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The transatlantic introduction of weakfish Cynoscion regalis (Sciaenidae, Pisces) into Europe


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Weakfish Cynoscion regalis (Bloch & Schneider, 1801) is a sciaenid fish native to the east coast of North America and has been recently collected in three areas of the Iberian Peninsula (Europe). We aimed to i) provide the first report of the presence of weakfish in Europe, ii) hypothesize the most likely introduction vector, iii) discuss the potential for ecological overlap between weakfish and meagre Argyrosomus regius (Asso, 1801), the native Sciaenidae species, and iv) highlight the importance of citizen science in the detection of non-native species. Weakfish were captured in the Sado estuary (July 2014), Gulf of Cadiz (November 2015) and the adjacent Guadiana estuary (June 2016), and in two Galician Rías (June 2016). Anglers reported that weakfish was present in the Sado estuary for “some” years, while their presence was only noticed recently in the other two areas. We hypothesize that ballast water was the introduction vector, that weakfish established a reproducing population in the non-native range, and that it dispersed from the Sado estuary, a central region of its current distribution range. The Sado estuary might have been the introduction area for weakfish via ballast water because there is a busy transoceanic commercial port in the estuary. Moreover, they are not used in European aquaculture facilities, nor in the aquarium trade. The collected specimens were ≤50 cm, with average lengths of 30 cm, which corresponds to a median age of 2 years and to individuals capable of reproducing. As a result, the year of introduction must be before 2012. Weakfish have a similar ecological niche to meagre, but the outcome of potential interactions is uncertain. Citizen science, especially the initiative of local fishermen, was critical to detect this non-native species.
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BioInvasions Records (2016) Volume 5 Article in press
© 2016 The Author(s). Journal compilation © 2016 REABIC
Open Access
Rapid Communication CORRECTED PROOF
The transatlantic introduction of weakfish Cynoscion regalis
(Bloch & Schneider, 1801) (Sciaenidae, Pisces) into Europe
Pedro Morais
and Maria Alexandra Teodósio
CCMAR – Centre of Marine Sciences, Campus de Gambelas, University of Algarve, 8005-139 Faro, Portugal
CIIMAR – Interdisciplinary Centre of Marine and Environmental Research, University of Porto, Terminal de
Cruzeiros do Porto de Leixões, Avenida Norton de Matos, 4450-208 Matosinhos, Portugal
E-mail addresses: (PM), (MAT)
*Corresponding author
Received: 28 June 2016 / Accepted: 28 September 2016 / Published online: 7 October 2016
Handling editor: Charles W. Martin
Weakfish Cynoscion regalis (Bloch and Schneider, 1801) is a sciaenid fish native to the east coast of North America and has been recently
collected in three areas of the Iberian Peninsula (Europe). We aimed to i) provide the first report of the presence of weakfish in Europe,
ii) hypothesize the most likely introduction vector, iii) discuss the potential for ecological overlap between weakfish and meagre
Argyrosomus regius (Asso, 1801), the native Sciaenidae species, and iv) highlight the importance of citizen science in the detection of non-
native species. Weakfish were captured in the Sado estuary (July 2014), Gulf of Cadiz (November 2015) and the adjacent Guadiana estuary
(June 2016), and in two Galician Rías (June 2016). Anglers reported that weakfish was present in the Sado estuary for “some” years, while
their presence was only noticed recently in the other two areas. We hypothesize that ballast water was the introduction vector, that weakfish
established a reproducing population in the non-native range, and that it dispersed from the Sado estuary, a central region of its current
distribution range. The Sado estuary might have been the introduction area for weakfish via ballast water because there is a busy transoceanic
commercial port in the estuary. Moreover, they are not used in European aquaculture facilities, nor in the aquarium trade. The collected
specimens were 50 cm, with average lengths of 30 cm, which corresponds to a median age of 2 years and to individuals capable of
reproducing. As a result, the year of introduction must be before 2012. Weakfish have a similar ecological niche to meagre, but the outcome
of potential interactions is uncertain. Citizen science, especially the initiative of local fishermen, was critical to detect this non-native species.
Key words: non-native, fish, ballast water, citizen science, Portugal, Spain, Iberian Peninsula
Reports on transoceanic marine invasions are
becoming more common (Callaway et al. 2006), and
they consist primarily of introductions of
holoplanktonic (Berg et al. 2002) and meroplanktonic
invertebrate species via ballast water (Roman 2006).
In the case of vertebrates (i.e. fish), intentional
introductions (e.g., for recreational fishing), escapees
from aquaculture facilities (Bartley 2011 (Copp et
al. 2007), and aquarium release (Brice et al. 2004)
are the most common vectors of introduction rather
than via ballast water (Wonham et al. 2000;
Grigorovich et al. 2003; Copp et al. 2007).
The presence of weakfish Cynoscion regalis
(Bloch and Schneider, 1801) (Sciaenidae, Pisces) in
the Iberian Peninsula (western Europe) is a recent
example of a transoceanic marine fish introduction.
This species is native to the east coast of North
America (Froese and Pauly 2016), was detected by
fishermen in several regions of the Iberian Peninsula
and subsequently announced in specialized magazines
(Mundo da Pesca 2016), personal blogs (OsPescas
2015), and regional online media (e.g., A Voz do
Algarve 2016; Europapress 2016; Vigoe 2016). The
native distribution of weakfish is from Florida’s
Atlantic coast (USA) to Nova Scotia (Canada), where
it is exploited in commercial and sport fisheries
(Froese and Pauly 2016; NMFS 2016). In Europe,
the meagre Argyrosomus regius (Asso, 1801) is the
most abundant Sciaenidae species. The meagre is a
valuable species for local and artisanal fisheries and
sport fishing, and it is also reared in aquaculture
(Mañanós et al. 2009; Duncan et al. 2013).
P. Morais and M.A. Teodósio
Weakfish and meagre share several ecological
traits (e.g. habitat use, reproduction period, diet)
(Froese and Pauly 2016) so their fundamental niche
might overlap where they now co-occur in the
Iberian Peninsula. In this paper we: i) provided the
first scientific report of weakfish in Europe;
ii) described the putative introduction vectors;
iii) discussed the potential ecological overlap
between weakfish and meagre; and iv) highlighted
the importance of citizen science in the detection of
non-native species.
Material and methods
Study area
The Guadiana River estuary is a mesotidal estuary
with an average depth of 6.5 m, occupying an area
of 22 km2, and the tidal amplitudes range from 1.3 to
3.5 m. The estuary drains into the Gulf of Cadiz
(Atlantic Ocean), extends inland for 70 km, and the
last 50 km serve as the southern border of Portugal
and Spain (Iberian Peninsula, Europe) (Figure 1).
The Guadiana River flow varies substantially within
and among years because of variations in rainfall.
However, after the completion of the Alqueva dam
in February 2002, the river discharge is usually lower
than 20 m3 s
-1 (Garel and Ferreira 2011), despite
episodic flooding events (e.g. March–April 2013).
Capture, identification, and distribution of weakfish
in Europe
One adult weakfish was collected in the Guadiana
estuary (SW-Iberian Peninsula) (Figure 1) using
longline fishing gear as part of a routine commercial
fishing operation. The longline was set in the estuary
11 km upstream from the river mouth (37º1533N;
7º2555W) during the night of 15 June 2016 and
retrieved 12 hours later. The identification of the
specimen was made according to Bigelow and
Schroeder (1953). The total length (TL, ±0.1 cm)
and total fresh weight (TFW, ±1 g) were determined,
and the meristic characteristics recorded: fin rays,
gill rakers, and lateral line scales.
After the identification of the specimen, we
established several contacts with fishermen and scien-
tists and also did online searches (in Portuguese,
Spanish, French, and English) to verify the existence
of previous records of this species in Europe. Then,
we made a press release (in Portuguese) announcing
the collection of weakfish in the Guadiana estuary to
reach a broad audience and get feedback from the
general public about the presence of this species in
Figure 1. Map of the Iberian Peninsula indicating the Guadiana
River basin (A) and location where the specimen of weakfish
Cynoscion regalis was collected in the Guadiana estuary on 16
June 2016 (white star) (B).
The morphological characteristics of the specimen
we obtained from the Guadiana estuary, based dorsal
pigmentation and dorsal fin pigmentation (Figure 2),
allowed its identification as weakfish Cynoscion
regalis. This specimen measured 32.6 cm TL and
Transatlantic fish introduction into Europe
Figure 2. The specimen of weakfish Cynoscion regalis collected in the Guadiana estuary on 16 June 2016 (A), and detailed photos of the
head and operculum (B) and of the pigmentation pattern in the dorsal area and second dorsal fin (C). Scale bars: 1 cm. Photographs by Pedro
Table 1. Meristic characteristics of the weakfish specimen collected in the Guadiana estuary, on 16
June 2016, of weakfish from its native
area on the east coast of North America and of meagre. Meristic data for North American weakfish is from Tagatz (1967) and Froese and
Pauly (2016), while meagre meristic data is from Chao (1986) and Dulčić et al. (2009).
Guadiana weakfish North America weakfish Meagre
Dorsal fins rays D
X, D
I+27 D
X, D
I+24–29 D
Pectoral fin rays 18 16
Pelvic fin rays 5 I–5
Anal fin rays II+11 II+10–13 II+7–8
Caudal fin rays 17
Gill rakers 5+12 4–5+10–12
Lateral line scales 78 76–86 53
weighed 381 g TFW. The meristic characteristics of
the specimen fell within the range described for the
species in its native North American range (Table 1).
As of 24 June 2016, there were three online media
reports of weakfish in Europe. Weakfish were
reported for the first time in regional online media in
February 2016 when mention was made of their
capture in the Gulf of Cadiz (SW-Iberian Peninsula)
in November 2015 (Europapress 2016). These speci-
mens were collected by fishermen and identified by
A Arias, J Cuesta, and R Bañón (R. Bañón, Grupo
de Estudo do Medio Mariño, Spain, pers. comm.).
The fish from the Gulf of Cadiz ranged between 28 cm
and 33 cm TL although there were unsubstantiated
accounts of fish of almost 50 cm TL (Vigoe 2016).
The capture of weakfish in two Galician Rías (Ría de
Vigo and Ría O Barqueiro) was reported on 20 June
2016 (Vigoe 2016). These fish ranged between 26 cm
and 32 cm TL. The capture of the Guadiana weakfish
(our specimen) was reported by regional media on
23 June 2016 (A Voz do Algarve 2016), and posted
on social networks (CCMAR 2016). As a result of
the media coverage, anglers came forward with
information that weakfish were present in the Sado
estuary (west coast of Portugal) for “some” years
(C Morais, P Santos, Portugal, pers. comm.). The
first online posting about weakfish in Sado estuary
including a photograph of the fish was made in a
personal blog on 24 September 2015 (OsPescas
2015). The Sado weakfish was similar in size to that
P. Morais and M.A. Teodósio
from the Guadiana estuary. Other weakfish were
caught by anglers in June and July 2016, one in the
southern coast of Portugal at Barranco das Belharucas
Beach (Olhos de Água county) on 5 June 2016
(E Pedro, pers. comm.) and two in the Sado estuary
(27 and 28 July 2016) (OsPescas 2015). Later on, an
anglers magazine also covered the report of
weakfish in the Guadiana estuary, and stated that
they mentioned the presence of weakfish in the Sado
estuary in July 2014 (Mundo da Pesca 2016).
Weakfish in Europe
Hanel et al. (2009) described the occurrence of
seven Sciaenidae species along the European
coastline and adjacent seas: Argyrosomus regius
(Asso, 1801), Cynoscion nebulosus (Cuvier, 1830),
Pseudotolithus senegalensis (Valenciennes, 1833),
Sciaena umbra Linnaeus, 1758, Umbrina canariensis
Valenciennes, 1843, Umbrina cirrosa (Linnaeus,
1758), and Umbrina ronchus Valenciennes, 1843.
Our reporting of Cynoscion regalis in the Iberian
coast raises the number of Sciaenidae in Europe to
eight, and the second native to the northwestern
Atlantic—the other species present is spotted seatrout
Cynoscion nebulosus (Froese and Pauly 2016).
Weakfish distribution in the Iberian coast encom-
passes ~800 km of coastline, from Galicia (Vigoe
2016) to the Gulf of Cadiz (Europapress 2016);
however, it was reported from only five sites—Rías
de Vigo and O Barqueiro in Galicia, Sado estuary,
Gulf of Cadiz and the adjacent Guadiana estuary.
First reports of weakfish in the Iberian Peninsula
date back to July 2014 (Mundo da Pesca 2016) but
the year of introduction was likely before 2012, as
anglers mention that weakfish were collected in the
Sado estuary for “some” years before being
described in a magazine devoted to recreational
angling (OsPescas 2015; Mundo da Pesca 2016).
Weakfish of approximately 30 cm TL are 1–2 years
old, while fish of 50 cm are 2–3 years old (Hatch
2012). Thus, weakfish spent at least 3–4 years
without being noticed by the scientific community in
the Iberian Peninsula. The potential expansion of
weakfish to the northern European coast and adjacent
seas will likely be controlled by water temperatures
because they cease feeding at 7.9 C and die at 3.3 C
in the native range (Bigelow and Schroeder 1953).
Thus, weakfish has the potential to expand its range
in Europe up to the English Channel, to the Irish Sea
and the western coast of Scotland, where winter
water temperature coincides with their cease-feeding
temperature (SeaTemperature 2016).
Introduction, establishment, and dispersion
Aquarium and/or aquaculture release are unrealistic
introduction vectors for weakfish because the
species is not used in the aquarium trade or in
Portuguese and Spanish aquaculture practices (Laura
Ribeiro and Pedro Pousão Ferreira, Instituto Português
do Mar e da Atmosfera, person. comm.). So, we
hypothesize that ballast water was the most likely
vector of weakfish introduction in Europe. The short
duration of transoceanic ship travel between the east
coast of North America and the western Iberian
Peninsula coast (e.g. nine days, SeaRates 2016), and
the physiological plasticity of weakfish larvae and
young-of-the-year (i.e. present in the inner
continental shelf and in the brackish and oligohaline
estuarine sites) (Able and Fahay 2010) suggests that
weakfish were able to circumvent ballast water
exchange regulations. Ballast water management
guidelines include practices that minimize the uptake
of organisms and sediment into ballast tanks at the
port of origin, exchange of ballast water at sea, and
the discharge of water to shore reception facilities at
the port of destination, treatment and even the non-
release of ballast water (IMO 2016).
Assuming that the introduction via ballast water
is possible, then there are two main hypotheses that
could explain the apparent establishment of weakfish
in the Iberian Peninsula shores. Weakfish may form
a population that does not reproduce in Europe, but
mantain its presence through continuous and success-
ful introductions via ballast water; alternatively, the
species is able to reproduce in the non-native range.
The validation of these hypotheses minimally requires
the collection of ichthyoplankton samples to detect
their presence (or not), and analysis of gonadal tissues
from adult fishes. However, the size of the indivi-
duals collected and its broad distribution range suggest
that weakfish reproduce in the non-native range.
Weakfish are present in three Iberian regions,
with the extreme regions separated by ~800 km of
coastline. This fact suggests that the introduction of
weakfish occurred in either: a) three distinct regions
with subsequent establishment of three localized
populations; b) one region located in one of the
extreme regions of distribution (Gulf of Cadiz or
Galicia) and subsequent dispersion; or c) one central
area with subsequent establishment and dispersion.
The first hypothesis is the least likely since the
establishment of fish after their introduction through
ballast water is unusual (Wonham et al. 2000). Thus,
the introduction and establishment of weakfish in a
specific region and its subsequent dispersion and
establishment in other areas seems to be the most
feasible scenario. Based on the available information,
Transatlantic fish introduction into Europe
we hypothesize that the Sado estuary was the
introduction site as it is the region with the highest
number of non-indigenous marine species in
Portugal (Chainho et al. 2015) and the first report on
the presence of weakfish dates back to July 2014.
Three main factors contribute to this hypothesis.
First, local anglers mentioned the presence of weakfish
for “some” years in the Sado estuary. Second, this
estuary has a harbor with the intense traffic of
transoceanic ships, which increases propagule pressure.
Lastly, the Sado estuary and adjacent coastal area is
a highly productive ecosystem with adequate abiotic
conditions to enhance fish survival and growth
(Lankford and Targett 1994; Able and Fahay 2010)
and could allow the establishment and subsequent
transport and migration of weakfish larvae and
adults to other regions.
Ecological overlap between weakfish and meagre
Weakfish and meagre share several ecological
characteristics, including: feeding upon similar types
of prey (e.g. fish, penaeid and mysid shrimps, crabs,
amphipods, clams, annelids); using estuaries as
nurseries during the same period (from spring until
late summer and early autumn); and seeking
protection in holes and deep channels (Bigelow and
Schroeder 1953; Froese and Pauly 2016). However,
they differ in longevity, maximum size and weight,
time of the first maturity and fecundity. Weakfish
usually live 9–12 years, although the oldest fish
reported was 17 years old (Lowerre-Barbieri 1994).
Most fish are <98 cm and <8.9 kg (Froese and Pauly
2016). Meagre can live to 44 years (Prista et al.
2009) and reach 2.3 m and 103.0 kg (Froese and
Pauly 2016). Weakfish mature at an early age. For
example, in North Carolina, 52% of females and
62% of males mature at age 0, and at age 1 all
females >17.5 cm are mature, and fecundity can
reach 5.0 million eggs for a fish of 57 cm (SL)
(Merriner 1976). In contrast, the first sexual maturity
of male and female meagres is at 45 cm and 47 cm,
respectively (~2 years old) (Abou Shabana et al.
2012), while fecundity ranges between 2.1–31.1
million eggs for females with sizes ranging from
1.0–1.7 m (Gil et al. 2013).
It seems the native meagre would have an
advantage over weakfish because it grows to a larger
size, its fecundity is up to 6.2 higher, and weakfish
larvae and juveniles can eventually serve as prey to
meagre. However, weakfish mature sooner, and
might acquire higher fitness if they are able to leave
their parasites behind (i.e. enemy release hypothesis)
(Torchin et al. 2001) after their introduction in the
Iberian Peninsula coast. Thus, given the lack of
knowledge about meagre ecology during their
estuarine phase (e.g. abundance, feeding habits, realized
niche), plus the uncertainties about the outcome of
competition between meagre and weakfish (coexistence
in the same habitats, exclusion of meagres, dominance
of meagres over weakfish and thus controlling weakfish
invasion success) and the economic importance of
meagre in the Guadiana estuary, at least since the
18th century (de Lacerda Lobo 1815), we recommend
the establishment of a monitoring program for these
two Sciaenidae species in the Gulf of Cadiz and
adjacent estuarine nursery areas.
Citizen Science
The putative introduction of weakfish in the Sado
estuary, perhaps earlier than 2012, suggested that the
species had gone unnoticed by the Portuguese
scientific community. Recent budget cuts made by
the Portuguese government can only explain part of
this lack of awareness since this could have been
circumvented with effective communication strategies
between scientists and the general public. Indeed,
citizen science has shown its utility in the detection
of non-native and cryptic invasive species in a way
that would be impossible to be made solely by
scientists or at exorbitant costs (Epps et al. 2014;
Scyphers et al. 2015). For example, the detection of
weakfish in the Iberian Peninsula was only possible
due to fishermen’s contributions. This initial aware-
ness pressures the scientific community to establish
more efficient means of communication with the
public to allow the detection of non-native species
and other ecological threats. The use of new
smartphone technologies, social media platforms,
and other applications is a path that needs to be
further explored. Applications allowing the upload
of a species photograph to alert a group of specialists
(after determining whether the specimen is a plant-
or animal-like specimen, or aquatic or terrestrial
specimen) could aid in the detection of non-native
species. Ideally, this could allow the establishment
of more efficient programs of species control or
eradication, and ultimately help to determine their
suitability for commercial exploitation (e.g. food
consumption, biomedical active compounds).
The dialogue between aquatic scientists and the
general public has to acknowledge and promote the
“Research Responsible and Innovation” concept,
which proposes that the research questions should be
derived from societal problems and formulated with
their collaboration and thus responding to their
concerns (European Commission 2016). For example,
scientific workshops on non-native species can demon-
strate that scientists can assist local communities in
P. Morais and M.A. Teodósio
tackling this issue and also explore new business
opportunities, while scientists increase the temporal
and spatial resolution of long-term monitoring
programs of aquatic ecosystems. Aquatic invasions
scientists need to implement more efficient ways of
communication with society, especially with local
fishermen, to facilitate earlier detection of non-
native species and other ecological problems that
affect aquatic ecosystem services with negative
potential social and economic consequences.
We thank A Fernandes and J Estica for giving us the first
specimen of weakfish collected in the Guadiana estuary and J
Babaluk for proof-reading the paper. C Morais, E Pedro, and P
Santos provided information on the capture of weakfish in
Portugal. R Bañón (Grupo de Estudo do Medio Mariño, Spain)
provided information on the identification of weakfish in Spain,
while L Ribeiro and P Pousão Ferreira, both from “Instituto
Português do Mar e da Atmosfera”, provided information on the
aquaculture of Sciaenidae in the Iberian Peninsula. MAT was
funded by Foundation for Science and Technology (FCT,
Portugal) through a sabbatical fellowship (SFRH/BSAB/113684/
2015) and the European Regional Development Fund
(COMPETE program- Operational Competitiveness Programme
and national funds through FCT-PEst-C/MAR/LA0015/2011).
We also thank three anonymous reviewers, CW Martin and JM
Hanson for their suggestions on how to improve the initial
versions of this paper.
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... Weakfish Cynoscion regalis (Bloch and Schneider, 1801) is a Sciaenidae native from the NE-coast of North America (NMFS, 2016;Froese and Pauly, 2021) and one of the most recent fish invaders in Europe, specifically in the SW-Iberian Peninsula (Morais and Teodósio, 2016;Morais et al., 2017). The Sado estuary (Portugal) seems to be in the centre of the species invasion history, where it has been present at least since the early 2010s, however, the introduction vectors and pathways remain unknown (Morais and Teodósio, 2016;Morais et al., 2017) (Fig. 1). ...
... Weakfish Cynoscion regalis (Bloch and Schneider, 1801) is a Sciaenidae native from the NE-coast of North America (NMFS, 2016;Froese and Pauly, 2021) and one of the most recent fish invaders in Europe, specifically in the SW-Iberian Peninsula (Morais and Teodósio, 2016;Morais et al., 2017). The Sado estuary (Portugal) seems to be in the centre of the species invasion history, where it has been present at least since the early 2010s, however, the introduction vectors and pathways remain unknown (Morais and Teodósio, 2016;Morais et al., 2017) (Fig. 1). Fishers and anglers expressed their great concern about the putative impacts of weakfish upon native prize fish given their voracity (Morais and Teodósio, 2016). ...
... The Sado estuary (Portugal) seems to be in the centre of the species invasion history, where it has been present at least since the early 2010s, however, the introduction vectors and pathways remain unknown (Morais and Teodósio, 2016;Morais et al., 2017) (Fig. 1). Fishers and anglers expressed their great concern about the putative impacts of weakfish upon native prize fish given their voracity (Morais and Teodósio, 2016). Unfortunately, there is no information on the ecology of this species in the non-indigenous range to support such claims. ...
Weakfish Cynoscion regalis (Bloch and Schneider, 1801) is one of the most recent invasive fish in the Iberian Peninsula (Europe). Weakfish has established in the Sado estuary (Portugal) since the early 2010s, and fishers and anglers have expressed concern about its impacts on native prize fish. However, almost a decade later, there is no information on the ecology of weakfish in the non-native area. So, we aimed to assess weakfish feeding strategy and feeding plasticity through stomach content analysis to evaluate if these factors may contribute to its invasiveness, as well as to determine the ecological overlap between weakfish and three native prize fish – European bass, white seabream, and particularly meagre (since they are taxonomically closer), through carbon and nitrogen stable isotopes. Our results demonstrate that Sado’s weakfish has a generalist feeding strategy and preys the same functional groups it targets in the native area, therefore feeding strategy may weigh on invasiveness but not feeding plasticity. Weakfish, meagre, and European bass were in the same trophic level and weakfish exhibited higher trophic overlap with meagre, suggesting that weakfish could directly impact meagre if food and habitat become limiting. This study is the first assessment about weakfish ecology in the non-native area and our findings are an excellent starting point to understand this invasion. It can also be useful for management programs that promote weakfish consumption to minimize its impacts, alleviate fishing pressure on native species, and raise public awareness.
... On the other hand, sporadic reports may also trigger the onset of a citizen science project. For example, the first record of weakfish Cynoscion regalis (Animalia, Perciformes) in southern Portugal was reported by a fisherman to scientists (Morais and Teodósio, 2016). This led to the development of a citizen science project-through social media and traditional media-which revealed that the species was going unnoticed by the scientific community for years in several locations across Portugal (Morais et al., 2017). ...
... Zenetos et al., 2013;Cigliano et al., 2015;Anderson et al., 2017) or fishing (e.g. Danielsen et al., 2009;Morais and Teodósio, 2016;Tiralongo et al., 2019). Our bibliographic survey disclosed that 41 articles (32.5%) delved into an aquatic ecosystem (Marine or Freshwater) (Figure 2), but only 25 involved field sampling or the report of observations by citizens. ...
... Several actions can be merged to increase the outreach of citizen science projects and the chance to convey the "right" message about biological invasions to the public and maximizing integrated management of biological invasions ( Figure 6). Thus, informed citizens with their intrinsic Local Ecological Knowledge can be recruited as citizen scientists and early warning agents to detect the introduction of NIS and track their expansion (Boero et al., 2009;Gallo and Waitt, 2011;Azzurro et al., 2013;Hoebeke et al., 2015;Morais and Teodósio, 2016;Hobson et al., 2017;Grason et al., 2018;Eritja et al., 2019;Encarnação, unpublished data). They can also be recruited to eradicate species during field restoration actions to reduce the impact of invasive species in highly invaded ecosystems-e.g., invasive terrestrial plants (Crall et al., 2010), intertidal invasive invertebrates (Miralles et al., 2016), marine invasive fish (Peiffer et al., 2017). ...
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Biological invasions are among the most challenging ecological and conservation riddles of our times. Fortunately, citizen science projects became a valuable tool to detect non-indigenous species (NIS), document their spread, prevent dispersion, and eradicate localized populations. We evaluated the most undisputed definitions of citizen science and proposed that a combination of two of them is a better reflection of what citizen science has become. Thus, citizen science is any environmental and/or biological data collection and analysis, including data quality control, undertaken by members of the general public, as individuals or as organized groups of citizens, with the guidance and/or assistance of scientists toward solving environmental and/or community questions. With this review, we also assessed how citizen science has been advancing biological invasions research and its focus, by analyzing 126 peer-reviewed articles that used citizen science methods or data concerning NIS. Most of the articles studied terrestrial species (68%) and terrestrial plants were the most studied group (22.7%). Surprisingly, most first detection reports were of non-indigenous marine fish probably due to the constraints in accessing aquatic ecosystems which delays the detection of new NIS. Citizen science projects running over broad geographical areas are very cost-effective for the early detection of NIS, regardless of the studied environment. We also discuss the applicability and need to adapt the methods and approaches toward the studied ecosystem and species, but also the profile of the participating citizens, their motivations, level of engagement, or social status. We recommend authors to better acknowledge the work done by contributing citizens, and the putative limitations of data generated by citizen science projects. The outreach planning of citizen science projects is also evaluated, including the use of dedicated web platforms vs. pre-existent and disseminated web platforms, while discussing how such outreach actions can be maximized. Lastly, we present a framework that contextualizes the contributions of citizen science, scientific research, and regional and national stakeholders toward the integrated management of biological invasions.
... New non-native species continue to invade the system. Silurus glanis (European catfish), widely introduced in Europe to support fishing, has colonized the upper estuary in recent years (Gago et al. 2016), while the lower reaches have recently been colonized by Cynoscion regalis (weakfish) from the Atlantic coast of North America, presumably via ballast water (Morais & Teodosio 2016, Gomes et al. 2017). In its native range, the weakfish is most abundant in the brackish waters of Chesapeake Bay where it supports commercial and sport fisheries, functions as an important prey species and is regarded as estuary-dependent. ...
... If so, then control efforts can be undertaken, recognizing that they most likely will just slow the spread or increase of the species. For example, the weakfish, Cynoscion regalis, a native of the Atlantic coast of North America, has recently invaded Portuguese estuaries; its presence was discovered when it started to appear in fisheries (Morais & Teodosio 2016). It is possible that this fish will eventually become abundant enough to support commercial fisheries, as it does in the USA. ...
Non‐native fishes are part of estuarine ecosystems worldwide, but especially in temperate regions. In some estuaries, entirely new assemblages of native and non‐native fishes with global origins have arisen. Major findings include: (i) large temperate estuaries heavily modified by human activity are most likely to support non‐native fishes; (ii) most successful non‐native fishes are euryhaline; (iii) there are no taxonomic restrictions as to which euryhaline fish species can invade estuaries as long as they have means and opportunity; (iv) few non‐native fishes have demonstrably done harm to estuarine ecosystems or fish assemblages; (v) most successful non‐native species eventually become naturalized and fit into local assemblages; (vi) most colonization events are not successful. Many estuaries have been modified so thoroughly and rapidly that they are increasingly inhospitable to both native and naturalized species, as demonstrated by the San Francisco Estuary.
... Additionally, reports from Local Ecological Knowledge experts-e.g., professional fishers, farmers, land managers, forest rangers-provide critical and timely insights into species distribution and behavior. For example, citizen scientists reported the first records of several marine NIS in the Mediterranean Sea (Azzurro et al., 2013(Azzurro et al., , 2019Zenetos et al., 2013), while fishers reported two new marine NIS in southern Portugal (Morais and Teodósio, 2016;Morais et al., 2019). ...
... The apparent fragmented distribution of the Atlantic blue crab in two ecosystems in southern Portugal , led us to hypothesize that this species has gone unnoticed by the scientific community, as it happens so often with other NIS (i.e., Azzurro et al., 2013;Morais and Teodósio 2016;Grason et al., 2018). This article focuses on the Atlantic blue crab as it became the most prominent marine invasive species in the Algarve, and aims to demonstrate the usefulness of citizen science to track the expansion of aquatic invasive species by 1) describing how we designed and implemented a citizen science campaign called NEMA (Novas Espécies Marinhas do Algarve-New Marine Species of the Algarve), and how it may serve as a model to other citizen science campaigns, 2) illustrating how effective a citizen science campaign can be in tracking the expansion of NIS using the Atlantic blue crab in Algarve as a model species, 3) elaborating a cost-benefit analysis to provide evidence on why we label NEMA as a low-cost citizen science campaign. ...
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Citizen science and informed citizens have become fundamental in providing the first records and accounts about the expansion of numerous non-indigenous species. However, implementing a successful citizen science campaign can be expensive and particularly difficult for aquatic species. Here, we demonstrate how a low-cost citizen science campaign and its outreach plan in social and traditional media enabled to track the expansion of the Atlantic blue crab Callinectes sapidus Rathbun, 1896 along the coast of Algarve (southern Portugal, Europe). We describe the outreach strategy and a cost-benefit analysis of the first year of the citizen science campaign. Social media platforms allowed us to reach a significant number of citizens (over 31,500 clicks in Facebook publications), while traditional media gave national visibility to the citizen science campaign and biological invasions. In only 1 year, we documented the spread of the invasive Atlantic blue crab across the entire 140 km of the Algarve coast with 166 valid observations referring to 1747 specimens, submitted by 62 citizen scientists. We spent 0 € on the citizen science campaign, but considering the time invested in the campaign the cost would have summed up to 3,751 €, while the total minimum cost for one scientist to go to the field and retrieve the equivalent information would have exceeded 11,000 €. We used free online tools of communication to obtain the records about the Atlantic blue crab, instead of a dedicated web platform or mobile app, and handled social media accounts ourselves, which saved us at least 18,815 €. The citizen science campaign revealed that the Atlantic blue crab is unequivocally established in southern Portugal and that females appear to exhibit summer migrations to coastal areas to spawn as in the native area. Overall, our low-cost citizen science campaign effectively documented the rapid spread of a marine invasive species while providing some insights into its ecology. Our strategy can be easily replicated and implemented elsewhere in the world to tackle the ever-growing problem of biological invasions while increasing the scientific literacy of local populations.
... Weakfish Cynoscion regalis (Bloch and Schneider 1801), a species native from the Northwestern Atlantic, is one of the most recent introduced fish in the Iberian Peninsula (Europe) where it has established at least one viable population (Morais and Teodósio 2016;Morais et al. 2017). Weakfish was probably introduced in Europe through multiple introduction events and ballast water is considered the most likely introduction vector. ...
... If correct, weakfish would belong to a restricted list of fish that were introduced via ballast water (see table 1 in Morais et al. 2017). Weakfish is present in the Sado estuary (Portugal) before 2012, where it has reached an invasive status (Mundo da Pesca 2014; Morais and Teodósio 2016;Morais et al. 2017). For extensive details about the invasion history of weakfish in Europe and the Iberian Peninsula please consult Morais et al. (2017). ...
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The consumption of edible aquatic invasive species has gained popularity as a means to minimize their impacts while easing pressure on native resources and ecosystems. Weakfish Cynoscion regalis (Bloch & Schneider, 1801) is one of the most recent invasive fish species in the Iberian Peninsula (Europe) which once sustained an important fishery in the native range (Northwest Atlantic Ocean). Portugal ranks third in the list of the world’s fish consumers, so promoting a weakfish fishery could at least minimize the impacts upon native species, since weakfish have innate traits that are appreciated by Portuguese fish consumers. However, introducing a new species to consumers is challenging owing to consumers’ habits and unfamiliarity with the species. So, we aimed to (i) evaluate the acceptance of weakfish by a panel of Portuguese fish consumers and (ii) create outreach actions—partnerships with local Chefs and press releases—to explain to a broader audience what invasive species are and promote the consumption of edible aquatic invasive species. We conducted a consumers survey that showed that weakfish has great chances of being well accepted by Portuguese fish consumers– 90% would buy weakfish because they appreciated its appearance, flavor, and texture, besides being a wild fish. The outreach actions reached a few million people because 46 online articles were published, and three news pieces were broadcasted on national television. Our strategy increased the public’s awareness about weakfish as an invasive species, which could be adapted for other non-indigenous marine species elsewhere in the world.
... The Sado estuary is the second largest estuarine system in Portugal and one of the most impacted by anthropogenic pressures. The aquaculture industry has grown significantly in recent years (Vieira et al. 2019) and important recreational marinas and fishing/commercial harbors are located in this estuary, one of which with intense traffic of transoceanic ships, boosting propagule pressure (Morais and Teodósio 2016). ...
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Research effort concerning biological invasions has increased significantly but the pressure of multiple vectors of introduction (MVI) on coastal areas is still poorly understood. The aim of this work is to provide a comprehensive list of non-indigenous species (NIS) occurring in the Sado estuary, identify and prioritize MVI to deliver recommendations for bioinvasions management. Fouling communities were sampled in five artificial systems during 2021 and 2022. Additionally, a thorough literature review was performed to provide a comprehensive NIS database for the Sado estuary. Native distribution of NIS was classified based on biogeographic realms and the most likely pathways and vectors of introduction were assigned to each introduction. A total of 52 NIS were catalogued, predominantly arthropods, 22% of which were reported until 2005, while 40% were recorded in the last 2 years. We also reported four new NIS to Portugal. Most NIS were native from the Temperate Northern Pacific and the Temperate Northern Atlantic. Shipping related vectors were dominant (61%). Aquaculture was not directly linked to many invasions (8%), however contaminants on animals was the second most significant vector (23%). Our results highlight the need for managing MVI in locations that may act as invasion hotspots. Additionally, it provides support for future policy and management measures by identifying areas that are vulnerable to biological invasions. The introduction of NIS is an important driver of changes on biodiversity, and it should be included as a key element for the creation of an integrated management tool for the Sado estuary.
... This has been particularly problematic in aquatic ecosystems due to the difficulty in access (Encarnação et al. 2021a). Therefore, it is unsurprising that numerous first records of marine NIS were made by citizen scientists (Boero et al. 2009;Azzurro et al. 2013;Ferreira et al. 2015; Morais and Teodósio 2016;Suaria et al. 2017; Bariche et al. 2018). Citizen science has made significant contributions in multiple areas (e.g., ecology, physics, astronomy) (Odenwald 2018;Andersson-Sundén et al. 2019;Encarnação et al. 2021a), often at low costs (Crall et al. 2010;Tulloch et al. 2013;Encarnação et al. 2021b). ...
The establishment of many non-indigenous species is primarily controlled by propagule pressure, local environmental conditions, and biological interactions. An introduction is doomed to fail if any one of these factors is unsuitable. A few Atlantic blue crab Callinectes sapidus Rathbun, 1896 specimens have been collected along a limited stretch of the central Portuguese coast since the late 1970s, but a viable population was never detected. However, starting in 2016, a population of the Atlantic blue crab has established and expanded along the southern Portuguese coast. The objective of the present study was to provide insights into the invasion of the Atlantic blue crab in Portugal based on unpublished museum collection records and new records made by citizen scientists on the western coast and to provide a mechanistic explanation for the recent expansion based on observational oceanography data. Citizen science records along with observational oceanography data from 2019 and 2020 suggest that the southern Portugal population is expanding towards the western coast due to warmer coastal countercurrent events that form in the Gulf of Cadiz during the reproductive period of the Atlantic blue crab (summer–early fall). This oceanographic feature facilitates the transport of larvae towards the western coast of Portugal, which increases propagule pressure, while estuaries along the southwestern coast may serve as stepping stones supporting the northwards expansion of the species in tandem with increasing sea temperature. This study also highlights the value of citizen science in detecting the range expansion of invasive species over wide geographical areas.
... For example, the platform Mosquito Alert allowed for the first detection of an exotic mosquito, Aedes japonicus (Theobald) (Diptera: Culicidae), in Spain (Eritja et al. 2019), and iNaturalist facilitated the detection of the European firebug, Pyrrhocoris apterus Linnaeus (Hemiptera: Pyrrhocoridae), in Ontario (Oviedo Rojas and Jackson 2018). Similarly, the first detection of a North American fish, Cynoscion regalis (Bloch & Schneider) (Pisces: Sciaenidae), in Europe was made by fishermen in Portugal and reported in specialised magazines, personal blogs, and regional media (Morais and Teodósio 2016). Although data collected through community science projects are sometimes criticisedfor example, for their lack of true absence data, their quality, or their bias in geographic coveragereported observations can often be validated, thereby making valuable contributions to science while also decreasing the costs of research and increasing community awareness (Crall et al. 2010;Bois et al. 2011;Johnson et al. 2020;Larson et al. 2020;Encarnação et al. 2021). ...
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The elm zigzag sawfly, Aproceros leucopoda Takeuchi (Hymenoptera: Argidae), was reported for the first time in North America during the summer of 2020. Characteristic zigzag defoliation was reported in the province of Québec, Canada, on the community science website, iNaturalist. Field trips conducted to the site resulted in the collection of live specimens (a few larvae and a cocoon from which an adult emerged) and onsite observation of diagnostic defoliation and empty cocoons, confirming the presence of this exotic species in Canada. Subsequent inspection of elm trees by naturalists and scientists in the south of the province led to the conclusion that the species is more widely distributed than first expected and that the invasion is not localised to a small area. Preliminary genetic data pointed to a possible European origin of the Canadian population, but conclusive assignment to source will require examination of more specimens and the collection of reference sequences from different European and Asian populations. This is a good example of the importance of community science in the detection of new invasive species.
... However, estuaries on the subcontinent are vulnerable to invasion by marine or estuarine fish species, as has occurred in the San Francisco Estuary in the USA (Stompe et al. 2020). Although gobies are the main threat via ship ballast water discharge (Kotta et al. 2016) in South African ports, other marine fish species also have the potential to be transported across oceans to new continents via ballast water or escape from aquaculture (Morais and Teodosio 2016). Possible reasons for the current lack of successful estuarine fish introductions via ballast water could be the length of time it takes for ships to reach South Africa from overseas ports, as well as the fact that the major ports of Cape Town, Port Elizabeth and Durban are either not situated on an estuary or the rivers entering the harbours are small and have limited estuarine functionality. ...
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We review the possible impacts of non-native biota on the indigenous fishes of South African estuaries, including macrophytes, algae, pathogens, invertebrates, and fishes. Freshwater macrophytes are one of the primary non-native groups in the oligohaline reaches of some predominantly open estuaries, lake and river mouth type estuaries, as well as the entire area of certain low salinity, temporarily closed estuaries. Anoxia and hypoxia in the water column below Salvinia molesta and Pontederia crassipes floating mats have caused fish kills in certain temporarily closed estuaries. Mass mortalities of fish in estuaries have arisen from harmful algal blooms (HABs) and a catchment-derived pathogenic water mould, Aphanomyces invadans. Non-native invertebrate species in local estuaries are derived from freshwater, estuarine and marine sources. The freshwater gastropod Tarebia granifera has invaded many subtropical estuaries and may be negatively impacting their food webs, with estuarine zoobenthivorous fishes not appearing to consume this mollusc. The marine polychaete Ficopomatus enigmaticus has invaded many South African estuaries and, in some of them, changed the zoobenthic food web by encrusting on hard surfaces and filtering particulate matter from the water column. This species also does not appear to be eaten by zoobenthivorous fishes within these systems. No non-native marine or estuarine fish species have been recorded in South African estuaries but non-native freshwater fish species now occur in 25% of estuaries in the region. Degraded estuaries in particular are more vulnerable to colonisation by non-native and translocated fish species than unimpacted systems. During the 1990s, a fish survey of 191 estuaries revealed that only 0.04% of the catch comprised non-native or translocated species but this percentage has increased in many estuaries in recent decades. Non-native and translocated freshwater fish species have successfully colonised the oligohaline and mesohaline reaches of many systems and there may be an impact due to predation on the eggs and larvae of resident estuarine taxa and the recruitment success of catadromous and some estuarine-associated fish species. However, most non-native fishes have a limited tolerance for the salinity regimes found in the lower and middle reaches of many South African estuaries, with an even larger threat to the indigenous estuarine ichthyofauna coming from non-native plant, invertebrate and pathogen invaders. Based on this review, and other similar global studies, there is a developing paradigm that non-native invasions by fishes and other organisms into South African and global estuaries are driven primarily from freshwater taxa and not estuarine or marine species.
... Even though this species is classified as endangered in the west Atlantic, it is a non-native species in Portugal. While further research is necessary to assess the effects of their introduction, the early maturity, and high fitness and appetite warrant a potential reduction of their prey species as well as the out-competition of native species (such as Dicentrarchus labrax or Argyrosomus regius - Gomes et al., 2017;Morais and Teodósio, 2016). We thus focus on the ecological impact on protected native species: High mortalities are found for species of low protection (LC, NT and VU) and the lowest mortalities for species classified as data deficient (DD) and critically endangered (CR). ...
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With the global increase of marine protected area (MPA) implementation, the need for monitoring and the evaluation of their effectiveness becomes ever more important. Currently there is a severe lack of information about the protection effects of soft-substrate ecosystems. While many different methods have been established for the monitoring of hard-substrate ecosystems, most of these minimally invasive methods prove ineffective for soft- bottom habitats. Information and quantification of the impact of monitoring methods is needed to provide decision makers with the necessary knowledge to choose appropriate and feasible monitoring methods. In this study we quantify the impact of experimental trammel net fishing as a monitoring method of the soft-substrate demersal fish community using the Arrábida MPA (Portugal) as a case study. Over the 14 biannual sampling campaigns (between 2010 and 2019) 21,873 individuals and 5.61 tonnes of fish were caught. The gear is highly effective with an average catch per unit effort higher than reported for commercial fisheries in adjacent areas. When excluding the pelagic species, mortality rates are 41.2% and 30.4% in numbers and biomass, respectively. Most of the dead individuals belong to small, non-protected species with relatively little commercial value while MPA conservation target groups such as Soleidae and Rajidae have high survival rates. Due to its low size- and species-selectivity and the high survival rate of protected valuable species, the trammel net experimental fishing proved to be an effective monitoring method for soft-substrate demersal fish communities. Given their relatively low impact on the local ecosystem experimental trammel nets are a good alternative for areas where non-extractive methods are not effective. Nevertheless, quantification of the impact of other monitoring methods is necessary to enable the determination of the methods with the lowest mortality and impact for future soft-substrate MPA monitoring.
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Despite the rapid expansion of the built environment, we know little about the biology of species living in human-constructed habitats. Camel crickets (Rhaphidophoridae) are commonly observed in North American houses and include a range of native taxa as well as the Asian Diestrammena asynamora (Adelung), a species occasionally reported from houses though considered to be established only in greenhouses. We launched a continental-scale citizen science campaign to better understand the relative distributions and frequency of native and nonnative camel crickets in human homes across North America. Participants contributed survey data about the presence or absence of camel crickets in homes, as well as photographs and specimens of camel crickets allowing us to identify the major genera and/or species in and around houses. Together, these data offer insight into the geographical distribution of camel crickets as a presence in homes, as well as the relative frequency and distribution of native and nonnative camel crickets encountered in houses. In so doing, we show that the exotic Diestrammena asynamora not only has become a common presence in eastern houses, but is found in these environments far more frequently than native camel crickets. Supplemental pitfall trapping along transects in 10 urban yards in Raleigh, NC revealed that D. asynamora can be extremely abundant locally around some homes, with as many as 52 individuals collected from pitfalls in a single yard over two days of sampling. The number of D. asynamora individuals present in a trap was negatively correlated with the trap's distance from a house, suggesting that these insects may be preferentially associated with houses but also are present outside. In addition, we report the establishment in the northeastern United States of a second exotic species, putatively Diestrammena japanica Blatchley, which was previously undocumented in the literature. Our results offer new insight into the relative frequency and distribution of camel crickets living in human homes, and emphasize the importance of the built environment as habitat for two little-known invading species of Orthoptera.
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Documenting and responding to species invasions requires innovative strategies that account for ecological and societal complexities. We used the recent expansion of Indo-Pacific lionfish (Pterois volitans/miles) throughout northern Gulf of Mexico coastal waters to evaluate the role of stakeholders in documenting and responding to a rapid marine invasion. We coupled an online survey of spearfishers and citizen science monitoring programs with traditional fishery-independent data sources and found that citizen observations documented lionfish 1-2 years earlier and more frequently than traditional reef fish monitoring programs. Citizen observations first documented lionfish in 2010 followed by rapid expansion and proliferation in 2011 (+ 367%). From the survey of spearfishers, we determined that diving experience and personal observations of lionfish strongly influenced perceived impacts, and these perceptions were powerful predictors of support for initiatives. Our study demonstrates the value of engaging citizens for assessing and responding to large-scale and time-sensitive conservation problems.This article is protected by copyright. All rights reserved.
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Introduced species often seem to perform better than conspecifics in their native range. This is apparent in the high densities they may achieve or the larger individual sizes they attain. A prominent hypothesis explaining the success of introduced terrestrial species is that they are typically free of or are less affected by the natural enemies (competitors, predators, and parasites) they encounter in their introduced range compared to their native range. To test this hypothesis in a marine system, we conducted a global assessment of the effect of parasitism and predation on the ecological performance of European green crab populations. In Europe, where the green crab is native, crab body size and biomass were negatively associated with the prevalence of parasitic castrators. When we compared native crab populations with those from introduced regions, limb loss (an estimator of predation) was not significantly lower in introduced regions, parasites infected introduced populations substantially less and crabs in introduced regions were larger and exhibited a greater biomass. Our results are consistent with the general prediction that introduced species suffer less from parasites compared to populations where they are native. This may partly explain why the green crab is such a successful invader and, subsequently, why it is a pest in so many places.
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Because the meagre (Argyrosomus regius) is not currently found around the Balearic Islands (western Mediterranean), the Balearic government is carrying out a restocking programme to recover its population. The success of this programme is critically dependent on improved knowledge of the meagre’s life cycle, and particularly its reproductive biology. Data on key reproductive parameters based on both reared and wild specimens are reported here. Histological examinations and gonadosomatic indices from 342 reared specimens demonstrated that 1) the potential reproductive season ranged from April to June and peaked in May, and 2) length at maturity (L50) was 49.3 cm for males and 57.2 cm for females, age at maturity (A50) was 2.7 years for males and 3.5 years for females, and weight at maturity (W50) was 1396 g for males and 1892 g for females. Histological examinations of 37 wild fish from Cádiz (SW Spain) demonstrated that the meagre has determinate fecundity. The annual potential fecundity of reared females ranged from 0.9 to 4.2 million oocytes, which is exponentially dependent upon female size.
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Fish are the largest phylum of living vertebrates, with around 30,000 fish species out of approximately 50,000 vertebrate species ( [1]. Fishes inhabit almost every aquatic environment on the planet, presenting an enormous variation in temperature, salinity, oxygen, and other chemical and physical water properties. These environments have exerted evolutionary pressures that have resulted in the evolution of the enormous number of fishes and an immense variety of reproductive strategies. Fish exhibit various types of sex determination, from genetic to environmental control, sex differentiation from hermaphroditism to gonochorism, age of puberty, from a few months to many years, fecundity, from a few to millions of eggs, internal or external fertilization, a wide range of egg sizes, some that float and others that sink or stick to substrates, uncared eggs scattered into the environment to parental care of eggs to live “birth” (ovoviviparity) [2-4]. The existence of these diverse reproductive strategies has important implications for finfish culture and broodstock management. Finfish culture is the fastest growing food production industry in the world, and in 2005 a total of 28.3 million T of finfish were produced, which is around 20% of the world’s fisheries production (aquaculture and capture fisheries) [5]. The number of species being cultured is also increasing rapidly, and 67 different cultured finfish species in 2005 had an annual production of over 10,000 T, which is twice the amount produced by the 28 species being cultured in 1980 [6]. One of the most important aspects at the basis of this continuing increase in the number of cultured species is our growing understanding of the complexities of the many different reproductive strategies of various fishes and how these behave in captivity. This is perhaps best demonstrated by the development of the culture of the catfishes (Pangasius ssp) in Vietnam. These catfishes do not mature in captivity, but during the 1990s hormone stimulation techniques were developed to induce ovulation/spermiation. This technology gave the control required to produce eggs, larvae and juveniles that formed the basis of an expanding aquaculture industry, producing 40,000 T in 1997 and 376,000 T in 2005 [6]. This chapter aims at giving a general vision of fish reproduction and the reproductive dysfunctions found in captive-reared fishes, and describe how this knowledge is used to develop treatments for the control of fish reproduction in aquaculture. This general view will be covered under four broad areas relevant to the control of gonad maturation and spawning of fish in captivity. First, it will be described the normal gonadal development as can be expected under optimal (natural) conditions, particularly the morphology of gonad development and its endocrine and environmental regulatory mechanisms. Second, the reproductive dysfunctions that are observed in fish held in captivity; often the captive environment does not provide the environmental conditions that a species requires to complete maturation. Third, the available techniques for the stimulation of ovulation and spermiation, both environmental manipulations and hormonal treatments of reproductively dysfunctional fish held in captivity. Finally, the last sections will describe the application of adequate broodstock management protocols and hormonal therapies for the stimulation of fish reproduction in captivity for some of the main food fish species under production, both as a reference and indication of the possible strategies available to stimulate ovulation and spermiation in species considered candidates for new aquaculture developments.