Fróðskaparrit - 01.01.2002, Síða 120

1 18 MYXIDIUM GADl (GEORGEVITCH, 1916) AND MYXIDIUM OVIFORME (PARISI, 1912)
IN THE GALL BLADDERS OF COD (GADUS MORHUA L.)
Table 7. Prevalence of infection at tlte dijferent stations cod were sampled.
Stat. I Stat. 2 Stat. 3 Stat. 4 Stat. 5 Stat. 6 Stat.7 Stat. 8
M. oviforme 12 0 34 23 10 13 27 12
Myxidium gadi 0 0 0 13 0 0 0 12
a reasonably high number of cods.
Magnussen (1993) was not able to de-
limitate the Faroe Bank cod from the Faroe
Plateau cod using isozyme markers. Re-
cently more advances molecular methods
such as AFLP as described by Vos et al.,
(1995) and methods using microsatelite
markers have proven to be ideal tools in re-
vealing the genetic variation amongst pop-
ulations. Faroe Bank and Faroe Plateau cod
would be interesting subjects to such inves-
tigations. In Iceland Jónsdóttir et. al.
(1999) were able to discriminate between
to different genotypes.
Traditional tagging experiments support
the delimitation of the Faroe bank cod
(Táning, 1943).
Whether the cod on the Faroe Bank stays
on the bank throughout its entire lifespan is
impossible to say, unless further knowledge
on the parasites lifecycle and the parasites
intermediate hosts geographical distribu-
tion is known.
The Faroe Plateau cod
Myxidium oviforme evidently has an equal
distribution throughout the Faroe Plateau,
which makes the parasite unsuitable as an
indicator of any kind on the plateau. The
prevalence seems to increase with age,
which indicates a Iife long duration of the
infection.
Myxidium gadi was only found in a
sparse number of fish on two of the sta-
tions. Whether Myxidium gadi is restricted
to cod in these areas, or has a clustered dis-
tribution throughout the region can only be
acknowledged by examining a larger num-
ber of fish using a different sampling strat-
egy-
Lernaeocera hranchialis has an interest-
ing geographical distribution in prevalence
of infection on the Faroe Plateau (Højgaard
1998 and my own observations). The cod
from the southern part of the Faroe Plateau
seems to be less frequently (appr. 10%) and
Iess severely infected than the cod on the
Northern part of the plateau (appr 90%).
The prevalence in samples taken on the
spawning grounds in spring is somewhere
in between (35%). This indicates intermin-
gling of cod l'rom the entire Plateau during
spawning. Same migrational pattern has
been shown for the Faroe plateau cod using
traditional tagging (Táning, 1943).
The North Atlantic
In the New Foundland area the prevalence
of Myxidium gadi on differenl locations
ranges between 23-48%. On Flemish cap
the prevalence is 92% (Khan et al., 1986).
My own investigations indicate a much
lower prevalence of Myxidium gadi on the
Faroe Plateau, and absence on the Faroe