting from damage to the gill and skin epithelia, and, in turn, leading to an osmotic imbalance between the water and the internal fluids. In addition, the progressive reduction of the red cells in the circulating blood may be a result of the absorption of parasite metabolic secretions through the gills or the bulla. Such absorption seems likely because of the observed variations of the cells in the leucocytic system and the significant increase in lymphocytes, neutrophils and "granulocyte cells" in relation to infection time. Furthermore, the blood of the infected fish clotted faster than that of the non-infected fish. During the course of infection a marked increase was also observed in the number of thrombocytes. Parasitized fish were less able to cope with environmental stresses. A water temperature of 21°C was found to be the median lethal temperature o infected fish. The swimming ability of infected fish was also reduced. The parasitized fish reached 50% fatigue when they swam in water of a velocity of 65 cm/sec for only 250 min. The chance of survival for the infected fish in this high water velocity is only 6.6% over the period of 600 min. The ability of the infected fish to transfer from fresh water to salt water was also affected. Mortality of the infected fish increased during this transition and these fish, as indicated by the salinity preference test, also avoided high salinity, suggesting that they may not have been ready to migrate. The critical period of infection where marked differences were found in all the parameters was that period when the parasites reached maximum size and a second infection took place with copepodids hatched from the original group.

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