Life Stages Of Fish Research Articles

Effects of incubation temperature on the upper thermal tolerance of the imperiled longfin smelt (Spirinchus thaleichthys).

Upper thermal limits in many fish species are limited, in part, by the heart's ability to meet increased oxygen demand during high temperatures. Cardiac plasticity induced by developmental temperatures can therefore influence thermal tolerance. Here, we determined how incubation temperatures during the embryonic stage influence cardiac performance across temperatures during the sensitive larval stage of the imperiled longfin smelt. We transposed a cardiac assay for larger fish to newly hatched larvae that were incubated at 9°C, 12°C or 15°C. We measured heart rate over increases in temperature to identify the Arrhenius breakpoint temperature (TAB), a proxy for thermal optimum and two upper thermal limit metrics: temperature when heart rate is maximized (Tpeak) and when cardiac arrhythmia occurs (TArr). Higher incubation temperatures increased TAB, Tpeak and TArr, but high individual variation in all three metrics resulted in great overlap of individuals at TAB, Tpeak and TArr across temperatures. We found that the temperatures at which 10% of individuals reached Tpeak or TArr and temperatures at which number of individuals at TAB relative to Tpeak (ΔN(TAB,Tpeak)) was maximal, correlated more closely with upper thermal limits and thermal optima inferred from previous studies, compared to the mean values of the three cardiac metrics of the present study. Higher incubation temperatures increased the 10% Tpeak and TArr thresholds but maximum ΔN(TAB,Tpeak) largely remained the same, suggesting that incubation temperatures modulate upper thermal limits but not Topt for a group of larvae. Overall, by measuring cardiac performance across temperatures, we defined upper thermal limits (10% thresholds; Tpeak, 14.4-17.5°C; TArr, 16.9-20.2°C) and optima (ΔN(TAB,Tpeak), 12.4-14.4°C) that can guide conservation strategies for longfin smelt and demonstrated the potential of this cardiac assay for informing conservation plans for the early life stages of fish.

Deciphering the microbial landscapes in the early life stages of a high-value marine fish, cobia (Rachycentron canadum, Rachycentridae) through high-resolution profiling by PacBio SMRT sequencing

Microbial dynamics across multiple ontogenetic stages represent one confounding feature in teleost microbiome research. The present study recorded the dynamics in the whole microbiome of early life stages and the juvenile gut microbiome of a high-value mariculture species, cobia (Rachycentron canadum), during standard culturing practices. This is the first report on using the PacBio system targeting full-length 16S rRNA sequences, for deciphering fish microbiomes. The results highlighted a temporal shift in the whole microbiome compositions along the host's ontogenetic development. There was a significant decrease in Cyanobacteria and Firmicutes to Bacteroidetes ratio with a corresponding increase in Plactomycetacea and Bacteriodata in the whole microbiome profiles of the post-metamorphosis samples. The gut microbiome data suggested an adaptive mechanism toward establishing beneficial strains (Bacilli and Actinobacteria) alongside the ontogenetic progression. Nevertheless, a small, abundant core bacterial community occupied ∼50% and ∼ 64% of total abundance in the whole microbiome and gut microbiome, respectively. The results revealed high-dimensional microbial biomarkers for various ontogenetic stages of cobia during standard culturing practices. The composite dataset generated offers several possible sustainable means of microbiome manipulations to improve the low survival encountered in the early life stages of cobia.

Spatial structuring in early life stage fish diversity in the Scotia Sea region of the Southern Ocean

AbstractThe fish community of the Scotia Sea is diverse and plays key roles in Antarctic food webs and biogeochemical cycling. However, knowledge of the spatial and community structure of their early life stages is limited, particularly in the region surrounding the South Orkney Islands. Here we examine the structure of the early life stage fish community in the epipelagic using data from a basin-scale survey conducted in early 2019, which sampled the top 200 m of the water column. 347 early life stage fish from 19 genera were caught in 58 hauls. A third of all specimens belonged to the genus Notolepis and the nine most common genera comprised over 90% of specimens. Cluster analysis revealed five distinct groupings, the most common were a group dominated by pelagic and shelf slope genera (Notolepis, Muraenolepis and Electrona) found mainly in oceanic waters (depth ≥ 1000 m), and a group dominated by species with demersal or benthopelagic adults (Chionodraco, Chaenocephalus and Nototheniops) found mainly in shelf waters. Bottom depth was the main environmental determinant of community structure, separating the diverse on-shelf assemblage at the South Orkneys from the less species-rich community of widespread oceanic taxa. Our results indicate the highest diversities of early life stages of endemic fish occur on the shelf and near-shelf areas. Dedicated monitoring is recommended to understand the seasonal differences in larval community assemblages and the implications of early life stages fish bycatch within the krill fishery.

Development and application of a bioenergetics growth model for multiple early life stages of an ecologically important marine fish

Spatial and temporal variability in temperature and food availability are key drivers of growth of marine fishes. Growth during the early life stages (ELS's) is tightly coupled to survival, and in turn, can set year-class strength (i.e. annual recruitment) and overall stock productivity of populations and fished stocks. Ontogenetic changes in physiology, dietary preferences, and growth across ELS's can be accounted for within bioenergetics models, but existing models lack resolution within larval and early juvenile stages. We leveraged daily output from a coupled physical-biogeochemical model to force a highly resolved ontogenetic bioenergetics model parametrized for an ecologically important rockfish in the California Current System. Size-at-age predictions closely track empirical growth trajectories of the ELS's. Scenario testing revealed that growth performance is disproportionately driven by changes in temperature compared to food availability. We then expanded the model to incorporate spatial climatological differences in temperature and prey concentration and found that preflexion growth potential is maximized in areas of historical spawning, suggesting the timing and location of reproduction is an adaptive strategy that places larvae in habitat favorable for survival. Growth potential for late-stage larvae (postflexion) is greatest over a broad areal extent, implying that if a particle tracking algorithm was coupled to the bioenergetics model, a wide range of larval dispersal pathways would place postflexion larvae in habitat suitable for rapid growth. Finally, growth potential of pelagic juveniles is maximized over the continental shelf and shelf-break, aligning with high juvenile catch rates from a fisheries-independent survey. In summary, this study (i) serves as a proof of concept that a bioenergetics model with high ontogenetic resolution can reproduce life stage-specific growth trajectories even though the underlying physiology data for model parameterization is imperfect and (ii) can aid future studies aimed at understanding how ecosystem processes interact with ontogenetic growth and changes in year class strength of early life stages of marine fishes.

EXAMINATION OF THE PHYSIOLOGICAL AND BIOCHEMICAL CHANGES AFFECTING NUTRITIONAL REQUIREMENTS THAT OCCUR IN DIFFERENT LIFE STAGES OF FISH

Fish undergo many physiological and biochemical changes throughout life, each demanding distinct nutritional consideration. This study explores the nuanced relationship between physiological and biochemical changes influencing nutritional requirements in different life stages of fish. The research involved an ethical and comprehensive investigation into various fish species' embryonic, larval, juvenile, and adult phases. Results demonstrated significant variations in growth rates, emphasizing rapid larval growth and unique reproductive hormone patterns during adulthood. Enzymatic activities reflected stage-specific digestive and metabolic demands, with larval stages exhibiting elevated digestive enzyme activities. Proximate composition analyses showcased protein, lipid, and carbohydrate content fluctuations, illustrating the evolving nutritional needs.

Environmental enrichment improves behaviors rather than the growth and physiology of rock bream Oplegnathus fasciatus.

Environmental enrichment has the potential to improve the welfare and post-release survival of hatchery fish stocked for conservation purposes. However, the effectiveness of environmental enrichment is partly dependent on the fish species, life stage, and specific enrichment structure used. To enhance the effectiveness of environmental enrichment, it is crucial to focus on characteristic differences in enrichment structures, such as type and level. This study investigated how differences in enrichment type and level affected physiological and behavioral aspects of the welfare of pre-release juvenile rock bream Oplegnathus fasciatus by evaluating growth performance, basal and stressed cortisol levels, antioxidant enzyme activities, and exploratory behaviors regarding anxiety and flexibility. Fish were reared for 4 weeks in different enrichment treatments: barren, low-level cover structure, high-level cover structure, low-level interference structure (LI), and high-level interference structure (HI). The results revealed that fish reared with the LI treatment showed less anxiety and greater flexibility with respect to exploratory behaviors, without oxidative damage being detected. Despite exhibiting less anxiety as well, fish reared in the HI treatment had oxidative damage, indicated by lower superoxide dismutase activity, compared to those in the barren treatment. In addition, none of these enrichment structures enhanced growth performance or mitigate chronic and acute stress responses. Overall, the low-level interference structure may be more favorable in promoting the behavioral welfare of the fish. Application of this type and level of enrichment may increase the survival of the hatchery fish after release, which is critical to stocking success.

Enrichment Effect of Artemia sp. with Fruktooligosaccharides to enhance Growth, Survival Rate and Digestive enzyme of Litopenaeus vannamei Larvae

Larvae are the most critical stage in the life stages of fish and shrimp due to the high mortality at this stage. The aim of this study was to evaluate the enrichment effect of Artemia sp. as live feed using different doses of Fructooligosaccharides (FOS) on the growth, survival rate and amylase, protease and lipase enzymes of vannamei larvae. Four Artemia sp. enrichments with different doses of FOS (P0: 0%, P1: 1.3%, P2: 1.5%, P3: 1.7%) were fed to vannamei larvae. The absolute weight, absolute length, daily growth rate, and protease activity of enrichment treatments were higher (P<0.05) than without enrichment. There are no differences (P>0.05) in protease activity of vannamei larvae between P2 and P3 treatment. Artemia sp. enrichment using different doses of FOS can increase the growth and protease enzyme activity of white shrimp larvae. The growth, protease and amylase activity of vaname larvae are improved with increasing FOS enrichment dose on Artemia sp. The FOS enrichment dose of 1.7% is the best because it can produce the best growth performance, survival rate and digestive enzyme activity.

Early life stage mechanisms of an active fish species to cope with ocean warming and hypoxia as interacting stressors

Ocean's characteristics are rapidly changing, modifying environmental suitability for early life stages of fish. We assessed whether the chronic effects of warming (24 °C) and hypoxia (<2–2.5 mg L−1) will be amplified by the combination of these stressors on mortality, growth, behaviour, metabolism and oxidative stress of early stages of the white seabream Diplodus sargus. Combined warming and hypoxia synergistically increased larval mortality by >51%. Warming induced faster growth in length and slower gains in weight when compared to other treatments. Boldness and exploration were not directly affected, but swimming activity increased under all test treatments. Under the combination of warming and hypoxia, routine metabolic rate (RMR) significantly decreases when compared to other treatments and shows a negative thermal dependence. Superoxide dismutase and catalase activities increased under warming and were maintained similar to control levels under hypoxia or under combined stressors. Under hypoxia, the enzymatic activities were not enough to prevent oxidative damages as lipid peroxidation and DNA damage increased above control levels. Hypoxia reduced electron transport system activity (cellular respiration) and isocitrate dehydrogenase activity (aerobic metabolism) below control levels. However, lactate dehydrogenase activity (anaerobic metabolism) did not differ among treatments. A Redundancy Analysis showed that ∼99% of the variability in mortality, growth, behaviour and RMR among treatments can be explained by molecular responses. Mortality and growth are highly influenced by oxidative stress and energy metabolism, exhibiting a positive relationship with reactive oxygen species and a negative relationship with aerobic metabolism, regardless of treatment. Under hypoxic condition, RMR, boldness and swimming activity have a positive relationship with anaerobic metabolism regardless of temperature. Thus, seabreams may use anaerobic reliance to counterbalance the effects of the stressors on RMR, activity and growth. The outcomes suggests that early life stages of white seabream overcame the single and combined effects of hypoxia and warming.

Effects of freshet events on early life stages of fish and macroinvertebrates in a highly turbid estuary of Iberian Peninsula

The present study investigates effects of three different types of freshet events (varying in intensity, duration, and period of discharge) on the early life stages of fish, macroinvertebrates inhabiting in the water column, and the environmental conditions within the hiperturbid estuary of the Guadalquivir River. Freshet events compressed the salinity gradient and increased turbidity; during the most intense freshet event, the oxygen concentration also decreased. These environmental changes had significant effects on the abundance and distribution of aquatic organisms, reducing the nursery area from 40 km upstream to 20 or 10 km, depending on the freshet. Recovery of physicochemical conditions was relatively rapid (within one or two weeks) for less intense freshets, while the most intense event showed only partial recovery even one month later. Biological responses varied among species and time periods. Pelagic species (e.g., anchovies) were flushed out of the estuary. The populations of these species can show a posterior reintroduction and a recovery to levels similar to before the freshet, or a nonrecovery, probably depending on larval supplied from the offshore stock. In contrast, benthic and estuarine species (e.g., gobies, mysids), were just displaced downstream during the freshets. In the most intense freshet event, which occurred before the high recruitment period of these species (early spring), their abundances increased significantly, exceeding the levels of normal years (without freshets). This suggests that, depending on the intensity and the period in which the freshet occur, they could act as attraction signals for certain species. In general, estuarine and benthic species, such as gobies and other macroinvertebrates, coped better with freshets than pelagic marine migrant species, such as anchovies. However, the estuary and its estuarine organisms showed high resilience to environmental fluctuations.

Strong water stratification provides a refuge for rainbow smelt larvae Osmerus mordax in a sub-arctic estuary (Lake Melville, Labrador)

Estuaries provide nurseries for early life stages of fish that rely on the interaction between fresh- and saltwater. The 250 km long Lake Melville spans 2100 km2 and is the largest estuary of Labrador (northeastern Canada). This sub-arctic fjard hosts freshwater, anadromous, and marine fishes on which depend marine mammals and seabirds, but also coastal communities. Yet, how different fish species and life stages use the estuary as a habitat, in particular the importance of the low salinity surface layer for the development of fish larvae, remains unknown. By pairing seasonal hydroacoustic surveys conducted in summers 2018–2019 and winters 2019–2020 with net sampling and environmental DNA (eDNA) analyses, we test the hypothesis that the strong water stratification prevailing in upper Lake Melville provides a nursery for early life stages of fish, where they are protected from their predators. Ichthyoplankton aggregated just above and at the pycnocline, in the low salinity surface layer down to 25 m. Most adult pelagic fish occupied the bottom waters below the sharp pycnocline, although some ventured in the low salinity surface layer. Ten species of adult fish were captured in gill and fyke nets and 53 species were detected with eDNA. Larvae of rainbow smelt (Osmerus mordax) were ubiquitous in the surface layer in July and August and represented 100% of the ichthyoplankton assemblage sampled during these months. No fish larvae were detected in winter (February). We conclude that the low salinity surface layer provides a refuge for rainbow smelt larvae, a key forage species in the estuary. This study provides baseline information from which to assess future changes in biodiversity and distribution of fish in the Lake Melville estuary. It further supports the use of eDNA as a complementary tool for monitoring fish diversity in sub-arctic estuaries.

Comparison of the accumulation and effects of copper pyrithione and copper sulphate on rainbow trout larvae

Copper pyrithione (CuPT) is used as a co-biocide in new antifouling paints but its toxicity remains little known. To compare the toxicity of copper-based compounds, rainbow trout (Oncorhynchus mykiss) larvae were exposed for 8-day to CuPT and CuSO4 at equivalent copper concentrations. CuPT exposure led to the greatest accumulation of Cu in larvae. Exposure to 10 µg.L−1 CuPT induced 99% larval mortality but only 4% for CuSO4-exposed larvae. The larval development and growth were affected by CuPT (from 0.5 µg.L−1 Cu) but not by CuSO4. Lipid peroxidation was not induced by either contaminant. The expression of genes involved in oxidative stress defence, detoxification and copper transport was induced in larvae exposed to CuSO4 and CuPT but at higher concentrations for CuPT. This study highlights the marked toxicity of CuPT for early life stages of fish and raises the question of the possible environmental risks of this antifouling compound.

A key evolutionary step determining osmoregulatory ability for freshwater colonisation in early life stage of fish.

Colonisation of freshwater habitats by marine animals is a remarkable evolutionary event that has enriched biodiversity in freshwater ecosystems. The acquisition of the tolerance to hypotonic stress during the early life stages is presumed to be essential for their successful freshwater colonisation, but very little empirical evidence has been obtained to support this idea. This study aimed to comprehend the evolutionary changes of osmoregulatory mechanisms that enhance the larval freshwater tolerance in amphidromous fishes, which typically spend their larval period in marine (ancestral) habitats and the rest of life history stages in freshwater (derived) habitats. We compared the life history patterns and changes in larval survivorship and gene expression depending on salinity among three congeneric marine-originated amphidromous goby species (Gymnogobius), which had been suggested to differ in their larval dependence on freshwater habitats. An otolith microchemical analysis and laboratory-rearing experiment confirmed the presence of freshwater residents only in G. urotaenia and higher larval survivorship of this species in the freshwater condition than the obligate amphidromous G. petschiliensis and G. opperiens. Larval whole-body transcriptome analysis revealed that G. urotaenia from both amphidromous and freshwater-resident populations exhibited the greatest differences in expression levels of several osmoregulatory genes, including aqp3, which is critical for water discharge from their body during early fish development. The present results consistently support the importance of enhanced freshwater tolerance and osmoregulatory plasticity in larval fish to establish freshwater forms, and further identified key candidate genes for larval freshwater adaptation and colonisation in the goby group.

A mathematical model predicting the abundance and spatio-temporal dispersal of adfluvial salmonid (Salvelinus malma) fry in a stream

Models describing the spatial and temporal distributions of fishes are necessary for conservation and management of populations and their habitats. The early life stages of fishes are a particularly important period that can influence population dynamics and fisheries productivity. The fry of riverine migratory fish species are particularly influenced by downstream transport although relatively few models have been used to predict spatio-temporal abundance and dispersion of fry in combination with life history parameters in unperturbed habitats. We present a novel model predicting the downstream dispersal of age-0 adfluvial Dolly Varden in a spawning stream draining into Kronotskoye Lake basin, Kamchatka Peninsula, Russia. The model accounted for the number of and distance between known spawning grounds, diel activity, daily fish growth, and intra-specific diversity (i.e., morphotype) to describe how fry abundance changed at a specific stream location over the course of spring and summer. Data were collected using a trapnet monitored periodically during spring and summer to record changes in abundance, size (growth), and life history composition (‘nosed’ or ‘white’ morphotype) of fish between age-0 and -2. The experimental data were fitted to the model using a gradient descent optimization algorithm and a mean squared error loss function was used to verify how well experimental data fit to the theoretical model. The predicted abundance of age-0 fish was 18,831 with a mean dispersion rate of ∼36 m/day and a transit time between spawning area and stream mouth ranging 32–76 days. The catch was mainly comprised (81%) of the slower growing ‘nosed’ morphotype and exhibited variation in abundance over time and decreased considerably by the end of summer. Our comprehensive model will be useful to simulate the downstream dispersal of salmonid fishes whose early life stages inhabit riverine systems.

Molecular epidemiology of Megalocytivirus in freshwater angelfish (Pterophyllum scalare) from Johor, Malaysia.

Malaysia has more than 630 culturists who are involved in the ornamental fish industry and culture 250 species, including local and exotic species. Among these viruses, megalocytiviruses have been associated with severe systemic diseases and economic losses in ornamental fish. The intensity of Megalocytivirus infection in Pterophyllum scalare in Malaysia remains unknown. Thus, this study aimed to investigate the occurrence of Megalocytivirus while discovering its associated risk factors and the genotypes of its causative agents in an ornamental fish farm in Malaysia. Seven broodstock pairs of P. scalare were used in this study to follow the life stages of fish, from egg to market size. Water samples and other samples, such as mucus swabs, gill swabs, P. scalare eggs, fries, juveniles, snails, snail eggs, live feed (Tubifex worms and Moina spp.), sediment samples, and wild fish, were collected periodically for initial environmental sampling from day 0 to day 60. Nested polymerase chain reaction amplifications were performed for megalocytivirus-related sequences. The phylogenetic tree, including the sampled causative agents of megalocytiviruses, was inferred from the major capsid protein genes of all known Iridoviridae species. Pearson's correlation coefficients were calculated to determine the strength of the correlation between the presence of megalocytiviruses in P. scalare samples and the associated risk factors. A total of 312 out of 935 pooled and individual samples tested positive for the presence of Megalocytivirus-related sequences, except snail eggs and wild fish (Poecilia reticulata). No clinical symptoms were observed in any fish samples. Megalocytivirus-associated viruses detected in water samples indicate horizontal transmission of the virus. All the nucleotide sequences found in this study had high nucleotide identities of 95%-99 % and were closely related to Megalocytivirus genotype I infectious spleen and kidney necrosis virus. Risk factors associated with Megalocytivirus include water temperature, dissolved oxygen (DO), pH, ammonia, nitrate, nitrite, and the life stages of P. scalare. High Megalocytivirus infection was detected when the water temperature, DO, and pH were high in P. scalare, high water temperature and nitrate in the water samples, and the same rate of Megalocytivirus infection in P. scalare fry and juveniles. This is the first study to confirm the existence of different possible routes of megalocytivirus distribution in ornamental fish farms in Malaysia. Nevertheless, the connection between the mode of transmission and the risk factors for this virus needs to be explored further to recognize the evolution and potential new host species.

Spatial and seasonal fluctuations of Ichthyoplankton assemblage in the Mediterranean coast of Morocco (Southwestern Alboran Sea)

Ichthyoplankton represent the first life stages of fish. The study of ichthyoplankton is crucial to understanding marine ecosystems and plays an important role in the management and durability of fisheries resources. During March and October of 2019, two oceanographic ichthyoplankton surveys were conducted in the Mediterranean Sea of Morocco from Tanger to Saadia by studying the horizontal structure of the ichthyoplankton species assemblage and its relation to environmental parameters. The average surface water temperature was (15.8°C in spring and 16.4°C in autumn). The fish eggs and larvae were more abundant in March than in October (21268 eggs/10m² and 14084 larvae/10m² in spring and 10094 eggs/10m² and 13796 larvae/10m²). In both seasons, fish eggs from the families Sternoptychidae and Sparidae were dominant (10101 eggs/10m² and 7527 eggs/10m² in spring and 4422 eggs/10m² and 3928 eggs/10m² in fall, respectively). However, Myctophidae larvae were the most abundant in the study area, reaching 7601 larvae/10m² in spring and 11021 larvae/10m² in autumn. The environmental parameters: temperature, salinity and chlorophyll-a (surface) seem to directly influence the spatial distribution of ichtyoplancton. On the other hand, it seems that predation by jellyfish (Pelagia noctiluca)was a very important factor that added to the factors that influenced the distribution of the species of fish eggs and larvae. This work represents the first survey conducted in the southwestern Alboran Sea, which studies the horizontal structure of the ichthyoplankton species assemblage and its relation to environmental factors in the spring and autumn of 2019.

Mind the gap – Relevant design for laboratory oil exposure of fish as informed by a numerical impact assessment model

Laboratory experiments provide knowledge of species-specific effects thresholds that are used to parameterize impact assessment models of oil contamination on marine ecosystems. Such experiments typically place individuals of species and life stages in tanks with different contaminant concentrations. Exposure concentrations are usually fixed, and the individuals experience a shock treatment being moved from clean water directly into contaminated water and then back to clean water. In this study, we use a coupled numerical model that simulates ocean currents and state, oil dispersal and fate, and early life stages of fish to quantify oil exposure histories, specifically addressing oil spill scenarios of high rates and long durations. By including uptake modelling we also investigate the potential of buffering transient high peaks in exposure. Our simulation results are the basis for a recommendation on the design of laboratory experiments to improve impact assessment model development and parameterization. We recommend an exposure profile with three main phases: i) a gradual increase in concentration, ii) a transient peak that is well above the subsequent level, and iii) a plateau of fixed concentration lasting ∼3 days. In addition, a fourth phase with a slow decrease may be added.

Identifying early life stages of Great Lakes fishes using a metabarcoding approach

Detection of early life stages of fishes is important for understanding life history patterns and critical spawning habitats. When feasible, identifying early life stages of fishes using morphology requires taxonomic expertise and can be challenging, time consuming, and imprecise. In this study, we used DNA metabarcoding to identify egg and larval batch samples from two sites in the species-rich East Sydenham River, Ontario, Canada. We used a two-step PCR metabarcoding approach to amplify a highly variable region of the mitochondrial COI gene from 1075 mixed species batch samples. Amplicon libraries were sequenced with Illumina Mi-seq and the sequencing reads were filtered and assembled using the software package mothur. Barcodes were then classified using a reference library comprised of Great Lakes fishes and potential invaders. In total, 34 species, including three at-risk species and three invasive species, were detected at the two sampling sites. This study shows the potential utility of metabarcoding for detection and identification of early life stage Great Lake fishes.

Management strategies can buffer the effect of mass mortality in early life stages of fish

Abstract Mass mortality (MM) events affecting early life stages of fish can have strong and long‐term consequences for population abundance and demography as well as the economic activity supported by exploited stocks. Adaptive fishery management may help mitigate economic impacts and ensure sustainable resource use following a MM event. Using a state‐space life cycle model, we simulated ‘what‐if’ scenarios of MM on Northeast Arctic cod (Gadus morhua) eggs and larvae. We compared the expected catches, total stock biomass (TSB), and interannual variability in catches over a period of 10 years after the simulated disturbance. We further evaluated a range of management mitigation strategies, namely reductions in fishing mortality of varying duration (1–10 years) and intensity (no fishing reduction to full ban). A large range of reductions in fishing led to an increase in expected catches over 10 years compared to no reductions, especially when applied immediately after the perturbation and when the cod population was characterized by a high mean age and high TSB. Severe fishing reductions can increase catches substantially but are associated with high interannual variability. Fishing reductions of moderate intensity applied between 1 and 4 years would allow to increase catches with only a slight increase in interannual variability. Our findings demonstrate the potential benefits of an adaptive approach to fisheries management and highlight that mitigation actions may ensure the sustainable exploitation of fish stocks in the wake of unexpected disturbances. Synthesis and application. Mass mortality events during early life stages of fish can potentially have substantial and long‐term effects on the population. Mitigation is more efficient when the affected population has a diverse age structure and when the mitigation strategy is applied immediately after the perturbation. Severe reduction in fishing mortality is an efficient measure to increase the expected average catch but is associated with high interannual variability. Fishing reduction of moderate intensity applied during 1–4 years after the event also increases the expected average catch with only slightly higher interannual variability in catches.

Temperature-dependent spawning behaviour and larval thermohaline associations of Bering Sea groundfish

Abstract The Bering Sea is a productive large marine ecosystem that supports numerous commercial fisheries, while climate change is introducing rapid warming and freshening, especially in coastal water. The success of early life stages of marine fish can impact adult abundance levels; little is known about how behavioural or physiological plasticity in relation to environmental changes at one stage (e.g. spawning) may affect survival during subsequent stages (e.g. larvae), nor whether trade-offs exist that affect how a species demonstrates such plasticity. We utilized a statistical approach to examine phenological and geographical flexibility in spawning behaviour for four species of groundfish. In situ sea surface temperature (SST) and salinity (SSS) associations were also estimated by statistical models for six species of groundfish larvae. All species exhibited greater spawning geography flexibility than phenological flexibility during the egg stage. All larval stages exhibited specific temperature and salinity associations across unique combinations of SST and SSS. These species-specific patterns, in the context of potential climate change impacts, suggest that flexibility in spawning behaviour may not adequately compensate for the presence of unfavourable habitats at the larval stage.

Are early and young life stages of fish affected by paroxetine? A case study with Danio rerio

Paroxetine (PAR) is a selective serotonin reuptake inhibitor (SSRI) antidepressant increasingly detected in surface waters worldwide. Its environmental presence raises concerns about the potential detrimental effects on non-target organisms. Thus, this study aimed to increase knowledge on PAR's potential environmental impacts, assessing the effects of commercial formulation (PAR-c) and active ingredient (PAR-a) on fish. Therefore, the short-term exposure effects of PAR-c and PAR-a were assessed on zebrafish (Danio rerio) embryos/larvae to determine the most toxic formulation [through median lethal (LC50) and effective concentrations (EC50)]. PAR-c and PAR-a induced morphological abnormalities (scoliosis) in a dose-dependent manner from 96 hours post-fertilization onwards, suggesting the involvement of a fully functional biotransformation system. As PAR-c exhibited higher toxicity, it was selected to be tested in the subsequent stage (juvenile stage), which was more sensitive (lower LC50). PAR-c significantly decreased fish swimming activity and disrupted fish stress response. Overall, the results highlight the ability of PAR-c to adversely affect fish swimming performance, an effect that persisted even after exposure ceases (21-day depuration), suggesting that PAR-c may impair individual fitness.