ISSN 10227954, Russian Journal of Genetics, 2013, Vol. 49, No. 9, pp. 937–944. © Pleiades Publishing, Inc., 2013.
Original Russian Text © A.N. Stroganov, M. Bleil, R. Oeberst, H. Winkler, A.V. Semenova, 2013, published in Genetika, 2013, Vol. 49, No. 9, pp. 1079–1087.
According to the opinion of the researchers, the
cod populated the Baltic Sea in postglacial period.
Over thousands of years, cod adapted to the specific
conditions of this halfclosed, running deep inland
water body of temperate zone, characterized by an
unstable saliferous regime of surface waters, pro
nounced saline stratification, oxygen deficiency, and
excess of hydrogen sulfide in bottom waters [1, 2].
The Baltic Sea cod was a subject of many investiga
tions focused on the analysis of biological and mor
phological characteristics [3–5], and migrations at
different stages of ontogeny [6, 7]. Genetic studies
examined hemoglobin polymorphism [8, 9]; polymor
phism of muscle proteins [10, 11]; and DNA varia
tions, including microsatellite loci [12–15] and the
pantophysin locus .
At the same time, there is no clearcut conclusion
on the population structure of cod inhabiting the Bal
tic Sea has been reached. For instance, the Baltic
(eastern Baltic) cod (
Gadus morhua collarias
which inhabits the Baltic Sea (Eastern Baltic), and
Atlantic cod (
L.), which inhabits west
ern basins, has been distinguished [8, 17–19]. Fur
thermore, the taxonomic status of the latter varies in
different studies, including the Belt Sea cod (
) [4, 5] and western Baltic cod (
) [19–21]. At present, the assessments of
cod stocks and systems of their management use ICES
recommendations, according to which two main cod
groups are distinguished, including eastern (SD 25–
32) and western (SD 22–24) groups .
Thus, additional investigations with the application
of different methods and analysis systems, as well as of
different genetic markers, including the selective and
neutral ones, will help to clarify the genetic structure
of the cod population in the Baltic Sea and adjacent
In the present study, using allozyme markers, we
assessed the level of genetic differentiation of cod
groups during the spawning period in the Baltic Sea
basin (with special emphasis on the relationships
between the eastern and western Baltic cod).
In addition, using the literature data, we intended
to assess the level of genetic differentiation of cod
groups from Baltic Sea and the Northeast Atlantic
basin (Skagerrak Strait, Norwegian Sea, Barents Sea).
MATERIALS AND METHODS
Cod samples were collected during spawning sea
son from the main spawning areas [22, 23] in Baltic
Sea in 2005 and 2006 during the voyages of the Solea
research vessel of the Institute of Baltic Sea Fisheries
(Rostock, Germany). The data on sample sizes are
demonstrated in Table 1.
The caught fishes were examined for weight, size
and age structure, sex ratio, and the gonad maturity
stage. The age was determined based on otoliths. Mat
uration stages of sexual products for females and males
were determined using Maier’s eightindex scale .
Genetic analyses were performed using white skel
etal muscle samples. The experiments were carried out
using the methods of protein polymorphism analysis,
providing, in association with the methods of DNA
analysis, fairly detailed characteristics of the genetic sta
tus of individual populations across the range [24, 25].
The cod white skeletal muscle samples were examined
On Differentiation of Cod (
L.) Groups in Baltic Sea
A. N. Stroganov
, M. Bleil
, R. Oeberst
, H. Winkler
, and A. V. Semenova
Department of Ichthyology, Lomonosov Moscow State University, Moscow, 119991 Russia
Institute of Baltic Sea Fisheries, Rostock, D–18069, Germany
University of Rostock, Rostock, D–18055, Germany
Received December 26, 2012; in final form February 14, 2013
allozyme markers, the differentiation
of cod groups during the spawning period in Baltic Sea was evaluated. It was demonstrated that cod samples
from the eastern and western parts of Baltic Sea (being statistically significantly different from the cod sam
ples from the Norwegian Sea, Barents Sea, and the Skagerrak Strait) demonstrated a high degree of identity
= 0.99–1.0), which could be associated with the observed from the beginning of the present millennium
increased migration of cod from eastern Baltic regions to the waters of Bornholm basin, and the distribution
of the part of migrants from Bornholm basin to Arkona basin.