Long-term Changes in the Ichthyofauna of Latvia's Inland Waters

Abstract

Changes in the ichthyofauna of Latvia's inland waters and their causes
have been analyzed. Information about the distribution and occurrence of
fish, obtained from various sources of literature, official reports,
"BIOR" data bases on fishery statistics, as well as field research done
from 1990 to 2010, has been collected and compared. Anthropogenic
activity in the 20th century, such as rivers blocking by dams and fish
introduction and acclimatization, has affected ichthyofauna more
significantly.

Full text

Scientific Journal of Riga Technical University
Environmental and Climate Technologies
DOI: 10.2478/v10145-011-0022-2 2011
_________________________________________________________________________________ Volume 7
9
Long-term Changes in the Ichthyofauna of Latvia’s
Inland Waters
Eriks Aleksejevs1, Janis Birzaks2, 1-2Institute of Food Safety, Animal Health and Environment – "BIOR" Fish
Resources Research Department
Abstract – Changes in the ichthyofauna of Latvia’s inland
waters and their causes have been analyzed. Information about
the distribution and occurrence of fish, obtained from various
sources of literature, official reports, "BIOR" data bases on
fishery statistics, as well as field research done from 1990 to 2010,
has been collected and compared. Anthropogenic activity in the
20th century, such as rivers blocking by dams and fish
introduction and acclimatization, has affected ichthyofauna more
significantly.
Keywords – Latvia, inland fish, changes of ichthyofauna,
inland waters
I.INTRODUCTION
The oldest data about fish which could be found in the
inland waters of the current territory of Latvia relates to
human settlements from 8-1 millennia BC and in the 11th-17th
centuries [12]. The first publications mentioning the
occurrence of fish in the Eastern Baltic region, as well as the
occurrence of fish in individual waterbodies in the current
territory of Latvia, were published in the 19th century and the
beginning of the 20th century [2,10].
Broader surveys on the species of fish occurring in Latvia,
including in inland waters, were published from 1935 to 1998
[7, 8, 9, 13, 19]. During this period, a range of articles were
published about rare species of fish [4], and research on
economically significant species and the occurrence of species
in separate lakes and rivers, as well as fisheries and fish fauna
related research in separate waterbodies, was conducted.
From 1990 to 2010, wider research was undertaken with the
goal of evaluating the composition of fish communities, and
the occurrence of species and their distribution in Latvia’s
rivers, lakes and artificial reservoirs. The results of this
research have not previously been published and long-term
changes in fish occurrence and distribution have not been
analyzed.
The potential effect of climate change on fish distribution is
the topic of wide discussion; the possible scenarios predict
changes in the structure of the fish community with warm
water fish species replacing cold water species. Climate
changes in the Baltic Sea basin have expressed themselves as
climate periods, which have replaced each other, starting from
the Sub-Arctic Boreal period 9000 years ago until the Sub-
Atlantic nowadays. Extremes of climate which were registered
in the Chronicles starting from the 13th century are known
about, but regular observations have been made since the 19th
century. The latter provide evidence of such significant
ecological parameter changes for fish as: changes in river
discharge, in the distribution of precipitation and in the biota
as a whole.
The most important regulating factor in the distribution and
occurrence of fish is the concentration of oxygen in the water.
In natural conditions, in the temperate climate zone, where
Latvia is located, the wide-scale deaths of fish in lakes can be
observed in winter quite often as a result of oxygen deficiency.
In certain types of lakes, as well as in the natural development
and evolution processes of lakes, fish winter kills determine
the composition of fish fauna in the short, as well as long
term.
Changes caused by anthropogenic influences in the
distribution and occurrence of fish took place mainly in the
last 50-100 year period. The distribution and occurrence of
diadromous species caused by a reduction in the number of
rivers available to them have been affected by anthropogenic
obstacles in rivers. At the same time, hydromorphological
transformation has taken place and water quality has
deteriorated as a result of pollution and eutrophication.
Beginning with the end of the 19th century, the introduction
of foreign species has taken place, as well as the transportation
of local fish species and their release to supplement fish
resources, and unsanctioned and casual distribution of foreign
and local fish species [15].
The aim of this work is, by collating the information at our
disposal, to make an assessment of what kinds of changes
have taken place in Latvia’s fish fauna within the 20th and 21st
century through natural and anthropogenic factors. Bearing in
mind that research conducted on the distribution and
occurrence of fish in Latvia was very limited until the 1990s,
one of the aims of the article is to collate and publish data
about the current actual distribution and occurrence of fish
species.
II. MATERIALS AND METHODS
In addition to the published information sources, the
following unpublished data have been used and analyzed in
the article:
 the former Baltic Fish Conservation and
Reproduction Administration archive
materials and official reports for the period
from 1946 to 1990;
 the “BIOR” Institute’s materials from 1953
to 2009;
 commercial fishing statistical data on 759
lakes, 22 rivers and 46 reservoirs from 1929
to 2010;

Scientific Journal of Riga Technical University
Environmental and Climate Technologies
DOI: 10.2478/v10145-011-0022-2 2011
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 fishermen’s catch results for 112 lakes, 3
rivers and 10 reservoirs from 1973 to 2009;
 data on the release of fish into 400 lakes, 55
rivers and 27 reservoirs from 1885, which
have been collected from publications,
archives and information provided by
hatcheries.
In total, data on 1097 lakes, 435 rivers and 227 reservoirs in
which at least one species of fish is mentioned as occurring,
are available in publications, official reports and surveys.
Wider scale research with the goal of evaluating the
structure of the fish community and the distribution and
occurrence of species has been taking place since 1990 at the
Latvian Fisheries Research Institute (currently the "BIOR"
Fish Resources Research Department). Over this time, 358
lakes, 313 rivers and 43 reservoirs have been covered. In
research fishing nets with varying mesh sizes (8 – 70 mm), a
beach seine or drag-net and electro-fishing equipment have
been used. In individual cases, fish caught in commercial
fishing have also been analyzed. In total, 45 species of fish, of
those 6 introduced, as well as 3 species of lamprey, have been
detected. The scientific names of the species used in the article
are according to Kottelat and Freyhof [3].
III. RESULTS AND DISCUSSION
The oldest evidence about fish which could be encountered
in the inland waters of the current territory of Latvia, which
date from 8-1 millennia BC and in the 11th-17th centuries, have
been provided by archaeological excavations. The bones of 21
species of freshwater and migratory fish have been found in
ancient settlement sites, hill forts and in the Riga City
archaeological layers. These were species which our ancestors
used for food [12].
In the 18th and 19th century publications about the fish of the
Eastern Baltic region [2, 10], 3 lamprey and 42 fish species
have been mentioned as occurring in the inland waters of the
current territory of Latvia, and the individual sites where they
were found, have been indicated.
The first reports about Latvia’s ichthyofauna were
published in the 1930s. The following 3 lamprey and 42 fish
species were ascribed to Latvia’s inland waters: the river
lamprey Lampetra fluviatilis, brook lamprey Lampetra
planeri, sea lamprey Petromyzon marinus, Atlantic sturgeon
Acipenser sturio, eel Anguilla anguilla, allis shad Alosa alosa,
twaite shad Alosa fallax, bitterling Rhodeus amarus, gudgeon
Gobio gobio, crucian carp Carassius carassius, carp Cyprinus
carpio, bream Abramis brama, schneider Alburnoides
bipunctatus, bleak Alburnus alburnus, asp Aspius aspius, blue
bream Ballerus ballerus, silver bream Blicca bjoerkna, sun
bleak Leucaspius delineatus, ide Leuciscus idus, dace
Leuciscus leuciscus, ziege Pelecus cultratus, minnow
Phoxinus phoxinus, roach Rutilus rutilus, rudd Scardinius
erythropthalmus, chub Squalius cephalus, vimba Vimba
vimba, tench Tinca tinca, spined loach Cobitis taenia, weather
loach Misgurnus fossilis, stone loach Barbatula barbatula,
catfish Silurus glanis, pike Esox lucius, smelt Osmerus
eperlanus, vendace Coregonus albula, whitefish Coregonus
lavaretus, Atlantic salmon Salmo salar, trout Salmo trutta of
two forms (migratory and sedentary), grayling Thymallus
thymallus, burbot Lota lota, threespine stickleback
Gasterosteus aculeatus, ninespine stickleback Pungitius
pungitius, bullhead Cottus gobio, ruffe Gymnocephalus
cernua, perch Perca fluviatilis and pike perch Sander
lucioperca [7, 11].
Reports on Latvia’s ichthyofauna released in the 1940s and
1950s [9, 19] are generally similar, with 3 lamprey and 49 fish
species mentioned in them. During this period, the barbel
Barbus barbus and Alpine sculpin Cottus poecilopus were
ascribed as natural and occurring species in Latvia’s inland
waters, but the sterlet Acipenser ruthenus, Prussian carp
Carassius gibelio, rainbow trout Oncorhynchus mykiss, arctic
chaar Salvelinus alpinus and brook trout Salvelinus fontinalis
were ascribed as introduced species.
In the latest publication of Latvia’s ichthyofauna [8], 3
lamprey and 62 fish species have been included, which
various authors have ascribed to Latvia’s inland waters, and
that have been caught in commercial fishing or brought in and
introduced in natural waters. But since this work was
published, a large amount of significant new and previously
unpublished information about fish distribution and
occurrence in Latvia’s inland waters has been gathered. This
data provides the opportunity to evaluate and analyze the
kinds of changes that have occurred to Latvia’s ichthyofauna.
A. Effect of natural factors on Latvia’s inland water
ichthyofauna
The detailed effect of natural factors on the distribution and
occurrence of fish is not known, but in the long term it has
obviously been linked to climate change.
Judging from findings in archaeological excavations,
warmwater fish species like the catfish, pike perch and the asp
were more widely distributed in ancient times than in the 19th -
20th centuries, but nowadays their distribution is once again
increasing.
Pikeperch bones have been found in excavations in the
whole territory of Latvia in 12 or 75% of the 16 settlements
and archeological layers inspected [12]. This provides
evidence that in the time period from 6 millennia BC until the
17th century the pikeperch was comparatively widely
distributed and often found.
Whereas, in the 1930s the pikeperch was still considered to
be a rare species of fish in Latvia’s waters [7]. This is also
confirmed by the lake inventory data done in the 1950s, where
it was found that the pikeperch only occurred in 27 lakes or
5% of the 549 lakes surveyed [17].
Judging from data from the Stone Age (6 – 8 millennia BC)
gained in archaeological excavations, asp and catfish also
lived in Burtnieku Lake [12]. In the 1950s these species of fish
could no longer be found in the lake [17]. They are not
mentioned in commercial fishing statistics in the period from
1928 to 2010. Neither asp, nor catfish were found in lake
surveys undertaken 4 times from 1996 to 2001.
From the 1960s until today, the Daugava with its largest
tributaries and the lakes connected to the river around Riga

Scientific Journal of Riga Technical University
Environmental and Climate Technologies
DOI: 10.2478/v10145-011-0022-2 2011
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were mentioned as the area of distribution of catfish in various
sources of literature [8, 13]. It is also mentioned that catfish
could once be found in Puzes Lake [2], but it had later
obviously disappeared.
Since the 1950s, catfish has also been found in the Sila
Lake connected to the Daugava, where it has been regularly
fished in the period from 1994 to 2009. Catfish was also
caught in the lake survey period in 2006, confirming the
existence of its population in this lake. From the survey data,
catfish can also be found in Riču Lake which is directly
connected to Sila Lake. In the last seven years the catfish has
been mentioned in fishing haul statistics in two additional
inland lakes - Dagda and Smiļģinu lakes which are not directly
connected to the Daugava.
Whereas, the stenothermic (cold water) species, lake smelt
and vendace have had a distinct tendency to reduce in both
population, as well as in number, beginning with the 20th
century [2].
In the 1930s, vendace and lake smelt, together or
individually, could be encountered in about 30 lakes in
Latgale, as well as in Alūksnes Lake, Limbažu Lielezers and
Puzes, Sventes and Usmas lakes [7]. From the inventory data
undertaken in the 1950s on 549 Latvian lakes, obtained by
collating information with varying levels of credibility,
vendace could be encountered in 39 lakes, but lake smelt in 18
lakes [17]. In the research work conducted over the same
period, vendace was found in only 8 lakes.
Nowadays, vendace has been detected in 11 lakes, but
according to the survey data, it could be encountered in 5
more lakes. In turn, lake smelt have been established in 6
lakes, but could be encountered in 5 more lakes, according to
the survey datam with varying levels of credibility.
Despite the lack of accurate information on the occurrence
of vendace and lake smelt at the commencement of the
previous century, their number has obviously decreased as a
result of climate change, biogenic pollution and lake
eutrophication. Thus, although vendace were found in three
lakes in the last century, they were not found during the
research fishing, were not mentioned in commercial fishing
statistics and were not found in the survey data since at least
1982.
In temperate zone lakes, large-scale fish deaths are
characteristic of winter, due to conditions of oxygen
deficiency. This is dependent on many factors, but lake
morphology is very significant. In shallow and closed (without
runoff) lakes, this phenomenon can be observed more often. In
Latvia, fish suffocation has been observed in more than 238
lakes, and it occurs regularly in 26 of them, but in 59 lakes
fish suffocation has been observed at least five times in the
past century. Fish suffocation is a significant regulating factor
of the ichthyofauna structure. In Latvia’s conditions, as a
result of fish suffocation, the disappearance of such species of
fish as bream and pike perch, have been observed. For
example, a comparatively large population of bream existed in
Lielauces Lake until 1996. After the large-scale deaths of fish
in the winter of 1995/1996, this population completely
disappeared and did not regenerate until 2004. However, in
Engures Lake, where large-scale deaths of fish occur
regularly, the self-regenerating bream population obviously
does not exist. A small number of bream migrate to Engures
Lake from the coast of the Gulf of Riga. Thus, in 11 research
fishing events done from 1992 to 2010, the number of bream
has been below 1% of the total number of fish caught, or they
were not caught at all.
In lakes, which are connected to other waterbodies, fish
winterkills are less intensive; fish can migrate to adjacent
bodies of water, as well as find places with a higher level of
oxygen in mouths of rivers and streams. In closed lakes, fish
suffocation can cause long-term changes in ichthyofauna,
which manifests itself as a reduction in the number of fish
species occurring in the lake where only 2-3 of the most
tolerant species survive. However, it is not usually the case
that all of the fish in a lake or all of the individuals of a species
die as a result of fish suffocation. That is why the structure of
the ichthyofauna and fish resources in these lakes renews itself
within a few years after separate winterkill.
B. Anthropogenic influence
Anthropogenic activity, which directly influences the structure
of the fish community, is diverse, but it can, in fact, be
reduced to a few main effects, like the development of barriers
in fish migration paths, transformation of habitats and a
reduction in water quality.
Anthropogenic activity has had the most effect on migratory
or diadromous fish. Their distribution, alongside with their
occurrence and number, is dependent on opportunities for their
migration along rivers to reach their spawning (anadromous
species) or living and feeding (catadromous species) sites.
Nowadays more than 700 artificial barriers have been counted
in Latvia’s waterways, which makes 60% of Latvia’s territory
inaccessible to migratory fish. The majority of them are
watermill dams, and small HPS (hydro power stations) have
been built on many of them in the period since 1990. In the
period from 1939 – 1974, three hydro-electric station cascades
were created on the Latvia’s largest river, the Daugava. As a
result of this, the number of rivers accessible to such
migratory species of fish as salmon, sea trout, vimba, river
lamprey and eel has been significantly reduced. The greatest
part of this river’s basin (24,700 km2 in Latvia’s territory) and
about 40 of its tributaries became inaccessible to migratory
fish (diadromous) species. In accordance with data from the
literature, up until the Daugava was dammed, these species of
fish reached the territories of Belorus and Russia, which are
located more than 500 km along the river away from the Gulf
of Riga. It should be noted that vimba has partly adapted to the
new situation, creating a landlocked population in the Pļaviņas
Reservoir in the middle section of the river.
Commercial fishing data clearly show a reduction in the
catches of migratory fish in Latvia, mainly in the Gulf of Riga
and the rivers flowing into it, starting from 1975. The fishing
haul of salmon and river lamprey has particularly declined
(Figure 1). They also have not regenerated, despite regular
restocking of their fingerlings and larvae in rivers.

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Environmental and Climate Technologies
DOI: 10.2478/v10145-011-0022-2 2011
_________________________________________________________________________________ Volume 7
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0
100
200
300
400
500
600
700
1945 1955 1965 1975 1985 1995 2005
Catch (t)
Sea trout
Eel
Salmon
Vimba
River lamprey
Fig. 1. Catches of migratory fish in Latvian coastal waters and rivers.
As opposed to the previously mentioned species of fish,
smelt and three spined stickleback spawn in the lower reaches
of rivers and their spawning places have not been destroyed as
a result of the HPS construction. But the catches of these
species decreased many times in the 1980s and have remained
at a low level even now or have been completely discontinued,
due to the shortage of resources (Figure 2).
0
1000
2000
3000
4000
5000
6000
7000
1945 1955 1965 1975 1985 1995 2005
Catch (t)
Stickleback
Smelt
Fig. 2. Catches of three spined stickleback and smelt in the Gulf of Riga,
coastal waters and rivers.
It is thought that the rapid reduction in the number of
migratory fish in the 1970s-1980s was caused by a number of
factors, in addition to the previously mentioned damming of
the lower reaches of the Daugava, being river pollution and
eutrophication and the morphological transformation of rivers.
Unfortunately, it has not been possible to express the influence
of these factors over time quantitatively. But, for example,
information, which has been collated in River Basin Districts
Management Plans, provides evidence that the majority of
Latvia’s surface water bodies are not of a good ecological
quality. It should be noted that the reduction in the number of
other species of fish in the Gulf of Riga was obviously also
caused by the expansion of cod at the end of the 1970s and
beginning of the 1980s. Still, the number of this species in the
Gulf of Riga since 1986 has been at a very low level, and its
fishing haul is almost zero. However, the number of migratory
fish (anadromous) has not regenerated to the levels of the
1960s-1970s.
Eel is the only catadromous species of fish in the Baltic Sea
basin. Eel is an ecologically flexible species and can be
encountered in the sea and coastal waters, as well as in inland
waters. Its distribution in Latvia nowadays has been
determined by two processes.
On the one hand, starting from the 1940s until the 1980s,
the release of glass eel and eel fingerlings was undertaken in
all of the largest river basins, and about 55 lakes in total. The
number of water bodies where this species could be
encountered increased accordingly. Data from surveys done
after the 1950s show that eel could be found in 150 lakes, but
occurred frequently in only 12 of them [17]. From 1946 to
1992 it was registered in commercial fishing in 98 lakes and in
all of the largest rivers (in the Daugava, Salaca, Gauja, Venta)
and the reservoirs developed on them. Eel was registered in 14
lakes in the catches of commercial fishermen. It should be
noted, that out of all of the abovementioned water bodies,
natural migration of eel was possible in only 10 lakes, and, as
to the others, eel was caught as a result of its artificial release
and distribution. After 1990, eel was mentioned in the fishing
haul statistics in 16 lakes, but only four of these water bodies
are freely accessible to natural migration of eel, and in the
others eels which were released in the 1960s-1990s were
caught.
On the other hand, the natural distribution area of eel, just
like for other species of migratory fish, has been reduced as a
result of anthropogenic barriers.
Its catches in coastal waters were relatively stable until the
1970s, but then it began decreasing rapidly, like in other
European countries. However, at the same time, the fishing
haul of this species in inland waters grew, due to the intensive
introduction of glass eel into the lakes in the Eastern part of
Latvia.
Historically, eel was the most widespread species of
migratory fish in Europe. Currently, its position has been
recognized as being critical, and a range of normative acts
have been adopted for its restoration, such as the Regulation
EC 1100/2007. It is considered that the main factors which
determine the condition of eel stocks nowadays are its fishing,
blocking of migratory paths, deaths in HPS turbines, water
pollution and diseases and parasites.
Changes in ichthyofauna to a large degree have also been
determined by attempts to introduce and acclimatize new
species. From 1885 until nowadays, at least 23 species of fish
have been released in Latvia’s inland waters. Work on the
introduction and acclimatization of fish in Latvia’s territory
was commenced at least from 1885 [20]. To this day 23
species of fish have been released in Latvian waters: sterlet
Acipenser ruthenus, Siberian sturgeon Acipenser baerii,
Russian sturgeon Acipenser gueldenstaedtii, beluga Huso
huso, Prussian carp Carassius gibelio, carp, silver carp
Hupophthalmichthys molitrix, bighed carp
Hupophthalmichthys nobilis, grass carp Ctenopharyngodon
idella, black carp Mylopharyngodon piceus, Baikal omul
Coregonus migratorius, muksun Coregonus muksun, broad
whitefish Coregonus nasus, peled Coregonus peled, inconnu
Stenodus nelma, pink salmon Oncorhynchus gorbuscha, chum

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salmon Oncorhynchus keta, coho salmon Oncorhynchus
kisutch and rainbow trout Oncorhynchus mykiss, Arctic charr
Salvelinus alpinus, brook charr Salvelinus fontinalis, striped
bass Morone saxatilis, as well as the unsanctioned – Amur
sleeper Percottus glenii [1, 8].
The release of local species in their natural waters is also
being undertaken, alongside the introduction of alien species
of fish in Latvian waters. The goal is to supplement the
resources of fish for the needs of fishing. The acclimatization
or re-acclimatization of local species of fish is also being
done, i.e. distribution in the waters, where at the time of
release these species had not occurred. Overall, the effect of
the release of fish has affected a significant portion of Latvia’s
inland waters (Table 1). TABLE 1
FISH INTRODUCTION AND RELEASE IN LATVIA’S INLAND WATERS
Water
body
Introduction
of alien
species
Release
of local
species
Total number of water
bodies where fish have been
released
Rivers
10
72
72
Lakes
246
299
405
Reservoirs
30
28
39
The majority of the species of fish introduced into Latvia’s
inland waters is not encountered nowadays, or can be
encountered for only a limited period after their release, or is
related to individuals caught after escaping from fish
hatcheries or fish ponds. Of the alien species, self-sustaining
populations have only developed for Prussian carp and Amur
sleeper [8].
Prussian carp was introduced into Latvia in 1948 [1] and by
2010 had been released in more than 210 lakes. From various
information sources, by 2010 Prussian carp could be ascribed
to 299 lakes, 30 reservoirs and 25 rivers. In Latvian
conditions, Prussian carp have also acclimatized to some
natural waterbodies. Self-sustaining populations with a normal
age structure can usually be found in lakes with a small
number of fish species, where crucian carp, tench and sun
bleak can also be encountered, in addition to Prussian carp,
but usually there are no predator species pike and perch.
Coastal lakes which are connected to the Gulf of Riga coast
are an obvious exception. Correspondingly, Prussian carps of
various ages (0 – 10 years) have established themselves in
Ķīšezers. In the last 15 – 20 years, a natural increase in the
number of Prussian carp has been observed. For example, in
coastal fishing, their fishing haul has increased from just
kilograms in 1992 to 5.1 t in 2010. A similar situation also
exists in Estonian coastal waters.
Amur sleeper is the only known species of fish, which has
been illegally introduced into Latvia’s natural water bodies
and which has acclimatized relatively successfully. It was first
found during test-fishing in 1996 in the Lielais Trijkārtu Lake.
From various information sources, Amur sleeper occurs in
more than 23 lakes and 4 rivers, as well as in 14 artificial
reservoirs. The number of waterbodies inhabited by Amur
sleeper is obviously significantly higher, as ichtyological
research is done very rarely in the water bodies which
regularly dry out, to which it is most suited. Amur sleeper can
be found in the former Bauska, Cēsis, Krāslava, Ludza, Ogre,
Preiļi, Rēzekne, Rīga, Tukums and Valmiera district
territories. Up to now, it has not been possible to find
information on its occurrence in Kurzeme (the western part of
Latvia).
Carp can be considered to be the first species of fish
introduced in Latvian waters. It had already been bred since
the 13th century in ponds created next to monasteries [1].
Information about their release in separate water bodies can be
found only from the 1920s. By 2010, carp had been released in
more than 226 lakes and 21 reservoirs. Carp also enter natural
waters when fish ponds overflow, as well as through migration
between connected water bodies. From various sources of
information, carp have been ascribed to 361 lakes, 61
reservoirs and 36 rivers up to 2010. Carp spawning has been
observed in a number of water bodies, but its effectiveness,
excluding artificial ponds, is not known. In research on natural
water bodies, individuals of only one age group are usually
caught. This shows that the regular and effective regeneration
of the carp population in natural waters in Latvia does not take
place. Obviously, the place of carp in Latvia’s ichthyofauna is
maintained by carps which have escaped from fish hatcheries
or those released in natural waters.
The artificial propagation of pike perch in Latvia’s inland
waters was commenced from at least 1904 and has continued
up until today, with the increasing intensity [8]. Up to 2010,
pike perch was released in more than 125 lakes, 13 reservoirs
and 4 rivers. The number of waterbodies in which pike perch
have appeared is even greater, as not all of its releases have
been registered. Many lakes are mutually interconnected with
waterways along which pike perch migration is possible. As a
result, pike perch can be encountered nowadays in a total of
188 lakes, 20 reservoirs and 29 waterways. It should be noted
that, as a result of the introduction of pike perch in waters in
which it has not previously lived, self-sustainable populations
have not always developed.
The results of field research, as well as data from
commercial fishing statistics, allow us to make estimations
about the actual occurrence of the pike perch currently. Of the
297 lakes inspected since 1990, pike perch have been found in
59 or in 20% of the total number. Over this time, pike perch
was also regularly caught by commercial fishing in 10 other
lakes as well. In addition to these 69 lakes, pike perch can also
be found in the Daugava, its reservoirs and the largest
tributaries, in the Gauja, Lielupe, Salaca and Venta, as well as
the Pakuļu Reservoir on the Ciecere River.
Alonside with the increase in the number of water bodies
inhabited by pike perch, caused by their artificial breeding,
significant changes in the size of their population in separate
lakes can also be observed. Thus, the commercial catches of
pike perch were 1 – 7 kg per year in Burtnieku Lake in the
1930s. In the 1950s and 1960s the catch periodically was from
12 kg to 258 kg per year, but in the last 5 years the average
catch has been 9,757 kg per year. Whereas, in Lubāna Lake,
from the 1950s to the 1980s pike perch practically was not
mentioned in the commercial fishing statistics, but from 1990

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it has been caught regularly and in the last five years the
average catch has been 10,515 kg per year.
In many lakes, the eutrophication level has reached the
particularly favorable conditions for the existence of the pike
perch population. For example, in Burtnieku Lake in the
1950’s, water transparency was from 1.0 m to 1.5 m, but
nowadays it has been reduced to 0.4 m. A similar situation
exists in Lubāna Lake, where the level of water transparency
is as low as in Burtnieku Lake. A favorable eutrophication
level for pike perch in certain circumstances can also lead to
disappearance of the population. For example, in Balvu Lake,
in the winter of 1995/1996 the wide-scale dying off of pike
perch as a result of oxygen deficiency took place. The pike
perch population in this lake was renewed later through the
introduction of their fingerlings.
The artificial propagation of catfish has also been
commenced in Latvia. They have been released in separate
bodies of water in the Gauja and Venta basins, as well as in at
least 3 lakes, although the development of self-sustainable
population in them has not yet been confirmed.
The catfish population associated with the Daugava has
obviously also been increasing, as catfish are regularly caught
in Ķīšezers, although captured rarely in previous years.
The distribution of asp in the last century was mainly
connected with the Daugava, Gauja, Lielupe and the Venta, as
well as the main tributaries of these rivers and lakes directly
connected with them. Nowadays, there is no news about asp in
angler's catches in the Bārta. An individual example has been
caught in Liepāja and Pape lakes.
From the 1950s lakes inventory data, asp could be found in
the three lakes directly connected with the Daugava.
Nowadays it is found in 12 lakes, which is thought to be
caused by the increase of the asp population in rivers and their
more intensive migration to lakes.
In Latvia, the artificial propagation of vendace was
commenced from at least 1900. It took place regularly in the
1930s, and later till the 1980s, when vendace were released in
at least 16 lakes [1, 8]. They were released in more than 45
Latvian lakes overall. However, the total size of the vendace
population in Latvia has tended to decrease, caused by
unfavorable climate and anthropogenic factors, mainly
eutrophication. It is quite probable that naturally regenerating
populations in many lakes did not develop and consisted only
of fish artificially released, and that they existed for only a
short period.
Grayling, which can be encountered mainly in the Gauja
and Venta basins’ waterways [8,13], is now also released into
the rivers of the Daugava and Lielupe basins, although the
development of a naturally regenerating population is not yet
known in these river basins.
The unplanned spread of various species of fish, as a result
of artificial fish propagation, has also taken place. Thus, for
example, in 2010, pike were released in some lake in the
Rēzekne County, and bettering, which had not previously been
found in Eastern Latvia, were also released together with the
pike.
The transportation and release of many local species of fish
is done regularly and in large numbers, as determined by the
National programme for the reproduction of fish resources.
These are mainly smolts or fingerlings of migratory fish of
different ages. Bearing in mind that the distribution of
migratory fish in Latvia is restricted by the number of
accessible rivers, these releases do not change their
distribution and occurrence in inland waters.
Up to the 1990s, a fisheries-type approach dominated in the
research on fish in Latvia’s inland waters. Research was done
mainly on commercially significant fish species, i.e. the
species of a greater commercial value or species which on
balance dominated in fishing. Fish, mainly from commercial
fishing catches, were analyzed in the research. Therefore,
views differ substantially on the frequency of the occurrence
of many species of fish at the beginning of the previous
century and currently.
Thus, in the literature from the 1930s, ide was considered to
be a fish which could be fairly regularly found. Chub, which
was a similar species in appearance, was considered to be
comparatively rare [7, 11]. From the 1950s lake inventory
data, ide was found in 36% out of 549 lakes inspected, but
chub - in only 9% [17]. However, in the last 20 years, in the
inventory fishing, ide was found in 6% out of 292 lakes
inspected, but chub in 10% of lakes. The proportions of these
species of fish in rivers are 3% and 42% respectively.
In the 1980s, a large population of ide had developed in
Lubāna Lake after the artificial enlargement of their habitat. In
the newly created lake – in the reservoir, the catch of ide
reached 11.6 t in 1987, but was only 26 kg in 2010. The
second largest ide population was in Engures Lake, where the
haul in 1969 was 10.9 t, but in 2010 it was only 10 kg. This
ide population was mainly created by the coastal semi-
migratory fish from the Gulf of Riga. The catches of ide in
coastal waters fell from 28 t in 1990, to 0.1 t in 2010. The
reduction in the ide population in Engures Lake is usually
explained by the rather intensive fishing on the coastal waters
in the Gulf of Riga. Whereas, the main reason in Lubāna Lake
has obviously been the changes in its hydrological condition.
In other Latvian water bodies, the reduction in ide numbers
has obviously been caused by changes in environmental
conditions.
The majority of species of fish which were not
commercially used in large volumes in the first part of the
previous century were considered to be rare [7]. They were not
included in surveys and were not the objects of research. That
is why there is practically no information about a whole range
of species, about their distribution and occurrence, even
relatively recently.
One such fish is bitterling, the occurrence of which is linked
to the lower reaches of the Daugava, the Lielupe and Venta,
with the lower reaches of the Daugava being assumed to be
the northern boundary of the area of distribution [10].
Nowadays bitterling is found in 54 lakes and 55 rivers and the
area of its distribution has reached the middle reaches of the
Salaca in the Northern part of Latvia. Up until now, bitterling
has not been found in the eastern part of Latvia.

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The situation is fairly similar with the sun bleak, with its
area of distribution, as opposed to bitterling, covering all of
Latvia’s territory, but it was, however, considered to be a
rarely found fish [7], as well as a common one [11].
Nowadays it is found in 229 lakes and 73 rivers.
Spined loach too was earlier considered to be a rarely found
fish [7], but actually it is a very widespread species of fish
which is often encountered. After 1990, spined loach has been
found in 205 lakes and 112 rivers.
A new species in Latvia’s inland waters is the northern
golden loach Sabanejewia baltica, which was first found in
2008 in the Gauja and in the lower reaches of the Amata, but
in 2009 in Kāša Lake. The occurrence of this species within
Latvia is quite unclear. It was also found in the Venta River in
the territory of Lithuania in 2002. The occurrence of the
northern golden loach is not known in other areas bordering
Latvia, like Belarus, Estonia and the Pskov region of Russia.
Bullhead and schneider were also considered to be rare fish
species in the 1930s, but are quite frequently encountered
nowadays. Thus, bullhead has been found in 152 rivers and 16
lakes, but schneider – in 74 rivers and one lake. Both fish
species are more suited to river biotopes, which determine
their rare occurrence in lakes.
In turn, Alpine sculpin, which was earlier ascribed to
Latvia’s coastal and inland waters [9, 13], obviously cannot be
found. No specific incident is known about where it has been
found in Latvia or in neighboring countries.
Some of the species have been relatively rare up until now,
such as twaite shad and sabrefish. Neither of these species of
fish is mentioned in the lists of fish bones found in
archaeological excavations [12], nor in the 19th century review
about the economic importance of the Daugava [20].
They have not been caught during the research fishing in
Latvia’s inland waters, and only data about occasional catches
in commercial fishing are available.
Twaite shad is mainly caught in coastal waters. It is found
more to the south of Latvia, in the Baltic Sea. The catches of
twaite shad in Lithuania in the first part of the previous
century in the Curonian Lagoon was about 200 – 300 tonnes
per year, while in Latvia the fishing has been occasional. In
later years, the catch in Lithuania has rapidly declined, and in
Latvia twaite shad has become rarer. From 1996, its numbers
in the Curonian Lagoon again started increasing.
Correspondingly, twaite shad has been caught more frequently
in Latvian coastal waters. So, in the period from 1992-2002,
only some examples were caught, but later it was regularly
registered in coastal fishing, with its catches reaching up to 0.6
t in 2004. Allis shad, which is similar in appearance to twaite
shad, which was earlier ascribed to Latvia’s ichthyofauna [6,
11], is obviously found neither in Latvia’s waters, nor in the
Baltic Sea basin.
In the literature of the first half of the previous century, the
catching of individual examples of sabrefish was noted in
coastal lakes [19]. Since the end of the 1990s, it was regularly
caught in Ķīšezers. In fishing of eel in Jugla Lake in 2006, 70
examples of sabrefish were analyzed as by-catch. The number
of sabrefish has rapidly increased in the Vistula Lagoon from
the 1990s.
It is thought that the increase in the number of sabrefish and
twaite shad since the 1990s is caused by improvement in water
quality of the lower reaches of the Nemuna and Vistula
Rivers, where the spawning sites of these species are located.
Their breeding in Latvia has not been confirmed until now, but
they might be more frequently found in our waters now, as a
result of climate change.
The occurrence of barbel Barbus barbus in Latvia’s inland
waters is doubtful. Initially though, barbel was reported to be
seen in the Riga market – it was caught in a raid on the
Liepāja port [4]. But a little later, news was received that one
example of this species of fish was caught in the lower reaches
of the Bārtas River, and since 1956 it has been included in the
list of fish found in Latvia’s freshwater (in the Bārtas River)
[13]. Later the occurrence of barbel was also ascribed to the
Daugava and Venta basins, even though no specific incidence
of it having been caught has been mentioned. One individual
from this fish species was also caught on the sea coast near
Liepāja in 2006. Bearing in mind that barbel was not
mentioned in fishing haul statistics from 1949 to 2010 for
Liepāja Lake, into which the Bārtas River empties, the
existence of a naturally regenerating population seems
doubtful. It is thought that in the two previously mentioned
examples barbel arrived to Latvia’s coastal waters from the
Curonian Bay in Lithuania, where this species of fish can be
found in the rivers which empty into it.
Individual species of fish can nowadays be considered to
have disappeared. Thus, for example, bones of blue bream
were found during archaeological excavations at a settlement
on the Lubāna lowlands (4 millennia BC) and near Dole Island
on the Daugava (1 millennium BC) [12]. In the 19th century
blue bream, which had entered from the Gulf of Riga, was
fished regularly in the Daugava [20]. In the last century
however, blue bream had been ascribed to the Latgale lakes,
as it was sold at the Daugavpils market [19]. It was rarely
found in the Gulf of Riga or in freshwater. It could be
encountered in the lower reaches of the Daugava and Gauja
[11]. In fishing literature, blue bream is also ascribed to the
waters of the Salaca and Venta basins. Whereas, in the
research about the lakes in suburbs of Riga, blue bream is
ascribed to Babīte Lake, Jugla Lake, Ķīšezers, Lielais
Baltezers and Mazais Baltezers [8].
However, the only time when it was proved that a blue
bream had been caught, was in the Pļaviņas Reservoir on the
Daugava River in 1988 [16]. Blue bream might enter the
Daugava, migrating from lakes in the Pskov region (in
Russia), where it is found [18]. After 1988, no instance of a
blue bream being caught is known in Latvia.
Archaeological excavations provide evidence that in the
past (1st millennium BC to 13th–14th century) sturgeon was a
fish that was found quite often in the Daugava [12]. All the
authors, who wrote about Latvia’s ichthyofauna in different
periods, mention sturgeon, like the Atlantic sturgeon, in
connection with Latvia’s rivers [7, 8, 11, 13]. In recent years,
however, the assumption has been made that the Atlantic

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sturgeon, which had disappeared from the Baltic Sea basin
over 800 years ago, was later replaced by the American
Atlantic sturgeon Acipenser oxyrinchus [3]. In such a case,
one can assume that both species of sturgeon could once be
found in Latvia’s waters.
The introduction of various fish from the sturgeon family in
Latvia’s and other Baltic Sea nations’ waters took place since
1885 [8, 20]. Neither morphological nor genetic analyses have
been done on the samples caught in Latvia’s waters and,
therefore, it cannot be proved whether they belong to the
"local" sturgeon. News of the capture of various sturgeon-like
species of fish in Latvia’s waters was already published in the
19th century, and it appeared in large numbers and more
frequently in commercial fishing catches in the first years after
their release.
The systematic belonging of some fish is being reviewed,
influenced by the latest scientific findings. Where it is possible
to establish morphological differences between sub-species or
forms which were provided earlier, they are looked upon as
new species with a species name.
Whitefish Coregonus lavaretus which can be found in the
Baltic Sea basin, was allocated in the migratory form which
spawns in rivers, and the form which spawns in the sea has
now been offered the names Coregonus maraena and
Coregonus widegren, respectively. Peipsi whitefish
Coregonus maraenoides and Ludoga whitefish Coregonus
lutokk [1], which were introduced into some Latvian rivers
and lakes, are now also considered as new species. In a similar
way, in the 1930’s one species of whitefish Coregonus
lavaretus, which was found in Latvia, was divided into three
forms and can be recognized by their morphological signs [6].
However, systematic morphological or genetic analyses on the
capture of a whitefish were not later done. Thus, currently it is
not and will not be possible to determine which of the
whitefish species have been found up till now in various water
bodies in Latvia.
A similar case exists with another fish from the whitefish
family – vendace. The ripus sub-species divided off earlier,
the Coregonus albula ladogensis, is considered to be a
separate species, Coregonus ladogae [26]. Ripus was
introduced into a number of Latvian lakes [1]. However, the
question about the overall status of this species and the
existence of its population in Latvia’s lakes is still debatable.
The research from 1949 published in the Russian language
mentions that bullhead is represented in the Daugava by a sub-
species - the Russian bullhead Cottus gobio koshewnikowi
[14]. The main morphological sign for distinguishing the
Russian bullhead from the common bullhead is an incomplete
lateral line. At the same time, it is noted that this difference
cannot be observed in all individual fish [14]. In another
research, it has been established that an incomplete lateral line
can only be observed in young bullhead individuals, but that in
adult fish it is the same as the common bullhead. Nowadays,
there is a suggestion that the Russian bullhead should be
recognized as a separate species Cottus koshewnikowi, naming
it the Volga bullhead [3].
It should be noted that a real difference of opinions can be
observed in systematic ichthyological research in relation to
the Cottidae. The view [5] is that only three species of
bullhead can be found in Europe. At the same time, other
authors [3] distinguish eight new species of bullhead. Neither
the Alpine sculpin, nor the common bullhead is on the
distribution maps for this family of fish in Latvia included in
this work. However, the Volga bullhead’s area is marked from
the Daugava northwards. At this moment, at least 100
common bullhead locations are known in the territory of
Latvia to the south of the Daugava and in 152 rivers
throughout the country. This species can also be found in all
countries neighbouring Latvia.
Russian (Volga) bullhead’s systematic status is obviously a
topic for discussion, as the works of some authors mention it
as a species [3], a sub-species [14], or a haplotype [5].
IV.CONCLUSIONS
1. When comparing archaeological excavation data with the
19th -20th century publications, statistical data from fishing and
the results of field research, it can be concluded that the
distribution and occurrence of individual species of fish has
been altered under the influence of climate change. The
distribution of warmwater species, such as catfish, pike perch
and asp, has increased, but that of coldwater species, like
vendace and lake smelt, has decreased.
2. In temperate zone conditions, a significant factor forming
the structure of the fish community in lakes is the wide-scale
winterkills of fish due to conditions of oxygen deficiency.
Anthropogenic factors also influence this phenomenon, as the
intensive suffocation of fish is more pronounced in eutrophic
and polluted waters.
3. Anthropogenic activity, like the building of barriers on
rivers, the hydromorphological transformation of rivers,
pollution and eutrophication, has influenced the occurrence
and distribution of fish much more significantly than natural
factors.
4. As a result of human activity, new species of fish have
been acclimatized in Latvia’s ichthyofauna. Two of them, the
Prussian carp and Amur sleeper, have adapted and are creating
self-regenerating populations. Such fish species as catfish,
pike perch, grayling and eel have been artificially spread in
Latvia’s inland waters by transporting and artificially
propagating them.
5. The occurrence of some species of fish in Latvia’s
waters, which in the 20th century were considered to be rare,
like sabrefish and twaite shad, is increasing, which could
possibly be caused by an increase in the number of individuals
in the populations in the Baltic Sea’s lagoons, in the Curonian
and the Vistula lagoons.
6. The blue bream and the Atlantic sturgeon, and from the
latest research, even the American Atlantic sturgeon, have
obviously disappeared in Latvia.
7. From 2007, a new fish species, the Northern golden loach
was registered in Latvia’s fauna. Its location in the Gauja
basin currently is the furthest known location of this species to
the north.

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8. The latest data gained in fishing research shows that the
species of fish, which were considered to be fairly rare in the
first half of the 20th century in Latvia, can be frequently
encountered nowadays. The reason for this difference might
be the lack of relevant research.
9. As a result of changes made in fish classification, in the
coming years some new fish species could be added to
Latvia’s ichthyofauna.
REFERENCES
1. Andrušaitis, G. Zivju savairošana un aklimatizācija Latvijā [Breeding
and acclimatization of fishes in Latvia]. Grām.: Latvijas PSR iekšējo
ūdeņu zivsaimniecība IV. Rīga, 1960., 41.-70. lpp.
2. Kawall, H. Fische in Kurland und an den Küsten der dasselbe
begränzenden Ostsee, mit Berücksichtigung von Livland. Das Inland.
23. Jahrg., 1858, Nr. 33, 534-536 S., Nr. 35, 561-598 S., Nr 36, 579-583
S.
3. Kottelat, M. and Freyhof, J. Handbook of European freshwater fishes.
Berlin, 2007, 646 pp.
4. Krēmanis, A. Jauna zivs mūsu ūdeņos [New fish species in our waters].
Zvejniecības mēnešraksts, 1937., Nr. 9., 278.-279. lpp.
5. Maitland, P. S. Guide to freshwater fish of Britain and Europe.
Hamlyn, London, 2000, 256 pp.
6. Mannsfeld, W. Studien an Coregonen des Ostbaltikums. Archiv Fur
Hydrobiologi, 1930, Band XXI, Heft 1, 65-94. S.
7. Mansfelds, V. Latvijas zivis [Fishes of Latvia]. Grām.: Latvijas zeme,
daba un tauta. II. Rīga, 1936., 490.-519. lpp.
8. Plikšs, M., Aleksejevs, Ē. Zivis [Fishes]. Rīga, 1998., 304. lpp.
9. Priedītis, A. Zivkopība [Fish farming]. Rīga, 1947., 422. lpp.
10. Schneider, G. Die Süsswasserfische des Ostbaltikums und ihre
Verbreitung innerhalb des Gebietes. Archiv für Hydrobiologie, 1925,
Bd. 16, 133-155 S.
11. Siliņš, J. Latvijas zivis [Fishes of Latvia]. Jaunais zinātnieks, 1936., Nr.
37., 87 lpp.
12. Sloka, J. Akmens laikmeta lomi. Grām.: Dabas un vēstures kalendārs
1989. gadam. Rīga, 1988., 35. lpp.
13. Sloka, J. Apaļmutes – Cyclostomata. [Jawless fishes- Cyclostomata].
Zivis – Pisces [Fishes- Pisces]. Grām.: Latvijas dzīvnieku pasaule. Rīga,
1974., 87.-101. lpp.
14. Берг, Л. С. Рыбы пресных вод СССР и сопредельных стран
[Freshwater fishes of USSR and thouse neighbouring countries]. Часть.
3., М. – Л, 1949., c. 929-1382.
15. Богуцкая, Н. Г., Насека, А. М. Каталог бесчелюстных и рыб
пресных и солоноватых вод России с номенклатурными и
таксономическими комментариями [Catalogue of freshwatwer and
brackhishwater lampreys and fishes of Russia with commentaries on
nomenclature and taxsonomy]. Москва, 2004, 389 с.
16. Дирипаско, О. А. О поимке синца Abramis ballerus в Плявиньском
водохранилище (Бассейн Даугавы) [Capture of blue bream Abramis
ballerus in the reservoir Plavinas (the river Daugava)]. Вопросы
ихтиологии, 1988, т. 28, вып. 4., c.688-689.
17. Котов, Н. Д., Никанорова, Е. А., Никаноров, Ю. И.
Рыбохозяйственные исследования озер Латвийской ССР [Lakes
fishery reserch of the Latvian SSR]. Рыбное хозяйство внутренних
водоемов Латвийской ССР. Вып. 2. Рига, 1958, c. 259-292.
18. Лесненко, В.К. Псковские озера [The lakes of Pskov]. Л., 1988, 112
с.
19. Николаев, И. И. Видовой состав рыб Латвийской ССР [The species
composition of fishes of Latvia SSR]. Труды Латвийского отделения
ВНИРО. Вып. 1. Рига, 1953, c. 5-27.
20. Сапунов, А. Река Западная Двина [The river Daugava]. Витебск,
1893, 512.
Eriks Aleksejevs researcher of Inland waters
laboratory, Fish Resources Research Department,
Institute of Food safety, animal health and
environment BIOR since 2010. Eriks Aleksejevs
has been staff of institutes and agencies of Fisheries
research (BaltNIIRH (1985- 1990), LATFRI (1991-
2004) and LATFRA (2004- 2009)). The main
research is lake fishes and fisheries. He has
participated as a lake fish expert in 6 different local
projects as well as is author of 7 publications.
He has a biologist diploma (1985).
Address: Lejupes 3, LV- 1076, Riga, Latvia
Phone: +371 67612536
E-mail: eriks.aleksejevs@bior.gov.lv
Janis Birzaks, head of Inland waters laboratory,
Fish Resources Research Department, Institute of
Food safety, animal health and environment
"BIOR" since 2010. Janis Birzaks has been staff of
institutes and agencies of Fisheries research
(BaltNIIRH (1986- 1990), LATFRI (1991- 2004)
and LATFRA (2005- 2009)). The main research is
river fishes ecology with special interest of
migratory species. He has involved in International
Council for the Exploration of the Sea (ICES) since
1995 as member of working groups of Baltic
salmon (WGBAST) and eel (WGEEL), as well as
member of ICES Advisory committee (ACOM). Janis Birzaks is author of
about 30 publications.
He has a biologist diploma (1987).
Address: Lejupes 3, LV- 1076, Riga, Latvia
Phone: +371 67612536
E-mail: janis.birzaks@bior.gov.lv
Ēriks Aleksejevs, Jānis Birzaks. Ilglaicīgās izmaiņas Latvijas iekšējo ūdeņu ihtiofaunā
Rakstā analizēta un salīdzināta informācija par zivju izplatību un sastopamību no zinātniskām publikācijām, dienesta atskaitēm, "BIOR" datubāzēm par zvejas
statistiku un zivju mākslīgo pavairošanu, kā arī lauka pētījumos, kas veikti no 1990. gada līdz 2010. gadam par 1097 ezeriem, 435 upēm un 227 mākslīgām
ūdenskrātuvēm.
Salīdzinot arheoloģisko izrakumu datus ar 19.- 20.gs zinātniskajām publikācijām un lauka pētījumu datiem pēc 1990.g. iespējams konstatēt, ka dažu zivju sugu
izplatība un sastopamība dažādos periodos ir mainījusies, kas acīmredzot saistītas ar klimata maiņu. Dažu eiritermo zivju sugu, piemēram, zandarta, sama un
salates izplatība Latvijas iekšējos ūdeņos senāk bijusi daudz plašāka kā 19. un 20. gadsimtā, taču pašlaik tā atkal palielinās. Savukārt stenotermo zivju sugu repša
un ezera salakas populāciju skaits Latvijas ezeros ir samazinājies laikā no 1950. gadiem.
Būtiskāk ihtiofaunu ir ietekmējusi antropogēnā darbība 20 gadsimtā. Tās ietekmi nepārprotami iespējams konstatēt uz ceļotājzivīm un to izplatību Latvijas upēs.
Daugavas HES kaskādes celtniecība būtiski samazināja diadromo zivju sugu izplatību Latvijā. Mazajās un vidēja lieluma upēs ir vairāk kā 700 antropogēni
šķēršļi.
Dažu tipu ezeros ichthyofaunas struktūru formējošs faktors ilgtermiņā ir zivju bojā eja skābekļa dfeficīta rezultātā.
Sugu izplatību un sastopamību ietekmējuši arī tādi faktori kā ūdenstilpju hidromorfoloģiskā pārveidošana un ūdens kvalitātes pasliktināšanās.
Latvijas iekšējos ūdeņos laikā no 19. gadsimta beigām veikti 23 zivju sugu aklimatizācijas mēģinājumi. Pašatražojošās populācijas izveidojušas sudrabkarūsa
Carassius gibelio un rotans Percottus glenii. Mākslīgi izplatītas tādas zivju sugas, kā plaudis, zandarts, zutis, sams un alata.
Palede Alosa fallax un kaze Pelecus cultratus 20. gadsimta sākumā uzskatītas par retām. No 1990. gadiem to daudzumam Latvijas piekrastes un iekšējos ūdeņos
ir tendence pieaugt. Jūras nēģis Petromyzon marinus uzskatāms par sugu, kas ieklīst Latvijas ūdeņos.
No 2008. gada Latvijā konstatēta jauna zivju suga Ziemeļu zeltainais akmeņgrauzis Sabanejewia baltica, tā atradne Gaujas upē pašlaik ir tālākā zināmā ziemeļu
virzienā.
Jaunāko pētījumu par zivju izplatību rezultāti ļauj mainīt priekšstatus par tādu zivju sugu kā sapals, spidiļķis, ausleja, pl atgalve un pavīķe statusu Latvijas
iekšējos ūdeņos. Vēl 20. gadsimta 30. gados tās uzskatītas par relatīvi reti sastopamām sugām, to noteicis pētījumu trūkums, nevis reālā situācija dabā.

Scientific Journal of Riga Technical University
Environmental and Climate Technologies
DOI: 10.2478/v10145-011-0022-2 2011
_________________________________________________________________________________ Volume 7
18
Spare Abramis ballerus un Atlantijas store Acipenser sturio, bet pēc jaunākajiem zinātniskajiem datiem arī Amerikas Atlantijas store Acipenser oxyrinchus,
Latvijā acīmredzot ir izzudušas.
Saskaņā ar izmaiņām zivju nomenklatūrā nākotnē Latvijas ichthyofaunai varētu tikt pievienotas vairākas jaunas zivju sugas.
Эрик Алексеев, Янис Бирзакс. Долгосрочные изменения ихтиофауны внутренних вод Латвии
В статье проводится анализ и сравнение распространения и встречаемости видов рыб на основе данных из научных статей, служебных отчетов, баз
данных института БИОР о промысловом рыболовстве и зарыблении, а также данные полевых работ с 1990 по 2010 годы, в цeлом о 1097 озерах, 435
реках и 227 водохранилищах. Сравнивая данные археологических раскопок с результатами публикаций 19-20 веков и полевых исследований, можно
заключить, что долгосрочные изменения в распространении рыб во внутренных водах Латвии были связаны с изменчивостью климата.
Распространение эвритермных видов, таких как: сом, судак и жерех, ранее былo значительно шире, чем в XIX и XX столетиях. В наши дни ареал этих
видов вновь расширяется. В свою очередь, число популяция стэнотермных видов ряпушки и озерной корюшки сокращается после 1950-х годов.
Влияние антропогенных факторов увеличилось с ХХ века. Это особенно четко проявляется в распространении мигрирующих рыб. Так, строительство
каскада ГЭС на реке Даугава существенно уменьшило распространение диадромных видов рыб. В реках среднего размера и малых реках число
плотин превышает 700. Существенным фактором формирования видового состава сообществ рыб являются заморы рыб, происходящие под
воздействием как природных, так и антропогенных факторов. Существенно на распространение и встречаемость видов рыб повлияло
гидроморфологическое преобразование рек и ухудшение качества природных вод.
С конца XIX века в водоемах на территории Латви было сделаны попытки аклиматизаци порядка 23 выдов рыб. Самовоспроизводящиеся популяции
образовали серебряный карась Carassius gibelio и ротан Percottus glenii. Искусственно были распространены такие виды, как лещ, судак, сом, угорь и
хариус.
Встречаемость финты и чехони, считавшимися редкими в водах Латвии с начала ХХ века, особенно увеличилась, в прибрежных водах. Морская
минога является видом, случайно посещающим реки Латвии. В 2008 году в реке Гауя был обнаружен новый выд рыб для Латвии - балтийская
щиповка Sabanejewia baltica.
Результаты исследований последнего времени позволяют пересмотреть предыдущие представления о распространении и встречаемости таких видов
рыб, как голавль, горчак, верховка, бычок-подкаменщик и быстрянка. Ещё в 20- 30-х годах эти виды рыб рассматривались как относительно редкие,
однако, это было обусловлено отсутствием исследований, а не реальным положением в природе. Синца и Атлантического осетра, по новейшим
представлениям также Американского Атлантического осетра, надо считать исчезнувшими видами во внутренних водах Латвии.