Marine Fish Research Articles

Swordfish (Xiphias gladius) is a large, migratory apex predator with a carnivorous diet, occupying a top position in the marine food chain. Although it is a valuable teleost pelagic fish with a significant commercial value, its gut microbiota has never been studied. The gut microbiota of 100 individuals was characterised by sequencing the V3-V4 region of the bacterial 16S rRNA gene. Gut microbiota findings were classified with consideration to diversity, taking into account their weight (10-20; 21-30; over 31 kg) and the FAO fishing areas in which they were caught (FAO 27, 34, 37.1.1 areas). Significant differences in the alpha diversity were observed among the weight categories for all metrics examined (except for the evenness index) and only by Shannon's index among the FAO fishing areas. Beta-diversity analysis revealed no significant differences. The phylum Pseudomonadota dominated the swordfish gut microbiota, followed by Fusobacteriota. Photobacterium was the most abundant genus across all weight categories and FAO fishing areas. Smaller fishes showed a less rich and diverse gut microbiota, dominated almost exclusively by Photobacterium. Conversely, Pseudoalteromonas, Psychrobacter, Psychrilyobacter, and Cetobacterium appeared to increase in abundance with fish weight. Although Photobacterium was dominant across the different FAO fishing areas, distinctive microbial community compositions were observed: Cetobacterium was more prevalent in FAO 27, while Pseudoalteromonas was more prevalent in the other areas. Unlike the gut microbiota of other marine fish species, Vibrio and Lactobacillus were largely absent. This study represents the first metataxonomic characterisation of the gut microbiota of swordfish using next-generation sequencing.

To develop a low-cost, environmentally friendly taurine fermentation method for sustainable marine fish culture using feed derived from photosynthetically produced agricultural products, it is crucial to study cysteine sulfinic acid decarboxylase (CSAD), a key enzyme in the taurine biosynthetic pathway in applicable microorganisms. In this study, a method was devised to screen for CSAD genes using Escherichia coli growth as an indicator, based on sulfur assimilation following the decarboxylation of l-cysteic acid, a taurine precursor compound. The E. coli used has a double deletion mutation of cysA (sulfate/thiosulfate ABC transporter) and ssuD (FMNH2-dependent alkanesulfonate monooxygenase) genes. If needed, an additional defect in enzyme genes, such as cysC (adenylyl-sulfate kinase), which participates in the pathway reducing sulfate to sulfite, is also introduced. Using this method, it was demonstrated that the glutamic acid decarboxylase gene from Yarrowia lipolytica possesses CSAD activity. The identified decarboxylase was further confirmed to act on l-cysteine sulfinic acid. Additionally, two observations made during method refinement to reduce background growth in screening are discussed: that SsuD is involved in sulfur assimilation from an unknown sulfur compound and that certain mscK (mechanosensitive channel) missense mutations enable external sulfate above a specific concentration to enter the cell.

Gene editing technologies such as CRISPR/Cas9 have revolutionized functional genomics, yet their application in marine fish cell lines remains limited by inefficient delivery. This study compares three delivery strategies—electroporation, lipid nanoparticles (LNPs), and magnetofection using gelatin-coated superparamagnetic iron oxide nanoparticles (SPIONs)—for CRISPR/Cas9-mediated editing of the ifi27l2a gene in DLB-1 and SaB-1 cell lines. We evaluated transfection and editing efficiency, intracellular Cas9 localization, and genomic stability of the target locus. Electroporation achieved up to 95% editing in SaB-1 under optimized conditions, but only 30% in DLB-1, which exhibited locus-specific genomic rearrangements. Diversa LNPs enabled intracellular delivery and moderate editing (~25%) in DLB-1 but yielded only minimal editing in SaB-1, while SPION-based magnetofection resulted in efficient uptake but no detectable editing, highlighting post-entry barriers. Confocal imaging and fluorescence correlation spectroscopy suggested that nuclear localization and Cas9 aggregation may influence editing success, highlighting the importance of intracellular trafficking in CRISPR/Cas9 delivery. Our findings demonstrate that CRISPR/Cas9 delivery efficiency is cell line-dependent and governed by intracellular trafficking and genomic integrity. These insights provide a practical framework for optimizing gene editing in marine teleosts, advancing both basic research and selective breeding in aquaculture.

The cryopreservation and transplantation of germline stem cells (GSCs) have become the key to conserving fish genetic resources and safeguarding species diversity. This study aimed to investigate the effects of post-mortem temperature and time on the preservation of oogonial stem cells (OSCs) in the marine fish Paralichthys olivaceus. OSCs remained viable after fish death, and they remained viable and could be cultured after storage at 19 °C for 15 h and at 4 °C for 24 h. Combined transcriptomic and metabolomic analysis was used to identify the pathways leading to OSC death. Several genes were differentially expressed in the ovarian tissue post-mortem, with the most enriched pathways being ferroptosis, fatty acid metabolism/biosynthesis, glutathione metabolism, citric acid cycle (TCA cycle), and arachidonic acid metabolism signaling pathways. Genes related to ferroptosis, such as vdac2, p53, and slc7a11, as well as metabolites such as adrenic acid and arachidic acid, can serve as reliable biomarkers for evaluating the viability of post-mortem OSCs. These findings provide valuable insights and theoretical support for the effective use of post-mortem GSCs and enhance strategies for germplasm resource conservation in fish.

Unveiling the environmental and toxicological implications of potentially toxic elements levels in three marine fish species from the Red Sea.

Pollution profiles and human health risk assessment of BPA analogues in seafood from a Chinese coastal city.

Understanding the role of biological, environmental and human-impact factors on mercury concentrations in a demersal mesopredator shark.

Imidacloprid impacts oxidative stress and neurotoxic biomarkers in different marine organisms (fish, mysid and clamworm).

Tracing PCB contamination in fish using shadow profiles and self-organizing maps.

The influence of boating disturbance on the parental care behaviors of smallmouth bass (Micropterus dolomieu).

Akirin2 regulates IL-6 expression and contributes to immune defense in Silver Pomfret (Pampus argenteus).

Exacerbating cadmium toxicity disrupts metabolism in black sea bass under marine heatwaves: insights from physiological and metabolic responses.

Progress in tailor-made of anti-fouling coating strategies for marine fish farming cages based on green synthesis of zinc oxide nanoparticles from Avicennia marina leaves

Background: The extensive use of antibiotics in aquaculture has raised serious concerns, emphasizing the need for sustainable and natural alternatives. This study evaluated the potential of red dragon fruit (Hylocereus polyrhizus) juice by-products (RJB) as a functional feed additive for juvenile red seabream (Pagrus major). Materials and Methods: The bioactive composition and antioxidant capacity of RJB were analyzed, and five experimental diets containing 0, 0.2, 0.4, 0.8, and 1% RJB were fed to fish for 56 days. Results: Growth performance, feed utilization, body composition, antioxidant enzyme activities, and lysozyme activity were evaluated. RJB contained substantial levels of phenolic and flavonoid compounds and exhibited strong radical-scavenging activity. Dietary inclusion of up to 1% RJB did not significantly affect growth, feed efficiency, or plasma biochemistry. However, fish fed the 1% RJB diet showed increased catalase and glutathione levels, significantly enhanced lysozyme activity, and improved survival following Edwardsiella tarda infection. Conclusion: These results demonstrate that RJB can be safely incorporated into marine fish diets to enhance antioxidant capacity and innate immune defense. The valorization of fruit-processing by-products such as RJB offers a promising strategy for developing antibiotic-free and sustainable aquaculture practices.

Health risk assessment of heavy metals-contaminated marine fishes from the Mediterranean Sea at Damietta city coast, Egypt.

Mercury (Hg) is a pervasive environmental contaminant with high bioavailability and toxicity, accumulating in aquatic food chains and posing significant risks to human health through seafood consumption. This systematic review aims to collect evidence on Hg bioaccumulation in seafood across Europe, assessing species that exceed legal limits. A total of 74 studies were identified on bioaccumulation among marine fish and seafood from European and adjacent seas, published between 2000 and 2024. Findings highlight that methylmercury (MeHg) constitutes the majority of total Hg in fish species, with concentrations often exceeding EU regulatory limits, especially in the Adriatic and Iberian areas. In general, teleosts exhibit higher tissue concentrations of both MeHg and total Hg compared to either selachians or mollusks. Species likely to exceed their legal limits are larger, apex predators, e.g., tuna, swordfish, and sharks, as well as benthic species, e.g., monkfish and mullet. In recent years, there has been a decrease in mercury contamination, probably due to agreed international regulations. However, significant regional variations still persist in Europe. To mitigate Hg contamination in seafood and ensure food safety, this study highlights the need for ongoing monitoring and management strategies, the interplay of environmental factors, food web dynamics, and species-specific biological characteristics.

Assessing species geographic distributions is critical to approximate their ecological niches, understand how global change may reshape their occurrence patterns, and predict their extinction risks. Yet, species records are over-aggregated across taxonomic, geographic, environmental, and anthropogenic dimensions. The under-sampling of remote locations biases the quantification of species geographic distributions and ecological niche for most species. Here, we used nearly one thousand environmental DNA (eDNA) samples across the world’s oceans, including polar regions and tropical remote islands, to determine the extent to which the geographic and ecological niche ranges of marine fishes are underestimated through the lens of global occurrence records based on conventional surveys. Our eDNA surveys revealed that the known geographic ranges for 93% of species and the ecological niche ranges for 7% of species were underestimated, and contributed to filling them. We show that the probability to detect a range filling for a given species is primarily shaped by the GBIF/OBIS sampling effort in a cell, but also by the number of occurrences available for the species. Most gap fillings were achieved by addressing a methodological sampling bias, notably when eDNA facilitated the detection of small fishes in previously sampled locations using conventional methods. Using a machine learning model, we found that a local effort of 10 eDNA samples would detect 24 additional fish species on average and a maximum of 98 species in previously unsampled tropical areas. Yet, a null model revealed that only half of ecological niche range fillings would be due to eDNA surveys, beyond a random allocation of classical sampling effort. Altogether, our results suggest that sampling in remote areas and performing eDNA surveys in over-sampled areas may both increase fish ecological niche ranges toward unexpected values with consequences in biodiversity modeling, management, and conservation.

The fish processing industry faces dual challenges: environmental impact and low-profit applications for by-products, emphasizing the need to valorize this waste. In this study, collagen was isolated from Seriola rivoliana fish scales. SDS-PAGE results indicated that the purified collagen consisted of two distinct chains (α1- and α2-), consistent with the composition of type I collagen. Fish scale collagen is composed of Gly, Ala y Pro amino acids, with high proportion of Pro (20%), and exhibits an absorption peak at 230 nm in the UV-Vis spectrum. Collagen was hydrolyzed with 60 and 120 mU of activity of Wobenzym (WE) and digestive gland extract from shrimp waste (SE). The resulting collagen-derived peptides from WE showed DPPH scavenging activity, while shrimp-derived peptides did not. Both WE and SE-derived peptides inhibited the growth of marine pathogens (Vibrio diabolicus, Vibrio parahaemolyticus, and Photobacterium) and human pathogens (Escherichia coli, Pseudomonas spp., and Salmonella spp.). However, SE-derived peptides demonstrated stronger inhibitory effects against human pathogens, while WE-derived peptides were more effective against marine pathogens. These results suggest that waste materials, such as scales from the marine fish S. rivoliana, have potential as a source of collagen for generating peptides with antioxidant and antimicrobial properties.

Otolith morphology serves as a powerful tool for species discrimination and ecological studies, yet traditional morphometric approaches often overlook the functionally significant complexity of otolith contours. Here, we apply fractal geometry to analyse 184 sagittal otoliths from five ecologically diverse marine fishes (Merluccius merluccius, Phycis blennoides, Gadus morhua, Lophius piscatorius, and Trachinus araneus) collected from NW Atlantic and Mediterranean waters. Using the Guida et al. (2020) method, we quantified three morphological descriptors: fractal dimension (Df, roughness), circularity (M), and angularity (m). Our results revealed distinct species-specific morpho-spaces. The demersal M. merluccius exhibited the highest contour complexity (Df = 1.06 ± 0.03) and elongation (M = 0.64 ± 0.03), while the other species displayed smoother, more circular otoliths. The strong negative Df-M correlation reflects an evolutionary trade-off between sensory adaptation and hydrodynamic efficiency. These findings establish fractal otolith analysis as an effective taxonomic tool and a window into ecological specialization, with direct applications for fisheries management, paleo-ecological reconstructions, and climate change monitoring in marine ecosystems.

The widespread diffusion and dilution of pollutants in the ocean lead to prolonged exposure of marine organisms to low-concentration contaminated environments, raising growing concerns about the potential risks associated with chronic low-level pollution. The gut microbiota of fish plays a pivotal role in essential physiological processes, which are critical for host health. Therefore, the key microbes in the gut could serve as valuable biomarkers for assessing the toxic effects of pollutants. This article systematically reviews the structure and functions of marine fish gut microbiota, outlines the primary methodologies for assessing gut microbiota, and highlights the impacts of typical pollutants (including petroleum hydrocarbons, antibiotics, heavy metals, and microplastic) on the composition, functionality, and metabolic activities of marine fish gut microbiota. In the future, integrating multi-technology approaches to investigate the toxic mechanisms of pollutants on gut microbiota and their biodegradation pathways will represent a pivotal direction in marine ecotoxicology research.