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Article

Microplastic Pollution and Its Physiological Effects on the Top Fish Predator Dentex dentex from the Western Mediterranean

by
Amanda Cohen-Sánchez
1,
Antònia Solomando
1,2,
Montserrat Compa
1,
Antonio Box
3,
Inmaculada Montero
4,
Silvia Tejada
5,6,7,
Samuel Pinya
2,6,
Maria Magdalena Quetglas-Llabrés
1,* and
Antoni Sureda
1,6,7,*
1
Research Group in Community Nutrition and Oxidative Stress (NUCOX), University of Balearic Islands-IUNICS (Institut Universitari d’Investigació en Ciències de la Salut), E-07122 Palma, Balearic Islands, Spain
2
Interdisciplinary Ecology Group, Department of Biology, University of the Balearic Islands, E-07122 Palma, Balearic Islands, Spain
3
Department of Agricultura, Ramaderia, Pesca, Caça i Cooperació Municipal, Consell Insular d’Eivissa, E-07800 Eivissa, Balearic Islands, Spain
4
Fundación Universidad y Empresa de las Islas Baleares (FUEIB), E-07800 Eivissa, Balearic Islands, Spain
5
Laboratory of Neurophysiology, University of the Balearic Islands-IUNICS (Institut Universitari d’Investigació en Ciències de la Salut), E-07122 Palma, Balearic Islands, Spain
6
Health Research Institute of Balearic Islands (IdISBa), E-07120 Palma, Balearic Islands, Spain
7
CIBER Fisiopatología de la Obesidad y Nutrición (CIBEROBN), Instituto de Salud Carlos III (ISCIII), E-28029 Madrid, Spain
*
Authors to whom correspondence should be addressed.
Microplastics 2025, 4(2), 28; https://doi.org/10.3390/microplastics4020028
Submission received: 1 April 2025 / Revised: 2 May 2025 / Accepted: 6 May 2025 / Published: 22 May 2025
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Abstract

:
Microplastic (MP) pollution is a growing environmental concern, particularly in marine ecosystems. This study investigated the presence and effects of MPs in the common dentex (Dentex dentex), a commercially and ecologically important species in the Mediterranean Sea. Fish (n = 22) were collected from Ibiza’s coastal waters (western Mediterranean, Spain), and their gastrointestinal tracts were analysed to determine MP ingestion rates and potential physiological impacts. MPs were detected in 90.9% of the specimens, with an average of 6.6 ± 1.2 MPs per individual. Fibres accounted for 78.9% and fragments for 21.1%. Stress and detoxification biomarkers were assessed by categorizing fish into two groups based on MP load: low (<6 MPs) and high (≥6 MPs). Fish with higher MP loads showed significantly increased detoxification and antioxidant enzyme activities in the digestive tract, while malondialdehyde levels remained similar between groups. No significant differences were observed in liver biomarkers. These findings indicate that MP ingestion triggers physiological responses in D. dentex, activating antioxidant and detoxification defences in the digestive tract. However, the lack of response in the liver suggests that the MP load is not sufficient to induce systemic changes. Further research is needed to assess long-term consequences on fish health and ecosystem sustainability.

1. Introduction

Microplastic (MP) pollution has become a pressing environmental issue, particularly in marine ecosystems, where it poses potential risks to a wide range of organisms [1]. MPs, defined as plastic particles smaller than 5 mm, originate from multiple sources and persist in aquatic environments due to their resistance to degradation [2]. They are broadly classified into primary MPs, which are intentionally manufactured at a microscopic scale (e.g., microbeads in cosmetics, industrial abrasives, and synthetic textile fibres), and secondary MPs, which result from the fragmentation of larger plastic items through photodegradation, mechanical abrasion, and biological processes. Once released into the environment, these particles accumulate in marine waters, sediments, and biota, where they can be mistaken for food by various aquatic organisms [3,4]. Fish, in particular, are vulnerable to microplastic ingestion due to their feeding strategies, trophic interactions, and habitat overlap with contaminated areas [5]. The ingestion of MPs can have a range of biological effects, including physical damage to the digestive tract, reduced nutrient absorption, and potential toxicity from associated chemical additives or adsorbed pollutants [6]. Furthermore, MPs in marine environments function as vectors for bacterial biofilms, predominantly composed of members from the phyla Proteobacteria, Firmicutes, and Bacteroidetes, as well as potentially pathogenic bacterial genera such as Vibrio, Pseudomonas, Salmonella, and Acinetobacter [7,8]. These microbial associations can lead to disruptions in the food chain, coral bleaching, and alterations in immune responses [8]. MPs can also carry other harmful substances, such as organic pollutants and heavy metals [9,10], further exacerbating their impact on marine organisms [11].
The Balearic Islands, located in the western Mediterranean Sea, constitute a region of significant ecological, economic, and social importance. Their coastal and marine ecosystems support high biodiversity, including numerous endemic and commercially valuable fish species. However, due to their geographical location and anthropogenic pressures, these islands are particularly susceptible to plastic pollution [12]. The Mediterranean Sea has been identified as one of the most affected marine regions in the world in terms of plastic accumulation, with estimates suggesting that it holds some of the highest concentrations of MPs globally [13]. Several factors contribute to this issue, including intense maritime traffic, densely populated coastal areas, inadequate waste management, and strong ocean currents that transport plastics from various sources. Additionally, the Balearic Islands are a major global tourist destination, receiving millions of visitors annually, which further amplifies plastic pollution through increased consumption and waste generation [14]. Previous studies have reported the presence of MPs in commercial fish from Mediterranean waters including Seriola dumerili, Xyrichtys novacula, Scyliorhinus canicula, and Galeus melastomus [15,16,17]. Given the ecological and economic importance of fish populations in this region, it is essential to assess the extent of microplastic ingestion and its potential effects on local marine species.
In organisms, the ingestion of MPs can induce both physical and toxicological effects. On one hand, direct contact with these particles may cause mechanical damage to the intestinal epithelium, potentially leading to inflammation, oxidative stress, and impaired digestive function [18]. On the other hand, MPs pose significant toxicological risks due to their polymer composition, the presence of chemical additives, and their high capacity to adsorb environmental contaminants [19]. Consequently, their ingestion may facilitate the transfer of hazardous substances, either through intrinsic additives or via the adsorption of persistent organic pollutants and heavy metals from the surrounding environment. To counteract these effects, all species possess detoxification systems that convert harmful chemicals into less toxic compounds [20]. However, this process often generates reactive oxygen species (ROS) as byproducts [21]. Experimental studies have established a clear link between MP ingestion and accumulation and the activation of antioxidant defence mechanisms, leading to increased ROS production [22,23,24]. If not efficiently neutralized, ROS can accumulate and induce oxidative damage to essential biomolecules such as lipids, proteins, and DNA through reactions with cellular components [25]. Consequently, both antioxidant enzymes—such as catalase (CAT) and superoxide dismutase (SOD—and detoxification enzymes—such as ethoxyresorufin-O-deethylase (EROD) activity of CYP1A, and glutathione s-transferase (GST)—along with oxidative stress biomarkers, including malondialdehyde (MDA), are widely used as biochemical indicators of pollutant-induced oxidative stress.
The common dentex (Dentex dentex) (Linnaeus, 1758) is a littoral demersal species (0–200 m) belonging to the Sparidae family [26]. It is highly valued in both commercial and recreational fishing due to its attractiveness and high market demand [27,28]. This species can reach a maximum length of 100 cm and a weight of 13 kg, with a lifespan exceeding 20 years [29]. An iconic coastal marine fish, D. dentex is distributed across the Atlantic Ocean, from the Bay of Biscay to Cape Blanc and Madeira, as well as throughout the Mediterranean Sea, including the Balearic Islands [30]. D. dentex predominantly feeds on coastal fish and cephalopods, with its diet likely varying according to prey availability [31]. As a high-level trophic predator (trophic level 4.5), it occupies a key position in the coastal marine food web [32], making it particularly vulnerable to the bioaccumulation of various pollutants. Also, this species is classified as “vulnerable” in the Red List of Threatened Species in the Mediterranean Sea [33], making it an interesting study case.
Understanding the extent and consequences of MP ingestion in fish populations is essential for assessing its ecological implications and potential risks to fisheries and food safety. In this study, we aimed to investigate the presence, abundance, and potential negative effects of MP ingestion in D. dentex from the Balearic Islands measuring diverse biomarkers of oxidative stress and detoxification.

2. Materials and Methods

2.1. Study Area and Fish Sampling

A total of 22 specimens of D. dentex were wild-caught of the southwestern coast of the island of Ibiza (Balearic Islands) (Figure 1) between September and November of 2021, using trolling lines. The island is subject to significant anthropogenic pressure, primarily driven by tourism—an activity that accounts for 42% of the gross value added (GVA) across all sectors [34]. This intense tourism activity increasingly strains natural resources and local ecosystems, contributing to elevated pollution levels [35,36,37], with debris contamination doubling during the summer months [38]. Additionally, the estimated extraction of over 570,500 tons of fish between 1950 and 2010 [39] has led to a notable depletion of fishery resources.
Right after being caught, the fish were placed in an aerated tank and anesthetized with tricaine methanesulfonate (MS-222) (0.1 g/L of seawater) to reduce stress. Subsequently, they were measured and eviscerated on board. First, the total length (TL; ±0.1 cm) of each specimen was recorded. Then, the entire digestive tract (from the upper oesophagus to the end of the gastrointestinal system) and liver samples were extracted and weighed, and the possible presence of recent prey was assessed. A small section from the end of the intestine was separated, immediately frozen, and stored at −80 °C as well as liver samples until further analysis. The digestive tracts for MP analysis were stored at −20 °C.
The experimental protocol was approved by the Animal Experimentation Ethics Committee of the University of the Balearic Islands (Reference CEEA 96/05/18).

2.2. Microplastic Analysis

Before undergoing chemical digestion, all digestive tracts were left at room temperature to thaw. Once fully defrosted, the entire soft tissue was placed in a properly labelled glass Erlenmeyer flask and incubated with 10% KOH (20 mL of KOH per gram of sample) for 48 h at 60 °C until complete dissolution of the organic material was observed (Figure 2). To prevent air contamination, all flasks were covered with aluminium foil. Once the organic matter had fully degraded, the remaining solution was filtered under a vacuum using polycarbonate membrane filters (FILTER-LAB, pore size 10.0 μm, diameter 47 mm, Prat Dumas, France) inside a fume hood to minimize airborne contamination.
Each Erlenmeyer flask was rinsed three times with 50 mL of distilled water, which was also filtered. To avoid cross-contamination, all work surfaces and materials were meticulously cleaned and rinsed with deionized water between samples. The filters were then placed in glass Petri dishes, covered, and left to dry at room temperature for 24 h. Finally, the dried filters were examined under a Leica EZ4 stereomicroscope to identify MP particles. MPs were counted per individual fish, and their colour and shape were recorded. The shape of the MPs was classified into two categories: ‘fibres’ (slender or elongated items) and ‘fragments’ (angular or flat items) [40]. Images of the recovered MPs were captured using a Leica DFC295 digital camera (with optical enhancement up to 11.5×) and analysed with Leica application suite software v4.
To check for potential airborne plastic contamination, blank controls using distilled water were also visually inspected under the stereomicroscope. Additionally, to minimize contamination, all personnel involved in the procedure wore 100% cotton lab coats and gloves, and all steps were carried out in enclosed spaces as much as possible to reduce air circulation.

2.3. Biochemical Analysis

Different biomarkers of oxidative stress—CAT, SOD, and MDA—and detoxification—EROD and GST—in the liver and digestive tract were analysed. Liver and gut samples were homogenized in a 1:10 ratio (w/v) with 100 mM Tris-HCl buffer (pH 7.5) using an Ultra-Turrax® Disperser (IKA, Staufen, Germany). The homogenate was then centrifuged at 9000g for 10 min at 4 °C (Sigma 3K30, Osterode am Harz, Germany). The resulting supernatants were collected and used for subsequent biochemical analyses.
The activities of CAT, SOD, and GST were determined used the previously described methods and monitored in a Shimadzu UV-2100 spectrophotometer at 25 °C [41,42,43]. The EROD activity was determined following the method of Burke and Mayer (1974) with a Bio-Tek Fluorescence Microplate Reader (Agilent Technologies, Madrid, Spain) [44]. MDA as a marker of lipid peroxidation was evaluated with a specific colorimetric assay kit (Merk Life Science S.L.U., Madrid, Spain). All biochemical data were normalized per protein concentration measured with Bradford reagent (Bio-Rad Protein Assay, Alcobendas, Madrid, Spain), using bovine serum albumin (BSA) as a standard.

2.4. Statistical Analysis

The potential impact of MP presence in the digestive tract and liver was assessed using the statistical software SPSS 29.0 for Windows (IBM SPSS Inc., Chicago, IL, USA). Fish specimens were classified into two groups based on the median number of MPs detected in the gastrointestinal tract: low MP levels (n < 6) and high MP levels (n ≥ 6). Data normality and homogeneity of variances were verified through the Shapiro–Wilk test and Levene’s test, respectively. Differences between groups were analysed using either Student’s t-test for independent samples or the Mann–Whitney U test, depending on whether the data met the normality assumption. Pearson’s correlation test was applied to assess the relationship between MPs and biomarkers. The results are presented as mean ± standard error of the mean (SEM), with statistical significance set at p < 0.05.

3. Results

3.1. Biometric Parameters

During the sampling period, 22 specimens of D. dentex were captured around Ibiza Island. The entire digestive tract of each individual was analysed to assess MP ingestion and perform biochemical analyses. The mean TL of the sampled fish was 68.5 ± 1.2 cm, ranging from 47.0 to 85.0 cm. The digestive tract weights of the analysed specimens averaged 30.4 ± 1.8 g, with no evidence of recent prey in their digestive tracts.

3.2. Microplastic Presence

Out of the 22 digestive tracts examined, MPs were detected in 90.9% of the specimens (20 individuals). The analysis of the digestive contents revealed the presence of both fibres and fragments. A total of 147 MP items were recovered, with fibres accounting for 78.9% (n = 116) and fragments for 21.1% (n = 31) (Figure 3).
The mean number of MPs per individual was 6.6 ± 1.2 (Table 1). Notably, two specimens showed no MP particles in their digestive tract, while four individuals contained more than 10 particles, with a maximum of 20 particles recorded in a single fish. No significant relationship was observed between MP ingestion and fish size (linear regression, R2 = 0.0014, F1,20 = 0.028, p = 0.868).
A wide range of colours was identified among the MPs, with black (35.4%) and blue (34.7%) being the most common, followed by transparent and red particles (5.4%) (see Supplementary Material, Figure S1). Seven additional colours were observed, but each accounted for less than 5% of the total MPs. No MPs were detected in any of the blank samples analysed.
By dividing the fish into two groups according to the number of observed MPs (N = 11 < 6 items and N = 11 ≥ 6 items) for subsequent biochemical analysis, two homogeneous groups in terms of size were obtained, with a TL of 68.1 cm ± 2.5 cm and 69.0 cm ± 3.5 cm, respectively. The group with a higher presence of MPs had a mean of 10.9 ± 1.5 items, while the group with fewer MPs had a mean of 2.27 ± 0.49 items.

3.3. Biomarkers in the Digestive Tract

The biomarkers determined in the gut showed statistically higher values in fish with a higher presence of MPs than in those with a lower presence, except for MDA (p = 0.299). The activities of antioxidant enzymes were 50% higher for CAT (p = 0.015) and 32% for SOD (p = 0.013) in the group with more MPs compared to the group with fewer (Figure 4).
Regarding detoxifying enzymes, the activity was 38% higher for GST (p = 0.006) and 76% for EROD (p = 0.006) (Figure 5).

3.4. Biomarkers in the Liver

When analysing the different biomarkers in the liver, Student’s t-test or the Mann–Whitney U test—depending on whether the data met the normality assumption—concluded that the results were not statistically significant for any of them (Table 2), meaning that values of biomarkers are considered statistically equal, and therefore no differences can be inferred in the different MP abundance group. However, there is a slight tendency for the biomarkers to be higher in the group with a higher presence of MPs.

4. Discussion

The widespread presence of MPs is a global issue affecting oceanic ecosystems [45]. In 2018, global plastic production reached nearly 360 million metric tons, rising to a staggering 403 million tons in 2022 [46]. Of this plastic waste, 11% ends up in aquatic environments [47], where it begins to break down and, due to its inability to biodegrade, forms MPs [48]. Thus, the persistence and ubiquity of MPs allows their entry into food chains when ingested by marine organisms. Their small size makes them accessible to even the smallest organisms and has led to their detection in the digestive tracts of a wide range of taxa [15,49,50,51].
The present study provides evidence of MP ingestion in D. dentex from the Balearic Islands and evaluates its potential impact on oxidative stress and detoxification biomarkers. Our results revealed that MPs were detected in 90.9% of the sampled fish, with fibres being the dominant type of particle. The absence of spherical plastic microbeads or pellets in D. dentex samples may reflect their low prevalence in Balearic waters, where fibres are the dominant form [52], likely due to textile sources and recent EU regulations limiting microbeads (EU 2019/904). Due to its high trophic position, this species is particularly susceptible to microplastic ingestion through both direct consumption and trophic transfer from contaminated prey. The feeding behaviour of D. dentex, which involves active predation and the ingestion of whole prey [29], increases the likelihood of ingesting MPs present in its prey or in the water column. Additionally, the ingestion of whole prey without mastication can lead to a concentrated MP accumulation through bioamplification [53,54]. These findings are consistent with previous studies reporting high levels of MP contamination in other Mediterranean sparid fish species such as Sparus aurada, Pagellus erythrinus, and Diplodus sargus [55,56,57] or other large predators such as the carangid Seriola dumerili. Ref. [10] highlights the vulnerability of marine organisms in this region due to intense anthropogenic activity and plastic pollution.
Regarding MP colours found in the digestive tracts, black and blue particles accounted for over 70%. These findings are consistent with previous studies [58,59,60,61]. Although these colours may reflect plastic availability in the environment, studies suggest that MP gut accumulation is selective and therefore is not an accurate descriptor of MP presence in the marine environment [62]. This different pattern could also be due to misidentification of MPs as prey, such as blue copepods [51,63]. In addition, when analysing the type of plastic found in D. dentex guts, almost 80% were found to be fibres. These MPs can accumulate in both the water column and sediment, making them highly available in the environment, being found much more frequently than MP fragments [52]. Additionally, fibres are found abundantly in the digestive tracts of marine animals as is the case of Mullus surmuletus, where 97% of MPs were fibres [46,47], or Boops boops, where all the ingested MP were filaments [59].
MPs not only cause direct physical damage by harming natural defence barriers and vital immune organs such as the liver and intestines, but plastic additives can also penetrate cells, affecting organisms in multiple ways. These include disrupting immune cytokine levels, altering intracellular signalling pathways, and ultimately compromising immune function [64]. Such substances induce oxidative stress, which triggers the response of the detoxification system, which acts by denaturalizing these pollutants, and generally produce ROS, as a byproduct of the reactions. These reactive species are then reduced by the antioxidant enzymes. Therefore, a high presence of antioxidant enzymes is indicative of increased production of ROS, derived from exposure to stressful situations, such as pollutants. In this sense, oxidative stress biomarkers such as CAT and SOD, detoxification biomarkers like GST and EROD, and the lipid peroxidation biomarker MDA are commonly used to assess the effect of pollutants such as plastics or plastic additives on marine organisms.
In D. dentex, antioxidant (CAT and SOD) and detoxification (GST and EROD) enzyme activities were significantly higher in the digestive tissue of individuals with greater MP ingestion compared to those with lower MP loads. However, MDA levels did not differ significantly between groups. Moreover, when liver tissue was analysed for the same biomarkers, no significant differences were observed between MP concentration groups, although there was a slight trend towards higher values in individuals with greater MP exposure. The increased enzymatic activity in the gut suggests a response to higher MP exposure, as observed in previous studies on S. aurata [23,65,66]. The increased activity of these enzymes serves to mitigate oxidative damage and facilitate detoxification, which may be triggered by the release of polymers constituting the MP, the leaching of plastic additives, and the desorption of pollutants adhered to MP surfaces [67,68]. While many studies reported increased MDA levels alongside CAT and SOD activity, indicating oxidative lipid damage, if antioxidant enzyme activity is sufficient, lipid peroxidation may be prevented. In this context, the lack of significant MDA variation between MP concentration groups could suggest that antioxidant defences effectively counteract oxidative damage. This may be due to the fact that increases in MDA are typically observed in laboratory studies, where fish are exposed to higher and more sustained doses of microplastics compared to those found in the wild. In this regard, no significant changes in MDA have been reported in other studies on wild fish [58,69]. Particularly for large predators, the amount of MPs in comparison to the body size could result in a lesser effect of the pollutants, as would be the case of Seriola dumerili in the Balearic Islands, where the grouping was similar (more and less than eight MPs), and despite CAT and SOD being significantly higher, MDA levels remained unchanged [15]. In addition, the absence of significant changes in hepatic biomarkers may be due to the limited systemic exposure to microplastics, as not all particles or associated contaminants can cross the intestinal barrier [70,71]. In this sense, the quantity of MPs and/or associated contaminants in the highest-exposure group may not be sufficient to induce significant biomarker changes in the liver compared to the least-exposed group. Given that the liver is a systemic organ, a higher or more prolonged exposure might be required to trigger measurable effects. Notably, the alterations in biomarkers observed in the gut could partly result from the direct interaction of MPs with the intestinal epithelium, as previous studies have reported histological damage and inflammatory responses in fish following MP exposure [66,72].
Changes in oxidative stress markers can be observed in various tissues, including the liver, gut, brain, and embryos, depending on exposure conditions [58,73,74,75]. Higher exposure increases the likelihood of altered biomarker detection, making the gut—the primary site of MP ingestion—the first tissue where oxidative stress markers become apparent at low MP concentrations.

5. Conclusions

Overall, this study provides evidence of the widespread presence of MPs in the digestive system of D. dentex, detected in nearly all sampled individuals from the Balearic Islands. The detection of MPs in gastrointestinal tissues highlights the extent of marine plastic pollution and its infiltration into the trophic web, raising concerns about its impact on marine biodiversity and food safety. The observed biomarker alterations in the gut suggest that MP exposure may induce oxidative stress, potentially compromising the health of this species. However, the absence of significant alterations in the liver indicates that MP concentration may not be high enough to trigger systemic effects in tissues without direct contact with plastics. These findings highlight the need for further research to elucidate the long-term effects of MP accumulation on fish physiology and population dynamics.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/microplastics4020028/s1. Figure S1: Different colours observed in the plastic items from the gastrointestinal tract of Dentex dentex (%).

Author Contributions

Conceptualization, A.B., S.T., S.P. and A.S. (Antoni Sureda); methodology, all authors; formal analysis, A.C.-S., A.S. (Antònia Solomando), M.C. and A.S. (Antoni Sureda); investigation, all authors; writing—original draft preparation, A.C.-S., M.M.Q.-L. and A.S. (Antoni Sureda); writing—review and editing, all authors; project administration, A.B. and A.S. (Antoni Sureda); funding acquisition, S.P. and A.S. (Antoni Sureda). All authors have read and agreed to the published version of the manuscript.

Funding

This research was partially funded by the Programme of Promotion of Biomedical Research and Health Sciences, Instituto de Salud Carlos III (CIBEROBN CB12/03/30038). This work has also been partially financed by the Biodibal project, within the framework of the Collaboration Agreement between the University of the Balearic Islands and Red Eléctrica de España. A.C. was supported by an FPI Fellowship co-financed by the Balearic Government and the European Social Fund Plus (EFS+) as part of the EFS 2021–2027 operational programme. (FPI 027/2023).

Institutional Review Board Statement

The experimental procedures were approved by the Animal Experimentation Ethics Committee of the University of the Balearic Islands (Reference CEEA 96/05/18).

Informed Consent Statement

Not applicable.

Data Availability Statement

Researchers wishing to access the data used in this study can make a request to the corresponding author: antoni.sureda@uib.es.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
CATCatalase
ERODEthoxyresorufin-O-deethylase
GSTGlutathione s-transferase
MDAMalondialdehyde
MPMicroplastic
ROSReactive oxygen species
SODSuperoxide dismutase
TLTotal length

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Microplastics 04 00028 g001
Figure 1. Map of the geographic location of the sampling area in the southwest of the island of Ibiza within the Balearic Islands region and a representative picture of the target fish Dentex dentex. The inset map in the upper right corner shows the Balearic Islands, with Ibiza highlighted within a square boundary. The map was generated in ArcGIS 10.8.2, and the basemap is the World’s Oceans basemap from Esri, Garmin, NOAANGDC, and other contributors.
Figure 1. Map of the geographic location of the sampling area in the southwest of the island of Ibiza within the Balearic Islands region and a representative picture of the target fish Dentex dentex. The inset map in the upper right corner shows the Balearic Islands, with Ibiza highlighted within a square boundary. The map was generated in ArcGIS 10.8.2, and the basemap is the World’s Oceans basemap from Esri, Garmin, NOAANGDC, and other contributors.
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Figure 2. Diagram representing the materials and methods, including both the microplastic extraction and analysis and biomarker determination.
Figure 2. Diagram representing the materials and methods, including both the microplastic extraction and analysis and biomarker determination.
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Figure 3. Representative MPs found in the gills of Dentex dentex: (A) blue fragment particle; (B) black fibre particle. Scale bar represents 0.5 mm. The red arrows point to the MP represented. The material surrounding the fragment and the fibre are remnants of the undigested soft tissue.
Figure 3. Representative MPs found in the gills of Dentex dentex: (A) blue fragment particle; (B) black fibre particle. Scale bar represents 0.5 mm. The red arrows point to the MP represented. The material surrounding the fragment and the fibre are remnants of the undigested soft tissue.
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Figure 4. Oxidative stress biomarkers determined in the gut homogenates of Dentex dentex sampled in Ibiza (Balearic Islands). Specimens were categorized into two groups according to the median value for the presence of MPs, counting fibre and fragment particles: ≥6 MPs (n = 11) and <6 MPs (n = 11). (A) Catalase (CAT); (B) superoxide dismutase (SOD); (C) malondialdehyde (MDA). Data are displayed as mean ± standard error of the mean (S.E.M.). * indicates significant differences (p < 0.05) between groups.
Figure 4. Oxidative stress biomarkers determined in the gut homogenates of Dentex dentex sampled in Ibiza (Balearic Islands). Specimens were categorized into two groups according to the median value for the presence of MPs, counting fibre and fragment particles: ≥6 MPs (n = 11) and <6 MPs (n = 11). (A) Catalase (CAT); (B) superoxide dismutase (SOD); (C) malondialdehyde (MDA). Data are displayed as mean ± standard error of the mean (S.E.M.). * indicates significant differences (p < 0.05) between groups.
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Figure 5. Detoxifying enzymes determined in the gut homogenates of Dentex dentex sampled in Ibiza (Balearic Islands). Specimens were categorized into two groups according to the median value for the presence of MPs, counting fibre and fragment particles: ≥6 MPs (n = 11) and <6 MPs (n = 11). (A) Glutathione S-transferase (GST); (B) ethoxyresorufin-O-deethylase (EROD). Data are displayed as mean ± standard error of the mean (S.E.M.). * indicates significant differences (p < 0.05) between groups.
Figure 5. Detoxifying enzymes determined in the gut homogenates of Dentex dentex sampled in Ibiza (Balearic Islands). Specimens were categorized into two groups according to the median value for the presence of MPs, counting fibre and fragment particles: ≥6 MPs (n = 11) and <6 MPs (n = 11). (A) Glutathione S-transferase (GST); (B) ethoxyresorufin-O-deethylase (EROD). Data are displayed as mean ± standard error of the mean (S.E.M.). * indicates significant differences (p < 0.05) between groups.
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Table 1. Data summary corresponding to the number of fish dissected, number of fish with microplastics (MPs), the mean number of particles per individual, the total number of particles identified categorized per shape, and the frequencies of each shape.
Table 1. Data summary corresponding to the number of fish dissected, number of fish with microplastics (MPs), the mean number of particles per individual, the total number of particles identified categorized per shape, and the frequencies of each shape.
Total Number of FishFish with MPsMPs/Ind.
(Mean ± S.E.M.)
(Range)		MPs Identified
Fibres/Fragments		Fibres/Fragments per Ind.
(Range)		Frequencies (%)
Fibres/Fragments
22206.6 ± 1.2
(0–20)		116/315.2 ± 0.9/1.4 ± 0.4
(0–17)/(0–8)		78.9/21.1
Table 2. Activities of antioxidant and detoxifying enzymes and malondialdehyde levels in the liver of Dentex dentex according to the presence of microplastics in their guts.
Table 2. Activities of antioxidant and detoxifying enzymes and malondialdehyde levels in the liver of Dentex dentex according to the presence of microplastics in their guts.
CAT
(mK/mg)		SOD
(pKat/mg)		MDA
(nM/mg)		GST
(nKat/mg)		EROD
(RFU/min/prot)
≥6 MPs27.5 ± 3.80.81 ± 0.061.46 ± 0.07120.4 ± 13.267.2 ± 8.35
<6 MPs23.1 ± 2.90.77 ± 0.061.42 ± 0.12101.7 ± 10.161.0 ± 10.0
p value p = 0.188 p = 0.321 p = 0.416 p = 137 p = 0.320
No statistical differences were observed in any parameter. Catalase (CAT); superoxide dismutase (SOD); malondialdehyde (MDA); glutathione s-transferase (GST); ethoxyresorufin-O-deethylase.
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Cohen-Sánchez, A.; Solomando, A.; Compa, M.; Box, A.; Montero, I.; Tejada, S.; Pinya, S.; Quetglas-Llabrés, M.M.; Sureda, A. Microplastic Pollution and Its Physiological Effects on the Top Fish Predator Dentex dentex from the Western Mediterranean. Microplastics 2025, 4, 28. https://doi.org/10.3390/microplastics4020028

AMA Style

Cohen-Sánchez A, Solomando A, Compa M, Box A, Montero I, Tejada S, Pinya S, Quetglas-Llabrés MM, Sureda A. Microplastic Pollution and Its Physiological Effects on the Top Fish Predator Dentex dentex from the Western Mediterranean. Microplastics. 2025; 4(2):28. https://doi.org/10.3390/microplastics4020028

Chicago/Turabian Style

Cohen-Sánchez, Amanda, Antònia Solomando, Montserrat Compa, Antonio Box, Inmaculada Montero, Silvia Tejada, Samuel Pinya, Maria Magdalena Quetglas-Llabrés, and Antoni Sureda. 2025. "Microplastic Pollution and Its Physiological Effects on the Top Fish Predator Dentex dentex from the Western Mediterranean" Microplastics 4, no. 2: 28. https://doi.org/10.3390/microplastics4020028

APA Style

Cohen-Sánchez, A., Solomando, A., Compa, M., Box, A., Montero, I., Tejada, S., Pinya, S., Quetglas-Llabrés, M. M., & Sureda, A. (2025). Microplastic Pollution and Its Physiological Effects on the Top Fish Predator Dentex dentex from the Western Mediterranean. Microplastics, 4(2), 28. https://doi.org/10.3390/microplastics4020028

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