Life Stages Of Fish Research Articles

Individual movement behaviour and habitat use of a small-sized cypriniform (Telestes muticellus) in a mountain stream

Knowledge about the biology and ecology of species is fundamental for their management and conservation. Despite this, many fish species and life stages are understudied, and there is a great need for research efforts to understand their ecology. Italian riffle dace (Telestes muticellus; order Cypriniformes) is a small-sized (< 15 cm) stream fish native to the Italian peninsula. There is a scarcity of research on its ecology and behaviour. In this study, we explored the movement ecology of Telestes muticellus in a Mediterranean mountain stream in Northern Italy using passive integrated transponder (PIT) telemetry. Over 15 months, 267 fish were located 2–27 times. Most fish remained stationary, while a few roamed over several hundreds of meters. Fish covered a larger linear range during spring and autumn than during other seasons. T. muticellus showed a strong preference for pools, and this preference was strongest during summer. We observed no differences in habitat use and movements between day and night, and fish size had no major effect. Within pools, many T. muticellus displayed remarkably small home ranges (median 8 m2). Fish increased their linear ranges over a period of flood events, indicating that high-flow events may be important for the downstream and upstream dispersal of T. muticellus in small mountain streams.

Acute and Subchronic Toxicity of 6PPD-Quinone to Early Life Stage Lake Trout (Salvelinus namaycush).

N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone (6PPD-Q) is a rubber-tire derivative which leaches into surface waters from roadway runoff, from tire particles and has been identified as a possible driver of urban runoff mortality syndrome in coho salmon. Sensitivity to this toxicant is highly variable across fish species and life stages. With environmental concentrations meeting or exceeding toxicity thresholds in sensitive fishes, the potential for ecologically relevant effects is significant. There is currently no data regarding the sensitivity of lake trout (Salvelinus namaycush) to 6PPD-Q. As early life stages of fishes are typically more sensitive than adults, the goal of this study was to evaluate the acute and subchronic toxicity of 6PPD-Q to early life stage lake trout. Alevins exposed from hatch until 45 days posthatch (dph) to time-weighted average 6PPD-Q concentrations ranging from 0.22 to 13.5 μg/L exhibited a 45 day median lethal dose (LC50) of 0.39 μg/L. Deformities throughout growth were observed, with a unique pooling of blood observed in the caudal fin and eye. A subsequent acute study with exogenously feeding lake trout fry determined a 96 h LC50 of 0.50 μg/L. From this study we can conclude that lake trout alevins and exogenously feeding fry are sensitive to 6PPD-Q, which underscores the relevance of this chemical to inland freshwater ecosystems.

Dynamics of thermal tolerance plasticity across fish species and life stages.

Climate warming with associated heat waves presents a concerning challenge for ectotherms such as fishes. During heatwaves, the ability to rapidly acclimate can be crucial for survival. However, surprisingly little is known about how different species and life stages vary in their acclimation dynamics, including the magnitude of change in thermal tolerance through acclimation (i.e. acclimation capacity; also known as the acclimation response ratio, ARR), the duration needed for the novel acclimation temperature to significantly alter thermal tolerance from the initial level (which we term the response induction time, tinduction), or the duration needed to achieve the new acclimation steady state (which we term the time to full acclimation, tsteady). To shed light on this knowledge gap, we studied the acclimation dynamics of three wild-caught fishes (goldsinny wrasse, three-spined stickleback and European flounder) by assessing upper thermal tolerance (CTmax) after different periods of time acclimating to a warmed environment. We also measured both CTmax and lower thermal tolerance (CTmin) in juvenile and adult lab-bred zebrafish acclimated to a warmed environment. Upper thermal tolerance of zebrafish and sticklebacks significantly increased after a 3h exposure to a warm treatment, while tinduction took six and 24h in the wrasse and flounder, respectively. Goldsinny wrasse had the highest ARR, and did not reach full acclimation of CTmax within the duration of the study (10 days). All other species fully acclimated within 4-10 days. Juvenile zebrafish showed similar acclimation dynamics to adults for both upper and lower thermal tolerance, but had a higher CTmin for all acclimation durations. Our results demonstrate that acclimation dynamics of thermal tolerance vary across species, but can be similar between life stages within species. Understanding species-specific thermal plasticity is important for accurately modeling the projected impacts of climate change.

Active biomonitoring of river pollution using an ex-situ exposure system with two model species.

In the context of increasing pollution pressure on aquatic ecosystems, it is essential to improve our knowledge of habitat quality and its suitability for organisms. It is particularly relevant to better integrate early life stages of fish into pollution biomonitoring programs, as they are reliable indicators of ecosystem integrity and because of their high sensitivity to pollutants. To avoid the influence of environmental parameters on their development, a lab-on-field approach, called the ex-situ exposure method, was developed. Aquatic organisms were exposed to a continuous flux of water under semi-controlled temperature, oxygen, and photoperiod conditions to avoid the influence of these confounding factors when interpreting the results. To investigate the potential role of water contamination, this active biomonitoring method was applied to the Garonne River (Southwest France), where migratory fish populations have declined. Two model species from different taxa were used: embryos of the Japanese medaka (Oryzias latipes) and adults of the crustacean Gammarus fossarum. The results showed a significant impact of water quality on embryo mortality and early hatching in two separate experiments on Japanese medaka. In addition, an induction of feeding rate was observed in exposed gammarids, but no impact on their embryo survival, suggesting differences in sensitivity between the two species selected. Chemical and biological analyses did not identify trace metals, pesticides, or microorganisms as potential sources of toxicity in medaka embryos or G. fossarum. These results raise concerns about the quality of the water in the Garonne River and its toxicity to aquatic organisms.

Growth Rates and Specific Aminoacyl-tRNA Synthetases Activities in Clupea harengus Larvae

Gaining robust in situ estimates of the growth rate of marine fish larvae is essential for understanding processes controlling year-class success and developing sustainable management strategies to maintain good environmental status. We measured the growth rate of Atlantic herring (Clupea harengus) larvae in the laboratory and compared it to the activity of aminoacyl-tRNA synthetases (AARS). Larvae were reared under controlled conditions for 20 days at three temperatures (7, 12, and 17 °C) using different prey concentrations (0.1, 0.3, and 2 prey·mL−1) of the copepod Acartia tonsa. The relationship between specific growth rates (SGR) and specific AARS activities was best described by a linear function—SGR = −0.1031 + 0.0017 · spAARS, r2 = 0.71, p &lt; 0.05—when only larvae fed ad libitum were considered regardless of the temperature. When larvae fed with low concentrations of food were included in the analysis, the relationship was SGR = −0.0332 + 0.0010 · spAARS, r2 = 0.42, p &lt; 0.05. This latter slope was rather low compared to other studies performed in zooplankton. We suggest protein degradation during the early life stages of fish as the cause of this low slope. We also studied SGR under food deprivation and the effect on specific AARS activities. We found rather high specific AARS activities in small individuals of early stages of fish, also suggesting protein degradation. Further research about protein degradation and turnover rates is needed in order to use AARS activity as a proxy for growth rates in field-caught larvae.

Community structure of fish larvae associated with advections of the Kuroshio and its neighboring waters

The Kuroshio has been long thought to be disadvantageous as nursery grounds for larval fishes due to the low plankton standing stocks under the oligotrophic conditions. Despite of the potential risk for survival and growth, early life stages of various fishes appear abundantly in the Kuroshio and its neighboring waters. Here, we report what kind of taxonomic groups establish community structure of larval fishes in the Continental shelf waters (CW) and the Kuroshio (KW). 16 orders and 78 families were classified in the present study. Mesopelagic fishes more abundantly appeared in the KW than in the CW, while larval fish abundance was not different between the two areas. Multivariate analysis demonstrated the regional difference of the taxonomic compositions, represented by Callionymidae, Bothidae, Labridae and Bregmacerotidae for the CW and Gonostomatidae, Myctophidae and Notosudidae for the KW. Abundance of fish larvae to ambient salinity exhibited significantly positive correlations for Gonostomatidae, Sigmops gracilis and Myctophum orientale predominated in the KW and negative correlations for Labridae appeared abundantly in the CW. These results suggest that mixture of advected specimens from the coastal and Kuroshio waters also contribute to larval fish community with high biodiversity and comparable abundance between the Kuroshio and its neighboring waters.

Ecological indicators for restoration success: Development of fish diversity in a large restored floodplain over twelve years

The restoration of rivers and their floodplains is complex, requires substantial financial efforts, intensive stakeholder involvement and long recovery times, making the identification of appropriate ecological indicators for restoration success a key challenge. Herein, one of the largest floodplain restorations along the European Danube was repeatedly assessed over a 12-year period. Changes in the fish community composition in relation to chemical and morphological habitat variables were assessed in all three restored habitat types free-flowing rivers (RS), reconnected oxbows (OS), and small floodplain ponds (FP) which are only temporarily connected to the main stem Danube. Fish species composition of RS, OS, FP and the Danube differed significantly. Species numbers (34 detected in 2022) remained largely constant since the last monitoring in 2013, whereas abundance increased by 15%. Small-bodied target species with short generation times were able to establish populations comprising all size classes shortly after restoration, whilst large-bodied species needed a decade after the restoration for full demographic representation. Highly specialised species such as the rheophilic Chondrostoma nasus used restored RS only during the life stages spawning and juvenile growth. Restoration increased habitat heterogeneity and the initialized hydromorphological processes are still ongoing, supporting the high species diversity. The observed differences in colonization patterns can be explained by species-specific life histories, resulting in diverse short and long-term responses of different fish species and life stages following restoration. Consequently, a comprehensive assessment of restoration success only becomes possible if multiple fish species as ecological indicators are combined in a long-term monitoring.

Composition of inshore ichthyoplankton community in the Canary islands from a spatial and seasonal perspective: Inshore ichthyoplankton of the Canary Islands

Early life stages of fish are insufficiently studied in most regions around the globe, and consequently, there is an important gap in knowledge on the life cycle of most teleosts. In the Canary Islands (Eastern Central Atlantic), most studies on ichthyoplankton communities are based on traditional net tows in open waters that provide information about early larval stages of pelagic species in the area, while nearshore benthic fish remain highly understudied. In this study, light traps were employed for the first time to assess post-larval stages of neritic fish in this archipelago. A two-year survey was carried out to collect nearshore fish larvae every 6 months at 11 localities from El Hierro, Tenerife and Lanzarote. A total of 3940 fish larvae classified into 13 orders, 28 families and 44 species were collected. These results provide a wide description of the composition of the inshore ichthyoplankton off the Canary Islands, across islands and seasons. Main environmental factors (SST, sea floor orography, oceanographic phenomena …) influencing the population dynamics of this community are discussed. Additionally, the ichthyoplankton assemblages were assessed from the intra-annual perspective, analyzing the species composition and abundances by months and seasons, and providing new insights into reproduction cycles of many common benthic fishes at shallow marine ecosystems of the islands. This study is important to further understand the life cycles of some of the most common fish species in the Canary Islands, unraveling main environmental factors that affect the success of their offspring that sustain populations.

Utilisation of macroalgal habitats by juvenile rabbitfishes on an inshore reef

Macroalgal beds are increasingly recognised as nursery habitats for coral reef fish; however, the extent to which they are used as a source of food and/or a refuge from predation remains largely unexplored. Here, we investigate the distribution, feeding behaviour, diet, and predation risk for juvenile rabbitfish in macroalgal habitats on Orpheus Island, Great Barrier Reef. Visual surveys revealed that juvenile and adult Siganus doliatus had different among-habitat distributions with juveniles being largely restricted to the reef flat and positively associated with macroalgal cover, while adults were abundant on the reef crest. Focal feeding observations show that within macroalgal habitats, juvenile S. doliatus targeted epiphytes on Sargassum (80% of bites), with relatively few bites taken on turfs or the Sargassum itself (27% and 8%, respectively). These observations were supported by stomach content analyses with filamentous algae being the dominant item in the stomach content of both small (< 4 cm total length, TL; 58%) and large juvenile S. doliatus (> 4 cm TL; 47%). The stomach content of juvenile S. doliatus, S. canaliculatus, and S. spinus collected from macroalgal habitats was similar, consisting primarily of filamentous algae and detritus. We found no relationship between the abundance of potential predators and juvenile rabbitfishes across the study sites. Collectively, our results suggest that juvenile rabbitfishes are using macroalgal habitats on this, and potentially other, inshore reefs as a food source and add to a growing body of literature highlighting the importance of these habitats for the early life stages of reef fish.

Local size structure and distribution of demersal fish in relation to sea pens and other benthic habitats in a deep-sea soft-bottom environment

Many fish species undergo ontogenetic habitat shifts as they grow to fulfill new biological, ecological and environmental requirements. While relationships between fishes and large hard-substrate cold-water corals (CWC) (e.g., Desmophyllum pertusum reefs) have frequently been studied, there are relatively fewer studies examining the relationships of fish with habitats specifically provided by smaller corals (e.g., sea pens) in soft-bottom environments. Despite this knowledge gap around soft-bottom corals, growing evidence of their importance has nonetheless justified their inclusion as conservation targets in numerous Marine Protected Areas (MPA), including the Canadian Laurentian Channel MPA. Here, we performed ROV and near-seabed drift-camera system surveys within the Laurentian Channel MPA in 2017 and 2018 to assess the influence of fish body size and habitat type on fish small-scale distribution in a low-relief deep-sea soft-sediment environment. We compared the local size structure of the four most abundant deep-sea demersal fish taxa of the channel (Redfish (Sebastes spp.), Witch Flounder (Glyptocephalus cynoglossus), Marlin-Spike Grenadier (Nezumia bairdii) and Longfin Hake (Phycis chesteri)) across one barren and five structural benthic habitats defined by the presence of nine dominant epibenthic invertebrates (actiniarians and CWCs). We used generalized additive models to identify biotic (benthic habitats) and abiotic (depth, bottom types) covariates of size for each taxon. We observed 15,381 fish within the 43.6-ha study area, of which 7,511 fish were measured. Juveniles represented 99% of all fish measured, with a notable increase in average fish size in 2018. While we did not find any associations between benthic habitats and fish life stages, the analysis revealed a significant increase in fish size within sea pen habitats for all four taxa. Conversely, we found a taxon-specific influence of bottom type on fish size for all taxa. In addition, Redfish and Longfin Hake size was positively correlated with depth. For deep-sea demersal fish taxa of the MPA, our results suggest that 1) sea pens provide nursery habitat for early-life stages, 2) fish undergo ontogenetic shifts in micro-habitat use and specialization, and 3) fish-habitat associations appear to be facultative rather than obligate. Through the use of in-situ video data, this study provided evidence that small and large fish do not use the same micro-habitats, and that sea pens contribute significantly to fish habitat despite providing less habitat heterogeneity than reef-forming scleractinians or large gorgonians. These results contribute to empirical understanding of fish-habitat relationships at different fish life stages and may inform fisheries management, as well as monitoring efforts in the MPA and other protected deep-sea environments.

Linking functional habitat and fish population dynamics modeling to improve river rehabilitation planning and assessment

In-stream habitat enhancement is widely used to improve ecological conditions in rivers, often prioritizing key fish life stages such as spawning and juvenile development. However, no standard approaches exist to predict their effects on fish recruitment and populations. Here, we use a spatially-explicit population dynamics model that integrates functional habitat dynamics to assess the impact of two rehabilitation measures in a hydropower-impacted section of the Inn River (SE Germany) on the recruitment potential of four rheophilic and lithophilic fish species — grayling, nase, barbel, and chub. Rehabilitation measures implemented included the construction of a bypass channel and an island side-channel system to improve both longitudinal connectivity and habitat conditions. In addition, we analyzed two alternatives, which would enhance functional availability of nursery habitats from actual 33.2% to 66.8% and 95.3%, respectively. The results suggest that the improved habitat conditions will yield on average additional 14.9 individuals/ha (5.6 kg/ha) of the target species. However, the limited accessibility of usable nursery habitat constitutes a significant recruitment bottleneck for all species. In the alternative scenarios, the increase of functional connectivity will result in average densities of 17.9 and 25.8 individuals/ha, respectively. However, potential further improvements are species-specific, because of distinct population responses to spawning-to-nursery habitat ratios, with density changes varying between -11.7% for grayling and +172.6% for chub. This study not only demonstrates the applicability of the modeling approach for assessing and planning rehabilitation measures but also emphasizes the importance of considering habitat ratios and their functional connectivity to optimize recruitment potential.

Integrating Habitat Suitability and Larval Drift Modeling for Spawning‐To‐Nursery Functional Habitat Connectivity Analysis in Rivers

AbstractHabitat suitability modeling is a commonly used methodology to plan and assess in‐stream habitat enhancement in rivers, such as for the key fish life stages spawning and juvenile development. However, their use only allows modeling the spatial distribution of habitats, but not their connectivity. By integrating micro‐scale habitat modeling and a larval drift model, we assess the functional connectivity between spawning and larval nursery habitats for four rheophilic and litophilic fish species in a channelized and hydropower impacted reach of the lower Inn River (Bavaria, Germany), in which two restoration measures, a bypass channel and an island side‐channel system, have been constructed to improve longitudinal connectivity and habitat conditions. The study aims to (a) map spawning and larval nursery habitats, (b) quantify their connectivity, and (c) optimize functional habitat connectivity through an alternative bypass channel location. Results show that the channel's morphological complexity influences quantity and quality of available spawning and nursery habitats and their connectivity. Despite the presence of nursery habitats across the analyzed channel, the slow lateral larval dispersion during drift limits their accessibility to only the left river bank, making only 33% of available habitats useable. The degree of functional connectivity and hence the percentage of useable habitats can however be increased up to 95.3 % when considering different spatial configurations of habitats, which were explored in two alternative restoration scenarios. The results demonstrate the importance of considering functional habitat connectivity in habitat assessments and restoration planning.

Spatiotemporal Distribution and Dispersal Pattern of Early Life Stages of the Small Yellow Croaker (Larimichthys Polyactis) in the Southern Yellow Sea

Nursery habitats play a significant role in completing fish life cycles, and they are now recognized as essential habitats. Monthly variations in nursery ground distributions of Larimichthys polyactis were investigated in the southern Yellow Sea in 2019. Bayesian hierarchical models with integrated nested Laplace approximation were utilized to model the preferential nursery habitats of L. polyactis larvae. The study analyzed the spatial and temporal distributions of the larvae and juveniles based on three environmental variables: sea surface temperature, sea surface salinity, and depth. Additionally, this study examined the utilization of habitats by different fish life stages and ontogenetic shifts. A total of 3240 individuals were collected from April to June, with the peak occurring in May (0.05 ind./m3), and the distribution areas varied between different months. The prediction of the model reveals the ecological adaptability of L. polyactis to temperature variations. The optimal temperature for L. polyactis density ranges from 12.5 °C to 16.5 °C in April and 16.5 °C to 17.5 °C in May, demonstrating a broad temperature tolerance for L. polyactis survival. In addition, there are variations in distribution patterns among different developmental stages. Larimichthys polyactis spawn in the inshore and nearshore waters, and after hatching, larvae in the pre-flexion stage tend to remain aggregated near the spawning beds. However, larvae in the advanced development stage (post-flexion) and juveniles move towards the sandy ridge habitats along the coast and start to migrate offshore in June. This study provides valuable insights for the effective management of fishery resources in the area and can be utilized to identify marine areas with specific habitat features that require conservation.

Moisture content in diets in the co-feeding phase of Pseudoplatystoma sp. influences performance and digestive process.

Live food in the initial life stages of neotropical fish is essential for their development and health; however, it can significantly increase production costs. This study uses complete diets with varying moisture contents (47%, 35%, 24%, and 8%) as a cost-effective alternative in the co-feeding phase of surubim larvae, assessing their influence on development, digestive enzymes, and liver metabolism. In a completely randomized design, 3200 three-day-old Pseudoplatystoma sp. larvae (0.001g) were distributed evenly among 16 aquariums (20L), with 200 individuals per aquarium. For the first five days, all larvae were fed Artemia exclusively, after which they were fed experimental diets with varying levels of humidity (47%, 35%, 24%, and 8%) six times a day across four treatments and four replicates. The 21-day feeding trial demonstrated that larvae fed with 24% and 8% moisture diets exhibited increased (p < 0.05) weight gain, final length, and protein efficiency rate. The remaining growth parameters (i.e., specific growth rate and condition factor) did not show significant differences (p > 0.05) among the dietary treatments. Enzymatic analysis revealed that the 47% moisture diet enhanced the amylase and alkaline phosphatase activities, whereas the 24% and 35% moisture diets elevated the lipase and protease activities. The 47% moisture diet also resulted in increased alanine aminotransferase, aspartate aminotransferase, and albumin levels, along with visible hepatic histopathologies in samples, such as visible lipid vacuoles, displacement of the nucleus of the hepatocyte, and increased sinusoid spaces. No significant liver changes were observed in fish fed with other diets. Principal component analysis showed that diets with 8-24% moisture content were the most beneficial during the co-feeding phase of surubim larviculture.

Lipids as biomarkers to assess the nutritional and physiological status of two diadromous fish (Anguilla anguilla and Chelon auratus) at early life stages in a temperate macrotidal estuary.

Estuaries are considered as key habitats for the early life stages of fish. However, in the face of massive destruction of many estuarine intertidal areas, management and conservation measures are needed. Fish condition indicators may be used as a proxy of habitat quality and provide valuable information for management of coastal areas. In this study, the larvae of golden mullet (Chelon auratus) and European glass eels (Anguilla anguilla) were sampled in three sites of the Gironde Estuary. Different lipid classes and fatty acids were quantified: phospholipids (globally, phosphatidylethanolamine and phosphatidylcholine), triglycerides, omega-3 (particularly docosahexaenoic and eicosapentaenoic acids), omega-6 and C18:1. These biomarkers provide information on the nutritional status of the larvae as well as on prey availability and larvae diet between sites. One site significantly differed from the others as it seemed to offer abundant and better-quality prey. The very high levels of omega-3 contained in mullet larvae suggested that this site provided a high amount of diatoms. However, the mullet larvae that colonized this site also showed physiological stress that could be explained by exposure to pollutants through their prey. This work constitutes an essential baseline for developing biomarkers to assess the quality of habitats in a global change context.

Chronic exposure to environmental concentrations of benzo[a]pyrene causes multifaceted toxic effects of developmental compromise, redox imbalance, and modulated transcriptional profiles in the early life stages of marine medaka (Oryzias melastigma)

Polycyclic aromatic hydrocarbons (PAHs) accumulate and integrate into aquatic environments, raising concerns about the well-being and safety of aquatic ecosystems. Benzo[a]pyrene (BaP), a persistent PAH commonly detected in the environment, has been extensively studied. However, the broader multifaceted toxicity potential of BaP on the early life stages of marine fish during chronic exposure to environmentally relevant concentrations needs further exploration. To fill these knowledge gaps, this study assessed the in vivo biotoxicity of BaP (1, 4, and 8 μg/L) in marine medaka (Oryzias melastigma) during early development over a 30-day exposure period. The investigation included morphological, biochemical, and molecular-level analyses to capture the broader potential of BaP toxicity. Morphological analyses showed that exposure to BaP resulted in skeletal curvatures, heart anomalies, growth retardation, elevated mortality, delayed and reduced hatching rates. Biochemical analyses revealed that BaP exposure not only created oxidative stress but also disrupted the activities of antioxidant enzymes. This disturbance in redox balance was further explored by molecular level investigation. The transcriptional profiles revealed impaired oxidative phosphorylation (OXPHOS) and tricarboxylic acid (TCA) cycle pathways, which potentially inhibited the oxidative respiratory chain in fish following exposure to BaP, and reduced the production of adenosine triphosphate (ATP) and succinate dehydrogenase (SDH). Furthermore, this investigation indicated a potential connection to apoptosis, as demonstrated by fluorescence microscopy and histological analyses, and supported by an increase in the expression levels of related genes via real-time quantitative PCR. This study enhances our understanding of the molecular-level impacts of BaP's multifaceted toxicity in the early life stages of marine medaka, and the associated risks.

Effects of Metabolic Disruption on Lipid Metabolism and Yolk Retention in Zebrafish Embryos.

A subgroup of endocrine-disrupting chemicals have the ability to disrupt metabolism. These metabolism-disrupting chemicals (MDCs) can end up in aquatic environments and lead to adverse outcomes in fish. Although molecular and physiological effects of MDCs have been studied in adult fish, few studies have investigated the consequences of metabolic disruption in fish during the earliest life stages. To investigate the processes affected by metabolic disruption, zebrafish embryos were exposed to peroxisome proliferator-activated receptor gamma (PPARγ) agonist rosiglitazone, the PPARγ antagonist T0070907, and the well-known environmentally relevant MDC bisphenol A. Decreased apolipoprotein Ea transcript levels indicated disrupted lipid transport, which was likely related to the observed dose-dependent increases in yolk size across all compounds. Increased yolk size and decreased swimming activity indicate decreased energy usage, which could lead to adverse outcomes because the availability of energy reserves is essential for embryo survival and growth. Exposure to T0070907 resulted in a darkened yolk. This was likely related to reduced transcript levels of genes involved in lipid transport and fatty acid oxidation, a combination of responses that was specific to exposure to this compound, possibly leading to lipid accumulation and cell death in the yolk. Paraoxonase 1 (Pon1) transcript levels were increased by rosiglitazone and T0070907, but this was not reflected in PON1 enzyme activities. The present study shows how exposure to MDCs can influence biochemical and molecular processes involved in early lipid metabolism and may lead to adverse outcomes in the earliest life stages of fish. Environ Toxicol Chem 2024;43:1880-1893. © 2024 The Author(s). Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Intraspecific variation in thermal performance curves for early development in Fundulus heteroclitus.

Thermal performance curves (TPCs) provide a framework for understanding the effects of temperature on ectotherm performance and fitness. TPCs are often used to test hypotheses regarding local adaptation to temperature or to develop predictions for how organisms will respond to climate warming. However, for aquatic organisms such as fishes, most TPCs have been estimated for adult life stages, and little is known about the shape of TPCs or the potential for thermal adaptation at sensitive embryonic life stages. To examine how latitudinal gradients shape TPCs at early life stages in fishes, we used two populations of Fundulus heteroclitus that have been shown to exhibit latitudinal variation along the thermal cline as adults. We exposed embryos from both northern and southern populations and their reciprocal crosses to eight different temperatures (15°C, 18°C, 21°C, 24°C, 27°C, 30°C, 33°C, and 36°C) until hatch and examined the effects of developmental temperature on embryonic and larval traits (shape of TPCs, heart rate, and body size). We found that the pure southern embryos had a right-shifted TPC (higher thermal optimum (Topt) for developmental rate, survival, and embryonic growth rate) whereas pure northern embryos had a vertically shifted TPC (higher maximum performance (Pmax) for developmental rate). Differences across larval traits and cross-type were also found, such that northern crosses hatched faster and hatched at a smaller size compared to the pure southern population. Overall, these observed differences in embryonic and larval traits are consistent with patterns of both local adaptation and countergradient variation.

Abnormal eyes and spine development in zebrafish (Danio rerio) embryos and larvae induced by triphenyltin

Triphenyltin (TPT) is widely used in crop pest control and ship antifouling coatings, which leads to its entry into aquatic environment and poses a threat to aquatic organisms. However, the effects of TPT on the early life stages of wild fish in natural water environments remains unclear. The aim of this study was to assess the toxic effects of TPT on the early life stages of fish under two different environments: field investigation and laboratory experiment. The occurrence of deformities in wild fish embryos and larvae in the Three Gorges Reservoir (TGR) and the developmental toxicity of TPT at different concentrations (0, 0.15, 1.5 and 15 μg Sn/L) to zebrafish embryos and larvae were observed. The results showed that TPT content was higher in wild larvae, reaching 27.21 ng Sn/g w, and the malformation of wild fish larvae mainly occurred in the eyes and spine under natural water environment. Controlled experiment exposure of zebrafish larvae to TPT also resulted in eye and spinal deformities. Gene expression analysis showed that compared with the control group, the expression levels of genes related to eye development (sox2, otx2, stra6 and rx1) and spine development (sox9a and bmp2b) were significantly up-regulated in the 15 μg Sn/L exposure group, which may be the main cause of eye and spine deformity in the early development stage of fish. In addition, the molecular docking results further elucidate that the strong hydrophobic and electrostatic interactions between TPT and protein residues are the main mechanism of TPT induced abnormal gene expression. Based on these results, it can be inferred that TPT is one of the teratogenic factors of abnormal eye and spine development in the early life stage of fish in the TGR. These findings have important implications for understanding the toxicity of TPT on fish.

Projecting marine fish distributions during early life stages under future climate scenarios

AbstractChanges to Earth's climate affect organisms globally; in marine systems, these impacts are seen through warming water temperatures, ocean acidification, hypoxia and frequent marine heatwaves. These effects may lead to the movement of species to more favourable conditions. While climate‐driven movement is well studied at the adult stage, how the early life stages of marine fish will respond to future variability is less clear. Many fish species are constrained by specific spawning locations or phenology. Spawning in certain locations allows for local retention of offspring, while precise timing can facilitate transport of offspring to nursery locations through seasonal circulation patterns. Our research investigates how changing oceans impact the location and timing of spawning of Bering Sea groundfishes over the next century. We used ROMS SST and SSS model output and NOAA survey data in species distribution models to hindcast and project distributions and centre of gravity for eggs and larvae of six groundfish species. Our analyses found that most of our study species exhibit flexible geography. However, the speed and direction of egg and larval movement did not track the speed and direction of their respective thermal niches. Hence, the projected distributional patterns of adult stages may be limited by their early life stages. This response is likely to be mirrored globally by other species with planktonic eggs and larvae. These results indicate that life history considerations are critical for the management of commercially important species, as effects on early life stages are strongly connected to the success or failure of adult populations.