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Human pharmaceuticals represent a major challenge in natural environment. A better knowledge on their mechanisms of action and adverse effects on cellular pathways is fundamental to predict long-term consequences for marine wildlife. The FTIRI Imaging (FTIRI) spectroscopy represents a vibrational technique allowing to map specific areas of non-homogeneous biological samples, providing a unique biochemical and ultrastructural fingerprint of the tissue. In this study, FTIRI technique has been applied, for the first time, to characterize (i) the chemical building blocks of digestive glands of Mytilus galloprovincialis , (ii) alterations and (iii) resilience of macromolecular composition, after a 14-days exposure to 0.5 µg/L of carbamazepine (CBZ), valsartan (VAL) and their mixture, followed by a 14-days recovery period. Spectral features of mussels digestive glands provided insights on composition and topographical distribution of main groups of biological macromolecules, such as proteins, lipids, and glycosylated compounds. Pharmaceuticals caused an increase in the total amount of protein and a significant decrease of lipids levels. Changes in macromolecular features reflected the modulation of specific molecular and biochemical pathways thus supporting our knowledge on mechanisms of action of such emerging pollutants. Overall, the applied approach could represent an added value within integrated strategies for the effects-based evaluation of environmental contaminants.

ABSTRACT Digestive microbiota provide a wide range of beneficial effects on host physiology and are therefore likely to play a key role in marine intertidal bivalve ability to acclimatize to the intertidal zone. This study investigated the effect of intertidal levels on the digestive bacterial microbiota of oysters (Crassostrea gigas) and clams (Ruditapes philippinarum), two bivalves with different ecological niches. Based on 16S rRNA region sequencing, digestive glands, seawater and sediments harbored specific bacterial communities, dominated by operational taxonomic units assigned to the Mycoplasmatales,Desulfobacterales and Rhodobacterales orders, respectively. Field implantation modified digestive bacterial microbiota of both bivalve species according to their intertidal position. Rhodospirillales and Legionellales abundances increased in oysters and clams from the low intertidal level, respectively. After a 14-day depuration process, these effects were still observed, especially for clams, while digestive bacterial microbiota of oysters were subjected to more short-term environmental changes. Nevertheless, 3.5 months stay on an intertidal zone was enough to leave an environmental footprint on the digestive bacterial microbiota, suggesting the existence of autochthonous bivalve bacteria. When comparing clams from the three intertidal levels, 20% of the bacterial assemblage was shared among the levels and it was dominated by an operational taxonomic unit affiliated to the Mycoplasmataceae and Spirochaetaceae families. Structuration of bivalve digestive microbiota is shaped by intertidal position after a 4-month field implantation.

    The Manila clam ( Ruditapes philippinarum ) is the second most exploited bivalve in the world but remains threatened by diseases and global changes. Their associated microbiota play a key role in their fitness and acclimation capacities. This study aimed at better understanding the behavior of clam digestive glands and extrapallial fluids microbiota at small, but contrasting spatial and temporal scales. Results showed that environmental variations impacted clam microbiota differently according to the considered tissue. Each clam tissue presented its own microbiota and showed different dynamics according to the intertidal position and sampling period. Extrapallial fluids microbiota was modified more rapidly than digestive glands microbiota, for clams placed on the upper and lower intertidal position, respectively. Clam tissues could be considered as different microhabitats for bacteria as they presented different responses to small-scale temporal and spatial variabilities in natural conditions. These differences underlined a more stringent environmental filter capacity of the digestive glands.

As the demand for Octopus maya grows, sustainable farming practices become essential to prevent overexploitation, so that farming can be developed as a sustainable alternative to traditional fishing. Understanding the digestive dynamics of the octopus is essential for devising optimal dietary formulations in aquaculture. Despite the progress in understanding cephalopod digestion, little is known about the specific functioning of the digestive enzymes responsible for breaking down protein substrates. This knowledge gap underscores the need for further research to support sustainable O. maya population management. In this paper, dietary formulations are identified for cephalopods by characterizing O. maya digestive enzymes present in the digestive gland and gastric juice. The investigation revealed that acidic proteases showed a peak activity at higher temperatures than alkaline proteases. Inhibitors confirmed the presence of H, L, and D cathepsins. The lower activation energy of alkaline enzymes compared to acidic ones observed highlights an intriguing aspect of O. maya's digestive physiology. This research provides valuable insights into O. maya digestive enzyme functions, representing a significant advancement in formulating diets crucial for successful octopus farming that may help to fully understand its physiology.

The aim of this study was to evaluate and compare the effects on biochemical parameters and organosomatic indices in the freshwater bivalve Diplodon chilensis exposed to a glyphosate-based formulation under direct and dietary exposures (4 mg a.p./L). After 1, 7, and 14 days of exposure, reduced glutathione (GSH) and thiobarbituric acid reactive substances (TBARS) levels and the activities of glutathione-S- transferase (GST), superoxide dismutase (SOD), and catalase (CAT) were evaluated in the gills and digestive gland. The hepatosomatic (HSI) and branchiosomatic (BSI) indices were also analyzed. Direct and dietary glyphosate-based formulation exposure altered the redox homeostasis in the gills and digestive gland throughout the experimental time, inducing the detoxification response (GST), the antioxidant defenses (SOD, CAT, GSH), and causing lipid peroxidation. After 14 days of exposure, the HSI and BSI increased significantly (43% and 157%, respectively) only in the bivalves under direct exposure. Greater changes in the biochemical parameters were induced by the dietary exposure than by the direct exposure. Furthermore, the gills presented an earlier response compared to the digestive gland. These results suggested that direct and dietary exposure to a glyphosate-based formulation induced oxidative stress in the gills and digestive glands of D. chilensis. Thus, the presence of glyphosate-based formulations in aquatic ecosystems could represent a risk for filter-feeding organisms like bivalves.

The adult fluke Stomylotrema vicarium (Stomylotrematidae, Microphalloidea) was described for the first time in Theristicus caerulescens in 1901, but the complete life cycle has remained unknown to date. Here, we found a stomylotrematid trematode in the digestive gland of the endemic apple snail Pomacea americanista. The digestive gland's tubuloacini were compressed by the trematode larvae placed on connective tissues and haemocoel spaces. Non-virgulate, stylet-bearing cercariae showed three pairs of penetration glands with a body, oral sucker and stylet morphometrically similar to those of stylet-bearing, unencysted young metacercariae of S. vicarium found in the aquatic coleopteran Megadytes glaucus, and at a lesser extent with cercariae of S. gratiosus found in the apple snail Pomacea maculata. The larvae molecular phylogeny was inferred using the markers rRNA 28S and ITS1, being these sequences grouped with the sequences of S. vicarium obtained from adult flukes. Together, these findings indicate that the life cycle of S. vicarium begins in P. americanista, thus supporting the hypothesis that the ampullariid snails act as a first intermediate host.

A potent and heat-stable tetrodotoxin (TTX) has been found to accumulate in various marine bivalve species, including Pacific oysters (Crassostrea gigas), raising a food safety concern. While several studies on geographical occurrence of TTX have been conducted, there is a lack of knowledge about the distribution of the toxin within and between bivalves. We, therefore, measured TTX in the whole flesh, mantle, gills, labial palps, digestive gland, adductor muscle and intravalvular fluid of C. gigas using liquid chromatography-tandem mass spectrometry. Weekly monitoring during summer months revealed the highest TTX concentrations in the digestive gland (up to 242 µg/kg), significantly higher than in other oyster tissues. Intra-population variability of TTX, measured in the whole flesh of each of twenty animals, reached 46% and 32% in the two separate batches, respectively. In addition, an inter-population study was conducted to compare TTX levels at four locations within the oyster production area. TTX concentrations in the whole flesh varied significantly between some of these locations, which was unexplained by the differences in weight of flesh. This is the first study examining TTX distribution in C. gigas and the first confirmation of the preferential accumulation of TTX in oyster digestive gland.

Microplastics (MPs) are a worldwide contaminant of significant environmental concern due to their persistence, widespread distribution, and toxic potential. These plastic particles are taken up by invertebrates such as bivalves. Previous studies have indicated that MPs can serve as carriers for other contaminants, such as heavy metals, thereby increasing their bioavailability to organisms, with unpredictable ecological consequences. Therefore, the main aim of this study was to evaluate the effects of exposure to MPs, cadmium (Cd), and their mixtures (Mix) in the gills, digestive gland, and gonad of the Asian clam, Corbicula fluminea, assessing the oxidative stress responses, LDH activity, and neurotoxicity over 7, 14, 21, and 30 days. The results show that exposure to MPs and their mixtures with the lowest Cd concentration led to the activation of the first line of antioxidant defenses, especially SOD and CAT, in the gills, digestive gland, and gonads. An increase in GST activity was also observed in the gonads. However, the response of GST activity in the gills and digestive gland was opposite that observed in the gonads. Furthermore, LDH activity exhibited contrasting responses, increasing in the digestive gland and decreasing in the gills and gonads. Exposure to MPs induced AChE activity, which contradicts previous findings. The results provide novel insights into the biological responses occurring in different target organs and shed light on the effects of MPs and their mixtures on C. fluminea.

Pyrethroids are among the most widely used insecticides. Permethrin and tetramethrin, which are synthetic pyrethroids, are generally used to control insects in agricultural areas and household applications. Due to broad use areas, they contaminate aquatic ecosystems and cause adverse effects to the non-target aquatic organisms. Even though permethrin and tetramethrin are known to alter the oxidative stress parameters of in vivo aquatic animal model organisms, there are limited studies in vitro. This study aims to determine the adverse effects of permethrin and tetramethrin in the in vitro models of freshwater mussels exposed to 1 mg/L, 10 μg/L, 100 ng/L and 1 ng/L concentrations of chemicals for 24 h. For this purpose, reduced glutathione activities were evaluated as biomarkers of the primary gill and digestive gland cell cultures. In both cell cultures, reduced glutathione values increased in the exposed groups, compared to the control group. Even though the results showed that reduced glutathione activities had not significantly changed concentration-dependently ( p > 0.05), significant differences were observed in the reduced glutathione activities of both cell cultures ( p < 0.05). This study showed that permethrin and tetramethrin had highly toxic effects in the in vitro models of mussels even at low concentrations.

A new intracellular parasite of the phylum Apicomplexa is described infecting the digestive gland of the gastropod Bulla striata from the south coast of Portugal. Only merogonial stages enclosed within parasitophorous vacuoles were observed by light and electron microscopy. The meront cytoplasm contained lipid droplets, rough endoplasmic reticulum cisternae, and several round or oval electron-dense microbodies closely associated with amylopectin granules, suggesting that these microbodies may represent glycosomes. Mitochondria or related organelles were not identified. A reticulum of branched tubules extending from the parasitophorous vacuole membrane was observed, likely increasing the surface available for metabolite exchange between parasite and host cell. Merozoites resulting from meront division were present within the parasitophorous vacuoles. They were elongated and slightly curved, measuring 7–8 µm in length and about 2 µm in width, and possessed an apical complex comprising numerous rod-shaped micronemes, rhoptries, and a conoid. Phylogenetic analyses based on a partial 18S rDNA sequence placed this parasite within the coccidian lineage, at the base of the ichthyocolid clade, a recently recognized group of apicomplexans previously known from fish blood cells. This finding expands the host range of ichthyocolids to gastropods and provides the first ultrastructural observations of this lineage, although only of merogonic stages.