Cisco - Lake Herring
Coregonus artedii Le Sueur Profiles and gill
rakers of the shallow water cisco and the whitefish are
ln the cisco, the bones in front of the snout
are angular; in the whitefish, the snout distinctly overhangs
the lower jaw, giving the snout a blunt profile. ln the cisco,
the gill rakers are longer and usually more than 31. The
whitefish gill rakers are fewer than 32. These projections are
located on the gill arches.
The shallow water, C. arredii are often
referred to as herring because of the superficial resemblance to
the marine herring (Clupea spp.). To avoid confusion, it is
better to call the members of the genus, Clupea, herring.
The shallow water cisco is usually dark blue
above and silvery below. With the possible exception of the
pelvics, the outer edges of the fins are slightly pigmented.
The whitefish family displays considerable
variation in body proportions, not only in two isolated
populations in two different bodies of water, but in a
population of an individual lake. Coregomzs arredii is probably
the most variable of the genus; it may be slim and elongate or
deep and laterally compressed. It is not clear what
environmental or other factors operate to produce the variety of
forms that occur in separate lakes, but they have probably
arisen by isolation.
The ciscoes are characteristic of the larger and deeper lakes of
the northern parts of North America, Europe and Asia, and the
distribution corresponds roughly with glaciated areas. C.
artedii is one of several ciscoes occurring in the Great Lakes
and it is the only one occurring in Lake Erie. Because of the
shallow ness of Lake Erie, it is probably closer in
environmental conditions to the inland lakes than the others.
Although the shallow water cisco is widely
distributed in the deep, inland lakes of Ontario, north to
Hudson Bay, knowledge of the actual species involved is limited.
The species may be represented by several
local races that resemble the typical form, C. artedii more or
less closely. To avoid confusion, it is better to call the
members of the genus, Coregonus, freshwater herring or cisco,
possessing the profiles and gill rakers illustrated in the
C. artedii inhabits the clear cold waters of most deep lakes. ln
Ontario, it occurs in all the Great Lakes and in numerous inland
lakes. It enters brackish water off the mouths of rivers
which How into Hudson Bay. The cisco needs an abundant source of
oxygen which is usually present in deep, infertile lakes, as
opposed to a deficiency of oxygen in some deep, fertile lakes in
The shallow water cisco is pelagic, moving about in schools in
the open water, and migrating to deep, cool water during the
In late spring and early summer, ciscoes begin
forsaking the shallow water and migrate into deep water. This
movement takes them out of the warmer and lighter surface waters
(the epilimnion) into a stratum of water (the thermocline) where
there is a phenomenal drop in temperature per unit of depth. A
temperature decline of one degree per metre of depth marks the
upper limit of the thermocline, and a temperature of less than
one degree per metre, with increasing depth, marks the lower
limit of the thermocline.
The rate of temperature decline within the
thermocline varies with different lakes, different seasons and
with the progress of the summer.
The ciscoes continue their movements below the
thermo cline into a deep and cool area of water (the hypolimnion)
where further declines in temperature are much more gradual. The
ciscoes remain in the hypolimnion for some time, distributing
throughout its extent. During late August and September, the
ciscoes return to shallow water. lt is believed that this
movement is correlated with the increase of carbon dioxide and
the decrease of oxygen in the bottom water, and the cooling of
the shallow water.
Spawning takes place on flat stones in about 8
to 10 feet of water.
A ciscoes food sources vary with the season.
they are predominantly plankton eaters but also ingest aqautic
insects and minnows.