Loss Of Fish Research Articles

Loss of pelagic fish and zooplankton density associated with subglacial upwelling in high Arctic estuaries may be mitigated by benthic habitat expansion following tidewater glacier retreat

Glacier fronts are hotspots of pelagic productivity due to upwelling of nutrient-rich water. As tidewater glaciers retreat into land, this subglacial circulation will disappear and sedimentation from terrestrial runoff will increase, leading to a decrease in pelagic productivity with a decline in the abundance of fish and zooplankton. We used Billefjorden, a high Arctic fjord with a glacier recently transitioned from sea- to land-terminating as a case study to identify spatial differences and small-scale environmental drivers of density and vertical distribution of fish and zooplankton along a gradient of glacier retreat (directly in front of the land-terminating glacier front, a river bay with terrestrial input from land-terminating glaciers further inland and a location with minimal glacial input). We developed a sustainable and efficient protocol to safely sample the glacier front and shallow coastal areas using hydroacoustics and a remote autonomous vehicle combined with oceanographic measurements and baited remote cameras. Over two years, pelagic density was lowest at the now land-terminating glacier front and highest at the site with lowest terrestrial input. Temperature, depth and turbidity explained less than 8% of the variation each.

Resistance patterns, virulence determinants, and biofilm genes of multidrug-resistant Pseudomonas aeruginosa isolated from fish and fish handlers

Pseudomonas aeruginosa (P. aeruginosa) is an opportunistic bacterium that is widely distributed in aquatic environments and causes major economic losses in fish and public health hazards.This study aimed to identify the occurrence of P. aeruginosa in samples collected from fish and fish handlers, and to investigate the antimicrobial susceptibility, virulence determinants, and biofilm genes of P. aeruginosa isolates. A total of 276 samples were cross-sectionally collected from Nile tilapia (53), Golden grey mullet (52), Mediterranean horse mackerel (50), Striped red mullet (71), and fish handlers (50) at five different retail fish markets in Damietta Governorate, Egypt. Pseudomonas species (spp.) were biochemically identified in 57.9% of the total examined samples. Peudomonas aeruginosa were the most prevalent species isolated from the fish and human samples via PCR technique. Peudomonas aeruginosa isolates exhibited full resistance (100%) to tobramycin (TOB), gentamicin (CN), and colistin (CL), with a high level of susceptibility (88.5%) to imipenem (IPM) using the disk diffusion method. Most P. aeruginosa isolates (84.6%) exhibited drug resistance, with 61.5% were multidrug resistance (MDR) and 23.1% were extensive drug resistance (XDR). Most isolates had at least four virulence-associated genes (lasB, toxA, exoU, and oprL) and three biofilm genes (psIA, peIA, and lasR) by using uniplex PCR. The lasI, and rhlR Quorum Sensing (QS) genes were identified in 84.6% and 61.5% in the examined P. aeruginosa isolates, respectively. The highest mortality rate in Nile tilapia experimentally infected with P. aeruginosa isolate encoding most of virulent genes. Multivariate analyses revealed high heterogeneity among the examined isolates. This study revealed the emergence of virulent and drug resistant P. aeruginosa isolates in fish, poses high risks to consumers and food. Thus, strict hygienic measures should be considered when catching, handling, and storing fish, in addition to the routine application of antimicrobial susceptibility testing.

Post-harvest losses of marine fish at fishers in Bangladesh

The marine fishing industry is considered as one of Bangladesh's most important contributors to the nation's economy. The post-harvest losses of marine fish have a substantial impact on the contribution of the industry. Therefore, the aim of this study was to assess post-harvest losses of marine fish at fishermen level and to identify the factors that influence post-harvest losses. In-person interviews were conducted in two coastal divisions of Bangladesh to collect data from 643 fishermen, which was then analyzed using multiple regression models. Results showed that the total post-harvest losses of marine fish in Bangladesh were 17.75 % of total caught, with physical and market losses accounting for 9.86 % and 90.14 %, respectively. The use of inadequate ice and uninsulated containers was estimated to increase post-harvest losses of marine fish by 40 %, all else being equal. Earning members, inadequate storage, longer time attached to the net, delayed marketing, and tide pressure were statistically significant and positively correlated with post-harvest losses, whereas family members and fish finder were negatively associated with post-harvest losses. This study thus recommends that those who harvest marine fish should be aware of the parameters they choose that affect post-harvest losses.

Post-harvest loss assessment of Hilsa (Tenualosa ilisha) along the value chain in Bangladesh

Hilsa, the national fish of Bangladesh, contributes more than 12 % of the country's total fish production. Considering the species' importance, this study assessed the post-harvest loss (PHL) of Hilsa across the value chain. Data were collected at the landing and distribution chain from 200 fisherman, 40 aratdars (Aratdar-I), 40 wholesalers at landing sites of the Chandpur district, 40 aratdars (Aratdar-II), and 70 retailers at the distribution sites of the Jamalpur district. The results revealed 12.56 % post-harvest losses in the value chains, most of which were caused by quality losses (8.41 %). Along the value chain, fishermen faced the highest losses 5.291 %, followed by 3.813 % in the retailers. These findings suggest fishermen and retail markets are hotspots of spoilage and fish loss. The OLS regression model indicated that inappropriate age and lack of experience of stakeholders, prolonged harvesting time, inadequate washing facilities, fishermen small size group, longer distances between fishing locations and landing sites, lack of proper education and training, delaying auctioning, insufficient infrastructure facilities, longer selling time, and insufficient cooling facilities were the significant factors causing PHL in the value chain. Nutritional analysis revealed substantial changes across the value chain. Moisture content increased steadily, which accelerated the spoilage. A significant decrease in protein, lipid and ash indicated the substantial loss of nutrients after harvesting up to the retail market. Principal Component Analysis (PCA) for nutritional composition analyses demonstrated that after the catch, aratdar-I, and boat had higher nutrient levels, while aratdar-II, local wholesaler, and post-transportation had higher moisture and lower nutrient levels. The PC1 accounted 95.92 % of the variation, indicating that handling and storage had significant influences in maintaining nutritional quality. To reduce post-harvest losses, the government must implement standardized practices throughout the Hilsa value chain to ensure food security and sustainability in the Hilsa fishery and boost the economy.

Molecular responses in the intestine of Atlantic salmon (Salmo salar) following light and diet stimulation of smoltification: Potential molecular markers for a seawater-ready smolt

The transfer to seawater (SW) represents a critical stage in the production of Atlantic salmon. The success of the transfer links with the optimal development of hypo-osmoregulatory capacities during smoltification. While various strategies are adopted in aquaculture to stimulate smoltification, considerable fish loss still occurs after transfer to sea cages. Therefore, we investigated the molecular responses in the anterior and posterior intestine of Atlantic salmon, following 1) a photoperiod treatment (24 h light (L):0 h dark (D) → 24 L:0D vs. 7 L:17D → 24 L:0D) and 2) dietary treatment (regular feed or feed enriched with a salt mix/tryptophan), combined with, or without a photoperiodic treatment in freshwater (FW), to evaluate how intestinal osmoregulatory mechanisms are modulated by these treatments, and to identify potential intestinal markers indicative of a SW-ready smolt. Using quantitative real-time PCR (qPCR), we investigated transcript levels of transporters and channels involved in ion movements through the enterocytes, tight junction components, and receptors (i.e., calcium-sensing receptor and prolactin receptor). The two intestinal regions showed different gene profiles and responsiveness towards the experimental treatments. In the anterior intestine, the exposure to short photoperiod (7 L:17D) upregulated Na+/K+ − ATPase subunit alpha 1c (nkaα1c), Na+/K+/2Cl− cotransporter 1 (nkcc1), Na+/K+/2Cl− cotransporter 2 (nkcc2), Cl−/HCO3− exchanger Slc26a6 (slc26a6), and cystic fibrosis transmembrane conductance regulator I (cftrI), in FW and SW. Also, Na+/K+ − ATPase subunit alpha 1b (nkaα1b), occludin (ocln), and prolactin receptor (prlr) were upregulated in FW and claudin 15 (cldn15) in SW groups exposed to this photoperiod. The posterior intestine was less responsive to the experimental treatments, although upregulation of nkcc1, nkcc2, slc26a6, and cftrI was observed in FW in the short photoperiod groups. Hence, our findings show that exposure to a winter signal in FW more effectively activates hypo-osmoregulatory mechanisms in the intestine of Atlantic salmon, where a coordinated and complementary role of the anterior and posterior intestine ensures optimal SW processing. Dietary treatment had a positive but more marginal effect on the regulation of the genes investigated, mainly enhancing the impact of short photoperiod when the two treatments were combined. Overall, we propose the apical Na+/K+/2Cl− cotransporter, nkcc2, and the apical Cl−/HCO3− exchanger, slc26a6, as potential FW molecular markers in the anterior intestine to assess “SW-readiness” in Atlantic salmon smolts.

Coral reef recovery in a remote and large marine protected area is resilient to cascading trophic interactions

Large marine protected areas (MPAs) will likely multiply worldwide to address accelerating biodiversity loss. Coral reefs are an especially at-risk ecosystem, but our understanding of whether and how large MPAs will benefit reef recovery from disturbances remains limited. Here, we evaluate how fishes influence coral reef recovery and if there are cascading trophic interactions in the fish community that influence recovery. We combine i) a meta-analysis of previous research evaluating how fishes affect coral reef succession, ii) field surveys of sharks, fishes, and benthic cover, and iii) a 2.5-year coral recruitment experiment of caged, uncaged, and partially caged settlement tiles in a remote and large MPA, in the Chagos Archipelago. In both our meta-analysis and field experiment, we found variable effects of fishes on coral recruitment with no overall significant effect, but strong control by fishes on the developing benthic communities, where fishes promote crustose coralline algae and reduce macroalgae. Within the Chagos, fishes had a positive effect on corals in protected microhabitats but a negative effect on exposed surfaces, leading to an overall neutral effect from fishes. Although mesopredatory fish abundance was negatively correlated with shark abundance, these top-down effects did not cascade down the food web through herbivores and corallivores to coral recruitment and benthic succession. Thus, our results suggest that within this large MPA, herbivores are important in limiting algae during recovery and there are compensatory responses to the loss of benthic feeding fishes and sharks, with implications for coral reef persistence in the face of global change.

Coping with collapse: Functional robustness of coral-reef fish network to simulated cascade extinction.

Human activities and climate change have accelerated species losses and degradation of ecosystems to unprecedented levels. Both theoretical and empirical evidence suggest that extinction cascades contribute substantially to global species loss. The effects of extinction cascades can ripple across levels of ecological organization, causing not only the secondary loss of taxonomic diversity but also functional diversity erosion. Here, we take a step forward in coextinction analysis by estimating the functional robustness of reef fish communities to species loss. We built a tripartite network with nodes and links based on a model output predicting reef fish occupancy (113 species) as a function of coral and turf algae cover in Southwestern Atlantic reefs. This network comprised coral species, coral-associated fish (site occupancy directly related to coral cover), and co-occurring fish (occupancy indirectly related to coral cover). We used attack-tolerance curves and estimated network robustness (R) to quantify the cascading loss of reef fish taxonomic and functional diversity along three scenarios of coral species loss: degree centrality (removing first corals with more coral-associated fish), bleaching vulnerability and post-bleaching mortality (most vulnerable removed first), and random removal. Degree centrality produced the greatest losses (lowest R) in comparison with other scenarios. In this scenario, while functional diversity was robust to the direct loss of coral-associated fish (R = 0.85), the taxonomic diversity was not robust to coral loss (R = 0.54). Both taxonomic and functional diversity showed low robustness to indirect fish extinctions (R = 0.31 and R = 0.57, respectively). Projections of 100% coral species loss caused a reduction of 69% of the regional trait space area. The effects of coral loss in Southwestern Atlantic reefs went beyond the direct coral-fish relationships. Ever-growing human impacts on reef ecosystems can cause extinction cascades with detrimental consequences for fish assemblages that benefit from corals.

From texture to structure: The key role of caspase-3 on grass carp myofibrillar protein during postmortem storage

The integrity of myofibrillar proteins during the initial post-mortem storage phase critically determines the shelf-life of fish, profoundly affecting consumer acceptance and market value. This research investigates the degradation of grass carp muscle texture and structure triggered by caspase-3-induced apoptosis, a key factor influencing early storage quality deterioration. By inhibiting endogenous caspase-3, the study tracks changes in apoptosis levels, muscle texture, microstructural integrity, protein organizational structure, and amino acid profiles. Apoptosis was found to peak between 48 and 72h post-mortem, during which caspase-3 activity led to significant muscle softening. This softening is attributed to disruptions in crucial structural components such as the Z-line and M-line, culminating in extensive degradation of myofibrillar proteins. Furthermore, protein structure modeling demonstrated that caspase-3 cleavage at ASP187 critically destabilizes the α-helix structure, underlining the enzyme's pivotal role in the early post-mortem softening of fish muscle. These insights provide a foundational understanding of the biochemical processes that underpin early quality loss in stored fish, offering potential targets for interventions aimed at enhancing fish storage outcomes and extending shelf life in the aquaculture industry.

Myo-inositol: A potential game-changer in preventing gill cell death and alleviating “gill rot” in grass carp (Ctenopharyngodon idellus)

Increasing evidence shows the potential threat of gill rot in freshwater fish culture. F. columnare is wide-spread in aquatic environments, which can cause fish gill rot and result in high mortality and losses of fish. This study investigated the effects of myo-inositol (MI) on the proliferation, structural integrity, and different death modes of grass carp (Ctenopharyngodon idella) gill epithelial cells, as well as its possible mechanism. 30 mg/L MI up-regulated CCK8 OD value and the protein level of solute carrier family 5A 3 (SLC5A3), and down-regulated the reactive oxygen species (ROS) content in gill cells and lactate dehydrogenase (LDH) release in the culture medium (P < 0.05). MI up-regulated the protein level of Beclin1, the protein level and fluorescence expression of microtubule-associated protein light chain 3B (LC3B) and down-regulated the protein level of sequestosome-1 (SQSTM1, also called p62) (P < 0.05). MI down-regulated the protein levels of Cysteine aspartate protease-1 (caspase-1), Gasdermin E (GSDME) and Cleaved interleukin 1 beta (IL-1β) (P < 0.05). MI up-regulated the protein level of caspase-8 (P < 0.05), but had no effect on apoptosis (P > 0.05). MI down-regulated the mRNA expressions and protein levels of tumor necrosis factor α (tnfα), TNF receptor 1 (tnfr1), receptor interacting protein 1 (ripk1), receptor interacting protein 3 (ripk3) and mixed lineage kinase domain-like protein (mlkl), and reduce the ratio of p-MLKL/MLKL (P < 0.05). The addition of MI or necrosulfonamide (NSA) alone, or the addition of MI after induction of necroptosis, significantly up-regulated the cell activity and the protein level of SLC5A3 in gill cells, and significantly reduced the LDH release in the culture medium and the intracellular ROS content, the number of necroptosis cells, the protein expression of TNFα, TNFR1 and RIPK1, and the ratio of p-RIPK3/RIPK3 and p-MLKL/MLKL (P < 0.05). It indicated MI induce autophagy may relate to Beclin1/LC3/p62 signaling pathway, inhibits pyroptosis may attribute to Caspase-1/GSDMD/IL-1β signaling pathway, and inhibits necroptosis via MLKL signaling pathway. However, MI had no effect on apoptosis.

Post-harvest losses in marine fisheries of Bangladesh

Existing literature highlights significant income loss due to Post-Harvest Loss (PHL) across the fisheries value chain in developing countries like Bangladesh. This is attributed to inappropriate fishing tools, poor infrastructure, inadequate storage facilities, and inefficient transportation. This study estimated PHL and its determinants in Bangladesh's marine fisheries using the Questionnaire Loss Assessment Method (QLAM) based on data collected from 1132 respondents, including fishermen and traders, from October 2019 to March 2021. The results reveal that physical, market, and monetary PHL in marine fisheries are 0.82 %, 6.41 %, and $228.52 per ton, respectively. Annually, the country loses approximately $151 million due to PHL in marine fisheries, with the highest market losses in Snapper, Pomfret, and Hilsa fish. The main reasons for PHL include the duration of fish remain in the net after being caught, insufficient ice, lack of insulated containers and storage facilities, delayed marketing, and oversupply. The study suggests adopting modern harvesting technology, enforcing regulations for scientific gear, and increasing storage capacity at landing and selling points to reduce PHL in marine fisheries.

The effects of light, rearing density, and fish size in culturing juvenile Lumpfish

AbstractObjectiveThere is an impetus for increasing Lumpfish Cyclopterus lumpus hatchery production and rearing efficiency due to the high demand for their usefulness as cleaner fish in salmonid ocean farming. One production bottleneck is the loss of juvenile fish due to aggressive behaviors, including cannibalism. Understanding which factors exacerbate Lumpfish aggression and providing mitigation guidelines to aquaculturists are warranted.MethodsTwo experiments were conducted for an 8‐week period in 2022 in 3‐L aquaria with different juvenile size‐classes (4 and 11 g) subjected to three rearing densities (40, 65, and 90 g/L) under different photoperiod regimes (12 h light : 12 h dark [113 lx]; 24 h light : 0 h dark [21 lx]; and 24 h light : 0 h dark [302 lx]), resulting in nine experimental treatments. Survival, growth, and aggression (occurrence and severity of caudal fin nipping) were evaluated.ResultFor 4‐g Lumpfish, light and density significantly affected growth (weight gain and specific growth rate), while an interaction between light and density significantly affected the occurrence of caudal fin nipping but not the degree of fin nipping or survival. None of the tested variables significantly affected 11‐g fish. Generally, a trend toward increased caudal fin nipping occurred in smaller fish (~45% occurrence in 4‐g fish vs. ~20% in 11‐g fish), indicating that cannibalism may be even greater when Lumpfish are smaller than 4 g but abates as the fish grow.ConclusionOur findings indicate that manipulation of lighting at rearing densities of up to 90 g/L can be used to control growth rates in small Lumpfish, often without resulting in increased fish aggression. For small (~4‐g) Lumpfish, constant low light intensity in combination with a low (40‐g/L) rearing density is recommended for reducing growth and caudal fin nipping. However, as Lumpfish grow, these variables are less effective at manipulating fish growth.

Functional diversity loss and taxonomic delays of European freshwater fish and North American breeding birds

Abstract Biodiversity is temporally dynamic, reflecting historical environmental conditions and influencing ecosystem stability. Colonisation and extinction dynamics frequently exhibit asynchronous patterns, resulting in net imbalances and thus to long‐lasting richness trends. If these trends are not functionally random, functional net imbalances between colonisations and extinctions (fNICE) are likely to emerge. Using community time series data of European freshwater fish and North American breeding birds, we investigated how fNICE differs from its taxonomic equivalent (tNICE), to provide a comprehensive picture of biodiversity dynamics. Our findings reveal that taxonomic and functional delays are a prevalent feature, challenging the assumption of an immediate response to environmental changes. Taxonomic delays manifest as extinction debts and colonisation credits, while functional delays indicate a shift in the balance between functional gains and losses over time. Moreover, we found that taxonomic and functional imbalances are not always directly correlated, although some specific patterns were found consistently for fish and birds. Early colonisations outpaced functional gains, indicating that although new species arrived earlier than the extinction of other species, the acquisition of new functional traits lagged. Although this may temporarily stabilise communities, as functional redundancy can mitigate loss of function via local extinctions, excessive redundancy can compromise biodiversity's capacity to respond to environmental variations, thereby undermining long‐term resilience. In conclusion, understanding the intricate temporal dynamics of biodiversity responses is paramount for effective conservation practices. While short‐term observations may suggest an equilibrium between diversity and the environmental conditions, our results underscore the importance of considering long‐term dynamics and the interplay between species traits and changing environments. The metrics tNICE and fNICE are valuable tools for quantifying these temporal dynamics and unravelling their consequences for ecosystem stability. Incorporating these insights into conservation strategies can aid in proactively preserving biodiversity and safeguarding the integrity of ecosystems. Read the free Plain Language Summary for this article on the Journal blog.

Combining nursery closed-system and pond grow-out common carp (Cyprinus carpio) production is a profitable business in Hungary

Extensive, large-scale long-term pond fish production has several challenges and high economic risks, such as continuous bird predation. Moreover, common carp (Cyprinus carpio) production costs are relatively high using this production strategy. To reduce risks and improve production safety and efficiency, European common carp farmers are challenged to shorten the classic 3-year production cycle. This study aimed to comprehensively analyze the main farm parameters, production efficiency, cost and revenue of a production strategy based on combining hatchery/nursery closed-system, a second phase of the nursery in ponds and a final phase of pond grow-out of common carp. A deterministic economic model was used. Combined production has a lower fish loss by bird predation, a shorter production cycle, a better feed conversion ratio than conventional pond fish production, and a similar yield at a cost of approximately 2.02 USD/kg. This value are higher than those assumed in the conventional extensive 3-year common carp, completely pond-based production strategy. However, the current assets turnover ratio is much lower in the latter case. The yearly average net revenue can increase by implementing a more intensive combined production strategy. The combined strategy can improve security and predictability of production while reducing the pond area used for grow-out of extensive common carp farm.

Genomic signatures associated with recurrent scale loss in cyprinid fish.

Scale morphology represents a fundamental feature of fish and a key evolutionary trait underlying fish diversification. Despite frequent and recurrent scale loss throughout fish diversification, comprehensive genome-wide analyses of the genomic signatures associated with scale loss in divergent fish lineages remain scarce. In the current study, we investigated genome-wide signatures, specifically convergent protein-coding gene loss, amino acid substitutions, and cis-regulatory sequence changes, associated with recurrent scale loss in two divergent Cypriniformes lineages based on large-scale genomic, transcriptomic, and epigenetic data. Results demonstrated convergent changes in many genes related to scale formation in divergent scaleless fish lineages, including loss of P/Q-rich scpp genes (e.g. scpp6 and scpp7), accelerated evolution of non-coding elements adjacent to the fgf and fgfr genes, and convergent amino acid changes in genes (e.g. snap29) under relaxed selection. Collectively, these findings highlight the existence of a shared genetic architecture underlying recurrent scale loss in divergent fish lineages, suggesting that evolutionary outcomes may be genetically repeatable and predictable in the convergence of scale loss in fish.

Inland navigation and land use interact to impact European freshwater biodiversity.

Inland navigation in Europe is proposed to increase in the coming years, being promoted as a low-carbon form of transport. However, we currently lack knowledge on how this would impact biodiversity at large scales and interact with existing stressors. Here we addressed this knowledge gap by analysing fish and macroinvertebrate community time series across large European rivers comprising 19,592 observations from 4,049 sampling sites spanning the past 32 years. We found ship traffic to be associated with biodiversity declines, that is, loss of fish and macroinvertebrate taxonomic richness, diversity and trait richness. Ship traffic was also associated with increases in taxonomic evenness, which, in concert with richness decreases, was attributed to losses in rare taxa. Ship traffic was especially harmful for benthic taxa and those preferring slow flows. These effects often depended on local land use and riparian degradation. In fish, negative impacts of shipping were highest in urban and agricultural landscapes. Regarding navigation infrastructure, the negative impact of channelization on macroinvertebrates was evident only when riparian degradation was also high. Our results demonstrate the risk of increasing inland navigation on freshwater biodiversity. Integrative waterway management accounting for riparian habitats and landscape characteristics could help to mitigate these impacts.

Destocking waterways: Evidence that stocked Murray Cod (Maccullochella peelii) were extracted at pumped irrigation diversions within 24 hours of release

SummaryMillions of native fish are entrained into irrigation pumps in Australian rivers every year. It is often assumed these fish are wild, but stocked fish may also be affected. During fish entrainment surveys at two pump intakes on the Macquarie River, New South Wales, a noticeable increase of entrained juvenile Murray Cod (Maccullochella peelii) was observed. DNA parentage analysis confirmed that a large proportion of these fish were linked to nearby fish restocking events. At both pump intakes, genetic analysis confirmed that at least 70% and 17% of the individuals sampled were stocked fish. This equated to up to 3% of the fish that were stocked – most of which were entrained less than 24 h after their release. Given the large number of unscreened irrigation pumps in this reach of river, and more broadly throughout the Murray–Darling Basin, fish losses at pump intakes have the potential to remove large numbers of stocked fish from the river where they are released to support native fish recovery and boost recreational fishing opportunities. The use of fish‐protection screens at pump intakes may be a suitable solution to reduce the number of fish entrained and thus increase the survival of recently stocked fish in the rivers.

Molecular plasticity to ocean warming and habitat loss in a coral reef fish.

Sea surface temperatures are rising at unprecedented rates, leading to a progressive degradation of complex habitats formed by coral reefs. In parallel, acute thermal stress can lead to physiological challenges for ectotherms that inhabit coral reefs, including fishes. Warming and habitat simplification could push marine fishes beyond their physiological limits in the near future. Specifically, questions remain on how warming and habitat structure influence the brain of marine fishes. Here we evaluated how thermal stress and habitat loss are acting independently and synergistically as stressors in a damselfish of the Western Atlantic, Abudefduf saxatilis. For this experiment, 40 individuals were exposed to different combinations of temperature (27°C or 31°C) and habitat complexity (complex vs simple) for 10 days, and changes in brain gene expression and oxidative stress of liver and muscle were evaluated. The results indicate that warming resulted in increased oxidative damage in the liver (p=0.007) and changes in gene expression of the brain including genes associated with neurotransmission, immune function, and tissue repair. Individuals from simplified habitats showed higher numbers of differentially expressed genes, and changes for genes associated with synaptic plasticity and spatial memory. In addition, a reference transcriptome of A. saxatilis is presented here for the first time, serving as a resource for future molecular studies. This project enhances our understanding of how fishes are responding to the combination of coral reef degradation and thermal stress, while elucidating the plastic mechanisms that will enable generalists to persist in a changing world.

Possible mechanisms of sequential and simultaneous ultrasonic thawing modes affecting the quality of small yellow croaker

The effect of ultrasonic thawing with different ultrasound working modes on the quality of quick-frozen small yellow croaker and its myofibrillar protein (MPs) structures and functional characteristics were investigated. Flow water (FW), tri-frequency sequential ultrasonic (TSEU), and tri-frequency simultaneous ultrasonic (TSIU) were used for thawing quick-frozen fish. The results showed that the quality of fish thawed by TSEU was the best, while the quality of fish thawed by FW was the worst. Compared to the MPs obtained by TSIU thawing, the MPs obtained by TSEU thawing had more α-helix structure, less β-turns content, smaller oxidation degree, and better thermal gelation ability, which was closest to fresh sample (FS) group. Therefore, compared with TSIU, the TSEU thawing can effectively improve the structure and functional characteristics of the MPs. The thawing loss, hardness and chewiness of fish were mainly affected by α-helix content, and TVB-N value was mainly affected by β-turns.

Quantitative analysis of mass mortality events in salmon aquaculture shows increasing scale of fish loss events around the world

Globally, salmon aquaculture promises to contribute to sustainable sources of animal protein for a growing human population. However, the growth of the industry also includes increased reports of mass mortality events—disaster events where large numbers of fish die in short periods of time. As salmon production increases in scale and more technology is used to grow salmon in contexts otherwise not suited for them, there is a possibility for more frequent and more severe mortality events. Despite investigations into specific cases of mass mortality events—no global study has been conducted to see if large scale mortality is increasing in frequency and scale. Using a global dataset of publicly available and government-collated data on salmon mortality events including nations responsible for the majority of salmon aquaculture, we document trends in mortality events, showing that in some of the major salmon producing nations of the world (in particular Norway, Canada, and the UK), mass mortality events have increased in frequency from 2012 to 2022. We also show that the scope of mass mortality events has increased over time—that is, the upper bound of how many fish were killed in a specific mortality event has increased over time. Finally, the expected maximum size of a mass mortality event differs from country to country, but is likely much larger than site and jurisdictional thresholds of concern for animal welfare, early warning thresholds, and capacity to respond to mortality events. The consequences of the increased scale and scope of mass mortality events extend past aquaculture production to include severe consequences to aquaculture companies and to coastal communities who depend on aquaculture. Our results agree with predictions of the concept of “manufactured risk”, which suggests that risk emerges from the aggressive use of technology to optimize production in variable environments, and we argue that there is a need for more fine-scale and standard data collection on salmon mortality events, and that future investigations into salmon aquaculture should increase focus on disaster potential and realization.

Herbivorous sea urchins (Echinometra mathaei) support resilience on overfished and sedimented tropical reefs

Human impacts are dramatically changing ecological communities, motivating research on resilience. Tropical reefs are increasingly undergoing transitions to short algal turf, a successional community that mediates either recovery to coral by allowing recruitment or transitions to longer turf/macroalgae. Intense herbivory limits turf height; subsequently, overfishing erodes resilience of the desirable coral-dominated reef state. Increased sedimentation also erodes resilience through smothering and herbivory suppression. In spite of this critical role, most herbivory studies on tropical reefs focus on fishes, and the contribution of urchins remains under-studied. To test how different herbivory and sedimentation scenarios impact turf resilience, we experimentally simulated, in situ, four future overfishing scenarios derived from patterns of fish and urchin loss in other reef systems and two future sedimentation regimes. We found urchins were critical to short turf resilience, maintaining this state even with reduced fish herbivory and increased sediment. Further, urchins cleared sediment, facilitating fish herbivory. This study articulates the likelihood of increased reliance on urchins on impacted reefs in the Anthropocene.