Fróðskaparrit - 01.01.2002, Page 119

MYXIDIUM GADl (GEORGEVITCH, 1916) og MYXIDWM OVIFORME (PARISI, 1912)
f GALLBLØÐRUNI Á TOSKl (GADUS MORHUA L.)
1 17
significant negative effect on the condition
factor of the fishes.
Dijference in prevalence
between age groups
To make sure that a difference in preva-
lence between localities is real, a good pic-
ture of the infection of different age groups
can exclude the possibility that the differ-
ences in prevalence at different localities
are caused by unequal distribution of dif-
ferent agegroups samples at the different
stations (Table 6).
It looks as if the the older ftshes are more
frequently infected with Myxidium ovi-
forme, while it is hard too say wether the
same pattern accounts for Myxidium gadi
because of the low number of fish infected.
Table 5. Tlie myxosporidiansin this study have no
patliogenic effects on cod
Cf. Uninfected Myxidium Myxidium
oviforme gadi
Average 0.93 0.90 0.95
+ /- S. E. 0.01 0.01 0.04
Geographical differences in prevalence
The basic criteria that must to be fulfilled
before a parasite can be used as an indica-
tor, is that there are statistically significant
differences in prevalence of infection be-
tween the geographical areas where the cod
is studied (Table 7).
There is a significant difference in the
prevalence of Myxidium gadi %2 (P =0.005)
between localities. Besides from station 2
(Faroe Bank) there is no significant differ-
ence in prevalence of Myxidium oviforme
between stations. None of the parasites
were found on the Faroe Bank.
Discussion
The Faroe Bank cod
None of the examined cods from the Faroe
Bank were infected with Myxidium gadi
nor Myxidium oviforme. In Højgaard
(1998) 1 out of 52 examined fishes was in-
fected with Lernaeocera branchialis while
the cod from the Faroe Plateau had a preva-
lence from 30-90%. Platt (1975) showed
that the prevalence of Pseudoterranova de-
cipiens was significantly higher on the
Faroe Plateau than it was on the Faroe
Bank.
We can conclude, based on former and
present investigations, that the cod stock on
the Faroe Bank, based on parasitological
investigations, can be delimitated as a sep-
arate cod stock. Migrations between The
Faroe Bank and the Faroe Plateau could be
detected by looking at the parasite fauna of
Table 6. The prevalence ofinfection of different age groups of cod.
2-ycar olds 3-year olds 4-year olds 5-year olds 6-ycar olds 7-8-year olds
M. oviformc 9 10 3 19 20 22
M. gadi 9 0 0 2 3 0