Assessing the physiological impact of sea lice (Lepeophtheirus salmonis Kroyer) on Atlantic salmon (Salmo salar L.).

摘要

The objective of this thesis was to investigate the physiological changes that sea lice (Lepeophtheirus salmonis) cause in Atlantic salmon (Salmo salar). Sea lice are parasitic copepods that naturally infect salmonids in low numbers across the Northern Hemisphere with infrequent epizootics. The increase in the period of these epizootics in wild salmonids has mirrored the rise of the aquaculture industry in coastal areas. Therefore, it is important to answer basic physiological questions about parasite-host interactions such as sub-lethal lice levels required to affect performance, and the behavioural implications of increased lice infection.; Two preliminary experiments were performed using rainbow trout ( Oncorhynchus mykiss) to refine the techniques used to measure fish physiological variables. The first was designed to determine which anaesthetic, between clove oil and MS-222, better minimised fish stress during surgery and recovery. Both clove oil and MS-222 reduced cortisol levels compared to non-anaesthetised controls within 10 minutes of blood sampling. The second preliminary experiment was performed to determine proper recovery and interval times for critical swimming speed tests (Ucrit), using hypoxia to stress fish in place of lice. Four hours of recovery following minor invasive surgery did not hinder the swimming performance of fish. Both 10 and 20 minute time intervals were found to be valid for measuring Ucrit, blood and cardiac variables.; The succeeding two experiments involved the artificial infection of Atlantic salmon with sea lice. In the first, the physiological impact of two sub-lethal levels of sea lice was measured on Atlantic salmon to determine when the health of fish is compromised. Fish with infection level of 0.13 lice g-1 suffered a significant decrease (19%) in Ucrit and impaired osmoregulatory ability. Infection levels of 0.05 lice g-1 did not affect the swimming performance of salmon compared to controls. The second infection study was designed to determine if the observed behaviour of heavily infected wild salmonids in seawater (SW) returning early to native freshwater (FW) streams had a physiological basis. The Ucrit of infected fish in SW decreased significantly (22%) compared to controls, similar to the preceding study.; The final study had an experimental and theoretical component. Lice with visibly ingested blood were first collected from infected fish, then their gut contents weighed. Juvenile trout then had repeated blood samples taken of two known quantities for one week and then had their Ucrit measured. Gut contents and decline in performance due to blood loss were used to predict the possibility of blood loss due to sea lice infection decreasing the performance of their host. (Abstract shortened by UMI.)