Search Results (1,063)

Background: The effects of climate change negatively affect marine bivalves’ health. Lately, the intensity of marine heatwaves poses serious threats to the aquatic environment setting of high-risk bivalve farming. Since temperature increases can jeopardize bivalves’ immunity response, pathogen infection becomes more evident. Reactive oxygen species (ROS) production, increased during the process of phagocytosis, is confronted by the animals’ antioxidant defense system. However, apart from pathogenic infections, antioxidant defense responses are also induced by seawater temperature increases; Methods: To enlighten the antioxidant status of Mytilus galloprovincialis originating from mortality events enhanced by intense heatwaves in Thermaikos Gulf, northern Greece, along with Marteilia refringens infection, we examined the expression of genes related to antioxidant defense (catalase, CuSOD and mt10) along with the lipid peroxidation levels and activity levels of antioxidant enzymes (catalase, SOD and glutathione reductase); Results: Our results exhibited increased levels of all these biomarkers. This increase was intensified in the Marteilia infected individuals; Conclusions: Our findings shed light on the oxidative and antioxidant status of farmed mussels led to mortality in the context of Marteilia infection. The latter is augmented by the synergistic effect of heatwaves causing a significant increase in oxidative damage and subsequent antioxidant defense. Full article

Southern swordtail fishes, which belong to the viviparous teleosts called Xiphophorus, are unique models for studies of evolution of sex chromosomes. Monofactorial sex-determining systems, with either the male or the female being the heterogametic sex, as well as sex determination involving more than two sex chromosomes, are found in swordtails and related species. Some swordtail species seem to have originated by crossing between two closely related species. Although the sword has disappeared in many Xiphophorus species during evolution, females of non-sworded species still prefer sworded males, demonstrating a discrepancy between natural and sexual selection. Natural sex change has not been documented sufficiently convincingly in swordtails, but, at least in some subspecies, two or more male phenotypes exist. In a laboratory experiment performed for over 30 years, it has been observed that sex-determining genes may be translocated from one chromosome to another in hybrids of these evolutionary young species. While the factors suggested to play central roles in sex determination and differentiation, e.g., Dmrt1 and AMH, are highly conserved during evolution, several master determining factors have been detected in teleosts. Endocrine-induced sex reversal has been demonstrated in the guppy Poecilia reticulata, another viviparous fish. In swordtails (X. helleri), endocrine disruptors such as nonylphenol and bisphenol A may cause testis cell degeneration and the inhibition of spermatogenesis. Furthermore, swordtails are very easy to breed in freshwater aquaria and, therefore, may be good models for studying the factors influencing sex determination and male differentiation. Full article

Post-mortem ovarian tissue degradation from handling effects, such as delays in preservation, can lead to inaccurate reproductive assessments. Therefore, it is important to understand the differences between handling effects and natural ovarian atresia. Seven treatments of various holding temperatures and times to preservation were applied to whole fish and extracted ovaries of three tropical deepwater snapper species. Ovarian post-mortem degradation was observed at 12 h at ambient temperature and after 48 h iced or refrigerated for both whole fish and extracted ovaries; however, degradation did not adversely affect correct reproductive phase classification in fishes stored in ice from 12 to 48 h post-capture. A clear histological indicator of post-mortem degradation was the breakdown of ooplasm organelles at the oocyte periphery observed in vitellogenic and cortical alveolar oocytes. However, the chorion typically remains intact during post-mortem degradation, in contrast to natural atresia. Effects on post-ovulatory follicles were most discernible after 96 h on ice or refrigeration. Freezing gonadal tissue resulted in drastic changes to oocyte shape and morphology, making reproductive phase classification challenging. We advise that (1) freezing ovaries should be avoided where possible, and (2) gonad tissue should ideally be preserved immediately but no later than 48 h post-capture. Full article

In fish, the immune system plays a crucial role in defending against pathogen-induced infections. The interleukin 17 (IL-17) family, which is a well-studied class of cytokines, serves as a key component of the immune response against external pathogens. In this research, four IL-17 ligands (IL-17A/F1, IL-17B, IL-17C and IL-17D) and one receptor (IL-17RB) genes were identified from spotted sea bass (Lateolabrax maculatus). Alignment analysis showed that the C-terminal region of IL-17 ligands in spotted sea bass was highly conserved. The expression of the IL-17 ligand and receptor genes differed in unstimulated tissues. To investigate the impact of various factors on the immune response of spotted sea bass, we assessed the effect of lipopolysaccharide (LPS), polyinosinic–polycytidylic acid [poly (I:C)] and Edwardsiella tarda treatment on the IL-17 ligands and receptor responses. Our results reveal that the expression of the IL-17 ligand and receptor transcripts is modulated by LPS, poly (I:C) and E. tarda, indicating their significant role in the immune system. Full article

Soy lecithin (SL) is a source of phospholipids, which play a crucial role in determining cell membrane structure, fluidity, and functionality. This study investigated the effects of dietary SL on the performance, nutrient digestibility, and body composition of Nile tilapia juveniles (average initial weight 12.2 g) raised at 22 °C. The experimental diets contained increasing levels of SL (0.0, 21.0, 43.0, and 64.0 g kg⁻¹). The best weight gain and feed efficiency occurred with 42.2 and 49.8 g kg⁻¹ of SL inclusion, respectively, estimated through quadratic regression after 90 days of feeding. The body composition of the fish was also affected by feeding with SL, with a decrease in total body lipids and viscerosomatic and hepatosomatic indices but an increase in polyunsaturated fatty acids. A digestibility trial using only two diets (0SLD and 43SLD) revealed increased lipid and fatty acids digestibility in fish fed with 43SLD. In addition, the consumption of digestible nutrients was the highest in fish fed the diet 43SL. Therefore, SL supplementation is beneficial in fall/spring diets for Nile tilapia juveniles as it can improve growth, lipid digestibility, and body composition when supplemented within the range of 42 to 50 g kg⁻¹ diet. Full article

Connectivity is critical for stream fish persistence, and fish passage structures are a useful conservation tool to reconnect fragmented systems. The design of fish passage structures is a tradeoff between the area available for construction, slope, and costs associated with the structure. The Longrie–Fecteau fish passage structure was designed to be modular, adjustable to barrier-specific needs, and to have a low slope (2%) to pass small-bodied fishes. We evaluated fish passage through this structure in Fountain Creek, Colorado, USA, via a PIT tag mark–recapture study. We documented four native Great Plains fish species successfully ascending the passage structure, with most passage occurring at night. We estimated a 3% probability of a released fish entering the structure, then 89% and 99% passage to the midpoint and exit of the 123 m structure, respectively. Low entrance efficiency was due to low recapture probability of small-bodied study organisms in a relatively large system, and the low percentage of space of the entryway on this barrier (<3% of the length of the barrier). Fish that entered the structure ascended quickly, with median time for successful ascent of 19 min, and minimum time of 6 min. The Longrie–Fecteau fish passage structure is a conservation tool that may broaden the adoption of fish passage structures for small-bodied fishes due to its modularity and low slope. Full article

The eastern Mediterranean Sea is one of the most invaded marine ecosystems due to the introduction of Lessepsian species, which migrated from the Red Sea to the Mediterranean Sea following the construction of the Suez Canal. Some of these species may initially appear to be beneficial for fisheries by providing additional income sources for fishers; however, this usually occurs at the expense of negatively impacted native species and, thus, the ecosystem, which leads to greater economic losses for the fisheries in the long term. Therefore, this study aims to quantify the impact of N. randalli, which is one of the Lessepsian species with increasing commercial importance for the fisheries, on the food web dynamics in a coastal ecosystem in the northeastern Mediterranean Sea using a mass-balance food web modelling approach by capitalising on field data obtained from trawl samplings conducted within the scope of the study. Results showed that the ecosystem was in a developmental stage and experienced an autotrophic succession. The keystone fish group with a structuring role in the food web was sea breams and porgies. Although N. randalli had positive impacts on certain commercially exploited indigenous demersal fish species by mitigating the negative impact of another Lessepsian species, i.e., Saurida undosquamis (Richardson, 1848), in the food web, it had a negative impact on the keystone group of the food web, i.e., sea breams and porgies. Therefore, N. randalli poses a potential threat to the ecosystem’s structure, and the interactions of N. randalli with other species in the food web may instigate an ecosystem reorganisation in the future. We suggest targeted fisheries exploitation and incentives for the fishery of N. randalli as management strategies to mitigate its negative impacts. However, the mitigating role of N. randalli in regulating the negative impacts of S. undosquamis could be adversely affected by its increasing exploitation; therefore, future modelling studies should consider scenario simulations to test such effects. Full article

In this study, we determined the biological characteristics and indices of abundance and biomass of two demersal species, turbot and thornback ray, through a scientific trawl survey of Bulgarian Black Sea waters in the autumn of 2020. Turbot is among the most valuable fish species in the Black Sea, and thornback ray is a sensitive cartilaginous species with a significantly declining abundance throughout the Mediterranean region. The stock biomass of turbot was estimated at 1467.6 tons, with a relative abundance of 896,922 individuals, and those of the thornback ray were 1187.9 tons and 519,606 individuals, respectively. Mean turbot abundance, interpolated into 0.5° latitude/longitude grid cells, ranged between 52 and 120 ind·km⁻², with a mean biomass of 78.26–238.31 kg·km⁻², and for the thornback ray, these indices were within the limits of 0–107 ind·km⁻² and 0–219 kg·km⁻². The distribution of the different length classes of the two fish species by depth layer was analyzed. Length–weight relationships were estimated based on combined samples of both sexes and separately for female and male individuals, allowing a better understanding of growth patterns. Full article

Despite the global decline in marine species biodiversity, relatively few countries have enacted national endangered and threatened species legislation. Tailoring an adequate legislative framework with clear objectives and regulations consistent with the available scientific evidence is fundamental for the effective conservation of marine endangered and threatened species. This paper analyzes the legal framework and current institutional tools for the conservation of marine endangered and threatened species in the Russian Federation. In this regard, important legislative tools include federal laws, as well as internationally binding signed agreements, among others, such as the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) and the Convention on Wetlands of International Importance Especially as Waterfowl Habitat (Ramsar). A strategy and an action plan for the conservation of biological diversity were also developed. Besides, the most important tool for the conservation and protection of marine endangered and threatened species is the Red Book of the Russian Federation (RBRF) and other regional Red Books. Responsibility for causing harm to the species listed in the RBRF and their habitat is specified in the code of administrative offenses and the criminal code of the Russian Federation. Finally, conclusions and identified gaps were highlighted in the last section, including, among other things, that legislation is still limited in how it takes the impacts of climate change into account. Such type of study is highly recommended, considering the relatively few number of papers dedicated to the study of the impact and/or implications of the conservation tools and strategies mentioned in this paper on the status of the marine endangered and threatened species. Full article

Atlantic goliath grouper (Epinephelus itajara), the largest reef fish in the Western Atlantic, exhibit high site fidelity to home reefs but also undertake annual migrations to distant spawning sites. Once relatively common throughout Florida and the Caribbean, the species; is now considered vulnerable (i.e., threatened with extinction) due to overfishing and loss of juvenile mangrove habitat. Goliath grouper in the southeastern US form annual spawning aggregations on high-relief reefs located offshore of both the Gulf and Atlantic coasts of Florida, US. To determine spawning site fidelity and describe migration patterns to aggregations, we implanted 50 adult goliath grouper with acoustic transmitter tags from 2010 to 2013. Fish were tagged at known spawning sites off the Florida Atlantic coast and tracked as they moved through the FACT Network array of acoustic receivers. From 2010 to 2020, we collected ~7 million detections from tagged goliath grouper at 153 sites along the southeastern US Atlantic coast. Results of this long-term tracking indicate that adult goliath grouper are relatively sedentary during non-spawning months (Nov to June) but move significantly more prior to, during, and immediately after spawning (July to Oct). Inter-annual spawning site fidelity was high: between 80–93% of tagged fish returned to the same spawning sites each year. Arrival timing at spawning sites coincided with the August new moon, with males arriving earlier than females. Some individuals migrated distances greater than 400-km per year, with observed migration rates of up to 44-km per day prior to spawning. Long-term tagging data are critical for understanding movement patterns and developing management strategies for this species of special conservation concern. Full article

Pseudomonas plecoglossicida is the pathogen of visceral white spot disease in marine fish, which usually occurs at 16–19 °C and has resulted in heavy economic losses. Our previous RNA sequencing revealed that the expression of the fliL gene in P. plecoglossicida was significantly up-regulated during infection of the host. In order to study the influence of the fliL gene on the virulence of P. plecoglossicida, the fliL gene of the NZBD9 strain was knocked out by the homologous recombination method, the fliL gene-deleted strain (ΔfliL strain) constructed, and complemented the fliL gene to the ΔfliL strain to obtain the C-ΔfliL strain. The growth curves of the NZBD9 strain, ΔfliL strain, and C-ΔfliL strain did not show significant differences. Compared with the NZBD9 strain, the motility, adhesion, and biofilm formation ability were tendered in the ΔfliL strain (p < 0.05); the complement of the fliL gene enhanced these abilities to the level of the NZBD9 strain. The results of artificial infection experiments showed that the LD₅₀ of NZBD9 strain, ΔfliL strain, and C-ΔfliL strain in hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂) were 5.0 × 10³ CFU/fish, 6.3 × 10⁴ CFU/fish, and 1.3 × 10³ CFU/fish, respectively. RNA sequencing was performed on wild-type strains and ΔfliL strains. A total of 126 differentially expressed genes (DEGs) were screened (p < 0.05), of which 114 were downregulated and 12 were upcontrolled, among which several genes related to the six-type secretion system and transport activity were significantly downregulated. The DEGs were aligned to the GO and KEGG databases and enriched to 44 GO pathways and 39 KEGG pathways, respectively. The active pathways of ABC transporters were significantly enriched in both databases. These results indicate that the fliL gene is related to the movement, biofilm formation, and adhesion ability of P. plecoglossicida, and may reduce virulence by affecting substance transport and bacterial secretion. Full article

Recently, our in vitro study on the effects of plasma-activated simulated seawater (PASW) demonstrated its potential as a novel, alternative disinfectant in oyster depuration. In this current study, PASW’s physicochemical and antimicrobial properties were identified and its effects on oyster quality were observed. Simulated seawater (SS) activated by plasma for 10 min (PASW10) increased in temperature, oxidation reduction potential, and electrical conductivity with a decrease in those parameters after 1:1 dilution with SS (PASW10 (1:1)). The pH decreased immediately after plasma activation and subsequently increased after dilution. Nitrate and nitrite concentrations were higher in PASW10 (1:1) compared to PASW10 (3:1). No free available chlorine was detected in undiluted PASW10. Processing using SS and PASW10 (1:1) depuration and refrigeration of E. coli-bioaccumulated oysters was observed. Significantly higher reductions in total coliform and E. coli were noted for PASW10 (1:1) treated oyster samples after 24 h compared to refrigerated samples. No significant differences in values for condition index or biting force of oyster meats were observed for the processed samples after 24 h. Overall, the novel and environment-friendly PASW could be used as an alternative antimicrobial disinfectant in oyster depuration systems because it does not negatively affect an oyster’s viability or quality. Full article

This study reveals the diet of pike-perch from two habitats within the Tersko-Caspian region. The feeding habits of pike-perch in the Sulak and Terek rivers and Tersko-Caspian region were investigated based on 354 specimens sampled monthly from a commercial catch in 2019. Their diet consisted of different prey, with fish representing the most important prey group (up to 90%). Rutilus caspicus dominated with a frequency of occurrence of 20.5, and Aspius aspius, Perca fluviatilis, and Chondrostoma oxyrhynchum, had 13, 9.5, and 8.3%. In the earlier ages 1+ and 2+, zooplankton dominated, followed by mysids and chironomids, which continues into the older ages but at decreasing rates. Analysis of monthly variations in stomach fullness indicated that feeding intensity fluctuated in time, with the highest values in March–April, and lowest in September and November. It was found that the diet of pike-perch in the western Caspian changed considerably from season to season. They begin to actively feed after wintering and before, or even during, spawning period. The spectrum of the diet of Sander lucioperca includes more than 20 elements, mainly juveniles of commercially valuable fish. This fish is characterized by a relatively low ontogenetic diet diversity and flexibility, which makes it sensitive to environmental changes, including anthropogenically induced ones. This fish partially compensates for this disadvantage with its lifestyle, namely, its active foraging movements and migrations from fresh water to salt water and back, following its prey species. Full article

Reliable data on Atlantic Goliath Grouper abundance are prerequisite to informed management decisions, particularly as the State of Florida reopened a limited harvest on the species in 2023 after a 32-year moratorium. Limited data exist for this purpose and fisheries data have been unavailable for over three decades due to a fishery closure that began in 1990. The purpose of this study was to compare absolute abundance estimates of Goliath Grouper between two years using an efficient, cost-effective method developed by Koenig. An underwater tagging method was used to collect mark and resight data for use in a Peterson deterministic model. These data were collected at the same spawning aggregation sites off Jupiter, Florida near the time of the new moon in September 2013 and August 2022. We found that Goliath Grouper abundance had declined at all but one of six sites since 2013. Because data were not collected during the intervening years, interannual variability is unknown. However, given the highly age-structured spawning stock of adult Goliath Grouper on the spawning grounds, the lower abundances measured in 2022 may reflect a real decline in the population rather than just representing a weak year of adult recruitment to these spawning sites. Full article