Fróðskaparrit - 01.01.2002, Blaðsíða 115

MYXIDIUM GADI (GEORGEVITCH, 1916) og MYXIDIUM OVIFORME (PARISI, 1912)
í GALLBLØÐRUNl Á TOSKI (GADUS MORHUA L.)
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Table 1. Investigations made on the parasite fauna ofcod, with the intention of finding suitable biological indicators for delimitating stocks or finding migration routes.
PARASITE REFERENCE
Protozoa, Trypanosoma murmannsis Khan et al. (1980) (Ncwfoundland)
Myxidium oviforme/gadi Larsen et al. (1997) (Barents Sea), Khan et al. (1986)
(New Foundland)
Digenea, Cryptocotyle lingua (metac.) Buchmann (1986) (Baltic Sea)
Hemiuris levinseni. Bojc (1987) (Greenland)
Nematoda, Hysterothylacium aduncum Boje (1987) (Greenland)
Copepoda, Lernaeocera branchialis Sherman and Wise (1961) (New England)
sites suitable as indicators of cod stocks,
and are usually based on a relatively low
number of cods examined.
Køie (1993) has made a host-parasite list
for all nematodes occurring in 43 different
fish species in the Faroe Islands. Køie
(1984) examined digeneans in 40 cods.
Køie (2000) publishes a complete list of all
parasites, except protozoans, in the 43 ex-
amined fish species. Højgaard (1998) in-
vestigated prevalence of Lernaeocera
branchialis in cod to fínd out whether the
infected cod had a significantly lower con-
dition factor (cf) than the non-infected cod.
Kreiss (1952) examined and described the
nematode Contracaecum clavatum. Ac-
cording to Køie (1993) C. clavatum (Kreiss
1952) is Hysterothylachium aduncum.
Kreiss also described Echinorhyncus gadi
from cod. Platt (1975) comes closest to
making quantitative investigations of a rel-
atively large nuntber of cod, with the inten-
tion of using the parasites as biological in-
dicators. Stephenson (1929) found four dif-
ferent copepod species in cod from the
Faroe Islands. These are Lernaeocera
branchialis, Clavella adunca, Caligus cur-
tus and C. rapax .
Another investigation should also be
mentioned although cod was not the exam-
ined físh. Kabata (1963), examined myxo-
sporidians in the gall bladder of whiting
(Merlangus merlangus) and haddock
(Gadus aeglefinus)in the North Sea and the
Faroe Islands. This is one of the first stud-
ies where parasites were considered as bio-
logical indicators.
Table 2. Platt's investigations.which are based nn a
reasonably large number ofcod specimens, P.
decipiens is clearly suited as a indicator for
migrations between the investigated localities, and
as a delimtator of the stocks.
(Platt 1975) FAROE PLATEAU FAROE BANK
P. decipicns 61% (n: 104) l%(n:278)
A. simplex 86% (n: 104) 73% (n: 278)
Materials and methods
Choice of parasites
The choice of Myxidium gadi and M. ovi-
forme is based on former investigations,
and the criteria set up by Kabata (1963),
Mackenzie (1987), Lester (1990), Moser
(1991), Williams et al. (1992) and Macken-
zie and Abaunza (1998). The weakness of