TUESDAY, APRIL 4, 2006

Topic: Descaling impairs the osmoregulatory ability of Atlantic salmon smolts

Authors: G. Zydlewski¹, J. Zydlewski², and R. Danner^3
1School of Marine Sciences, University of Maine, Orono, ME;
²USGS, Maine Cooperative Fish and Wildlife Research Unit, University of Maine, Orono, ME;
³Maine Department of Inland Fisheries & Wildlife, Augusta, ME

Descaling is a commonly observed injury in Atlantic salmon smolts migrating in watersheds that have dams with poor downstream passage. These injuries are particularly observed towards the end of the migratory season. The effect of this type of injury on the ability to osmoregulate upon seawater entry was investigated using hatchery smolts. A series of seawater transfers was conducted three times to reflect “early”, “middle” and “late” periods of migration (April 25, May 11 and May 31). Before each transfer, 120 fish were anesthetized and measured (length and weight). Half served as controls and received no injury. The other half received a descaling injury of 20 % of the body surface. Immediately after recovery, 15 control and 15 treatment fish were subjected to a 35 ppt seawater challenge. After 24 h blood was collected (for plasma osmolality, hematocrit, and on day 7 septic bacterial load) and gill biopsies taken to measure gill Na⁺,K⁺-ATPase activity. Three additional seawater challenges were carried out at 1, 3, and 7 days after the initial sampling. Gill Na⁺,K⁺-ATPase activity levels indicate that the time series spanned the period from early smolting (increasing activity) to desmolting (decreasing activity). In each group, descaled fish showed greater osmotic perturbation than control fish. Control fish stabilized within 3 days for early and middle series; however, descaled fish failed to recover in this time frame. For the “late” fish, plasma osmolality was elevated in both groups; descaled fish did not differ from controls at days 3 and 7. No clear pattern of septic bacterial load and treatment was apparent. The evidence suggests that descaling impairs osmoregulatory performance during smolting and full recovery occurs within 3 days. Therefore, descaled smolts entering seawater within 3 days of the injury may have compromised long-term survival.

Speaker: Gayle B. Zydlewski

EDUCATION:

• Doctor of Philosophy, Oceanography, University of Maine, Orono, ME, 1996
• Master of Science, Zoology, University of Rhode Island, 1992
• Bachelor of Science, Marine Biology & Biology, Southeastern Massachusetts University, 1990

PROFESSIONAL EXPERIENCE:

• After Ph.D. conducted a postdoc at the USGS Conte Anadromous Fish Research Center
• Directed the Behavioral Physiology Program at the US Fish and Wildlife Service’s Abernathy Fish Technology Center (5 years).
• Currently: Assistant Professor at the University of Maine in the School of Marine Sciences.

Contact: Gayle Zydlewski ph: 207-581-4365 fax: 207-581-4990 Email: gayle.zydlewski@umit.maine.edu