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Article

Reproductive Parameters of the Western Tubenose Goby (Proterorhinus semilunaris) from Žitný Island, Slovakia, in Connection with Its Invasive Potential

by
Eva Záhorská
1,*,
Mária Balážová
2,
Andrea Kečkéšová
1 and
Daniel Gruľa
3
1
Department of Ecology, Faculty of Natural Sciences, Comenius University, Ilkovičova 6, 842 15 Bratislava, Slovakia
2
Department of Biology and Ecology, Pedagogical Faculty, Catholic University, 034 01 Ružomberok, Slovakia
3
Department of Zoology, Faculty of Natural Sciences, Comenius University, Ilkovičova 6, 842 15 Bratislava, Slovakia
*
Author to whom correspondence should be addressed.
Fishes 2025, 10(10), 528; https://doi.org/10.3390/fishes10100528
Submission received: 15 September 2025 / Revised: 9 October 2025 / Accepted: 14 October 2025 / Published: 17 October 2025
(This article belongs to the Special Issue Community Ecology of Freshwater Animals and Biodiversity)
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Abstract

Three populations of the western tubenose goby were analysed during the reproductive season of 2024 in the area of Žitný Island, Slovakia. Specimens were processed in the laboratory, where meristic and reproductive parameters were detected. Populations were female-dominated and all in good condition. Males showed a decrease in condition, probably due to different roles during reproduction. Females were characterised by increased values of the absolute (114–3997; mean 1299 oocytes) and relative number of oocytes (114–3206; mean 1225 oocytes), gonadosomatic index (3.02–93.27%; mean 19.49), and oocyte size (0.10–1.93 mm) compared to other native and/or invasive areas of occurrence. Comparing populations from 2024 with 2015, we found that females from the present study have smaller body sizes, higher values of absolute and relative number of oocytes, but lower values of gonadosomatic index and larger sizes of oocytes. This would suggest a shift to a more generalistic strategy based on a hypothesis derived from the theory of alternative ontogenies and invasive potential. Although the western tubenose goby is regarded as a native species in Slovakia, its reproductive parameters suggest a shift to more opportunistic behaviour. This pattern is consistent with its invasiveness in other non-native regions, such as parts of Europe and the Laurentian Great Lakes.
Keywords:
phenotypic plasticity; invasive fish species; specialistic and generalistic strategies
Key Contribution: The western tubenose goby exhibits a considerable flexibility in modifying its life-history traits, as reflected in an increase in the absolute and relative number of oocytes and smaller size at maturation. Due to these parameters, it can colonise new areas of occurrence faster and become a serious threat to native biota.

1. Introduction

Phenotypic plasticity refers to an organism’s capacity to alter its phenotype in response to environmental variation [1]. Adaptive phenotypic plasticity allows organisms to persist across diverse environments by modifying traits such as gene expression, physiology, behaviour, and morphology [2,3]. The extent of adaptive plasticity varies within and among species and is widespread. This variation is significant for understanding the mechanisms by which some organisms survive and diversify in novel environments [4,5]. Investigating the existence and mechanisms of phenotypic plasticity is fundamental, as it integrates multiple levels of biological research.
When environmental conditions change, an individual organism must detect and process new environmental information to adapt. The organism then initiates responses that may include alterations in gene expression, neural activity, and the production of hormones, enzymes, or proteins necessary for phenotypic adjustment. Performance or fitness consequences can occur if an individual’s phenotype does not match the current environmental optimum, as supported by recent evidence [6]. Developmental and phylogenetic constraints influence phenotypic expression pathways in addition to natural selection. As a result, the phenotype expressed in a given environment reflects both adaptive and developmentally determined aspects of plasticity [7]. Each phenotype produced by a genotype arises from the expression of its genome under specific conditions. Therefore, reaction norms for a species are determined by genotype, environmental context, and the trait under consideration [3].
Invasive species are often distinguished by elevated phenotypic plasticity (e.g., [8]). This can facilitate colonisation of new environments and enhance survival under novel environmental stressors, such as altered thermal regimes, changing water levels, different food sources, etc., during the initial stages of the invasive process (e.g., [9]). Consequently, it may promote the establishment of local populations and subsequent range expansions (e.g., [10]). Numerous invasive fish species exhibit increased phenotypic plasticity in morphology and life-history traits (e.g., [11,12,13]). The western tubenose goby (Proterorhinus semilunaris), native to the Ponto-Caspian region, exemplifies this pattern. Compared to other Gobiidae species, such as the round goby (Neogobius melanostomus) and the bighead goby (Ponticola kessleri), the western tubenose goby spreads more slowly. Its native range in the Danube basin remained practically unchanged from the 19th century until the beginning of the second half of the 20th century [14]. For example, the species has been documented in the Morava basin (Slovakia) since at least 1874, at the mouth of the River Morava, which flows into the Danube. But it was not recorded earlier than 2014 in eastern Slovakia [12]. Due to this, it has a specific position in Slovakia, where it should act more like a non-native or naturalised species these days, rather than as a species with invasive-like traits. P. semilunaris was also introduced to North America by ballast water in the 1990s into the St. Clair River (Michigan; [15]). A decade after the introduction, its distribution was limited to the Hudson–Erie corridor and Lake Superior (e.g., [16]). Between 2011 and 2016, a slow and steady eastern expansion resulted in its distribution to Eastern Lake Erie, Lake Ontario, and the Upper St. Lawrence River [17,18]. Lastly, it was discovered in Quebec, its uppermost distribution area so far [19]. Even while it is the slowest-spreading species among all invasive goby species, it still has a substantial impact on native biota. Predation on fish larvae [20], competition with native benthic fishes due to diet or habitat overlap [16,21,22], competition for spawning sites [23], possible overlap with vulnerable or endangered species [24], and changes to the food web [21] are the leading causes of concern. Despite its impact as an invasive species in Europe and North America, it has received relatively limited research attention. Thus, this study aimed to (1) analyse life-history traits of three populations coming from Žitný Island, Slovakia, (2) compare them with the other nine populations from our previous study [25], and (3) evaluate their possible invasive potential demonstrated by their successful spread in the area of Žitný Island, Slovakia.

2. Materials and Methods

Fish were sampled using electrofishing gear from April to June 2024 at three sites on Žitný Island, Slovakia (Figure 1). The Veľkolelské arm (47.7541942 N, 17.948890 E) is a part of the Danube River basin, which was cut off from the main stream at the end of the 20th century as part of preparations for the construction of the Gabčíkovo–Nagymaros waterworks. Thus, the arm gradually became covered with sediment and began to overgrow. Between 2013 and 2015, it underwent complete restoration, and now it is directly connected to the Danube River. The Foki site (47.8282708 N, 17.5603889 E) is entirely dependent on the amount of water in the Danube River. It is replenished from the lower connection, and if there is little water in the main stream due to high temperatures it misses the water in the upper parts. The last site, Vojka (47.9568872 N, 17.397678 E), is refilled with water from artificial floods, which occur twice a year during spring and summer. They should simulate conditions at the Danube River before the building of Gabčíkovo–Nagymaros, where the water reaches places that would not survive without it.
A total of 178 tubenose goby specimens (86 females, 92 males) were collected, anesthetised with clove oil, and immediately preserved in 4% formaldehyde solution. Samples were stored at room temperature (approximately 20 °C) in airtight plastic containers in a dark environment. The weight, eviscerated weight, and gonad weight of each specimen were measured to the nearest 1 mg using a KERN ABJ 120-4M balance. The sex ratio (females to males) was calculated by dividing the number of males by the number of females. Spawning period specimens were analysed for oocyte diameter, oocyte size groups, and both absolute and relative oocyte numbers. Gravimetric analysis determined the absolute (ANO) and relative (RNO) number of oocytes [26]. The gonadosomatic index (GSI) was calculated using eviscerated female body weight and a standard formula (e.g., [26]). A random subsample of 50 oocytes from each gonad was used to determine the oocyte size range. Oocyte diameters were measured to the nearest 0.0025 mm using an ocular micrometre. Oocyte size distribution and size groupings were then evaluated. To investigate the condition of the three populations, Fulton’s condition factor [27] was determined using the following formula:
K = 100000 × W/TL3
where W is the total body weight (g) and TL is the total length (mm).
Populations from our previous study came from nine different sites [25]. They were sampled during April 2015 along a 10–160 m stretch of artificial melioration channels of Žitný Island, Slovakia. However, the sampling sites differed from those used in the present study (Figure 1). In populations, we analysed the same parameters as in the present study, namely body weight, eviscerated body weight, gonad weight, GSI, ANO, RNO, oocyte diameter, and size groups of oocytes.
The normality of the data distribution was assessed using the Shapiro–Wilk test. When the assumption of normality was not rejected (p > 0.05), one-way analysis of variance (ANOVA) and Student’s t-test were applied for statistical comparisons. Due to this, the differences in meristic and reproductive parameters among all examined populations were evaluated in this way. Fulton’s factor of condition was assessed using a t-test for single means in females and males separately. In contrast, the differences between males and females within the population were tested using a t-value test for dependent samples. The analysed populations were later compared with samples from our previous study [25] using discriminant functional analysis (DFA) and ANOVA (STATISTICA 13) to test differences in all parameters analysed.

3. Results

The sex ratio (F:M) was 0.45:1 at Foki, 1:0.92 at Vojka, and 1:0.38 at the Veľkolelské arm.
The standard length (SL) of examined females (n = 86) ranged from 26.60 to 53.00 mm (mean 36.04 mm), body weight from 0.37 to 3.75 g (mean 1.46 g), and eviscerated body weight from 0.17 to 2.76 g (mean 1.08 g; see Table 1 for more details). During the spawning period in 2024, the absolute number of oocytes ranged from 114 to 3997 (mean 1299), while the relative number of oocytes varied from 114 to 3206 (mean 1225). The GSI values also ranged from 3.03 to 93.27 (mean 19.49; see Table 2 for more details). There were statistically significant differences among all meristic and reproductive parameters (except GSI) between females from all sites (p < 0.05). For ANO (F (2, 83) = 84.284, p < 0.01, Figure 2a; SL (F (2, 83) = 6.640, p < 0.01, Figure 2b), W (F (2, 83) = 82.146, p < 0.01), RNO (F (2, 83) = 11.791, p < 0.01), and FC (F(2, 83) = 6.527, p < 0.01).
In females from all sites, 1–2 size-groups of oocytes were clearly distinguished. During the spawning season, 84.6–100% of the females had oocytes in the two size-groups (for more details, see Table 3). Only one size-group of oocytes was formed in 8.7 to 15.4% of the females (Table 3). The oocyte diameter ranged between 0.10 and 1.09 mm (mean 0.47 mm) in size-group I, and between 0.41 and 1.93 mm (mean 0.63 mm) in size-group II.
The SL of examined males (n = 92) ranged from 30.70 to 62.00 mm (mean 45.37), body weight from 0.57 g to 6.59 g (mean = 2.94 g), eviscerated body weight from 0.42 g to 6.01 g (mean = 2.64 g), and weight of gonads from 0.01 to 0.12 g (mean = 0.05 g). The GSI of the males during spawning season ranged from 0.52 to 10.72 (mean = 2.32; for more details, see Table 4).
Differences in Fulton’s factor of condition were statistically significant (F(2, 172) = 3.5643; p < 0.05) between females as well as males from all populations. It was the lowest in females (mean 1.35) and in males (mean 1.45) at Foki, and the highest in females at the Veľkolelské arm (mean 1.64) and in males at Vojka (mean 1.51; Table 5, Figure 3).
Comparing the parameters of females from the present study and our previous study [25], we found statistically significant differences (p < 0.05) in ANO (F(1, 320) = 13.140, p < 0.01; Figure 4a) and SL (F(1, 320) = p < 0.01; Figure 4b). The DFA revealed significant differences between the two datasets, with ANO and RNO identified as key variables contributing to their discrimination (Figure 5). However, the reclassification into the correct population was only 34%, with the Vojka population being the most clearly separated, reaching 73% correct reassignment, while the remaining two populations were indistinguishable from the populations in our previous study (both with 0% assignment to the correct population).

4. Discussion

The prediction that the western tubenose goby exhibits plasticity in life-history traits at various stages of invasion is supported by the diversity in sex ratio, reproductive attributes, and condition among study populations.

4.1. Sex Ratio and Condition

The western tubenose goby demonstrates reproductive behaviour common to all gobiid species. This relates to typical roles in males and females, leading to generally increased body size and weight. Indeed, males in our study were bigger and heavier compared to females from all sites (except the SL of males from the Veľkolelské arm). Proportionally, they were in lower numbers (the sex ratio was in favour of females in two sites), which could be explained by specific reproductive behaviour, where males are usually beneath the stones preparing the nests and protecting them [28]. Due to this, their sampling is less effective [29]. Similar outcomes were also found in other invasive populations at different areas of occurrence (e.g., [25,30,31,32]).
The condition of females and males from all sites showed statistically significant differences. However, each sample was generally in good condition, with females in better condition compared to males (except at site Foki, where the opposite was observed; Figure 3). Differences in condition are again connected with different roles during reproduction, where males need to prepare and protect the nest. At the same time, females invest more energy into the production of oocytes and an increase in the size of the ovaries.

4.2. Reproductive Parameters

All females were mature during the analysed season (April-June) with high values of GSI (13–20%). In the native area (Turkey; [33]), as well as in other invasive areas of occurrence (Czech Republic [32]; Poland [31]), the values were lower (between 11 and 12%). On the other hand, our previous research showed higher values of GSI (17–24%; [25]). The smallest mature female reached 26.60 mm, which was comparable with our previous study (26.27 mm) but smaller compared to other areas of occurrence where the research was conducted (e.g., [24,31,32]). Here, the smallest females reached 38–42 mm (Turkey; [34]) and 46–47 mm, respectively [31,32]. From the results, it is evident that the females from the Slovakian part mature at a very small size.
At the same time, the females were characterised by higher values of ANO (except the population from Foki). These values were comparable to those in our previous study. Still, they were higher than in populations from other native areas (56–344 oocytes [33], respectively, 123–155 oocytes [34]) or invasive areas of occurrence (510–772 [24], respectively, 504–1250 [31] in Poland, and 140–1349 oocytes in the Czech Republic [32]). Asynchronous oocyte development, which is linked to batch spawning that lasts for the duration of the reproductive season, is typical for gobiid species, as well as for the western tubenose goby (e.g., [24,35]). Thus, it is usually characterised by 1 to 3 groups of oocytes ready for spawning events over time. All examined populations were characterised by two size groups of oocytes, with variable percentages and sizes reached in different size groups (Table 3). Although the oocytes were larger in mean size and maximum size compared to other populations from Slovakia (0.06–1.46 mm [25]), they remained smaller than eggs from native areas (1.31 mm in average; [33,34]) and/or invasive areas of occurrence (0.15–1.92 mm; [31]).
Determining why fecundity is increased or decreased, and why the size of oocytes is larger or smaller in populations, is always a matter of several observations. In invasive species, which are characterised by increased levels of phenotypic plasticity, the reason can be changing environmental conditions, various levels of the invasive process, and different strategies in the production of alternative ontogenies. Research on fish invasions in European waters indicates that, contrary to popular belief, many of these successful invaders are specialists (in their native region) rather than generalists in terms of their life histories, with bighead and round gobies as classic examples (e.g., [36]). On the other hand, a generalistic strategy typically emerges during the early stages of invasion or in permanently changing conditions. In this way, it is characterised by decreased body size and an increased number of reproductive cells, which relate to a shift of energy into reproduction rather than somatic growth [11,37]. This is also evident in our research (Figure 2 and Figure 4). However, P. semilunaris has occurred in Slovakian waters for a substantial period; thus, we should not consider this species a “newcomer”. Because of this, it is more likely to hypothesise that changing conditions, especially water level fluctuations, are responsible for the increased influence of phenotypic plasticity on modifying life-history traits. All three analysed sites have different connections to the Danube River, with varying water supplies throughout the year. The hypothesis derived from the theory of alternative ontogenies and invasive potential (AIOP) is based on the premise that successfully spreading and/or invasive species benefit from their developmental plasticity, i.e., the ability to generate alternative ontogenies and life-histories. In their native areas of occurrence, they create more specialised forms characterised by larger oocytes, accompanied by larger body proportions and lower values of fecundity. The same pattern can be expected under stable conditions, meaning conditions which are loaded by the smallest number of disturbances and/or pressures. Yet, if conditions are unpredictable and/or under permanent disturbance, species experience higher levels of stress and shift their strategy to be more generalised. This will be evident in the production of smaller oocytes, earlier maturation with smaller body sizes, and increased values of fecundity. However, a life-history that is beneficial at the beginning of the invasion, and/or in permanently disturbed habitats, may become adverse once the population has established and achieved high density. Due to this, ontogenies and/or life-histories within such a population tend to return to more specialised trajectories, typical of native populations and/or those occurring in stable conditions (e.g., [24]). A similar assumption can also be drawn from the classic ecological concept, where newly colonised habitats typically feature r-selected individuals. Still, these individuals tend to become K-selected once the population has established itself (e.g., [38]). The first type of strategy—generalistic—may be a contributing factor to the rapid population expansion. Similar behaviour was also observed in other species with expanding ranges, including the highly invasive round goby [39] and/or topmouth gudgeon (Pseudorasbora parva; [40]). Comparing the parameters mentioned above, we can say that all western tubenose goby populations coming from Slovakia (from this study, or from our previous study [25]) differ from other populations from native as well as invasive areas of occurrence [24,31,32,33,34] and are characterised by a generalistic strategy.
Interesting questions arise in connection with the variable values of life-history traits across different sites in the western part of Slovakia. As is obvious, populations from our previous study were larger (longer SL), heavier, and had higher values of GSI. However, they had lower values of ANO and RNO (Figure 4), which would suggest a shift toward a more specialistic strategy. This could be explained by the character of the sites from which the populations originate. Populations from our previous study originated from artificial melioration channels on Žitný Island, characterised by minimal fluctuations in water levels. Although other environmental characteristics were not collected, it appears that water fluctuation, as evident in our present study, has a very strong effect on life-history traits. In our previous study [25], we found that the populations from nine sites were characterised by a generalist strategy, compared to variable studies from the Czech Republic, Poland, and/or Turkey. However, comparing only populations from Slovakia, we can see that even on a small scale they are very flexible in creating two different strategies. On the one hand, they are more generalistic in comparison with the world, and on the other hand, they are more specialistic compared to other Slovakian populations. Specific shifts in strategies have also been observed in other species considered as invasive. One example is the topmouth gudgeon from a long-established population (with values of reproductive parameters comparable to those of native populations), which underwent a disruption of its habitat connected with a flood and a rapid increase in water level. Here, the population immediately increased the number of oocytes in the next reproductive season and started to act as invasive again [41]. Accordingly, the population of round goby was able to form a post-flood batch of eggs, which means they were able to create not two batches during the reproductive season, but three [11]. Although the analysed populations had only two batches (not three or more as in other studies), they were able to modify the size of oocytes and their final amount. Of course, there can be arguments about the short time of research, because we had only one sampling at each site, which can be problematic in batch spawners. Nevertheless, we were able to assess the beginning of the reproductive season and thus analyse ANO. Another question is the small number of individuals at sampling sites, especially at the Veľkolelské arm. Yet, the results are comparable to those from our previous study [25]. The most considerable difference, which was also statistically significant, was observed at the Vojka site. Here, the population was characterised by the highest number of specimens and the most generalistic strategy (based on the size of oocytes and values of ANO). However, a smaller sample size can be potentially problematic for analyses related to the relationship between reproductive effort and shifts in a species’ strategy. Due to a lack of data during the reproductive season, the predictions can be limited.

4.3. Invasive Potential

Determining the invasive potential of each non-native species is a considerable challenge. Populations may benefit from flexibility in the short term, but it is uncertain if this will be sufficient given the rate of environmental change. Population recovery and persistence may result from an evolutionary answer, a plastic answer, or a combination of the two, depending on the type and rate of environmental change [42]. It seems that the western tubenose goby will be able to survive not only at new sites of occurrence, but also in a changing world. Based on an AOIP, we can say that a species’ capacity for invasion increases with the range of phenotypes it can produce, from the most generalised to the most specialised (e.g., [41]). The ability to alternate the strategies can buy time for populations to establish or persist in new and/or occupied areas. Exhibition of variable phenotypes as a response to biotic or abiotic conditions will help the persistence and successful spread of invasive species. The ecological and evolutionary consequences of phenotypic plasticity depend on whether it arises as an organism’s general strategy or in response to a particular environmental change. According to the tested hypothesis, individuals from invasive western tubenose goby populations will mature sooner and will have higher fecundity and smaller oocytes than those from native populations. As we have already mentioned, the western tubenose goby has a specific position in Slovakian waters, and it is considered a native species (according to the Slovak Republic’s Fisheries Act No. 216/2018 and Executing Decree No. 381/2018 Coll). Comparing the values of the analysed populations with other non-native and/or invasive populations, we should potentially reanalyse their position. Even as a range-expanding native species, it uses a generalistic strategy as demonstrated by the highest values of ANO, the smallest sizes of oocytes, and the smallest sizes of SL reached during maturation. A generalistic strategy is usually used by species that occur in new areas and/or are under permanent stressful conditions. This shift in strategy gives species the possibility to survive and maintain viable offspring able to spread. Such behaviour is also well known in other invasive fish species, e.g., the topmouth gudgeon [43], the round goby [20], or the pumpkinseed (Lepomis gibbosus; [13]). These highly invasive species are flexible in modifying their morphology and/or life-history traits. Considering several hypotheses and theories related to invasive organisms, the “Matthew effect” is also applicable. The term has been adopted in multiple fields because it refers to the theory that initial advantages lead to further cumulative advantages, whereby high-condition individuals have the opportunity to show adaptive, plastic responses to rapid environmental change and low-condition individuals fall by the wayside (e.g., [44]). This pattern can also explain the successful dispersion of the western tubenose goby to 11 countries in Europe [20] and also to North America, where its spread continues [19].
Not to mention, environmental conditions can also be a source of such shifts in strategies. Due to human activities, conditions are changing and are responsible for the formation of variable pressures. Based on the Water Framework Directive in the European Union, pressure is defined as a physical expression of human activities that alters the environment’s status, such as discharge, abstraction, and environmental changes [45]. The creation of channels, water level fluctuations, and erosion of benches can all serve as potential disturbances responsible for such shifts. Importantly, a stronger pressure from predators can also lead to a change in strategy as a result of maintaining viable offspring. Unfortunately, such parameters were not detected in this study, which represents a possible weakness of the presented research.

5. Conclusions

The ability of species and populations to adapt to altered environmental conditions is critical to their persistence. Without a question, the winners and losers will depend on both the ability of individuals to exhibit phenotypic plasticity and the ability of populations to adapt. The western tubenose goby in the area of Western Slovakia acts as a species with a generalistic strategy and thus with the capability of modifying its life-history traits, which manifests in decreased SL, increased ANO and RNO, as well as a reduced sizes of oocytes compared to the other native and/or invasive areas of occurrence. Based on this, we can say that it demonstrates traits typical of successful colonisers, which can lead to potential invasiveness in water systems where it has not yet appeared.

Author Contributions

Conceptualisation, E.Z.; validation, E.Z. and M.B.; investigation, E.Z., A.K. and M.B.; data curation, E.Z. and M.B.; writing—original draft preparation, E.Z.; funding acquisition, E.Z.; writing—review and editing, E.Z., M.B. and D.G.; supervision, E.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Slovak Scientific Grant Agency (Project No. 1/0448/23).

Institutional Review Board Statement

The standards set for fish rearing in laboratory conditions, according to Directive 2010/63/EU of the European Parliament and of the Council of 22 September 2010 on the protection of animals used for scientific purposes, were followed carefully. The permission for sample collection was granted by the Ministry of Environment of the Slovak Republic (License No. 12/2/2024).

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors on request.

Conflicts of Interest

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Abbreviations

The following abbreviations are used in this manuscript:
ANOAbsolute number of oocytes
RNORelative number of oocytes
GSIGonadosomatic index
WBody weight
TLTotal length
FFemale
MMale
SLStandard length
AOIPAlternative ontogenies and invasive potential

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Figure 1. Location of sampling sites of the western tubenose goby from Žitný Island (Slovakia). (Dark grey circles: VJ—Vojka, F—Foki, VL—Veľkolelské arm; light grey circles: KK1—Dunajský Klátov, KK2—Potôňske lúky, KVK1—Amadeho Kračany, KVK2—Štrkovec, KB—Mad, KKB—Boheľov, KSJ—Trstená—Jurová, VH—Vrbina, VMH—Veľký Meder; [25]).
Figure 1. Location of sampling sites of the western tubenose goby from Žitný Island (Slovakia). (Dark grey circles: VJ—Vojka, F—Foki, VL—Veľkolelské arm; light grey circles: KK1—Dunajský Klátov, KK2—Potôňske lúky, KVK1—Amadeho Kračany, KVK2—Štrkovec, KB—Mad, KKB—Boheľov, KSJ—Trstená—Jurová, VH—Vrbina, VMH—Veľký Meder; [25]).
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Figure 2. Differences between means of standard length (a) and absolute number of oocytes (b) in three populations of the western tubenose goby from Žitný Island (Slovakia).
Figure 2. Differences between means of standard length (a) and absolute number of oocytes (b) in three populations of the western tubenose goby from Žitný Island (Slovakia).
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Figure 3. Differences between means of Fulton’s factor of condition in males (M) and females (F) in three populations of the western tubenose goby from Žitný Island (Slovakia).
Figure 3. Differences between means of Fulton’s factor of condition in males (M) and females (F) in three populations of the western tubenose goby from Žitný Island (Slovakia).
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Figure 4. Differences between means of standard length (a) and absolute number of oocytes (b) in twelve populations of the western tubenose goby from Slovakia. “A” represents populations from Žitný Island analysed in our former study [25], and “B” represents populations from the present study. In the corners of the figure are values for each site from both studies.
Figure 4. Differences between means of standard length (a) and absolute number of oocytes (b) in twelve populations of the western tubenose goby from Slovakia. “A” represents populations from Žitný Island analysed in our former study [25], and “B” represents populations from the present study. In the corners of the figure are values for each site from both studies.
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Figure 5. Discriminant functional analysis scatter plot (DFA) with means of canonical variables and 50% ellipsoids about the centroid of each population of the western tubenose goby from nine different sites on Žitný Island (Slovakia) used in [25] and three sites from the present study (Foki, Vojka, Veľkolelské arm), with discrimination based on variability of absolute and relative number of oocytes (KK1—Dunajský Klátov, KK2—Potôňske lúky, KVK1—Amadeho Kračany, KVK2—Štrkovec, KB—Mad, KKB—Boheľov, KSJ—Trstená—Jurová, VH—Vrbina, VMH—Veľký Meder; [25]).
Figure 5. Discriminant functional analysis scatter plot (DFA) with means of canonical variables and 50% ellipsoids about the centroid of each population of the western tubenose goby from nine different sites on Žitný Island (Slovakia) used in [25] and three sites from the present study (Foki, Vojka, Veľkolelské arm), with discrimination based on variability of absolute and relative number of oocytes (KK1—Dunajský Klátov, KK2—Potôňske lúky, KVK1—Amadeho Kračany, KVK2—Štrkovec, KB—Mad, KKB—Boheľov, KSJ—Trstená—Jurová, VH—Vrbina, VMH—Veľký Meder; [25]).
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Table 1. Quantitative parameters in the western tubenose goby females within observed populations from Žitný Island (Slovakia) (n—number of females, SL—standard length, W—body weight, EW—eviscerated body weight, W—weight; mean values are in brackets).
Table 1. Quantitative parameters in the western tubenose goby females within observed populations from Žitný Island (Slovakia) (n—number of females, SL—standard length, W—body weight, EW—eviscerated body weight, W—weight; mean values are in brackets).
nSL (mm)W (g)EW (g)W Gonads (g)
Foki1340.20–53.00 (46.25)1.77–3.60 (2.55)1.48–2.66 (1.96)0.05–0.71 (0.28)
Vojka6526.60–44.70 (32.85)0.37–2.45 (1.08)0.17–1.66 (0.79)0.04–0.72 (0.16)
Veľkolelské arm836.50–52.5 (45.40)1.52–3.75 (2.79)1.07–2.76 (2.02)0.11–0.83 (0.39)
Table 2. Reproductive parameters in the western tubenose goby females within observed populations from Žitný Island (Slovakia) (n—number of females, GSI—gonadosomatic index, ANO—absolute number of oocytes, RNO—relative number of oocytes, OD—oocyte diameter; FC—Fulton’s condition factor; mean values are in brackets).
Table 2. Reproductive parameters in the western tubenose goby females within observed populations from Žitný Island (Slovakia) (n—number of females, GSI—gonadosomatic index, ANO—absolute number of oocytes, RNO—relative number of oocytes, OD—oocyte diameter; FC—Fulton’s condition factor; mean values are in brackets).
nGSI (%)ANORNODO
Foki133.02–28.83(13.75)114–1121 (613)181–1916 (1183)0.10–1.80 (0.61)
Vojka655.64–93.27(20.46)163–3997 (1469)114–3206 (1140)0.08–1.81 (0.61)
Veľkolelské arm86.15–38.24(20.93)474–2049 (1035)833–2868 (1979)0.10–1.93 (0.66)
Table 3. Oocyte parameters in the western tubenose goby females from all examined sites from Žitný Island (Slovakia).
Table 3. Oocyte parameters in the western tubenose goby females from all examined sites from Žitný Island (Slovakia).
Percentage of Oocyte Size GroupsSize of Oocytes in Each Size Group
Siten12III
Foki1315.484.60.10–0.950.41–1.80
Vojka658.792.30.08–1.090.65–1.81
Veľkolelské arm80.1100.00.10–0.970.42–1.93
Table 4. Parameters in the western tubenose goby males within observed populations from Žitný Island (Slovakia) (n—number of males, SL—standard length, W—body weight, EW—eviscerated body weight, W—weight; mean values are in brackets).
Table 4. Parameters in the western tubenose goby males within observed populations from Žitný Island (Slovakia) (n—number of males, SL—standard length, W—body weight, EW—eviscerated body weight, W—weight; mean values are in brackets).
SitenSL (mm)W (g)EW (g)W Gonads (g)GSI
Foki2936.00–62.00 (56.00)1.11–6.59 (4.75)1.00–6.01 (4.30)0.02–0.12 (0.06)0.52–2.69 (1.45)
Vojka6027.20–57.40 (40.30)0.57–5.37 (2.08)0.42–4.76 (1.85)0.01–0.09 (0.04)0.56–10.72 (2.66)
Veľkolelské arm330.70–54.80 (44.03)0.83–4.57 (2.65)0.67–4.17 (2.36)0.04–0.08 (0.07)1.65–6.26 (3.90)
Table 5. Fulton’s factor of condition for the western tubenose goby from all examined sites on Žitný Island (Slovakia) (n—number of females/males).
Table 5. Fulton’s factor of condition for the western tubenose goby from all examined sites on Žitný Island (Slovakia) (n—number of females/males).
SitenFemalesnMales
Foki131.18–1.69 (1.35)291.17–1.73 (1.45)
Vojka650.68–2.02 (1.55)601.27–1.83 (1.51)
Veľkolelské arm81.22–1.99 (1.64)31.41–1.59 (1.47)
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Záhorská, E.; Balážová, M.; Kečkéšová, A.; Gruľa, D. Reproductive Parameters of the Western Tubenose Goby (Proterorhinus semilunaris) from Žitný Island, Slovakia, in Connection with Its Invasive Potential. Fishes 2025, 10, 528. https://doi.org/10.3390/fishes10100528

AMA Style

Záhorská E, Balážová M, Kečkéšová A, Gruľa D. Reproductive Parameters of the Western Tubenose Goby (Proterorhinus semilunaris) from Žitný Island, Slovakia, in Connection with Its Invasive Potential. Fishes. 2025; 10(10):528. https://doi.org/10.3390/fishes10100528

Chicago/Turabian Style

Záhorská, Eva, Mária Balážová, Andrea Kečkéšová, and Daniel Gruľa. 2025. "Reproductive Parameters of the Western Tubenose Goby (Proterorhinus semilunaris) from Žitný Island, Slovakia, in Connection with Its Invasive Potential" Fishes 10, no. 10: 528. https://doi.org/10.3390/fishes10100528

APA Style

Záhorská, E., Balážová, M., Kečkéšová, A., & Gruľa, D. (2025). Reproductive Parameters of the Western Tubenose Goby (Proterorhinus semilunaris) from Žitný Island, Slovakia, in Connection with Its Invasive Potential. Fishes, 10(10), 528. https://doi.org/10.3390/fishes10100528

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