Estuarine Fish Research Articles

Range expansion and population shifts of estuarine fishes in a changing subtropical estuary

Catastrophic losses (ca. 95%) of seagrass and increased environmental degradation have occurred during the past decade in the Indian River Lagoon (IRL) estuary on the US Atlantic coast of Florida. Changes were observed in the abundance of 2 closely related sparid fishes in these estuarine waters based on fishery-independent monitoring efforts over 22 yr: sea bream Archosargus rhomboidalis significantly increased, while sheepshead A. probatocephalus simultaneously declined. These abundance trends and a northward expansion of sea bream into areas where they had never been documented were associated with an annual minimum water temperature increase of approximately 1.5°C, an annual mean water temperature increase of 0.9°C, and an annual mean salinity increase of 7.6 ppt. Lost seagrass habitat was often replaced by species belonging to the attached macroalgae genus Caulerpa or remained bare. Our findings suggest that sea bream, a tropical herbivore, are expanding poleward into the northern IRL, which may further negatively impact the potential recovery of sheepshead populations via competition. Furthermore, observed declines in seagrasses and populations of dependent species, including sheepshead, will likely continue if anthropogenic perturbations persist or expand. Long-term monitoring is essential for the timely detection of population changes and range shifts to better refine direct fisheries management of existing species and determine the potential need for management of recently expanding fish species should new fisheries emerge. Effective monitoring also allows for more proactive restoration of critical habitats and water conditions to minimize further adverse effects on fishes and other estuarine biota.

Short and long-term temperature variations drive recruitment variability in marine and estuarine juvenile fishes

Understanding the long-term effects of climatic factors on key species' recruitment is crucial to species management and conservation. Here, we analysed the recruitment variability of key species (Dicentrarchus labrax, Platichthys flesus, Solea solea, Pomatoschistus microps and Pomatoschistus minutus) in an estuary between 2003 and 2019, and related it with the prevailing local and large-scale environmental factors. Using a dynamic factor analysis (DFA), juvenile abundance data were grouped into three common trends linked to different habitat uses and life cycle characteristics, with significant effect of temperature-related variables on fish recruitment: Sea surface temperature and the Atlantic Multidecadal Oscillation. In 2010, a regime shift in the North Atlantic coincided with a shift in the common trends, particularly a decline in P. flesus and S. solea trend. This work highlights the thermophilic character of fish recruitment and the necessity to investigate key biological processes in the context of species-specific responses to climate change.

Spatial patterns in host-associated and free-living bacterial communities across six temperate estuaries.

A major goal of microbial ecology is to establish the importance of spatial and environmental factors in driving community variation. Their relative importance likely varies across spatial scales, but focus has primarily been on free-living communities within well-connected aquatic environments rather than less connected island-like habitats such as estuaries, and key host-associated communities within these systems. Here we sampled both free-living (seawater and sediment) and host-associated (estuarine fish hindgut microbiome, Pelates sexlineatus) communities across six temperate Australian estuaries spanning ∼500km. We find that spatial and environmental factors have different influences on these communities, with seawater demonstrating strong distance-decay relationships (R = -0.69) and significant associations with a range of environmental variables. Distance-decay relationships were weak for sediment communities but became stronger over smaller spatial scales (within estuaries, R = -0.5), potentially reflecting environmental filtering across biogeochemical gradients or stochastic processes within estuary sediments. Finally, P. sexlineatus hindgut microbiome communities displayed weak distance-decay relationships (R = -0.36), and limited variation explained by environmental variables, indicating the significance of host-related factors in driving community variation. Our findings provide important ecological insights into the spatial distributions and driving forces of both free-living and host-associated bacterial patterns across temperate estuarine systems.

The bycatch of piramutaba, Brachyplatystoma vaillantii industrial fishing in a salinity and depth gradient in the Amazon estuary, Brazil

ABSTRACT The piramutaba, Brachyplatystoma vaillantii is a freshwater catfish that is the most abundant fishery resource in the Amazon estuary. Piramutaba trawling is done on industrial fishing scale and is characterized by the presence of many freshwater and marine bycatch species, with and without commercial value. Here we describe the bycatch of the industrial fishery of piramutaba in the Amazon estuary and evaluate the relationship of two important environmental factors, depth and salinity, with the accidental capture of freshwater and marine fishes in the Amazon estuary in the rainy and dry seasons. We identified 21 cartilaginous fish species (19.1% freshwater and 80.9% marine) and 125 bony fish species (25.6% freshwater and 74.4% marine). The bycatch included 64 species without commercial value (43% of all bycatch species), which are always discarded. Freshwater and estuarine fishes exhibited significantly higher abundances in shallower environments, while marine fishes were similarly abundant along the entire depth gradient. On the contrary, the abundance of freshwater fishes significantly decreased, and that of estuarine and marine fishes significantly increased with increasing salinity. Regarding the conservation status of the bycatch species, one is classified as vulnerable (VU), and seven as critically endangered (CR). The information on the bycatch of piramutaba fishery in the Amazon estuary is important to subsidize regional fisheries policies and the management of protected areas.

Southern Flounder Life History Diversity and Contributions to Fisheries from Differing Estuarine Salinity Zones

AbstractOtolith chemistry is a useful natural tracer for discerning habitat‐use of estuarine fishes. For Southern Flounder Paralichthys lethostigma, recent otolith chemistry studies have revealed a diversity of residency patterns across salinity gradients. However, the contribution of recruits with specific residency patterns to fisheries is poorly understood. The objectives of this study were to (1) use otolith chemistry from fishery‐independent and fishery‐dependent collections in Mobile Bay, Alabama, to classify lifetime residency patterns (i.e., freshwater, transient, estuarine) in Southern Flounder collected across a large estuarine salinity gradient (0–30 psu); (2) to test if Southern Flounder exhibited resident or migratory behavior by determining if lifetime residency patterns in fishery‐independent samples matched expected salinity patterns in the region of collection after accounting for annual variation in river discharge; and (3) to examine which residency patterns contributed to the commercial and recreational Southern Flounder fisheries in nearby coastal waters. Age‐0 residency patterns in fishery‐independent samples were strongly correlated with region of collection and annual river discharge, suggesting that the majority of Southern Flounder had resided in the same region in which they spent their age‐0 growth phase. Southern Flounder with a combination of freshwater and estuarine salinity signals and classified as “transient” did not appear to have conducted large‐scale movements across salinity gradients, but instead resided in regions of the estuary experiencing seasonal fluctuations in salinity. The majority (57%) of commercially and recreationally harvested Southern Flounder were transients, while a minority (39%) were estuarine residents and lifetime freshwater residents (4%) were rarely harvested. Results from this study suggest that Southern Flounder settle in and remain in the certain habitats during the estuarine residency phase. Given the lack of movement across habitats, future efforts to understand how habitat‐specific conditions (e.g., abiotic, biotic, fishing exploitation) affect vital rates seems warranted for a species currently experiencing population declines.

Assessing the application of the revised Remane Model to fish species in a fluvially dominated cool-temperate southern African coastal system

Estuaries are ecologically important areas which support a variety of aquatic species, particularly marine and estuarine fish species. This study represents a case study of the Orange River and Estuary (ORE) to understand patterns in fish assemblages and diversity trends that were compared to the revised Remane Model predictions in an estuary with poor marine fish species richness. A total of 30 species were recorded in the River continuum that comprised 14 freshwater, 10 marine and six estuarine species. Species diversity revealed seasonal variation in fish assemblages during the high-flow and low-flow seasons but not inter-annually. The results revealed that species diversity is lower in higher salinity areas when compared to low salinity areas. These patterns are consistent with the biogeographical trend of decreasing species richness along the South African coast from east to west, however, inconsistent with Remane predictions. The extremely low marine fish richness at its lower end and the extremely large freshwater influx at its upper end are the primary causes of the inconsistency. This may reflects the unsuitability of the Remane model for the Orange Estuary. In comparison to similar river-dominated South African estuaries, the ORE has a low marine species richness. When compared to more conventional South African estuaries, the ORE has a unique biotic environment with low fish species richness of estuarine-associated marine species adjacent to the Benguela upwelling zone and therefore the region does not offer suitable habitat for such species. As a result, the ORE is not a good candidate to test the Remane Model. The data does, however, confirm the left-hand part of the Remane model, which shows a decline in the fish species richness of freshwater fish species as salinity rises towards mesohaline and polyhaline levels.

Body condition of larval roundherring, Gilchristella aestuaria (family Clupeidae), in relation to harmful algal blooms in a warm-temperate estuary.

Eutrophication-driven harmful algal blooms (HABs) can have secondary effects on larval fishes that rely on estuaries as nurseries. However, few studies worldwide have quantified these effects despite the global rise in eutrophication. This study presents a novel approach using biochemical body condition analyses to evaluate the impact of HABs on the growth and body condition of the larvae of an estuarine resident fish. Recurrent phytoplankton blooms of Heterosigma akashiwo occur in the warm-temperate Sundays Estuary on the southeast coast of South Africa. The response in body condition and assemblage structure on larval estuarine roundherring (Gilchristella aestuaria) was measured in conjunction with bloom conditions, water quality and zooplanktonic prey and predators. Larvae and early juveniles were sampled during varying intensity levels, duration and frequency of hypereutrophic blooms. This study demonstrated that extensive HABs could significantly impact larval roundherring, G. aestuaria, by decreasing larval nutritional condition and limiting their growth, resulting in poor grow-out into the juvenile phase. Poor condition and growth may likely affect recruitment success to adult populations, and since G. aestuaria is an important forage fish and zooplanktivore, poor recruitment will hold consequences for estuarine food webs.

Freshwater discharge disrupts linkages between the environment and estuarine fish community

Freshwater diversions and damming have altered coastal ecosystems greatly, resulting in fundamental changes in salinity, eutrophication, and ensuing shifts in ecological communities. Recently, efforts to restore water delivery and water quality in coastal systems have increased. To explore the impacts of altered freshwater discharge to a subtropical estuary, here Bayesian structural equation models are used to quantify the relationships among water quality properties, nutrients, and predator (sport) and prey (forage) components of the fish community. During periods of relatively low freshwater input, predatory sport fish and lower trophic level forage fish guild dynamics were tightly coupled with water quality and one another. In this low freshwater discharge system, water quality and nutrients were the most strongly linked components of the system. Conversely, during periods of high-water discharge, there was virtually no link between water quality and sport or forage fish guilds, and the sport fish and forage fish guilds became the most tightly coupled components. Ultimately, freshwater discharge disrupted existing linkages within the broader ecosystem. Based on these results, we expect the restoration of low freshwater flow into the estuary would strengthen the relationship between the fish community and the environment. As restoration of estuaries and rivers continues globally, freshwater delivery to downstream systems will be altered. Following the approach presented here, Bayesian structural equation models can be used to generate insight regarding potential system wide shifts following alteration of freshwater delivery, thereby providing a critically important tool for evaluating management strategies.

Community structure characteristics of ichthyoplankton during the water-sediment regulation scheme in the Yellow River in 2020 and 2021

The Water-Sediment Regulation Scheme (WSRS) will deliver large amounts of water and sand to the Yellow River basin within a short period of time. This will significantly change the physicochemical environment of the Yellow River estuary and the surrounding marine ecosystem. Its effects on the spatial and temporal distribution patterns of ichthyoplankton are still unknown. In this study, six surface horizontal trawl surveys of ichthyoplankton were conducted during the WSRS in 2020 and 2021 using plankton nets. The results were as follows: (1) the estuarine sedentary fish Cynoglossus joyeri was the main species controlling the succession pattern of summer ichthyoplankton communities in the Yellow River estuary. (2) The WSRS influenced the ichthyoplankton community structure by changing the runoff, salinity, and suspension environment in the estuary. (3) The northern and southeastern parts of the estuary near Laizhou Bay were the main aggregation areas of the ichthyoplankton community.

Microplastic contamination from surface waters and commercially valuable fishes of Karachi Coast, Pakistan

Microplastic (MPs) pollution is a major concern due to extensive human plastic dependency that is deteriorating ecological health of the world’s oceans. This study was conducted to observe MPs contamination in surface water samples and gastrointestinal tracts of 127 fishes attributed to 15 species from Karachi coast, the busiest port of Pakistan. Total of 6319 MPs/m3 were recorded during this study from water samples where 73% MPs recorded from Manora channel (Karachi harbor) and 27% from open ocean. The most dominant MPs were fibers (42%), pellets (27%), and fragments (20%) respectively. MPs abundance differed significantly among species and ranged between 20.833 ± 2.522–76.400 ± 7.869 item ind.−1. Fibers were the most dominant type in all samples (53.39–90.0 %) followed by pellets (4.88–20.22 %) and blue (21.60–66.23 %) was the most common color. The mean size of MPs ranged between 0.34 mm (Otolithus ruber) to 2.1 mm (Terapon jarbua). The mean highest number of MPs were recorded from shallow coastal fishes (440 item ind.−1) followed by estuarine and shallow coastal fishes (385 item ind.−1). MPs abundance differed significantly among species from different habitat type (Kruskal–Wallis Test, P < 0.0001) with negative correlation between MPs abundance in GITs of fishes and their habitat (Spearman’s rho, r = -0.143) whereas MPs abundance was not significantly correlated with body weight (F = 0.002, p = 0.963), suggesting that MPs ingestion is independent of body weight. There is a need to work about origin, composition, interaction of MPs with biota and impacts of consuming fishes contaminated with high levels of MPs on human health. This is the preliminary study from the Karachi coast and will be a gateway for future studies in this area.

Exploring fatty acid connections between estuarine fish Chelon planiceps and its diatom diet as taste and nutraceutical property influencing factor

Chelon planiceps is a widespread commercial fish of Indian Sundarbans with appreciable taste. Taste of fish is primarily influenced by polyunsaturated fatty acids, and since precursors of PUFA in fish cannot be generated de-novo, they are majorly obtained from phytoplankton diet. In the present study, C. planiceps (N = 10) were analysed for fat content in different body parts, and diatoms present in the gut were compared with diatoms found in habitats of the sampled fish. Significant difference in t-test (p ≤ 0.01) was found for lipid content compared between neck, abdomen and tail regions. The gut analysis revealed highest species richness of Coscinodiscus spp. Four species, namely C. radiatus, C. jonesianus, C. oculus-iridis and C. wailesii, were found to be abundant. Other diatoms too were found in the gut (N = 15) and in the habitat (N = 37). Present study focussed on implications of the most abundant Coscinodiscus. The total lipid content and FA profiles revealed 31FAs, with 12SFAs, 11MUFAs and 8 PUFAs together in both the diatom and fish. Coscinodiscus showed a profile of 28FAs of which 19FAs had a minimum representation of >1 % and C. planiceps showed a profile of 9FAs, all showing minimum representation of >1 %. Comparison of the two FA profiles showed Coscinodiscus to be richer in terms of total SFA (47.34 %) and MUFA (33.03 %) whereas, C. planiceps was richer in terms of PUFA (22.17 %). Pearson's correlation coefficient of (−)0.144 indicated a negative correlation between C. planiceps and Coscinodiscus and though this was expected to be a direct impactor the −ve correlation is attributable to the fish's FA metabolism that affects the dietary FA profile that lowers the similarity between the two profiles to a large extent. The nutraceutical significance of the FAs of the fish and its diet highlights the aquaculture implication of the study.

Archaeological and modern whitemouth croaker fish (Micropogonias furnieri) of southeastern Brazil: A geochemical proxy for environmental preference

In this study, laser ablation–inductively coupled plasma–mass spectrometry was used to characterize the growth patterns of otolith of Micropogonias furnieri from southeastern Brazil under the influence of coastal marine upwelling. Archaeological fish sagittae otoliths of M. furnieri recovered from Brazilian shell mounds (5820‒4980 cal BP) were analysed and compared with those of modern specimens. Otolith Sr/Ca analysis indicated that off southeastern Brazil, M. furnieri shifted from freshwater/brackish in archaeological specimens to brackish/marine in modern times. Regular core-to-edge Sr/Ca oscillations suggest that both modern and archaeological M. furnieri are resident estuarine fish that also use the marine waters adjacent to the coastal zone. Based on analyses of a wide range of otolith edge Sr/Ca values measured in archaeological samples, pre-colonial fishing activities in the coastal regions of Guanabara Bay occurred throughout the year. This study reinforces the importance of M. furnieri as a precolonial fishing resource in this area and demonstrates a shift in fishing practices, where smaller fish are targetted within the bay and larger fish are caught beyond the bay. These data may also be indicative of a shift in the life cycle of this species, possibly caused by the overfishing of this important resource and significant increase in human activities in protected coastal waters in modern times.

Effects of atorvastatin on the Sirtuin/PXR signaling pathway in Mugilogobius chulae.

Atorvastatin (ATV) is a hypolipidemic drug widely detected in the aquatic environment. Nevertheless, limited information is provided about the toxic effects of ATV on estuary or coastal species and the underlying mechanisms. In the present study, the responses of genes expression in pregnane X receptor (PXR) signaling pathway and enzymatic activities in the liver of the estuarine benthic fish (Mugilogobius chulae) were investigated under acute and sub-chronic ATV exposure. Results showed that PXR was significantly inhibited in the highest exposure concentration of ATV for a shorter time (24h, 500μg L-1) but induced in a lower concentration (72h, 5μg L-1). The downstream genes in PXR signaling pathway such as CYP3A, SULT, UGT, and GST showed similar trends to PXR. P-gp and MRP1 were repressed in most treatments. GCLC associated with GSH synthesis was mostly induced under ATV exposure for a long time (168h), suggesting that reactive oxygen species (ROS) were generated under ATV exposure. Similarly, GST and SOD enzymatic activities significantly increased in most exposure treatments. Under ATV exposure, SIRT1 and SIRT2 displayed induction to some extent in most treatments, suggesting that SIRTs may affect PXR expression by regulating the acetylation levels of PXR. The investigation demonstrated that ATV exposure affected the expression of the Sirtuin/PXR signaling pathway, thus further interfered adaption of M. chulae to the environment.

Resident species, not immigrants, drive reorganization of estuarine fish assemblages in response to warming.

Climate change is reshaping biological communities, as species track environmental temperature. Assemblage reorganization is underpinned by shifts in species abundance and distribution, but studies often focus on documenting compositional turnover. As a consequence, phenomena such as the tropicalization of temperate communities have been widely associated with increased occupancy of warm-affinity species. Abundance-weighted change in thermal affinity can be tracked with the Community Temperature Index (CTI), and decomposed into four processes: tropicalization (increasing warm-affinity), borealization (increasing cold-affinity), deborealization (decreasing cold-affinity), and detropicalization (decreasing warm-affinity). Further evaluation of these processes according to species persistence (i.e., immigrant, emigrant, and resident) may provide insights on whether novel communities emerge primarily from local shifts in species abundance or distribution. Using long-term data on fish assemblages undergoing climate change's effects across 19 temperate estuaries surveyed for at least 20 years, we hypothesized (1) deborealization is the main process reshaping communities under climate change, and (2) the contribution of resident species to processes reshaping communities surpass the ones from immigrants and emigrants. Community dissimilarity was calculated through the Temporal Beta Index (TBI), which was further decomposed into species and individual losses and gains. These values were then used as effect sizes in the meta-analyses performed to detect systematic trends in assemblage reorganization in response to climate change. We also calculated CTI and the strength of temperature-related processes for resident, immigrant and emigrant species. Species and individual gains outweighed losses in estuaries. Temperature was correlated with changes in species abundance, but not occurrence. Fish abundance decreased with warming, and initially cooler estuaries gained more fish than warmer ones. Novel communities were shaped by a variety of processes, but mainly tropicalization. Assemblage reorganization was primarily driven by shifts in abundance of resident species with distinct thermal affinities, while contributions of arriving and exiting species played a secondary role. These findings reveal that novel communities are drawn primarily from the local species pool, due to changes in climate-related drivers that favor distinct resident species.

Terrestrial Carbon Additions to Zooplankton Prey Influence Juvenile Estuarine Fish Growth

Freshwater inflows are linked to the abundance and catch rates of fish in estuaries. The role of terrestrial carbon resources brought into estuaries after inflows may be important, but this is currently not well understood. Therefore, we performed a study examining the effect of terrestrial dissolved organic matter (tDOM) dietary additions on the growth of food-limited juvenile Australian bass (Macquaria novemculeata). Crustaceous zooplankton Artemia franciscana (Artemia) were reared for two days under control conditions (no addition) or with additions of tDOM leachate at dissolved organic carbon (DOC) concentrations of 5 mg/L or 10 mg/L. Artemia were fed to juvenile bass in their treatment tanks over 42 days at feeding rates reduced by 65–75% of ad libitum. Juvenile fish from the 5 mg/L treatment exhibited no statistical difference in weight or standard, fork and total lengths compared to the control treatment. In contrast, the fish in the 10 mg/L tDOM treatment had significant increases (p &lt; 0.05) in all length parameters after 42 days compared to the other treatments. The greater lengths of fish where tDOM is available indicate that tDOM can contribute to improved growth and development in juvenile Australian bass. While stable isotope analysis of fish tissue showed only minor changes toward terrestrial carbon signatures, increased terrestrial resource availability in the juvenile fish diets may have subsidised energetic needs, facilitating the greater utilisation of endogenous resources. Overall, the results indicate that freshwater inflows that deliver terrestrial resources may be important for the growth and development of estuarine fish.

Fish fauna from the estuaries of Cear&amp;aacute; state, Brazil: a checklist in support of conservation of the Brazilian semiarid coast

We provide extensive surveys in eight estuaries along the coast of Cear&amp;aacute; State in Northeastern Brazil, including local samples and data compiled from online data bases and literature. Samplings resulted in a checklist of the estuarine fish fauna, which recorded 126 fish species, and provides original information of some estuaries. Most of the sampled marine species are widely distributed and many are important commercial species for the artisanal fisheries. The addition of records from existing inventories and online collections increases the number of species to 245, of which 11 are threatened (critically endangered or vulnerable) and six are introduced. Our study provides an updated list of fish species of the estuaries along the semiarid coast of Brazil and is intended as a subsidy for further research, conservation and management efforts.

The future of fish and fisheries in Australia: prioritisation of research needs through a horizon scanning approach

Context In Australia, the health of our marine, estuarine and freshwater fishes are of critical importance. The aquatic and marine ecosystems, and the fishes that occupy them each have an important role in our country’s ecological, economic, cultural and social wealth. Climate change, resource over-exploitation, invasive animals and diseases, and habitat degradation are just a few of the burgeoning threats that researchers and managers must address to ensure the prosperity of Australia’s natural fisheries resources. In addition, differences in legislative frameworks among jurisdictions hinder our ability to coherently manage fish resources at scales that are relevant biologically, ecologically and socially. Aims Here, we identify the key research priorities for fish and fisheries research in Australia, across seven thematic fields of study. Methods Research priorities were evaluated using a horizon scanning approach which identified research questions related to the field of fish and fisheries research in Australia. Key results A total of 284 unique research questions were categorised and prioritised, resulting in the formation of the top 10 highest priority research questions across each of the seven themes. Conclusions The outcomes from this work can be used to directly complement ongoing work from research providers working in the field of fish and fisheries as well as the development of new areas of research. Implications The priorities identified will enable researchers and policy makers to identify critical knowledge gaps, develop collaborative research programs, investigate novel approaches, and to improve transparency around decision-making processes.

Relating absolute abundance of an estuarine fish to habitat area in an urbanizing environment

Organisms that rely on salt marsh habitat are an important trophic link, helping to maintain estuarine ecosystem productivity. We used GIS to quantify intertidal (assumed salt marsh) area from aerial photographs taken in 1939 and from software-supplied satellite imagery taken in 2021 for tidal creeks in North Carolina (USA) that have experienced minor (&lt;20%), moderate (20-60%), or substantial (&gt;60%) losses of intertidal habitat over the 8 decades. The current (2022) absolute abundance of adult Fundulus heteroclitus, a trophically important resident fish in US Atlantic estuaries, was estimated over each season in each creek by fitting a Lincoln-Petersen model to tag-recapture data. Current abundances of F. heteroclitus were lowest in creeks with the lowest intertidal area. The median and 2.5/97.5 credible intervals of the posterior probability distribution for the slope of a regression model relating current fish abundance to current intertidal area were positive, demonstrating that intertidal area was a meaningful covariate of abundance. Loss of intertidal area in the creeks between 1939 and 2021 ranged from 8 to 93%. The correlation between current intertidal area and historical loss of this habitat was negative and significant (Pearson r = -0.91, p = 0.012). Parameters from the regression relating current abundance to intertidal area were used to estimate historic F. heteroclitus abundances in each creek using GIS-derived estimates of historic intertidal area. Historic abundances were predicted to have been on average (across study creeks) 7.5 times greater in 1939 than in 2022. Reduced abundances, and thus reduced trophic relay by F. heteroclitus to higher-order consumers, can be expected in estuaries that have lost salt marsh due to inter-decadal development.

Elevated estuary water temperature drives fish gut dysbiosis and increased loads of pathogenic vibrionaceae

Marine water temperatures are increasing globally, with eastern Australian estuaries warming faster than predicted. There is growing evidence that this rapid warming of coastal waters is increasing the abundance and virulence of pathogenic members of the Vibrionaceae, posing a significant health risk to both humans and aquatic organisms. Fish disease, notably outbreaks of emerging pathogens in response to environmental perturbations such as heatwaves, have been recognised in aquaculture settings. Considerably less is known about how rising sea surface temperatures will impact the microbiology of wild fish populations, particularly those within estuarine systems that are more vulnerable to warming. We used a combination of Vibrio-specific quantitative PCR and amplicon sequencing of the 16S rRNA and hsp60 genes to examine seawater and fish (Pelates sexlineatus) gut microbial communities across a quasi-natural experimental system, where thermal pollution from coal-fired power stations creates a temperature gradient of up to 6 °C, compatible with future predicted temperature increases. At the warmest site, fish hindgut microbial communities were in a state of dysbiosis characterised by shifts in beta diversity and a proliferation (71.5% relative abundance) of the potential fish pathogen Photobacterium damselae subsp. damselae. Comparable patterns were not identified in the surrounding seawater, indicating opportunistic proliferation within estuarine fish guts under thermal stress. A subsequent evaluation of predicted future warming-related risk due to pathogenic Vibrionaceae in temperate estuarine fish demonstrated that warming is likely to drive opportunistic pathogen increases in the upper latitudinal range of this estuarine fish, potentially impacting adaptations to future warming. These findings represent a breakthrough in our understanding of the dynamics of emerging pathogens in populations of wild aquatic organisms within environments likely to experience rapid warming under future climate change.

Hypoxia aggravates the burden of yellowstripe goby (Mugilogobius chulae) under atorvastatin exposure

In the present study, an estuarine benthic fish, Mugilogobius chulae (M. chulae), was exposed to hypoxia, atorvastatin (ATV), a highly used and widely detected lipid-lowering drug in aquatic environment, and the combination of hypoxia and ATV for 7 days, respectively, so as to address and compare the effects of the combination of hypoxia and ATV exposure on M. chulae. The results showed that lipid metabolism in M. chulae was greatly affected: lipid synthesis was blocked and catabolism was enhanced, exhibiting that lipids content were heavily depleted. The combined exposure of hypoxia and ATV caused oxidative stress and induced massive inflammatory response in the liver of M. chulae. Signaling pathways involving in energy metabolism and redox responses regulated by key factors such as HIF, PPAR, p53 and sirt1 play important regulatory roles in hypoxia-ATV stress. Critically, we found that the response of M. chulae to ATV was more sensitive under hypoxia than normoxia. ATV exposure to aquatic non-target organisms under hypoxic conditions may make a great impact on the detoxification and energy metabolism, especially lipid metabolism, and aggravate the oxidative pressure of the exposed organisms.