The Biology of arctic charr
(Salvelinus alpinus (L.)) in
Lake Þingvallavatn, Iceland. II.
Parasites: Plerocercoids of the
Hilmar J. Malmquist,
Sigurður S. Snorrason
and Skúli Skúlason.
Insíitute of Biology
University of Iceland
Lake Þingvallavatn (66° 10' N and 22°
10' W) is the largest lake in Iceland, 83.7
km2 and 2860 mill. tonns. It is a deep
oligotrophic lake (mean depth 34.1 m,
max depth 114 m) and cold (min in Jan.,
0-2°C, max in Aug.-Sept., 10-12°C).
Four dífferent charr morphs inhabit the
lake; dwarf charr (dvergbleikja), snail
charr (kuðungableikja), pelagic charr
(murta) and piscivorous charr (síla-
bleikja). The charr morphs are quite easily
distinguished on the basis of outer morp-
hology and colour pattern and the diet of
each charr morph is quite distinct (Hilmar
J. Malmquist et al. 1985). Dwarf and snail
charr feed on zoobenthos in the littoral.
Snail charr feed almost exclusively on
Lymnaea peregra. Dwarfs feed mainly on
Lymnaea, but the diet is more heterogene-
ous and includes chironomid larvae and
pupae. Pelagic charr feed mostly on zoo-
plankton, mainly Cyclops abbyssorum and
Daphnia longispina. Piscivorous charr
feed almost solely on three-spined stickle-
back (Gasterosteus aculeatus).
Diphyllobothrium spp. (D. ditremum
and D. dendriticum) are common parasites
in Icelandic lake-resident populations of
arctic charr. A relatively high percentage
of the arctic charr in lake Þingvallavatn
was infected by Diphyllobothrium spp.
The main species involved is probably D.
1299 charr were examined for infection
of Diphyllobothrium spp. plerocercoids on
intestines (stomach, pylorus and liver). In-
fection (percentage cover of plerocerco-
ids) was estimated and grouped into four
classes (Fig 1). Formation of connective
tissue around and between intestines was
estimated and grouped into four classes
There was a clear difference in frequ-
ency of infection between the charr
morphs (Fig. 1): Only 0.3 % of the dwarfs
were infected and just 6.2 % of the snail
charr. On the other hand 76.9 % of the
pelagic charr were infected and 90.1 % of
the piscivorous charr.
Formation of connective tissue around
intestines followed a very similar pattern
as plerocercoid infection (Fig. 2).
Intensity of infection increased with age
(Tables 12). Heavily infected piscivorous
charr with intestines adhering in a bundle
of connective tissue were common (Fig.
3). Pelagic charr were seldom found in this
condition. On the contrary, intestines of
dwarf and snail charr were invariably well
Both copepods (e.g. Cyclops) and the
three-spined stickleback are well known
intermediate hosts for Diphyllobothrium
spp., but the gastropod Lymnaea is not.
Thus, Diphyllobothrium infection of arctic
charr in lake Þingvallavatn reflects very
clearly the specialized feeding habits of the
An increase in intensity of infection with
age probably results from an accumalation
of plerocercoids. A higher intensity of in-
fection in piscivorous charr compared with
pelagic charr may be traced to fish eating.
The lifecycle of D. ditremum in lake
Þingvallavatn is discussed in relation to the
feeding habits of the charr morphs (Fig.