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A risk analysis of sunfishes (Centrarchidae) and pygmy sunfishes (Elassomatidae) in The Netherlands


Abstract and Figures

The family Centrarchidae includes about 34 species, which all have their native range in North America. In the Netherlands the most ill famous member is Lepomis gibbosus. This in the Netherlands invasive species is the only member of the family with established populations. These populations can be found all over the Netherlands and the species seems to be still expanding. Its negative image is caused by its presence in many isolated water bodies where it has a strong negative impact on the fauna, including rare amphibians such as the common spadefoot (Pelobates fuscus) and the European tree frog (Hyla arborea). Because of this impact a wholesaler has decided stop selling this species in 2010. In this study it is shown that another nine species of Centrarchidae should be considered to be potentially invasive. They are all at least available for export in North America and have a high probability of establishment based on their thermal biology: A. rupestris, P. annularis, P. nigromaculatus, L. cyanellus, L. macrochirus, L. megalotis s.l. (L. megalotis s.s. & L. peltastes), M. dolomieu & M. salmoides. When considering possible climate change in the period 1990-2050 L. auritus should be included in this list. These species are all flexible in their habitat preferences and are likely to find suitable habitats in most regions in the Netherlands. With these centrarchids known to be good dispersers, it is likely that they will spread relatively easily after establishing reasonable populations. The family Elassomatidae, which is also reviewed as they might be a potential substitute for centrarchids in trade, is considered to be of no risk as they are unlikely to survive Dutch winters. Like L.gibbosus also other Centrarchidae are likely to affect ecosystems mainly by predation (amphibians, smaller fish species, damselflies, etc.) and competition with other predatory fish. Especially ecosystems, lacking comparable native predatory fish species prior to the establishment of such an exotic centrarchid, are susceptible to significant ecological impact. Centrarchidae have not been reported to be vectors for parasites or diseases of special concern. The establishment of larger centrarchid species will have a small, positive social and economic impact to commercial fisheries, the angling society and related business. When established, centrarchid populations can in most instances only be eradicated with rigorous measures like dewatering or the use of piscicides. Obviously, the prevention of entries and further spread reduces the need for such actions. The major components of prevention are banning of potential invasive species from trade and educating the public about the impact of centrarchids.
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D.M. Soes
S.J. Cooke
H.H. van Kleef
P.B. Broeckx
P. Veenvliet
A risk analysis of
sunfishes (Centrarchidae)
and pygmy sunfishes
(Elassomatidae) in the
A risk analysis of sunfishes (Centrarchidae) and pygmy sunfishes (Elassomatidae) in the
D.M. Soes
S.J. Cooke
H.H. van Kleef
P.B. Broeckx
P. Veenvliet
Commissioned by: Food and Consumer Product Safety Authority
21st of March 2010
Report nr 11-042
final report
Report nr.:
Date of publication:
21st of March 2011
A risk analysis of sunfis hes (Centrarchidae) and pygmy s unfishes
(Elassomatidae) in the Netherlands
ir. D.M. Soes
prof. dr. S.J. Cooke
dr. H.H. van Kleef
ir. P.B. Broeck x
P. Veenvli et
Number of pages incl. appendices:
Project nr :
Project ma nager:
Ir. D.M. Soes
Name & address client:
Food and Consumer Product Safety Authority, Invasive Alien
Species Team, P.O. Box 9102, 6700 HC, W ageninge n
Reference client:
Order bon nr/contract nr/letter nr/dd mmm 200x
Signed for public ation:
Manager Aquatic ecolgy
drs J. Spier
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work or other data obtained from Bureau Waardenburg bv; client indemnifi es Bureau Waardenburg bv against third-
party liability in re lation to these ap plications.
© Bureau Waardenburg bv / Food and Cons umer Product Safety Authori ty
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Several species of Centrarchidae are known to be invasive species of special
concern. The Elassomtidae have been mentioned to be an alternative for these
species. To gain insight into the occurrence of exotic centrarchid and elassomatid
species in the Netherlands, the possibility of them becoming invasive, the possible
ecological, economical and social impacts, and the possibilities of risk management
the Invasive Allien Species Team of the Food and Consumer Product Safety Authority
have commissioned Bureau Waardenburg to carry out a risk analysis.
This risk analysis was carried out by Bureau Waardenburg:
ir. D.M. Soes (project leader and report)
prof. dr. S.J. Cooke (report & review)
dr. H.H. van Kleef (report)
ir. P.B. Broeckx (report)
P. Veenvliet (report)
L. Anema (GIS)
From the Team of Invasieve Exoten of the Food and Consumer Product Safety
Authority the analysis was supervised by Mrs. dr. ir. Jo H. Vos and ir. J.W.
We would like to thank the following people for their effort and contribution: J.L. Spier
(Bureau Waardenburg), J. Klungers (specialist aquarology of subtropic fish species),
S. Fenoglio (Università del Piemonte Orientale, Italy), P. Keith (Muséum national
d¹Histoire Naturelle), J. Freyhof (Leibnitz Institute of Freshwater Ecology and Inland
Fisheries), G.H. Copp (CEFAS), R. Gozlan (Bournemouth University), E. Tricarico
(Università degli Studi di Firenze), E. Kruidenier (Naturalis), H. Verreycken (INBO), D.
P.J. van Heugten (De Kreeften en Garnalen shop), J. Bohlen (Academy of the
Sciences of the Czech Republic), RAVON, Sportvisserij Nederland,,
A. Ploeg (Dibevo), T. Demol (Service public de Wallonie) & A. Lamboj
We acknowledge that much of the material of chapter 5 is from a recent book on
centrarchid fish by Cooke & Philipp (2009) with particular reliance on the chapters that
focused on natural history accounts (Warren, 2009), winter biology (Suski & Ridgway,
2009) and organismal physiology (Kieffer & Cooke, 2009). We thank the authors for
giving permission for using these texts.
Table of contents
Table of contents.................................................................................................................................................5
Summary .............................................................................................................................................................7
1 Introduction .................................................................................................................................................9
2 Taxonomy and distribution..................................................................................................................... 11
2.1 Centrarchidae ............................................................................................................................ 11
2.2 Elassomatidae ........................................................................................................................... 22
3 General ecology ....................................................................................................................................... 25
3.1 Centrarchidae ............................................................................................................................. 25
3.2 Elassomatidae............................................................................................................................ 28
4 Chances of entry...................................................................................................................................... 31
4.1 Presence in Dutch pet trade...................................................................................................... 31
4.2 Presence in American trade...................................................................................................... 31
4.3 Aquaria ........................................................................................................................................ 32
4.4 Garden ponds............................................................................................................................. 35
4.5 Angling......................................................................................................................................... 37
4.6 Aquaculture.................................................................................................................................39
4.7 Entry from neighboring countries .............................................................................................. 40
5 The probability of establishment............................................................................................................. 45
5.1 Centrarchidae ............................................................................................................................. 45
5.2 Elassomatidae............................................................................................................................ 67
6 The probability of spread & endangered areas..................................................................................... 69
7 Impact........................................................................................................................................................ 71
7.1 Ecological impact........................................................................................................................ 71
7.2 Economic and social impact...................................................................................................... 74
7.3 Conclusions impact.................................................................................................................... 75
8 Risk identification conform the Fisk method.......................................................................................... 77
9 Risk Management .................................................................................................................................... 79
9.1 Prevention of entry and spread.................................................................................................79
9.2 Eradication and physical control methods ............................................................................... 83
10 Conclusions............................................................................................................................................ 87
11 Literature ................................................................................................................................................. 89
The family Centrarchidae includes about 34 species, which all have their native range
in North America. In the Netherlands the most ill famous member is Lepomis
gibbosus. This in the Netherlands invasive species is the only member of the family
with established populations. These populations can be found all over the Netherlands
and the species seems to be still expanding. Its negative image is caused by its
presence in many isolated water bodies where it has a strong negative impact on the
fauna, including rare amphibians such as the common spadefoot (Pelobates fuscus)
and the European tree frog (Hyla arborea). Because of this impact a wholesaler has
decided stop selling this species in 2010.
In this study it is shown that another nine species of Centrarchidae should be
considered to be potentially invasive. They are all at least available for export in North
America and have a high probability of establishment based on their thermal biology:
A. rupestris, P. annularis, P. nigromaculatus, L. cyanellus, L. macrochirus, L.
megalotis s.l. (L. megalotis s.s. & L. peltastes), M. dolomieu & M. salmoides. When
considering possible climate change in the period 1990-2050 L. auritus should be
included in this list. These species are all flexible in their habitat preferences and are
likely to find suitable habitats in most regions in the Netherlands. With these
centrarchids known to be good dispersers, it is likely that they will spread relatively
easily after establishing reasonable populations. The family Elassomatidae, which is
also reviewed as they might be a potential substitute for centrarchids in trade, is
considered to be of no risk as they are unlikely to survive Dutch winters.
Like L.gibbosus also other Centrarchidae are likely to affect ecosystems mainly by
predation (amphibians, smaller fish species, damselflies, etc.) and competition with
other predatory fish. Especially ecosystems, lacking comparable native predatory fish
species prior to the establishment of such an exotic centrarchid, are susceptible to
significant ecological impact. Centrarchidae have not been reported to be vectors for
parasites or diseases of special concern.
The establishment of larger centrarchid species will have a small, positive social and
economic impact to commercial fisheries, the angling society and related business.
When established, centrarchid populations can in most instances only be eradicated
with rigorous measures like dewatering or the use of piscicides. Obviously, the
prevention of entries and further spread reduces the need for such actions. The major
components of prevention are banning of potential invasive species from trade and
educating the public about the impact of centrarchids.
1 Introduction
The pumpkinseed (Lepomis gibbosus) originates from North America. Since the late
late 19th century this species has been introduced and proven to be invasive in many
countries in Europe, including the Netherlands. Also the largemouth bass (Micropterus
salmoides), another member of the Centrarchidae is invasive in Europe, but this
species has not arrived in the Netherlands yet. Furthermore several other members of
both the families Centrarchidae and Elassomatidae are also considered to be potential
invasive species in Europe. As at least Centrarchidae have the potential to cause
serious ecological, economic and social impacts, they therefore can interfere with the
goals of various European Directives such as the Water Framework Directive (WFD)
and the Habitat Directive (Nature 2000).
In this study, commissioned by the Invasive Alien Species Team of the Food and
Consumer Product Safety Authority, a risk analysis was undertaken to provide more
insight into the present distribution of Centrarchidae and Elassomatidae, their
(potential) impacts, the probability of entry (introduction pathways), the probability of
establishment, the probability of further spread and endangered areas. Subsequently,
measures are identified to prevent further spread of these species and eradication and
physical control methods are described that can be used to reduce the number of
especially L. gibbosus in The Netherlands.
Figure 1.1: Micropterus salmoides.
2 Taxonomy and distribution
2.1 Centrarchidae
2.1.1 Taxonomy
The Centrarchidae is a family of fishes belonging to the order Perciformes, which is
endemic to North America. In total 32-34 species are included in the Centrarchidae,
depending on the bibliographic source. The differences between the lists of with 32 species and the list of Near & Koppelman (2009) with 34 species
are due to the two species which were formerly considered to be subspecies of
respectively L. megalotis and M. punctulatus: L. peltastes and M. henshalli (Baker et
al., 2008; Bailey et al., 2004). It is expected that several additional centrarchid species
are likely to be identified after further research using molecular techniques (Near &
Koppelman, 2009), especialy in polymorhic taxa like L. megalotis and L. macrochirus.
Hybridization is common among centrarchid fishes and is known from the genera
Lepomis and Micropterus. This makes the task of identifying species that have already
proven to be difficult to identify almost impossible. An example are the basses.
Especially M. salmoides and M. floridanus are difficult to seperate without the aid of
molecular methods. Because of this, it is actually unclear what species status should
be assigned to European populations of these species. After molecular work it might
become clear that some populations are actually M. floridanus or hybrids instead of
pure M. salmoides populations as now commonly assumed.
Figure 2.1: Spanish bass: M. salmoides, M. floridanus or a hybrid? Photo by
Table 2.1: List of known extant centrarchid species. Based on Fishbase, Near &
Koppelman (2009) and several Dutch publications.
Acantharchus pomotis (Baird 1855)
Mud sunfish
Ambloplites ariommus (Viosca 1936)
Shadow bass
Ambloplites cavifrons Cope 1868
Roanoke bass
Ambloplites constellatus Cashner & Suttkus 1977
Ozark bass
Ambloplites rupestris (Rafinesque 1817)
Rock bass
Archoplites interruptus (Girard 1854)
Sacramento perch
Centrarchus macropterus (Lacepède 1801)
pauwoogzonneba ars
Enneacanthus chaetodon (Baird 1855)
Blackbanded sunfish
Enneacanthus gloriosus (Holbrook 1855)
Bluespotted sunfish
diamantb aars
Enneacanthus obesus (Girard 1854)
Banded su nfish
diamantb aars
Lepomis auritus (L. 1785)
Redbreast sunfish
Lepomis cyanellus Rafinesque 1819
Green sunfish
groene zonnebaa rs
Lepomis gibbosus (L. 1785)
Lepomis gulosus (Cuvier 1829)
Lepomis humilis (Girard 1858)
Orangespotted sunfish
Lepomis macrochirus Rafinesque 1819
Lepomis marginatus (Holbrook 1855)
Dollar sunfish
Lepomis megalotis (Rafinesque 1820)
Southern longear
langoorzo nnebaars
Lepomis microlophus (Günther 1859)
Redear sunfish
Lepomis miniatus Jordan 1877
Redspotted sunfish
Lepomis peltastes Cope 1870
Northern longear sunfish
Lepomis punctatus Valenciennes 1831
Spotted sunfish
Lepomis symmetricus Forbes 1883
Bantam sunfish
Micropterus cataractae Williams & Burgess 1999
Shoal bass
Micropterus coosae Hubbs & Bailey 1940
Redeye bass
Micropterus dolomieu Lacepède 1802
Smallmouth bass
zwartbaars/ zwarte baars
Micropterus floridanus (LeSueur 1822)
Florida bass
Micropterus henshalli Hubbs & Bailey 1940
Alabama bass
Micropterus notius Bailey & Hubbs 1949
Suwannee bass
Micropterus punctulatus (Rafinesque 1819)
Spotted bass
Micropterus salmoides (Lacepède 1802)
Largemouth black bass
Micropterus treculii (Vaillant & Boco urt 1874)
Guadalupe bass
Pomoxis annularis Rafinesque 1818
White crappie
witte zilverbaars
Pomoxis nigromaculatus (Lesueur 1829)
Black crappie
zwarte zilverbaars
2.1.2 Description
Centrarchidae are perch-like fish which are characterised by a double dorsal fin. The
first part consists of strong spines while the second part has branched, soft fin rays. In
a few species these parts are separate fins or only on the basis connected. Two main
groups can be distinguished within Centrarchidae: relatively small species with a deep
body shape and large, more streamlined species. The smaller species have a small
mouth and predate on invertebrates, amphibian larvae and larval fish while the large
species have a large mouth and actively pursue middle sized fishes.
Figure 2.2: The deep bodied L. macrochirus and the elongated M. punctulatus.
2.1.3 Native range
The Centrarchidae are native to the area east of the Rocky Mountains from southern
Canada to northern Mexico. Only one species, A. interruptus, occurs west of the
Rocky Mountains in California. The range of fossil centrarchids is more extensive,
including Alaska and southern Mexico (Berra, 2007). Most species are subtropical in
their range with only a few species having northern ranges up into Canada.
Figure 2.3: Natural range of the family Centrarchidae in North America.
2.1.4 Introductions
Within North America several centrarchid species have been introduced outside their
natural range. M. salmoides and L. macrochirus have been widely and successfully
translocated to many states in the USA, provinces in Canada and to numerous
localities in Mexico. They also have been introduced to many other countries
worldwide. Tabel 2.2 based on Lever (1996) gives an overview of successfully
reported introductions that resulted in established populations. Although the data
include erroneous records, e.g. M. dolomieu records in Europe, this overview gives an
impression which species have been exported in what extent. Evidently one species
stands out: M. salmoides. With more than fifty countries with reported successful
introductions, this species is in the top five of most introduced fish species worldwide.
Other species that have been repeatedly been introduced are L. cyanellus, L.
gibbosus, L. macrochirus and M. dolomieu. Other Centrarchid species have been
introduced outside their natural range only occasionally.
Table 2.2: Naturalized populations of Centrarchidae worldwide. Based on Lever, 1996.
Ambloplites rupestris
Lepomis auritus
Lepomis cyanellus
Lepomis gibbosus
Lepomis gulosus
Lepomis macrochirus
Lepomis microlophus
Micropterus coosae
Micropterus dolomieu
Micropterus punctulatus
Micropterus salmoides
Pomoxis annularis
Pomoxis nigromaculatus
Six species of Centrarchidae are reported to have been introduced in European
waters, of which probably only three have established populations that persist until
now (Kottelat & Freyhof, 2007; J. Freyhof, pers. com.). The first imports for these
introductions are early in date with the first trials already from 1877, and most species
were already imported before 1900 (Table 2.3). Some of the stocked species, such as
L. gibbosus and A. rupestris, are remarkable because of their small body size, which
makes them uninteresting for human consumption or angling. In general the first
introductions of exotic fish species around 1900 had the purpose to improve
commercial fish stocks (Van Drimmelen, 1987). Most likely, the stocking of smaller
species was more out of scientific interest and realising the possible drawbacks. In
fish farms these smaller species were cultured for aquaristic purpossess only.
Table 2.3: Some first imports of centrarchid species in Europe. Based on Stansch
(1914), Nijssen & De Groot (1987). Per species the year of the first import, the person
of the first import, the destination and the purpose of the import are given.
Ambloplites rupestris*
Von Begg
aquacult ure/stocking
Centrarchus macropterus
O. Preuße
Enneacanthus gloriosus
P. Nitsche & P. Matte
Lepomis auritus*
Max von dem Borne
aquacult ure/stocking/
Lepomis cyanellus*
H. Stüve
Lepomis gibbosus*
Max von dem Borne
Lepomis gibbosus*
Von Begg
aquacult ure/stocking/
Lepomis gibbosus*
Max von dem Borne
aquacult ure/stocking/
Lepomis megalotis
P. Matte
Mesogonistius chaetodon
W. Geyer
Micropterus dolomieu*
Max von dem Borne
aquacult ure/stocking
Micropterus salmoides*
Marquis of Exeter
Micropterus salmoides*
Max von dem Borne
aquacult ure/stocking
Pomoxis nigromaculatus
aquacult ure/stocking
Pomoxis sparoides
Max von dem Borne
aquacult ure/stocking
* Species reported to be introduced in European waters.
The six species reported to have been introduced in European waters are discussed
per species in the following paragraphs.
Ambloplites rupestris
Currently the only existing population of A. rupestris known in Europe is located in
France. This population is present in the Loire River, east of where the Allier River
joins this river (fig. 2.4). It is a result of stocking between 1904-1910, so it has been in
existence for around one hundred years (Keith & Allardi, 2001). In total this population
exists throughout one hundred kilometres of river, but it is thought not to have actually
expanded much in the period 2000-2010. Why its territoy has not expanded is not
known (P. Keith, pers. com.).
Figure 2.4: The distribution of Ambloplites rupestris in France with data upto 2010.
Provided by P. Keith, Muséum national d¹Histoire Naturelle.
In England a population of A. rupestris has been present for more then 25 years. This
population was present in an artificial lake (said to be a former gravel pit) of about 1.2
hectares near Oxford. The first specimen was caught in July 1937 by an angler who
subsequently collected a number of smaller specimens in the same water, proving
that this was an established, breeding population at that date. The first specimen is in
the British Museum (Natural History) together with further collected specimens in
1956. The 1956 specimens were received from Mr D. F. Leney who wrote that the
pond was teeming with ‘bass’ but few exceeding 15 or 18 centimeters. Enquiries
made at the time, produced no record of the history of this introduction. This
population was still in existence in the 1960s (Wheeler & Maitland, 1973). Currently
this population is thought to be extinct (Copp et al., 2007; G.H. Copp, pers. com.; R.
Gozlan, pers. com.).
Lepomis auritus
L. auritus has not become a great succes in aquaristics. With the exception of reports
from Italy not much is heard from this species after the first imports. Maitland (1977)
listed this species as occuring in Italy and describes the surroundings of Rome as its
range. This is confusing as the only documented reports of this species are from Lago
di Varano and Lago di Monate (Besana, 1908), both at considerable distance from
Rome. Besana (1908) describes in his paper the result of his stockings of this species,
which he calls ‘sunfish Lepomis auritus’, in these two lakes. Especially from Lago di
Varano he reports a success with a total catch in 1907 of almost 13,000 kilograms.
Remarkably no subsequent reports of this species are known, which is suprising with
the great success according to Besana (1908). A recent review of the exotic fishes in
Italy does not list L. auritus (Gherardi et al., 2008) and Fenoglio et al. (2010) actually
suggest that Besana (2008) misidentified the ‘sunfish’ and that he actually introduced
L. gibbosus. More likely is confusion with an older name for L. gibbosus: Eupomotus
aureus. The second part is a bit similar with auritus. Another illustration of the
confusion about the Italian Lepomis are two samples in the collection of Naturalis
(15001, Florence, 6-9-1934 & 15002, Rome, 8-9-1934) named Apomotis punctatus.
This is an old, hardly used name for L. punctatus. Both samples are actually L.
gibbosus (D.M. Soes, pers. observ.). Overall there has been a lot of confusion about
the identity of the Lepomis introduced in Italy and it is highly uncertain that L. auritus
has actually been established in the past in Italy and clearly there are no recent
records (E. Tricarico, pers. com; S. Fenoglio, pers. com.).
Figure 2.5: L. auritus (left) and L. gibbosus (right) probably confused in Italy.
Lepomis cyanellus
Regulary this species is reported to have been introduced in the surroundings of
Frankfurt (Germany). These stockings supposedly resulted in established populations
in this area (Maitland 1977). This is contradicting the statement of Sterba (1959) that it
had vanished from Europe. According to Lelek (in Arnold, 1990) no proof for the
occurrence of L. cyanellus is present and he noted that L. gibbosus is very common
around Frankfurt. For L. auritus and L. cyanellus there is no conclusive evidence for
established populations in Europe and clearly no established populations are present
in Germany nowadays (J. Freyhof, pers. com.).
Lepomis gibbosus
Often the import in 1881 by Max von dem Borne is considered the onset of the
settlement of L. gibbosus in Europe, but actually there have been several shipments
from North America that are likely to have been involved in the settlement of L.
gibbosus in Europe. Such imports are e.g. known from France (1885), Germany
(1881), Czechoslovakia (late 19th century), Italy (between 1880-1920) and Spain
(between 1910-1913) (Lever, 1996). Other European countries, like the Netherlands,
received first shipments from European countries.
After the first imports it became quickly established in e.g. France, South England and
Italy, and has actually become one of the most successful exotic fish species with
populations in almost every European country (Tomecek et al., 2007). Not only its
biological characteristics have made this species so successful, also the diversity in
vectors has probably played a role. Its first releases might have been for angling
purposes, for serving as a food item for M. salmoides or just scientific curiosity. More
recent releases are mainly associated with aquaristics, garden ponds and even its use
as a bait-fish in especially the Iberian Peninsula (Tomecek et al., 2007).
Micropterus dolomieu
M. dolomieu is reported to be released in numerous countries, but in many instances
its identification is doubtful. Introductions of young fish believed to be M. dolomieu
were in fact M. salmoides (this is also the case in the US, where some M. dolomieu
introductions mentioned in the literature were later believed to have been M.
salmoides), and similarly, some supposed M. salmoides introductions (from German
suppliers) were probably pikeperch (Sander lucioperca), because the former was
never found but S. lucioperca was later found established in these waters. The
problem with much of the old literature was that in general only the proper taxonomists
were reliable sources and other persons were not very good in their identifications of
Micropterus-species (G. Copp, pers. comm.). Some more reliable reports of releases
in the beginning of the 19th century, like e.g. in several English lakes and lakes in Italy
and Germany, never resulted in self sustaining populations (Vooren, 1972; Wheeler &
Maitland, 1973; Arnold, 1990). Currently this species is thought to be absent from
Europe (Kottelat & Frey hof, 2007).
Figure 2.6: M. dolomieu (left) and M. salmoides (right) probably often confused in
Micropterus salmoides
The first import of M. salmoides in Europe is an attempt of the Marquis of Exeter in
1879. Several specimens obtained in the USA were unsuccesfully stocked in 1881 or
1882 in Loch Baa, Scotland. After the import of M. salmoides in 1883 by Max von dem
Borne the species has been successfully cultured in Germany. The developed stock
has been used to introduce this species in waters in several European countries
(Lever, 1996). The first introductions of this species in England, Scotland, Germany
and the Netherlands have been unsuccessful in producing selfsustaining populations
in the long run (Kottelat & Freyhof, 2007). In England, populations have been present
for some time in clay pits, gravel pits and similar watertypes, but all have failed to
persist (Lever, 1996).
Introductions in Southern Europe have been much more successful. Nowadays this
species is widely naturalized in the Mediterranean region: Portugal, Spain, southern
France, Italy, Switzerland (Ticino) and the Adriatic basin from Slovenia to Albania.
Naturalized populations are also known from the Slovenian Danube drainage and the
lakes of Carynthia (Austria) (Kottelat & Freyhof, 2007).
The Netherlands
Centrarchids have been rare in Dutch aquaculture. M. dolomieu is reported to have
been imported (Mulier, 1900), but this hasn’t resulted in a successful culture or
stocking program (Nijssen & De Groot, 1987). Reports of successful introductions of
M. dolomieu (Vooren, 1972) are considered to be erroneous and a possible result of
confusion with M. salmoides (Nijssen & De Groot, 1987). This latter species, which is
not listed for the Netherlands by Vooren (1972), has actually been present in Dutch
aquaculture and has also been released in Dutch waters.
“Zwarte baars”
Probably some of the confusion about the
presence M. dolomieu in the Netherlands
originates from the use of the name “zwarte
baars”. This Dutch name is both used for M.
dolomieu and stunted European perch (Perca
fluviatilis) populations. Such populations are found
in densely vegetated waters with high fish
densities. In the Dutch peat district these “zwarte
baarzen” are common (Looijen, 1948). Photo: Ron
Micropterus salmoides
The first trial to import M. salmoides from America already took place in 1884. But this
order by Artis didn’t survive the shipment across the ocean. A few years later another
shipment was more successful and five specimens arrived in Artis Zoo. Successive
attempts to breed them were not very successful and no introductions seem to have
been attempted by Artis (Nijssen & De Groot, 1987). In the 1920s experimental
stockings have been undertaken in a single small fishing lake. The location of this lake
is not clear as it is not reported. The stocked M. salmoides were able to reproduce
well, creating a well noticed high density (Anonymous, 1930). The fish farm in Gulpen
seems to have been involved because in the collection of Naturalis a single M.
salmoides specimen (RMNH.PISC.36087) is present labeled: Gulpen, 25-2-1927. This
specimen was before part of a small RIVO collection.
Figure 2.7: The fish farm of Gulpen in 1943 (photo: and
the Micropterus salmoides specimen present in the collection of Naturalis (photo: E.
The experiment in 1920s with M. salmoides was treated remarkably critical
(Anonymous, 1930). Its quality as a game fish was questioned and it is thought to
have reduced populations of much appreciated course fishes to an extent that it was
needed to restock these course fishes. The article ends with a general warning about
the introduction of exotic fish species: Vóór alles dient men de zekerheid te hebben
dat hetgeen men plant geen onkruid is, dat gelijk de forelbaars en meer dergelijke
vraatzuchtige en waardeloze producten een ware plaag wordt voor degenen, die er
mede wordt opgescheept”.
M. salmoides is known from a single recent record. This specimen, caught in 2005 by
an angler in the River Waal near Nijmegen, was only published in ‘Beet’, a magazine
for anglers (Ahlen, 2005). As this species is not stocked recently in the Netherlands
this specimen probably originated from outside the Netherlands, see also chapter 4.
Figure 2.8: The Micropterus salmoides specimen ( 60 cm) caught in the River Waal
near Nijmegen, the Netherlands. Photo by R. Ahlen.
Lepomis gibbosus
In 1902 L. gibbosus arrived for the first time in the Netherlands in the fish farm in
Vaassen. It reproduced easily, but its qualities for consumption or angling were
considered insufficient to start a stocking program. L. gibbosus has never been
officially stocked and only kept in culture for ornamental purposes. From its first import
it has been present continuously in Dutch fish farms until today (Looijen, 1948), see
also chapter 4.
Its first releases or escapes have been badly recorded and the first establishments are
rather speculative. In the 1920s L. gibbosus was present in the fish farm of
Valkenswaard in the south of the Netherlands (Iven & Van Gerwen, 1974). The used
ponds were not isolated well from the Tongelreep, a stream running through the fish
farm. This is illustrated by the unwanted colonization of these ponds by European
perch, which was abundant in the Tongelreep (Iven & Van Gerwen, 1974). Escapes
from this farm might have resulted in the population in the Dommel drainage in the
province Brabant which is mentioned by Ruting (1958).
L. gibbosus is nowadays a rather widespread species in the Netherlands (fig. 2.9). It is
present in all provinces, including the province of Drenthe. Records from this province
are lacking in fig. 2.9, but this species has actually been recorded from this province,
although with hardly any established populations (Brouwer et al., 2008). Also in the
provinces of Friesland, Groningen, Overijssel, Flevoland and Zeeland L. gibbosus is
not very common, occurring mostly in isolated locations. The species is more common
around Amsterdam, in the provinces Brabant and Limburg and in the eastern parts of
the province of Gelderland. Remarkable are the records on the Wadden Islands
Terschelling (Meisterplak) and Schiermonnikoog. These records show clearly the
extent of the introduction of this species by humans in the Netherlands.
Figure 2.9: The distribution of Lepomis gibbosus in the Netherlands, Based on data
provided by, RAVON and Limnodata.
2.2 Elassomatidae
2.2.1 Taxonomy
The Elassomatidae form a small family
consisting of only seven species (table 2.4),
which are all placed within one genus
(Elassoma). The group has been thought to
be closely related to Centrarchidae and was
placed within this family for some time as a
subfamily (Elassominae). Although they
superficially resemble small individuals of
the family Centrarchids the have been,
particularly since 1962, regarded as a
separate family (Gilbert, 2004). Increasing
evidence has even suggested that they are not even closely related to the
Centrarchidae and might even be a sister group of the Gasterosteiformes (Roe et al.,
2002; Wiley et al., 2000; Gilbert, 2004). Currently they are placed in their own order
(Elassomatiformes) which is still considered to be incertae sedis, meaning of uncertain
taxonomy (
Table 2.4: List of the species of Elassomatidae. Given are the scientific name, the
English common name and the Dutch common name. Based on Gilbert (2004),
Snelson et al. (2009) and
Elassoma alabamae Mayden 1993
Spring pygmy sunfish
Elassoma boehlkei Rohde & Arndt 1987
Carolina pygmy sunfish
Elassoma evergladei Jordan 1884
Everglades pygmy sunfish
Elassoma gilberti Snelson Jr, Kr abbenhoft
& Quattro 2009
Pygmy sunfish
Elassoma okatie Rohde & Ar ndt 1987
Bluebarred pygmy sunfish
Elassoma okefenokee Böhlke 195 6
Okefenokee pygmy
Elassoma zonatum Jordan 1877
Banded pygmy sunfish
2.2.2 Description
The Elassoma-species are small with maximum lengths up to 45 millimeters. The
body is shallow and laterally compressed with a terminal mouth. The lateral line is
absent. Males and females exhibit substantially different color patterns. This is
especially explicit during the breeding season. The males of several species have the
vivid colors which make them popular with specialized aquarists.
Fig 2.10: Elassoma okefenokee
Figure 2.11: Elassoma okefenokee male (left) and female (right). Photos by Jörg
2.2.3 Native range
Elassomatidae are mainly subtropical family restricted to the south-eastern parts of
the United States. Two of the species are relatively widespread, the other five have
restricted ranges. E. zonatum is the most widespread species with a distribution
basically equal to that of the genus as a whole. The, also relatively common, E.
evergladei occurs on the Atlantic and Gulf coastal plain from North Carolina south to
the northern edge of the Everglades. The other species are more localized, with E.
alabamae the most confined, occurring only in Moss Spring and some adjacent
springs in the middle Tennessee River drainage in Alabama (Berra, 2007).
Figure 2.12: Natural range of the family Elassomatidae in North America.
2.2.4 Introductions
None of the species belonging to the family Elassomatidae is known to be introduced
outside its natural range (Welcomme, 1988;, except for an introduction
of E. evergladei in an artificial warm water stream in Germany. This introduction took
place in the Ore Mountains (Erzgebirge) near Chemnitz (Karl-Marx-Stadt). The
individuals released by aquarianists were able to maintain a small population for some
years, but this population had gone extinct by 1988 (Arnold, 1990).
3 General ecology
3.1 Centrarchidae
3.1.1 Reproduction
The reproductive behavior of the Centrarchidae has been well studied and is similar in
most species. Males excavate a shallow, bowl-shaped depression in the gravel or
sand by fanning vigorously with the caudal tail from a near vertical position. Spawning
occurs in mid-spring to early summer and involves a ritual courtship. A male and a
female may circle over the nest with their heads and ventral surfaces touching, and
eventually the female swoops down to the nest on her side and releases the eggs.
The male follows and fertilizes the eggs. Several females might spawn in the same
nest. The males will then proceed to guard the nests until the offspring leaves the nest
(Berra, 2007).
In addition to the territorial, large males that builds and defends the nests, smaller
males, called ‘sneakers’ may dart in and try to fertilize eggs as well, and intermediate-
sized males in female colours may gain admission to a nest by posing as a receptive
female (Neff et al., 2003).
3.1.2 Habitat
The members of the Centrarchidae occupy the shallows of warm, rocky, and
vegetated lakes, ponds, slow moving streams, back waters, swamps and other
standing or slowly flowing waters. Fast flowing streams and rivers are generally
avoided, and when they are found within this habitat they are found in slow moving
parts. Within this range of habitats most species are rather flexible and found in
several types of habitats. L. gibbosus for instance can be found in small lakes, ponds,
shallow, weedy bays of larger lakes, and in the quiet water of slow-moving streams
(Scott & Crossman, 1973).
3.1.3 Diet
Centrarchids are predatory fish that do not include plant material and detritus in their
diets. Four main types of predators can be recognized (Collar & Wainwright, 2009):
Piscivores/crayfish predators: Typical examples are members of the genus
Micropterus and L. gulosus. These species have relatively shallow bodies and
large mouths. Most species forage in the open water, with some being
specialized to hunt in densely vegetated areas (e.g. L. gulosus).
Zooplanktivores: Rare amongst Centrarchids in the adult stage and best
represented by L. macrochirus. This species is small-mouthed and has a
deep body. In the day it can feed heavily on zooplankton in the open water or
in vegetated areas.
Molluscivores: L. gibbosus and L. microlophus are the two Centrarchid species
which have specializations for predating mollusks. In body shape and the size
of the mouth gape they resemble L. macrochirus, but their pharyngeal jaws
have been strengthened to allow them to crush molluscs.
Generalist invertivores: These species tend to have intermediate values for
body depth, mouth size and robustness of the pharyngeal jaws. This is actual
a rather variable group that feeds mainly on smaller invertebrates that can be
amongst vegetation, on the bottom or at the water surface.
All Centrarchid species are opportunistic and rather flexible in their diet. This flexibility
is well presented by L. gibbosus. The actual diet of this species varies seasonally and
is highly associated with the abundance of local macroinvertebrates (Tomecek et al.,
2007). Adult L. gibbosus are able to feed heavily on molluscs that they crush between
their pharyngeal jaws (fig. 3.1) (Wainwright et al., 1991). This includes the in the
Netherlands highly invasive Dreissena-species (Tomecek et al., 2007). The
development of the muscles and bones of these pharyngeal jaws is depended on the
mollusk density which is represented by the numbers of molluscs in diets of L.
gibbosus. In mollusk rich habitats robust pharyngeal jaws will be build. In mollusk poor
habitats they will happily feed on other invertebrate prey and develop less
hypertrophied pharyngeal jaws (Wainwright et al., 1991; Almeida, 2009).
Figure 3.1: Illustrations of the snail-crushing mechanism in the pumpkinseed sunfish.
Taken from Wainwright et al. (1991).
The diet of especially the larger Centrarchids changes during their development. In
e.g. M. salmoides the small young of the year (YOY) feed first on zooplankton,
typically shifting to insects and other smaller invertebrates as they grow and then to
crayfish and fish. The shift to crayfish and fish usually begins at 50-70 millimeters
standard length and in general bass are almost exclusively piscivores at 80-100
millimeters standard length. In some instances M. salmoides predates mainly on
larger invertebrates at larger sizes, especially when crustaceans such as shrimps and
crayfish are abundant (García-Berthou, 2002).
3.1.4 Predators
With the Centrarchids being variable in size and habitat use, they meet with a wide
range of predators, ranging from predaceous water insects, piscivorous fishes,
piscivorous waterbirds to aquatic mammals. In large piscivorous Centrarchids, such
as Micropterus-species, cannibalism is also likely to play a role. In Europe pike (Esox
lucius), zander (Sander luciopercus), European catfish (Silurus glanis) and several
species of piscivorous waterbirds are probably the most important predators (Arnold,
Figure 3.2: Pike (Esox lucius) and Perch (Perca fluviatilis) predate on L. gibbosus.
Photos: Hans Waardenburg & Floris Brekelmans
3.1.5 Parasites and diseases
Centrarchidae are known to harbor a great diversity of parasites. From well studied
species like M. salmoides and L. gibbosus more than 150 species of parasites per
species have been recorded. This includes the whole range of usual groups of fish
parasites like e.g. protozoan’s, trematodes, cestods, acanthocephalans, leeches and
crustaceans (Hoffman, 1999).
One of the most important diseases recorded from Centrarchidae is the largemouth
bass virus (LMBV). This is the only virus to have been associated with large fish kills
of M. salmoides. While LMBV has been isolated from a number of other species of
warm-water fishes, the disease response has only been observed in largemouth bass
(Cooke et al., 2009;
3.2 Elassomatidae
3.2.1 Life cycle
In suitable conditions Elassoma-species mature quickly and can reproduce at an age
of three to four months (Arnold, 1990). Based on experiences in aquaria they may
reach an age of four to five years (Fischarten-Datenblätter Aqua4you, 2010), although
for at least E. okefenokee it is thought that they usually live only up to one year (Tate
& Walsh, 2005)
3.2.2 Reproduction
The starting and length of the breeding season seems to be rather variable amongst
the different Elassoma-species. E. alabamae seems to breed almost throughout the
year, with larvae being recorded from April to September (Center for biological
diversity, 2009). Comparable data are known from E. evergladei (Fischarten-
Datenblätter Aqua4you, 2010). A population of E. okefenokee in Florida, on the other
hand, behaved like an annual species, with breeding adults only found from late
January through mid-March. After mid-March adults were absent from conducted
samplings (Tate & Walsh, 2005).
Males defend territories including suitable egg laying substrates, e.g. Myriophyllum sp.
or aquatic mosses. When receptive females approach a territory a complicated ritual
involving fin undulation, weaving, vertical bobbing, and dashing is performed. After
this courtship, which is among the most complex behaviour described for fishes, the
female will deposit her 30-120 eggs in dense, fine-leaved vegetation and cover it with
a protective gelatinous mass. The eggs and earliest larvae stages will be guarded by
the male (Center for biological diversity, 2009; Tate & Walsh, 2005; Bohlen & Nolte,
3.2.3 Habitat
All Elassoma-species are mainly found in slow flowing and stagnant waters with
dense submersed vegetations. Typical habitats are heavily vegetated swamps,
ditches, stream pools, and sluggish streams with a muddy bottom. Most species
prefer soft, tannic waters and avoid hard-water streams (Center for biological diversity,
2009; Bohlen & Nolte, 1993).
3.2.4 Diet
The Elassoma-species are stalking predators of mainly invertebrates, using dense
vegetation to conceal their activities. They are not cannibalistic and are not known to
regularly predate on fish or amphibian larvae. Plant material is not an important food
item, and might normally actually be ingested accidentally.
Typical prey items are cladocerans, copepods, amphipods, isopods, ostracods,
dipteran larvae, and snails. Especially daphnids and other cladocerans are regular
prey items of all Elassoma-species and comprise usually 25-30% of the volumetric
consumption (Center for biological diversity, 2009; Tate & Walsh, 2005).
3.2.5 Predators
The main predators of Elassoma-species are large predatory insects like giant water
bugs (Belostomatidae), piscivorous fish species like pickerels (Esox) or larger
Centrarchids, birds like herons and kingfishers, and aquatic mammals like otters
(Center for biological diversity, 2009; Tate & Walsh, 2005).
3.2.6 Parasites and diseases
With Elassomatidae not being cultured or of importance in fisheries relatively little
information on their parasites and diseases is present. Some parasites are reported
including three species of monogeneans which are only known from Elassoma-
species (Urocleidus circumcirrus, U. udicola and Gyrodactylus heterodactylus). Two
species of nematods are known, both cosmopolitans. E. zonatum is reported as a final
host for the trematod Rhipidocotyle septpapillata, a North American species with a
wide range of hosts. Another four species have been reported from Elassoma-species
in juvenile stages: Caecincola latostoma, Cryptogonimus spinovum,
Posthodiplostomum minimum and Textrema hopkinsi. All four are mainly known from
Centrarchidae (Hoffman, 1999).
4 Chances of entry
4.1 Presence in Dutch pet trade
4.1.1 Centrarchidae
Information on the presence of Centrarchidae in the Dutch pet trade has been
collected by consulting three wholesalers in ornamental fish, visiting pet shops and
checking numerous internet resources such as forums and websites associated with
pet shops and hobbyists.
Only L. gibbosus is sold regularly and is available in most larger shops dealing in
ornamental fish for garden ponds. According to wholesalers the numbers sold are
rather low in comparison to other species such as goldfish and koi. Actual numbers
could not be obtained. Other species encountered in pet shops are E. gloriosus, E.
chaetodon, C. macropterus, L. cyanellus and M. salmoides. All these species are
currently rare in trade and probably only imported incidentally.
In 2010 one wholesaler announced that they stop distributing L. gibbosus because of
the reported impact of this species on native species, particularly amphibians, see
also §10.1. It is not unlikely that other wholesalers may follow as this species is
actually not considered to be of high economic value. To what extent wholesalers
might search for alternatives (e.g. other Centrarchids) remains unclear.
4.1.2 Elassomatidae
So far all species of Elassomatidae have been very rare in the Dutch pet trade, but
one wholesaler expressed intentions of increasing the import from the USA in 2011.
4.2 Presence in American trade
Recent introductions of virile crayfish (Orconectus virilis), white river crayfish
(Procambarus acutus/zonangulus) and Chinese mystery snail (Bellamya chinensis)
showed that presence in European trade is not a good predictor for the chances of
entry of North-American species (Soes & Koese, 2011; Soes et al., 2011). All
mentioned species have established populations in the Netherlands but could not be
directly traced in the Dutch pet trade. These North American species have probably
only been imported on an experimental basis. Knowledge on the availability of such
species in American trade is likely to be a more reliable source of information. In
addition to species available for aquaria or garden ponds, species cultured for
consumption or angling (e.g. bait) should be included in risk assessments.
We present a list of all 34 species of centrarchid fishes using the Latin Binomial.
Relative rarity is a subjective measure of the population size and distribution of each
species in North America. “Rare” denotes a restricted range and relatively low
population size. If present in Europe, distribution is also noted. North American export
serves as an indication of the relative ease with which Dutch citizens could obtain
centrarchids. Based on the relative rarity, distribution in Europe and availability for
export from North America we have identified species that will be included in the
report for further discussion related to the potential for introduction in the Netherlands.
Table 4.1: Potential threat to introduction of the 34 species of Centrarchidae. The
rarity in their natural range, their presence in Europe and their availability in American
trade are given.
Latin Binomial
Rarity in
Present in
North American
Export (for stock
enhancement or
ornamental trade)
Inclusion in Report
as Potential Thr eat
to Introducti on
Acantharchus pomotis
Ambloplites ariommus
Ambloplites cavifrons
Ambloplites constellatus
Ambloplites ruprestris
Archoplites interruptus
Centrarchus macropterus
trade only
Enneacanthus chaetodon
trade only
Enneacanthus gloriosus
trade only
Enneacanthus obesus
trade only
Pomoxis annularis
Pomoxis nigromaculatus
Lepomis auritus
Lepomis cyanellus
trade only
Lepomis gibbosus
Lepomis gulosus
Lepomis humilis
Lepomis macrochirus
Lepomis marginatus
Lepomis megalotis
trade only
Lepomis microlophus
Lepomis miniatus
Lepomis peltastes
Lepomis punctatus
Lepomis symmetricus
Micropterus cataractae
Micropterus coosae
Micropterus dolomieu
Micropterus floridanus
Micropterus henshalli
Micropterus notius
Micropterus punctulatus
Micropterus salmoides
Micropterus treculii
4.3 Aquaria
4.3.1 Centrarchidae
In the first half of the last century aquarists concentrated on keeping coldwater and
later subtropical species. Early books that made this hobby popular, such as those of
Den Hollander (1900), Heimans (1912) and Portielje (1925), primarly discuss
indigenous fish species like three-spined stickleback (Gasterosteus aculeatus),
European bitterling (Rhodeus amarus) and Crucian Carp (Carassius carassius).
Coldwater species that were imported early such as goldfish (Carassius auratus) and
eastern mudminnow (Umbra pygmaea), and some subtropical species such as
paradise fish (Macropodus opercularis) and chameleon cichlid (Cichlasoma facetum),
quickly became popular.
This interest in more exotic fish species also stimulated the import and keeping of
several centrarchid species. A relatively large number of centrarchid species were
kept in the early days of the aquarium trade. According to Den Hollander (1900),
species such as E. chaetodon, E. obesus, L. gibbosus and L. megalotis s.l. were
regularly available in the aquarium shops. Heimans (1912) and Portielje (1925) added
A. rupestris, P. nigromaculatus, C. macropterus, M. salmoides and M. dolomieu to the
list of kept species. The last species is probably erroneous, see also 2.1.3. The
drawing in the book of Heimans (fig. 4.1) was made with a photo as an example and
did not use specimens obtained from trade.
Figure 4.1: Micropterus dolomieu and Ambloplites rupestris taken from Heimans
Figure 4.2: Ambloplites rupestris and Enneacanthus chaetodon taken from Portielje
After the Second World War there were a number of technical developments (e.g.,
cheap heating systems; Frey, 1983) that enabled the general public to be able to keep
a variety of tropical fish species. With a wider choice of fish species, the interest in
Centrarchidae declined (Pinter, 1968). Nowadays, centrarchids are rarely kept in
aquaria and most species that have been kept in the past are hardly available in
aquaria shops.
There are several reasons for the decline in interest in centrarchids in the pet trade in
The Netherlands. Several species have relatively large body sizes for normal sized
aquaria, e.g. A. rupestris and P. nigromaculatus. Further more, some centrarchids
such as L. gibbosus and A. rupestris are difficult to raise/house with other fish species
because of their aggressive territorial behavior. These territorial species are also very
aggressive towards conspecifics and need spacious aquaria with a lot of cover if one
wants to keep several specimens in one aquaria. Too little space is likely to result in
fatalities (D en Hollander, 1900).
Centrarchid species tend to be difficult to train to eat dry fish foods, and need live
animal food if they are to survive and grow. It is also necessary to keep them at lower
temperatures (8-12°C) in winter to maintain their health and make it possible to breed
in the spring (Pinter, 1968). With hundreds of other species that are regarded as
equally or more attractive than centrarchids, as well as a number of species that are
easier to raise, the decline in interest is understandable.
Chance of entry
Centrarchid species are rarely available in pet shops in The Netherlands. They are not
sought after as centrarchids are not particularly popular anymore in the aquarium
trade. This makes most species relatively rare in aquaria. Only L. gibbosus is regularly
From internet forums it is clear that inexperienced buyers of L. gibbosus are regularly
disappointed as they have not been well informed about the aforementioned
downsides of keeping centrarchids. These fish might end up being released in nature.
This may also be the case in the few instances that people breed centrarchid species
in aquaria. All species that are kept in aquaria nowadays are known to be possible to
breed (
The chance of entry from aquaria (introductions from aquarium trade) is moderate for
L. gibbosus and low for the other Centrarchid species.
4.3.2 Elassomatidae
At least three species of Elassomatidae have been imported to Europe for aquaria: E.
zonatum, E. okefenokee and E. evergladei. E. zonatum has not become very popular
and seems to have disappeared (Arnold, 1990). Only Bohlen & Nolte (1993) reported
keeping and breeding E. zonatum, which they had caught and imported themselves
from the USA. No Dutch papers on this species or discussions about this species in
Dutch internet forums could be found. In a Belgian internet forum it was mentioned to
be extremely difficult to obtain. According to J. Klungers (pers. comm.) this species is
not available in the Netherlands.
E. okefenokee was imported to Europe in 1980 and ever since it has been irregularly
available. The first imports of E. evergladei to Europe are probably from around 1925
and this species is still the most kept one of the Ellasoma species (Arnold, 1990). Also
in the Netherlands both species are kept in aquaria, with E. evergladei being the most
common one of the two (D.M. Soes, pers. observ.). Beside Dutch pet shops, sources
for these species are aquarist, which are successful in breeding these species, and
the German pet shop Zoo Zajac (J. Klungers, pers. comm.). This shop claims to be
the largest in the world and did in October 2010 actually sell E. evergladei (13.50 euro
per pair).
Elassoma species are only suitable for specialist and experienced aquarists. For
common household aquaria they are unsuitable and are not likely to survive for a long
time. Especially for breeding, which is hard to accomplish, it is best to keep them in
tanks specifically arranged for their needs with no other species present. Further
complicating factors for their keeping and breeding are their need for lower
temperature during the winter and their need to be fed with small, live food
(Anonymous, 1948; J. Klungers, pers. comm.; D.M. Soes, pers. observ.).
Chance of entry
All Elassoma-species are rarely available in pet shops and need to be purchased from
specialist shops or other aquarists. This makes them relatively rare in aquaria. With
breeding being difficult and never over-productive, surplus animals will easily be sold
to other aquarists and are not likely to end up in nature. Instead of being aggressive
fish that may be released because of damaging/killing other fish species, Elassoma
species tend to be shy, non-aggressive species. Although deliberate stocking can
never be excluded, the chance of entry by aquarist releasing animals in nature is
considered to be quite low.
4.4 Garden ponds
4.4.1 Centrarchidae
L. gibbosus
In Dutch garden ponds L. gibbosus is by far the most commonly kept centrarchid. This
species is regularly recommended as a controller of ‘vermin’ in garden ponds, such as
fish parasites (e.g. fish lice (Argulidae) and leeches (Hirudinea)) and harmful insects
(e.g. mosquito’s (Culicidae), predaceous diving beetles (Dytiscidae) and dragonfly
larvae (Anisoptera)). It is also recommended for controlling the numbers of fish
species which easily breed in garden ponds, such as goldfish (Carassius auratus),
gudgeons (Gobio gobio) and fathead minnows (Pimephales promelas). In shops, this
species is usually displayed in glass containers showing their colorful appearance.
True-life experiences in garden ponds are often less positive. When seen from above,
the appearance of L. gibbosus is often a disappointment as its colorful flanks are not
as striking. Furthermore they turn out to be aggressive fish which, especially when
present in higher numbers, also attack and harm larger fish species such as koi and
goldfish. Besides invertebrates they also predate on amphibian larvae, which is often
regretted by pond owners. Some garden pond keepers report that L. gibbosus is able
to adjust to dry fish pellets and start competing for this artificial food with other
residents in their garden ponds.
When both male and female L. gibbosus are present, they are most likely to
reproduce. Often garden ponds end up being populated with hundreds of L. gibbosus.
Most fish species regularly spawn in garden ponds, but resulting eggs are quickly
eaten by other fish. Only in densely planted ponds some species (e.g. goldfish,
fathead minnow) are successfully reproducing, as part of the eggs can survive in the
vegetation. In contrast, L. gibbosus can reproduce successfully also in “bare” ponds
with a high density of egg-eating fish. Prior to the spawning act, male L. gibbosus
clear a small area from debris. On the resulting bare stones, sand or pond bottom, the
female deposits her eggs. After spawning the male chases away the female. The male
then proceeds to care for eggs by regularly fanning water over them, which provides
oxygen and prevents debris from settling on the eggs. Egg guarding male L. gibbosus
are aggressively chasing all fish which come close to the eggs. The reported
aggression of L. gibbosus likely originates from this nest guarding activity. The
guarding of eggs continues until the eggs are hatched and young are able to swim. At
this age, young L. gibbosus can successfully evade most other pond fish and have a
high survival rate.
In small ponds it is possible to manipulate numbers by removing fish regularly. In
larger ponds this is often not practical and the only possibility to remove L. gibbosus,
is to drain the entire pond. It is not without reason that it is often advised just to keep
only one L. gibbosus per garden pond.
When trying to dispose excess animals it is probably impossible to sell sufficient
numbers. Killing fish is to many people an inhumane act they not want to commit.
Releasing them in the wild is then the only option left. Pond owners then search for
“nice living areas” for their surplus fish, as their fish should have a “good future when
no longer cared for”. As a consequence, they are frequently released in places with a
high value for nature, like moorland pools and amphibian reproduction sites.
Other species
Other Centrarchidae are rarely kept in Dutch garden ponds as their availability through
garden trade and pet shops is low. In books, magazines, internet forums, etc., hardly
any information on Dutch experiences with e.g. L. cyanellus or E. gloriosus can be
At least five Centrarchidae species are sold in the Netherlands in recent years, which
can be categorized in two groups: M. salmoides and L. cyanellus are relatively large
species with aggressive predatory behavior. This makes them less suitable for ponds
that offer too little space and cover. Like L. gibbosus they are likely to injure even
species with larger body sizes. E. gloriosus, E. chaetodon and C. macropterus are
smaller, timid species that will tend to stay amongst cover. These species will do
especially well in densely vegetated garden ponds with non-aggressive inhabitants.
Figure 4.3: L. cyanellus from a Dutch garden pond bought as ‘diamantbaars’.
Photos by Sander den Bleeker
All mentioned species are likely to be able survive through the winter in larger ponds,
although Enneacanthus in particular are reported to be sensitive. In smaller ponds
with temperatures dropping below 4°C for a longer period they are less likely to
survive the winter outdoors. As an alternative they can be kept in aquaria during the
In Germany two further species are kept: L. megalotis and E. obesus. These species
that also might turn up in the Dutch trade are also reported to be winter hardy in larger
garden ponds, with E. obesus again being a bit more sensitive
Chance of entry from garden ponds
With L. gibbosus still being sold in large numbers the chance of entry due to releases
of fish from garden ponds is high due to their high reproduction capabilities in garden
ponds and their aggressive behavior towards other fish species. The chance of entry
of other centrarchid species is low, mainly because of their low availability in shops.
4.4.2 Elassomatidae
With Elasoma species not being able to survive Dutch winters in garden ponds (see 5)
they are not of interest to common garden pond keepers. Also they have never been
found to be sold for garden ponds (P. Veenvliet, pers. comm.). The chance of entry
from garden ponds is considered to be negligible.
4.5 Angling
4.5.1 Centrarchidae
M. salmoides and other Micropterus-species are the most popular freshwater game
fishes of North America, supporting a multi-billion dollar industry (U.S. Department of
the Interior et al., 2006). This popularity is not restricted to North America and black
bass have been stocked in many parts of the world mainly for recreational fishing
( Also in Europe it has become a popular game fish in Spain en France
(Maitland, 1977).
Although still absent, the popularity of M. salmoides has also reached the
Netherlands. When questioned, several commercial fishing farms (Visdorado De Kool,
De Ronde bleek and De Berenkuil) indicated to be interested in stocking ponds with
M. salmoides and having studied the possibilities of doing so. The lack of nearby fish
farms that breed M. salmoides resulting in high transportation costs of importing fish
(e.g., from southern France) have apparently prevented the introduction of the species
in fishing ponds. But, based on the uttered intentions of the fishing farms, the chance
of this happening in the future is very realistic. Other large centrarchids have not been
considered by the questioned farms.
Figure 4.4: A big largemouth bass makes an angler happy. Photo by Pieter-Bas
The interest in black basses extends to an increasing interest in stocking exotic fish
species other then the traditional trout species in fishing farms. Recent examples are
striped bass (Morone sp.), African sharptooth catfish (Clarias gariepinus), claresse
(hybrid between Heterobranchus longifilis en Clarias gariepinus) and sturgeons like
the Russian sturgeon (Acipenser gueldenstaedtii) (D.M. Soes. pers. observ.). One of
the reasons to stock such species is to provide fishing opportunities in the summer
season. In this season water temperature in many fishing ponds becomes too high for
trout species because they lose their appetite in this period. In such conditions anglers
have no opportunity to catch trout and business becomes low. Including species such
as African sharptooth catfish or M. salmoides can increase and sustain business in
the summer season, making fishing farms more profitable.
Trout are known to escape and be released from fishing farms. Ther is no reason to
assume that this would be different for M. salmoides specimens if they are actually
stocked in fishing ponds. Numbers that escape or are released from farms tend to be
low (Soes & Broeckx, 2011).
During the project no intentions to stock centrachid species in waters other then
fishing ponds were noted. Furthermore current legislation (Fisheries law & Flora- and
fauna law) forbids stocking of any centrarchid species in nature.
The chance of entry from fishing farms or angling related stocking programs is low.
4.5.2 Elassomatidae
The Elassomatidae are because of their small size not of interest to the angling
community. The chance of entry by activities associated with angling is considered to
be negligible.
4.6 Aquaculture
4.6.1 Centrarchidae
In North America centrarchids are of some importance in aquaculture. Lepomis sp.
and M. salmoides are both dominating this production (Morris & Clayton, 2009).
Lepomis sp. sales in the USA had in 2005 a value of around 5 million dollar and M.
salmoides over 10 million dollar ( The primary markets are sport-fish
stocking and fee-fishing operations, but they are also sold for human consumption
(Morris & Clayton, 2009).
On a worldwide scale, centrarchids are of minor importance in aquaculture
( Extensive introductions of M. salmoides in Europe, Africa and Asia were
primarily to improve fisheries stocks and centrarchids were mainly taken into culture
for supporting these stocking programs (Liao, 1999; Jackson, 1988; Welcomme,
In the Netherlands none of the centrarchids can be legally cultured for human
consumption as only species listed in the Animal Health and Welfare Act (Artikel 34
van de Gezondheids- en Welzijnswet voor dieren) are permitted. None of the
centrarchids is included in this list (
A review of possible new species for innovation of the Dutch aquaculture didnot lis t
centrarchid species as being promising (Kals et al., 2005). But with increasing interest
in especially M. salmoides for stocking in fee-fishing operations some small scale
(experimental) rearing might be possible, comparable with e.g. Atlantic trout (Salmo
trutta) and ‘Elsasser saibling’ (hybrid Salvelinus alpines and S. fontinalis). The
‘Elsasser saibling’ has been reared for fee-fishing operations although it is not
included in the list of the Animal Health and Welfare Act (Soes & Broeckx, 2011).
This legislation does not include ornamental fishes and at least two ornamental fish
farms in the Netherlands did in 2010 actually culture and sell L. gibbosus. The risk of
fishes escaping from these fish farms has not been assessed.
The chance of entry from fish farms is considered to be very low.
4.6.2 Elassomatidae
None of the Elassoma-species is commercially cultured. The chance of entry by
activities associated with aquaculture is considered to be negligible.
4.7 Entry from neighboring countries
4.7.1 Centrarchidae
In Flanders only L. gibbosus is established. Past introductions of M. salmoides and
maybe M. dolomieu have not resulted in established populations (Vrielynck et al.,
L. gibbosus is widespread in Flanders occurring in all but one basin (Yser), but being
most abundant in the eastern part of Flanders (basins of Demer, Nete and Meuse),
where where they locally have become abundant. The presence of these fishes in
north-east Flanders is assumed to be due to the high concentration of pond fish farms
in this area, where numerous abandoned peat diggings provided suitable conditions
for pond farming (Verreycken et al., 2007).
Figure 4.5: The distribution of Lepomis gibbosus in Flanders, including Baarle-Nassau
and Baarle-Hertog. Based on data from
Several Belgium streams, e.g. Mark, Dommel, Prinsenloop and Aa Beek, with
populations of L. gibbosus are entering the Netherlands. Therefore, it is inevitable that
this species enters the Netherlands from Flanders.
In Wallonia M. dolomieu has been stocked in the 1950s in the River Semois. This
species was first thought to be established, but with no records after 1964 it should be
considered extinct for already a long time.
L. gibbosus is widespread but much rarer compared to Flanders. This relative rarity is
due to the absence of preferred habitats. The pools and other smaller standing waters
that are the dominant habitat of L. gibbosus in Flanders are much less abundant in
Wallonia. Furthermore is stocking of e.g. lakes with salmonids or other large predatory
fish is more common in Wallonia, when compared to Flanders. Such large predators
decrease the chance of establishment of L. gibbosus.
It is recorded the most in the Meuse Basin, making it likely that fish from Wallonia
might enter the Netherlands.
Figure 4.6: The distribution of Lepomis gibbosus and Micropterus dolomieu in
Wallonia. Data are from the period 1954-2009 and provided by Service public de
Wallonie - Direction générale opérationnelle Agriculture, Ressources naturelles et
Environnement - Département de l'Étude du Milieu naturel et agricole.
In Germany only L. gibbosus is established. M. salmoides has not been officially
stocked, but among anglers rumors about illegal stockings are circulating (J. Freyhof,
pers. com.).
L. gibbosus is especially common in the Rhine river basin, but is also recorded from
the Ruhr and the Swalm (fig. 4.7). Also during a recent visit to Karlsruhe it was noticed
that L. gibbosus was abundant and widely distributed in most flood plain waters in the
Rhine Valley near this city (D.M. Soes, pers. observ.). L. gibbosus is known to use
smaller and larger rivers, such as the Ruhr and the Rhine, for dispersion and is likely
to enter the Netherlands from Germany.
Figure 4.7: Distribution of Lepomis gibbosus according to, accessed
24 October 2010. Black = recent recordings, Grey = data from literature, Red = data
from literature with exact locality uncertain.
In France three species of Centrarchidae have established: L. gibbosus, A. rupestris
and M. salmoides. L. gibbosus is widely distributed and also present in the Meuse
basin. A. rupestris is limited to the Loire basin, making it unlikely that this species
might enter from France. M. salmoides is widespread and also occurs in the northern
part of the Seinne basin. Anglers are expecting specimens of this species, originating
from stockings in France, to show up in the nearby future in the Dutch stretches of the
Meuse. However, data confirming the presence of a significant population of M.
salmoides in the Meuse basin are still lacking (fig. 4.8).
Figure 4.8: The distribution of Micropterus salmoides in France with data upto 2010.
Provided by P. Keith, Muséum national d¹Histoire Naturelle.
4.7.2 Elassomatidae
Introduced populations of Elassoma-species are not known from Europe. The chance
of entry by dispersing from other countries is considered to be zero.
5 The probability of establishment
5.1 Centrarchidae
5.1.1 Thermal Biology of Centrarchids
Although there are a number of factors that influence the invasion potential for a given
species, water temperature is certainly one of the most important in inland waters.
Since fish are ectothermic, changes in ambient water temperatures are realized
throughout the animal, and can have pronounced impacts on cellular function
(Prosser, 1991), protein structure (Somero, 1995), enzyme activity, diffusion rates and
metabolism (Fry, 1971; Brett & Groves, 1979; Farrell, 1996; Kieffer et al., 1998).
Temperature is also an important determinant of many behavioral attributes (Fry,
1971; Ultsch, 1989) and overall organismal performance (Kieffer & Cooke, 2009). For
centrarchids and other fishes, it also influences factors such as geographic range,
spawning date, food consumption (Hathaway, 1927), digestion rates (Fänge & Grove,
1979), growth, swimming abilities and activity (Malizia et al., 1984; Demers et al.,
1996), winter biology (Suski & Ridgway, 2009), and habitat selection and distribution
(Neill & Magnuson, 1974; Neill, 1979; Armour, 1993). Moreover, temperature can also
be lethal at both low and high extremes. In fact, temperature plays such an important
role that it has been termed the abiotic “master factor” (Brett, 1971).
Water temperatures have been cited as regulating the distribution of warmwater fishes
such as centrarchids. As air temperatures increase with climate change, the thermal
habitat of most northern waterbodies lakes would become suitable for warmwater fish
habitation (Magnusson et al., 1985; DeStasio et al., 1996). There is also the possibility
that populations of centrarchid fishes would be able to expand their distributions
farther north. It has been theorized that the northern limit of centrarchid distributions
are regulated by the fact that during winter months, foraging is restricted and
starvation occurs (Shuter & Post, 1990). As climate change warms North America, the
duration of winter would decrease and starvation would not occur as often in northern
waterbodies (Shuter & Post, 1990). This would then allow centrarchid populations to
expand northward (MacCauley & Kilgour, 1990; Shuter & Post, 1990). As centrarchid
distributions shifted farther north, local fish communities could suffer from shifts in
community structure associated with the introduction of centrarchid fishes (Jackson,
As outlined by Coutant (1975a), the responses of fish to temperature vary across
different life stages (e.g., eggs, larvae, adults), so no single temperature can be
viewed as good or bad. Instead, the temperature must be viewed in the context of the
life stage as well as the activities that the organism is trying to perform. Here, we
focus on adult thermal tolerances given that it is the most relevant in the context of
invasion potential. Fry classified physical and chemical aspects of fish habitat as 1)
lethal, 2) controlling, or 3) directive, based on how they influence fish (Fry, 1947;
1971). In this context, extreme temperatures can kill fish and would be viewed as
lethal. When not at extremes, temperature can control developmental and
physiological rates and processes (i.e., metabolism) of fish. Temperature can also
direct the position or habitat preference of an individual fish (i.e., orientation
response). Fry’s paradigm also included another group of factors commonly referred
to as “limitingsuch as those that are in short supply (e.g., oxygen) or others that are
“masking” the influence of other environmental factors.
5.1.2 Lethal Temperatures
In general, survival in response to extreme temperatures (either high or low) depends
on three primary factors 1) the initial acclimation or holding temperature, 2) the exact
test temperature, and 3) the duration of exposure to the test temperature (Hart, 1952).
Other factors such as individual variation in energy stores, parasite/disease burdens,
reproductive state, etc., can also play a role in temperature related mortality but these
effects are typically manifested over longer periods (See Suski & Ridgway, 2009).
Obviously when acting as a lethal factor, temperature has the most dramatic effects
(Fry, 1947).
Figure 5.1: Critical thermal maxima data for centrarchid fishes. Taken from Kieffer &
Cooke (2009).
Methods used to determine thermal tolerances are critically reviewed in Becker &
Genoway (1979) and Beitinger et al. (2000). Critical Thermal Maxima (CTM) tests
involves exposing fish that are usually acclimated to specific temperature(s) to a
constant linear change in temperature until a near lethal endpoint is reached. The
endpoint is determined when locomotory movements are impaired and represents the
CTminima or CTmaxima. Overall, CTM measurements are generally regarded as the
most realistic (Beitinger et al., 2000). For centrarchids studied to date, CTmaxima
values range from a low of 29.2º C for largemouth bass to a high of 41.8º C for Florida
largemouth bass (Kieffer & Cooke, 2009). CTminima has also been determined on an
infrequent basis (only 2 species) relative to CTmaxima. In both cases, CTminima were
varied extensively with acclimation temperature and were as low as 1.7º C for L.
macrochirus acclimated to 15º C (Beecher et al., 1977), and 3.2º C for largemouth
bass acclimated to 20º C (Currie et al., 1998).
5.1.3 Preferred Temperatures
Centrarchid fishes have long been the focus of work on thermal preferences. Data on
thermal preferenda are more common that quantitative data on lethal temperatures. In
fact, even some of the less economically valuable species of centrarchid fishes have
experimentally determined values (e.g. E. gloriosus; Casterlin & Reynolds, 1979;
Stauffer, 1981). One of the few studies that provides comparative data for several
centrarchid (and salmonid) species is Cherry et al. (1977). The authors exposed A.
rupestris, L. macrochirus, M. punctulatus, and M. dolomieu to a range of standardized
acclimation temperatures and thermal gradients. In general, thermal preferences
increased with acclimation temperatures until acclimation temperatures reached 30ºC.
As the fish approached lethal temperatures (i.e., > 30ºC), preferences decreased. For
all the centrarchids the authors evaluated, final thermal preferenda were near 30ºC.
Kieffer & Cooke (2009) generated a figure that illustrates the range of final thermal
preferenda for all centrarchid fish for which they exist.
Figure 5.2: Thermal preferenda data for centrarchid fishes. Taken from Kieffer &
Cooke (2009).
In general, the thermal preferenda are between 28 and 32º C with few exceptions.
What is particularly interesting is the general conformity of all species to a rather
narrow range of preferred temperatures. There are a number of clear ecological
correlates of preferred temperature, which make it an important consideration for
invasion biology (Magnuson et al., 1979). The majority of physiological processes are
optimized at the thermal preferenda (e.g. Coutant, 1975a). However, in the wild some
species spend very little of their time at temperatures that fall within their preferred
temperature ranges as a function of constraint from available temperatures.
Magnuson & DeStasio (1996) illustrated this succinctly for M. salmoides across the
United States. The authors concluded that M. salmoides occupy suboptimal thermal
habitats for much of the year. In fact in some regions, fish may not ever experience
preferred temperatures.
5.1.4 Winter as a Limiting Factor
As noted above, toward the northern edge of their range (or in areas such as Europe),
it is believed that centrarchid distributions are regulated by the fact that during winter
months, foraging is restricted and starvation occurs (Shuter & Post, 1990). Temperate
latitudes in both North America and Europe experience a predictable annual cycle of
alternating warm and cold periods that can result in below freezing conditions, ice
cover, and alterations to aquatic habitats that persist for a substantial portion of a
year. Winter represents a very challenging time of year that exerts a strong selective
pressure on individual survival, community structure and year class strength for
centrarchid fishes (Suski & Ridgway, 2009). Winter is typically defined as the period of
the year between the autumnal equinox and prior to the onset of spawning in
centrarchid fishes. Centrarchids can experience a broad range of climatic conditions
during winter across their range. Pronounced latitudinal gradients in winter conditions
exist with growing degree days and summer temperatures both declining with latitude,
while winter severity (i.e., lower daily temperatures) and winter length both increase
with latitude. The reality is that all centrarchids experience winter but there is certainly
local adaptation such that fish that have co-adapted gene complexes tailored to a
given suite of winter conditions typically survive, however, if fish from those
populations are moved to areas where there experience harsher winters, chance of
survival is reduced.
5.1.5 Species Accounts for those with Invasion Potential in The Netherlands
For those species identified in table 4.1 as being a potential threat to introduction we
present a brief overview of their natural history with a focus on distribution in North
America, thermal biology and winter ecology. For most species little is known about
their thermal biology aside from inferences derived from the distribution of the species.
The information is derived from a thorough review of peer reviewed literature. We
acknowledge that much of the material of chapter 5 is from a recent book on
centrarchid fish by Cooke & Philipp (2009) with particular reliance on the chapters that
focused on natural history accounts (Warren, 2009), winter biology (Suski & Ridgway,
2009) and organismal physiology (Kieffer & Cooke, 2009). We thank the authors for
giving permission for using these texts.
Ambloplites rupestris Rock Bass
In North America A. rupestris occurs in the St.
Lawrence River-Great Lakes, Hudson Bay (Red
River), and Mississippi River basins. A. rupestris
has been widely introduced and is established in
Atlantic Slope drainages as far south as the
Roanoke River, Virginia, and in the Missouri and
Arkansas river drainages. The species is also
established in several western states (Page & Burr,
1991; Fuller et al., 1999).
A. rupestris frequents cover in pools of creeks to
small and medium rivers and the rocky and
vegetated margins of lakes, being most common in silt-free rocky streams. Little is
known about the winter biology of A. rupestris. Collections of fish through the ice in
Ontario by Keast (1968) noted that A. rupestris collected at water temperatures
between 6.5-8.5°C appeared to have not eaten for several weeks suggesting that this
species is quiescent in the winter. Further support for this idea is that in laboratory
experiments, A. rupestris preferred to remain solitary during winter simulations, and
often migrated to non-flowing water (Breder & Nigrelli, 1935). Coble (1965) presented
evidence that seasonal growth begins at temperatures of 10-14°C in A. rupestris
whereas reproduction typically occurs at 16°C.
Both the growth and reproductive temperatures for A. rupestris fall within the range of
temperatures commonly experienced in the Netherlands. There is no doubt that
extreme winter conditions can impact overwinter survival of A. rupestris, but in Ontario
and Quebec the species resides in regions with mean monthly minimum temperatures
of -16°C in both January and February. Such temperatures are rarely experienced in
the Netherlands. Suitable habitat this species might especially find within the larger
rivers, streams in the eastern parts of the Netherlands in larger lakes like e.g. Veluwe
Lake and Loosdrecht Lake.
Centrarchus macropterus Flier
C. macropterus occurs primarily on the
Coastal Plain from the Potomac River
drainage, Maryland, to central Florida, and
west to the Trinity River, Texas. The species
penetrates the Mississippi Embayment to
southern Illinois and southern Indiana, where
it occurs above the Fall Line (Page & Burr,
C. macropterus is a lowland species, inhabiting swamps, vegetated lakes, ponds,
sloughs, and backwaters and pools of small creeks and small rivers. The species
usually is associated with densely vegetated, clear waters (Page & Burr, 1991;
Jenkins & Burkhead, 1994; Pflieger, 1997; Boschung & Mayden, 2004). C.
macropterus is among the earliest, lowest temperature, spawners in the family. The
ovaries enlarge and continue developing in the fall and over winter (Conley, 1966),
which is likely an adaptation for early spawning. Nest-building is initiated at 14°C and
the brief 10-14 day spawning period begins at water temperatures of 17°C in March
and April (Dickson, 1949; Conley, 1966; Pflieger, 1997).
There is no information on the thermal biology of the species although its distribution
is towards the southern edge of the range of centrarchids suggesting that they may
respond poorly to the cold winters and relatively cool summers of the Netherlands. In
aquaristics this species is considered to be sensitive to low temperatures and it is
generally advised to overwinter this species in the Netherlands indoor.
Enneacanthus chaetodon - Blackbanded Sunfish
E. chaetodon is sporadically distributed
below the Fall Line in Atlantic and Gulf slope
drainages from New Jersey to central Florida
and west to the Flint River, Georgia. Large
distributional gaps occur across the range
(e.g., entire western Chesapeake basin), and
populations in Georgia and Florida are
isolated and widely scattered (Gilbert, 1992b;
Jenkins & Burkhead, 1994). Four areas of
concentration are evident. Three of these, the pine barrens of New Jersey, the
sandhills in southeastern North Carolina, and the central highlands of Florida, are
characterized by well-drained sandy soils with vegetation of pine and scrubby oak
species and dystrophic, acidic waters. The fourth area is the acidic Okefenokee
Swamp in Georgia (Gilbert, 1992b).
E. chaetodon inhabits vegetated lakes, ponds, and quiet sand- and mud-bottomed
pools and backwaters of creeks and small to medium rivers (Page & Burr, 1991).
Knowledge of the reproduc tive behaviour and biology of E. chaetodon is limited
largely to aquarium observations by hobbyists, and almo