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Healing, classification and hematological assessments of sea lamprey
(Petromyzon marinus) wounds on lake trout (Salvelinus namaycush).
Shawn M. Nowicki1 and Jill B. K. Leonard1
1 Northern Michigan University, Marquette, MI
The Great Lakes parasitic sea lamprey (Petromyzon marinus) population is currently modeled using wounding statistics, subjectively assessed by experts for each lake. Effects of parasitic sea lampreys on lake trout (Salvelinus namaycush) in the Great Lakes are monitored based on counts of stage A1 to A3 wounds subjectively assessed using the King (1980) classification per 100 lake trout captured in commercial fishing nets. To assess the time required for wounds to progressively heal to stage A3, wounded lake trout collected from northern Lake Huron were sampled, photographed, their wounds were classified, and fish were then tagged and released. Recaptured wounded fish showed that 45.9% of wounds healed by at least one stage within a year, 48.6% were unchanged and 5.4% were degraded. Substantial healing occurred following a lamprey attack, but the rate of healing varied (46 – 704 days) and was insufficient to characterize healing time progression. King (1980) wound classifications and two new classification indices (quantitative index and mixed index) were evaluated and compared by conducting Kmeans cluster analysis. Cluster analysis grouped quantitative wound measures; however, these groups did not relate to established classification schemes. The King classification index did not relate to healing any better or worse than did the other two indices.ii
However, the new mixed index, which incorporates the King characteristics and morphometry of the wound would provide better data to the viewer by using quantitative and minimally subjective qualitative measures to make a better decision on wound healing. Hematological methods were used to assess immune response in lake trout after sea lamprey wounding. Both wounded and unwounded lake trout were sampled to determine if there was a detectible difference in immune status as indicated by differential leukocyte counts, hematocrit and leukocrit. There were significant differences in hematological parameters between wound classes and between gear type groups. It appeared that wound class, specifically A1, changed hematological parameters in lamprey-wounded lake trout. Stress caused by gear or immediate sampling after lamprey removal also appeared to play an integral role in the changes of white blood cell counts present in the sampled fish. The King (1980) wound classification system is the current index, but it is not reliable according to numerous classification workshops. An increased amount of improved data needs to be collected to construct a new wound index that would incorporate a multitude of wound characteristics and measurements. I also suggest that hematological assessments of wounded fish be studied both in the laboratory and the field to better understand the parameters of wound healing in lake trout. This additional information could provide a more reliable classification index and a concurrent parasitic abundance model.