Physiological stress, smoltification and seawater adaptation in New Zealand's sockeye and quinnat salmon.
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
This study investigated smoltification and seawater adaptability of sockeye (Oncorhynchus nerka) and quinnat salmon (O. tshawytscha). Both species were introduced into New Zealand with an anadromous population of quinnat and a totally freshwater population of sockeye salmon becoming established. The sockeye were found to be capable of successfully adapting to sea water and appeared not to have lost their hypoosmoregulatory ability despite being landlocked for approximately 90 years. The physiological changes associated with smoltification and seawater adaptation were studied and were viewed in part with reference to physiological stress. Salmon exposed to a handling or temperature stressor showed an increase in plasma cortisol concentrations and depending on the severity of the stressor, a change in haematocrit and an osmotic imbalance could also result. The physiological state of the salmon (pre-smoltified, smoltified, desmoltified) was assessed in a variety of ways and the reliability of the parameters measured related to the seawater adaptability of the salmon. Increased gill Na+-K+-ATPase activity provided the best indicator of smoltification. Plasma cortisol concentrations also increased in smoltifying salmon. The seawater adaptability of the salmon was found to be dependent on both the degree of smoltification that had occurred in the salmon and on the temperature of the sea water. High seawater temperatures limited the ability of the salmon to successfully adapt. Rapid increases in plasma cortisol occurred when salmon were transferred directly to sea water, but returned to basal levels within 12 hours in the fish that successfully adapted. Plasma cortisol concentrations remained elevated in the salmon that failed to adapt to the sea water. Morphological changes in the gills of sockeye salmon that successfully and unsuccessfully adapted to sea water were also investigated.