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Vol. 43 No. 2, 2004
Histological Characteristics of Abnormal Protrusions on
Copepods from Lake Michigan, USA
Gretchen
A. Messick1,*, Henry A. Vanderploeg2, Joann F.
Cavaletto2 and Suzanne S. Tyler1
1National
Oceanic and Atmospheric Administration, National Ocean Service,
Cooperative Oxford Laboratory, Oxford, MD 21654-9724, USA
2National Oceanic and Atmospheric Administration,
Great Lakes Environmental Research Laboratory, Ann Arbor, MI 48105, USA
Gretchen
A. Messick , Henry A. Vanderploeg, Joann F. Cavaletto and Suzanne S.
Tyler (2004) Abnormal protrusions have been observed on
crustacean zooplankton species from Lake Michigan since 1994. Copepods
collected from 1994 to 2000 were assayed for the prevalence of
protrusions, and histologically characterized for various morphologies.
Protrusions occurred more frequently on nauplii than on copepodites or
adults. Most protrusions were located laterally on the copepod body.
External shapes and surfaces of the protrusions varied from smoothly
rounded to bossulated and amorphous. Protrusions had diverse
histological characteristics. Necrotic tissue was present in 58% of
protrusions. Some protrusions had hyaline, crystal-like structures
either on the surface or embedded within tissues of the protrusion.
Nearly 40% contained what appeared to be herniated host tissue. A few
copepods (3%) had elongated, symmetrical, somewhat transparent gross
protrusions that were histologically identified as ellobiopsid
parasites. Other protrusions had a histology that suggested ellobiopsid
parasites such as a bossulated, bud-like external morphology or a
smoothly rounded covering. Additionally, round structures observed
within protrusions were similar to sporulation bodies of ellobiopsid
parasites. It is unlikely that these protrusions were due to fixation
artifacts or were caused by diatoms puncturing copepods in the
collection devices. A few protrusions were obvious ellobiopsid
parasites, but the histology of most protrusions is not consistent or
obvious enough to allow identification of a plausible etiological
agent.
Key words: Cyclopoid,
Calanoid, Ellobiopsid, Herniated, Necrotic.
*Correspondence: Tel:410-226-5193. Fax:410-226-5925. E-mail:
Gretchen.Messick@NOAA.gov
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