Marine Fish Research Articles (Page 6)

Streptococcus iniae is a highly pathogenic microorganism that poses significant economic threats to marine aquaculture, notably impacting commercially valuable species such as snubnose pompano, seabass, groupers, and snappers. The recent emergence of new infection cases in both farmed and wild fish populations, domestically and internationally, underscores the urgent necessity for comprehensive data collection for the development of effective disease management strategies. Such measures are vital to reducing economic losses in Vietnam’s marine fisheries sector. This review explores the mechanisms of infection, virulence factors, antibiotic resistance, and the current approaches to disease control in marine fish affected by S. iniae. The review highlights ongoing research and practical applications involving vaccines, probiotics, and botanical products aimed at enhancing immunological defences and resistance against this pathogen. Furthermore, the review discusses future prospects and research directions pertinent to S. iniae infections in Vietnamese marine fish, thereby supporting the advancement of sustainable aquaculture practices and effective disease management.

Humic substances, including humic acid and fulvic acid, are a class of naturally occurring complex compounds found in soil, water and sediments. In aquatic ecosystems, humic substances have an important influence on the properties and functions of natural aquatic systems, as they play a direct role in shaping the physical and chemical environment of a water reservoir. Artificial fish farming has become necessary not only to meet the demand for edible animal proteins, but also to replenish and conserve depleted stocks and endangered fish populations. Humic substances have positive effects on many organisms, also improve some vital parameters of fish such as growth performance, stress tolerance and immune response. The fungistatic effect of humic substances on Saprolegnia parasitica, a common parasite of freshwater and marine fish, is known. Humic substances reduce the number of pathogens Vibrio harveyi and Acinetobacter in the intestines of fish. However, the addition of humic acid in high concentrations to the feed of juvenile common carp (Сyprinus carpio) caused not only improved growth and feed eating efficiency, but also had detrimental effects on gill, liver and kidney tissues. This article is a literature review that explores the advantages and disadvantages of using humic substances in aquaculture.

Arsenic is a widely studied toxic element that exists in various species with different oxidation states and forms in the environment and biological systems. The different physicochemical properties, environmental behaviors, and toxicities of these arsenic species make speciation analysis essential for environmental monitoring and human health risk assessment. In this study, we demonstrated the determination and monitoring of six arsenic species, including arsenite (AsIII), arsenate (AsV), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), arsenocholine (AsC), and arsenobetaine (AsB) in seafood using high-performance liquid chromatography coupled with inductively coupled plasma mass spectrometry (HPLC-ICP-MS). We optimized the chromatographic condition and sample preparation for the separation and extraction of arsenic species, and the method was validated with accuracy and reproducibility using certified reference materials and actual samples. Baseline separation of the arsenic species was achieved within 12 min, and oven heat extraction was selected for sample preparation. The method showed excellent linearity for arsenic species from 0.1 to 100 μg L-1, with recoveries ranging from 92% to 123%, intra-day precision of 0.9-5.0%, and inter-day precision of 1.1-19.4%. The method was further used to determine the arsenic species in 109 mollusks, 195 crustaceans, and 195 marine fish samples from Guangdong, China. Distinctive patterns of arsenic species distribution were observed among different seafood categories. AsB was consistently the predominant species across all samples, with a detection frequency higher than 97.9% and contributed to more than 90% of total arsenic, other arsenic species showed marked variations in their occurrence and concentrations.

Background: Primordial germ cells (PGC) are the progenitor cells of sperm and eggs during the embryonic stage. The maternal gene vasa has been widely studied for its role in PGC origin, and other genes like dead end (dnd) have also been identified. Objectives: Spotted sea bass is an important economic marine fish, and the study of its germ cell characteristics provides important basic data for future population breeding and protection. Methods: In this study, we cloned the full-length sequences of Lmvasa (2384 bp, encoding 1905 aa) and Lmdnd (1523 bp, encoding 386 aa) using RACE. Temporal and spatial expression patterns of Lmvasa and Lmdnd in embryos and gonads were analyzed by PCR, immunohistochemistry, and in situ hybridization. We also used microinjections of chimeric RNA containing GFP and Lmvasa 3′ UTR to visualize PGCs. Results: Our results showed that Lmvasa and Lmdnd are expressed primarily in early embryonic development (pre-blastula stage) and were expressed only in the gonads. Immunohistochemistry revealed abundant expression of Lmvasa and Lmdnd proteins in spermatogonia, weak expression in spermatocytes, and no expression in spermatozoa. In ovaries, both genes were expressed throughout oogenesis. Furthermore, PGCs in spotted sea bass belonged to an early localization pattern. Microinjection experiments demonstrated that Lmvasa 3′ UTR effectively labeled PGCs in embryos of spotted sea bass, zebrafish, and medaka. Conclusions: These findings may contribute to understanding PGC development in spotted sea bass and other Percidae.

Caligus species are mostly parasites of marine fish hosts with a few reports from fresh and brackish waters and additional reports from plankton samples with no host records. Currently there are about 279 Caligus species. Of these, 42 species have been reported from marine hosts off the southern African coast. Caligus species have been collected from a variety of hosts off South Africa and preserved in 70% ethanol. These specimens were examined and identified using stereo- and light microscopes. Nine additional Caligus species (C. asperimanus, C. antennatus, C. brevicaudus, C. elasmobranchi, C. izmiriensis, C. mulli, C. quadratus, C. cf. schlegeli and C. spinosus) are reported with distinguishing features illustrated while a new species C. pillaii n. sp. is described and illustrated. Additionally, two possible new species are also reported and illustrated as Caligus sp. 1 and Caligus sp. 2. Therefore, the number of Caligus species reported from southern African waters is raised to 52 with the addition of new host records from South African waters. Lastly, an updated key for the species groups of Caligus species is provided.

Finfish aquaculture improves household food security and reduces poverty levels, particularly when conducted for market purposes. However, little is known about the relationship between farm-level management practices and market participation among finfish farmers in developing countries such as Tanzania. Herein, we investigated the relationship between specific aquaculture farm management practices and market participation in finfish farming and their effect on market participation and sales revenue using data from the Tanzania National Sample Census of Agriculture (TNSCA). We found that market participation was influenced negatively by stocking frequency and affected positively by geographical locations of farms. Furthermore, 42% of the farms participated in the market, with an average quantity of fish sold of 2,141.03 ± 9,007.90 kg. Tilapia and African catfish polyculture dominated market sales (56%) during within-group comparison, whereas marine fish were mainly for subsistence. Moreover, the quantity of fish sold from shallow water cage, natural pond and dug out pond was negative when compared to deep-water cages. Furthermore, the size of aquaculture production system and stocking frequency influenced positively fish sales revenue. Taken together, our findings indicate that stocking frequency and geographical locations of farms influence aquaculture market participation. Tailored aquaculture policies by locations can enhance farmers market participation and income generation.

The yellowfin seabream (Acanthopagruslatus), a commercially important marine fish in Vietnam, faces threats from overfishing and habitat degradation and requires a deeper understanding of its genetic structure and evolutionary history for effective conservation. This study investigated the genetic diversity, population structure and demographic history of A.latus across three populations in Central Vietnam using mitochondrial control region (mtCR) sequences and multivariate analyses. A total of 125 fish samples were collected between January 2023 and June 2024, with DNA extracted from pectoral fin tissues and amplified for mtCR sequencing. Phylogenetic and haplotype network analyses revealed three main haplogroups with high genetic diversity (haplotype diversity: 0.993 ± 0.002), but minimal population differentiation (Fst = 0.00029, p = 0.39188), indicating significant gene flow, facilitated by coastal currents as these populations maintain strong genetic connectivity with the coastal populations of southern China. Neutrality tests, mismatch distribution and Bayesian Skyline Plots have suggested a historical population expansion followed by recent stability and slight decline. These findings highlight the species’ resilience, but underscore the need for regionally coordinated conservation strategies to protect critical habitats like estuaries and mangroves, ensuring the sustainability of A.latus populations in Vietnam.

High biological diversity (or biodiversity) is thought to bolster communities against disturbances, leading to higher levels of ecosystem functioning. While the biodiversity-ecosystem function (BEF) relationship is evident in studies equating diversity to species richness, it is still unclear which ecological mechanisms can produce different observational BEF effects. Here, we combine 7686 individual growth curves across 1480 species with 2957 local community surveys to generate a process-based estimate of biomass production to assess the BEF relationship across marine reef fishes. We find that the effects of Hill diversity emphasising abundances outpace those of species richness and community evenness on biomass productivity. In high-latitude temperate regions, species abundances and richness have parallel effects on reef fish productivity. However, in the tropics, species abundances surpass species richness in their effects on functioning. These latitudinal disparities can be explained by trade-offs in the relationship between abundance and per-capita productivity. As whole-community productivity remains relatively stable across most of the diversity gradient, these trade-offs are presumably driven by metabolic constraints on growth and body size imposed by warmer temperatures. It appears that biodiversity can only support ecosystem functioning to a limited extent and environmental stressors likely limit the biomass production of marine fishes globally.

Mugil cephalus is a cosmopolitan marine fish highly relevant from ecological and economic perspectives. Previous studies identified sex-associated variants in the follicle-stimulating hormone receptor (fshr) gene following an XX/XY sex determination (SD) system. However, these variants could not be fully associated with sex in all samples. This suggests other genes and/or environmental factors may be involved in the SD of this species, denoting intraspecific variation. In this study, we constructed a new high-quality genome assembly of M. cephalus. We then re-sequenced the whole genome in males and females from two divergent Mediterranean populations to ascertain whether other genetic variants could also be involved in SD. fshr gene variants showed to only partially explain SD, while a new intronic variant in the sestd1 gene appeared to be associated with SD following a ZZ/ZW system. The presence of other putative candidate SD variants showing significant differences between the two populations suggested a regional pattern of variation in SD in the Mediterranean Sea. The incomplete association of all the identified variants also pointed to a potential role for environmental factors.

Sillago japonica is a commercially important marine fish species in the Northwestern Pacific, and understanding its genetic diversity and population structure is crucial for germplasm resource conservation and elucidating population evolution mechanisms. This study specifically aimed to systematically explore the genetic diversity and population structure of S. japonica across five geographic regions (DJW, YSW, ST, ZS, and RS) in its distribution range. A total of 50 S. japonica individuals from the five geographic regions were analyzed using high-throughput mitochondrial genome sequencing data. We identified single nucleotide polymorphisms (SNPs) and insertion-deletion (InDel) loci, followed by comprehensive population genetic analyses including phylogenetic tree construction, principal component analysis (PCA), ADMIXTURE analysis, and calculation of genetic differentiation indices (Fst) and genetic diversity parameters. A total of 2966 SNPs and 414 insertion-deletion loci were identified. Phylogenetic tree topology, PCA, and ADMIXTURE 1.3.0 analysis consistently showed low genetic differentiation among the five populations, a pattern supported by low pairwise Fst values ranging from 0.00047 to 0.05589, indicating extensive gene flow across regions. Genetic diversity parameters varied slightly among populations: observed heterozygosity (0.00001-0.00528), expected heterozygosity (0.04552-0.07311), percentages of polymorphic loci (19.41-30.36%), and nucleotide diversity (0.04792-0.07697). The low genetic differentiation and diversity observed in S. japonica populations may result from the combined effects of historical bottleneck-induced gene pool reduction and extensive gene flow. These findings provide essential theoretical support for formulating targeted conservation strategies for S. japonica germplasm resources and further studies on its population evolution mechanisms.

The nutritional value of lipids depends not only on their fatty acid composition but also on their stereospecific positioning on the glycerol backbone. This study investigated the fatty acid composition and sn-2 positional distribution of triacylglycerols (TAG), as well as the composition of major phospholipids in golden pompano (Trachinotus ovatus) juveniles (initial weight: 10 g) fed five diets including graded levels of dietary n-3 highly unsaturated fatty acids (HUFA; 0.64-2.10%) for 56 days. With increasing dietary n-3 HUFA levels, the proportions of eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA), docosahexaenoic acid (DHA), and total n-3 HUFA in muscle TAG, phosphatidylcholine (PC), and phosphatidylethanolamine (PE) significantly increased. Phospholipids, especially PC and PE, were preferentially enriched with n-3 HUFA, and the sn-2 positions of TAG showed a significantly increased deposition of DHA and reduced n-6/n-3 ratios. RNA-Seq analysis was performed on muscle tissues of T. ovatus subjected to different dietary n-3 HUFA levels to further investigate the molecular mechanisms of lipid compositional and structural changes. A total of 126,792 unigenes were obtained, of which 47.78% were successfully annotated. KEGG pathway enrichment analysis implicated the glycerophospholipid, glycerolipid, and sphingolipid metabolism pathways in lipid composition and distribution regulation, identifying gpat4, agpat3, agpat8, lpeat1, and lpgat1 as potential regulators. These findings offer insights into lipid remodeling in marine fish and support strategies to enhance aquaculture product quality.

Recruitment in marine fish is a complex process influenced by multiple ecological factors that often interact in unpredictable ways, making reliable forecasting challenging. Environmental variability further amplifies this uncertainty. This study analyzed the abundance of 0-year class blue whiting (Micromesistius poutassou) from the Spanish bottom trawl survey on the Porcupine Bank (Irish shelf) between 2001 and 2020, focusing on the exceptional recruitment event in 2020. We examined the effects of wind, chlorophyll-a concentration, salinity, temperature, and ocean currents during the spawning season, along with the spawning stock biomass (SSB). Results indicate that recruitment was primarily influenced by the wind-mixing index, chlorophyll-a concentration, and retention index, with no significant correlation to SSB. Although interannual variability in both environmental conditions and recruitment was high, the relationship between environmental factors and recruitment was not always predictable. For instance, while warm and saline years are generally associated with higher recruitment, the period 2002-2012 (characterized by warm and saline waters) only showed strong recruitment in 2003, 2004, 2007, 2009, and 2010. Conversely, although cold and low-salinity conditions are typically linked to lower recruitment, 2020 saw very strong recruitment despite the below-average SSB. Our findings suggest that the exceptional recruitment in 2020 resulted from a unique combination of favorable conditions. Unusually low wind conditions triggered the formation of a stable Taylor column circulation over the Porcupine Bank, promoting phytoplankton accumulation, as evidenced by the elevated chlorophyll-a concentrations. This likely increased food availability for larvae, while the Taylor column also acted as a retention mechanism for larvae and prey. Lagrangian simulations supported this retention hypothesis. Additionally, temperature and salinity conditions during the 2020 spawning season likely optimized the ascent of early life stages from spawning depths to the food-rich surface waters, improving larval feeding success and contributing to the historical recruitment event.

ABSTRACT Artemia (brine shrimp) is a foundational live feed in global aquaculture, renowned for its adaptability, ease of production, and favorable nutritional profile. However, in its natural state, Artemia contains suboptimal levels of highly unsaturated fatty acids (HUFAs), particularly docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), which are vital for supporting growth, survival, and immune function in both marine fish and freshwater fish. To enhance its nutritional efficacy, various enrichment strategies have been developed, utilizing oil emulsions, microalgae, yeasts, probiotics, soy lecithin, and trace elements such as selenium and zinc. Each enrichment method offers unique physiological benefits: oil emulsions and microalgae increase PUFA concentrations; soy lecithin enhances fatty acid absorption and digestive efficiency; yeasts improve immune response and pigmentation; probiotics promote gut health and pathogen resistance; and trace minerals contribute to improved metabolic and reproductive performance. Although Artemia is extensively used in crustacean hatcheries, its use as live feed in shrimp larviculture is comparatively limited, despite its well‐documented benefits. This review highlights the need for greater inclusion of enriched Artemia in shrimp culture, emphasizing its potential to improve larval performance and overall production outcomes. Optimized enrichment protocols are essential to advancing sustainable and resilient aquaculture systems. Future research should focus on cost‐effective, species‐specific enrichment strategies to meet the evolving nutritional requirements of modern aquaculture.

Lactococcus petauri is an emerging bacterial pathogen associated with disease outbreaks in freshwater and marine fish species worldwide. While it has been increasingly reported in countries bordering the Mediterranean Sea, no official records of L. petauri have yet been made in Italy for saltwater species. This study reports, for the first time, the presence of L. petauri in European seabass (Dicentrarchus labrax) farmed in land-based tanks along the south-western coast of Italy, based on a retrospective analysis of previously isolated strains. Although only a single isolate was positive, the finding is of notable significance as it originated from a sample collected in 2012. This temporal aspect highlights the likelihood that L. petauri has been circulating in Italian aquaculture systems for at least a decade. The isolate also exhibited a broad antimicrobial resistance profile, including resistance to amoxicillin, fluoroquinolones and trimethoprim/sulfamethoxazole. The historical misidentification of L. petauri is linked to its clinical similarity with Lactococcus garvieae. This highlights the value of re-analysing archived strains with modern tools and underlines the need for accurate diagnostics in aquaculture. The detection in D. labrax extends the known host range and suggests a longer, undetected presence in the Mediterranean.

Recent decades have seen significant alterations to ocean soundscapes. These changes are primarily driven by human-generated sources (i.e., anthropogenic noise), which is now recognized as a marine pollutant of emerging concern. In contrast to research on marine mammals and fish, studies on the effects of noise on marine invertebrates are limited, and while behavioural changes have been observed in some invertebrate taxa, few investigations have considered whether marine invertebrates can develop a tolerance to this pollutant. We examined the behavioral impacts of shipping noise on the shore crab Hemigrapsus oregonensis and whether they can develop tolerance to noise. Cohorts collected from sites with low and high noise levels were exposed to playbacks of ship noise in the laboratory. We measured initial responses to a simulated predator attack, time taken to seek shelter following the attack, and disruption during feeding. Our results indicated that ship noise significantly impacts shore crabs' initial response after a simulated predator attack, with a 66% likelihood of movement in noise-exposed individuals compared to 32% in the controls. However, ship noise did not significantly impact whether the crabs retreated to shelter after a predator attack, nor did it disrupt feeding. The interaction between treatment and site type was not significant for any of the behavioral metrics, indicating no evidence of tolerance related to prior noise exposure. Finally, we assessed broader relationships between sound and marine arthropods' behavior by combining our results with 71 data points extracted from 17 published studies. A meta-analysis of these data indicated that sound can have a positive, negative, or null effect on marine arthropods. Our results highlight the importance of considering marine invertebrates when evaluating the ecological impacts of anthropogenic noise, and suggest that more work is required to identify the contexts in which this emerging pollutant is particularly detrimental.

The swim bladder, or air bladder, is an internal gas-filled organ commonly found in most large marine fish, including the giant catfish (Arius thalassinus). During fish processing, the swim bladder is often discarded as a byproduct. Fresh swim bladders contain protein levels ranging from 12–33%, and when dried, they are marketed as fish maw. Fish maw has significant potential to be further processed into a high-value fish protein isolate (FPI). This study aimed to produce and characterize protein isolate derived from the fish maw of A. thalassinus using the alkaline extraction method. The results showed that fish maw flour contains 11.20% moisture, 85.3% protein, 0.94% ash, 0.94% fat, and 1.59% carbohydrates. It is also a rich source of amino acids, including glycine (16.6%), L-proline (9.4%), L-alanine (8%), L-arginine (8%), L-glutamic acid (8.1%), and L-threonine (4%). The FPI produced via the alkaline extraction method exhibited a protein content of 91%, with solubility of 66.94% in water, 56.65% in acidic solvents, and 80.64% in basic solvents. Additionally, the FPI demonstrated a water-holding capacity of 1.44 ± 0.09 g/g and an oil-holding capacity of 0.54 ± 0.05 g/g.

The Spotted Scat Scatophagus argus, particularly in aquaculture, is commonly affected by intestinal parasitic infections that impact its health and growth. Filisoma spp., an acanthocephalan parasite, and Cryptosporidium spp. cause intestinal inflammation in various marine fish; however, infections with Cryptosporidium spp. or co-infection with these parasites have not been identified in Spotted Scat. Host-parasite interactions in fish, including the inflammatory responses of the intestine, were investigated in 32 cultured Spotted Scat from Songkhla, Thailand. The study used parasitological examination, including polymerase chain reaction and nucleotide sequencing of the ITS1 and ITS2 regions of the ribosomal RNA gene for acanthocephalans and the 18S ribosomal RNA gene for Cryptosporidium. Additionally, histopathology and immunohistochemistry for interleukin-4 expression were performed. Most of the infected fish showed no significant clinical signs, with postmortem findings of hemorrhagic, congested, and edematous intestines. Parasitological analysis revealed that 84.37% of the fish were infected, with 9.37% having a single helminth infection, 40.62% being infected with coccidia, 34.37% having mixed infections with both parasites, and 15.62% of the fish being free from intestinal parasites. Polymerase chain reaction and nucleotide sequencing indicated that F. argusum and C. bollandi were the parasites involved. Histopathology showed increased inflammatory cell infiltrations, particularly eosinophilic granule cells and mononuclear cells, as well as higher levels of histopathological changes (vascular congestion, tissue necrosis, and epithelial desquamation) in the single F. argusum infection and co-infection with F. argusum and C. bollandi compared with C. bollandi infection alone. Similarly, significantly elevated interleukin-4 expression in the intestines, indicating a strong proinflammatory immune response, was observed in these groups. This study highlights the detrimental effects of F. argusum, regardless of whether it is a single or concomitant infection, which may impact the health of fish.

Impact of degradation and time of sampling on gut Microbiome composition in wild-caught marine fish.

Faustulidae sensu lato is a polyphyletic assemblage of digeneans that parasitise marine or euryhaline fish as adults in the gastrointestinal tract. In previous phylogenetic reconstructions, this family appeared to be represented by two groups nested within the Gymnophalloidea and Microphalloidea. However, the choice of a correct name for these groups was impossible without assessing the phylogenetic position of the type genus of the Faustulidae, Faustula Poche, 1925. In the current study, we provide morphological and molecular data on Faustula gangetica (Srivastava, 1935), which represents the first molecular data for the genus Faustula. Specimens of F. gangetica were found in Tenualosa ilisha (Hamilton) from Shatt Al-Arab River, southern Iraq. We report the presence of discernible muscle fibres between the pharynx and the oral sucker, as well as a zone of distinctly differentiated transversely oriented muscle fibres located anterior to the common genital pore in this species for the first time. All molecular markers used in our study (ITS2 region, 28S rRNA gene) indicated that the genus Faustula is nested within the clade of gymnophalloid faustulids. Thus, Faustulidae sensu stricto is confirmed to belong to the Gymnophalloidea.

Palm ruff (Seriolella violacea, Guichenot 1848) has been identified as a promising candidate for aquaculture in northern Chile. During the winter of 2023, an outbreak of an external infectious disease affected 3740 juvenile Palm ruff at the Marine Fish Farming Laboratory of the Universidad Católica del Norte. The macroscopic signs, particularly external ulcers, were consistent with tenacibaculosis. Microbiological, genomic and typing analyses were conducted to determine the cause of fish mortality. Sixteen isolates were recovered from four moribund fish, primarily from external lesions organs such as the mouth (n = 4), skin lesions (n = 4) and gill (n = 1). All isolates exhibited phenotypic traits characteristic of Tenacibaculum dicentrarchi: Gram-negative, motile rods, positive catalase and oxidase activity, Congo red absorption and an absence of flexirubin pigment. PCR analysis confirmed the identity of the isolates as T. dicentrarchi, with 16S rRNA and fusA gene sequencing clustering the isolates with the T. dicentrarchi type strain 35/09T. Multiplex PCR-based O-AGC typing classified all 16 Chilean isolates as Type 1, which could aid in the development of an autogenous vaccine to prevent future tenacibaculosis outbreaks. RAPD analysis revealed clear genetic heterogeneity among all isolates, with a dominant genetic group comprising 11 isolates, regardless of the primer used. This study represents the first report of a bacterial disease in Palm ruff, expanding the list of endemic species susceptible to tenacibaculosis caused by T. dicentrarchi.