Estuarine Fish Research Articles

Global meta‐analysis reveals diverse effects of microplastics on freshwater and marine fishes

AbstractMicroplastic debris is a globally ubiquitous pollutant with diverse consequences for fishes, ranging from severe negative impacts to neutral, or even, positive effects. In the present study, we conducted a systematic review and meta‐analysis of experimental and observational studies to test for the impacts of microplastic exposure on freshwater, estuarine and marine fishes across diverse taxonomies, geographies, and ecosystem contexts. We report evidence for the detrimental, albeit variable, impacts of microplastics, including reduced consumption, altered feeding behavior, obstructed digestion and assimilation, decreased growth, and compromised immunity. By contrast, microplastics appeared to invoke neutral responses in several other ecological and physiological processes, such as body condition, fecundity, hatching success and survival. The results from this study also point to the mismatch between the types, shapes, and sizes of microplastics investigated in experimental settings versus those found in fish in the wild, as well as a striking difference between the 728 fish species investigated for microplastic contamination in the wild versus the only 22 fish species evaluated for the effects of microplastics in the laboratory. The present study reiterates the necessity for more consistent methodological approaches to analyzing and reporting the effects of microplastic exposure, including greater taxonomic breadth and the use of environmentally relevant polymers in future studies. Furthermore, model simulations that explore individual‐ and population‐level implications of realistic exposure scenarios are needed. Overall, the current weight of evidence supports continued management and policy actions to reduce the microplastic production, use, and release into the world's waters.

Predatory fish diets shift towards an invasive mullet in a traditional Hawaiian aquaculture system

AbstractTraditional Hawaiian fishponds, called loko iʻa, are a low‐impact and culturally important aquaculture system that historically produced significant fish yields. To better understand the structure of the contemporary food web of the restored Heʻeia fishpond, a mark‐recapture experiment was conducted to estimate the population abundance of the three dominant predatory fishes, and gut content, genetic barcoding, and stable isotope analyses were used to assess their diets. Great barracuda Sphyraena barracuda had the largest estimated population at 190 individuals, followed by 89 giant trevally Caranx ignobilis and 19 bluefin trevally Caranx melampygus. The three species were caught throughout the pond, with C. ignobilis concentrated in the deeper northwest area near a mangrove island. Diets of the three species consisted mainly of nearshore, estuarine fishes, and crustaceans. Prey taxonomic resolution was greatly improved with the use of genetic barcoding since most fish were too degraded to be visually identified. Trophic level calculations and isotopic niche breadth comparisons indicated that C. ignobilis and S. barracuda occupied similar ecological niches in the fishpond, and stable isotope mixing models revealed that their long‐term diets were mostly comprised glass shrimp (Palaemon sp.), mangrove swimming crab (Thalamita crenata), and an invasive Australian mullet (Osteomugil engeli). The native mullet (Mugil cephalus), a primary food fish species from the fishpond, was not identified in the diets of the predatory fishes in this study nor in a previous diet study decades ago prior to the introduction of Australian mullet. The inclusion of the invasive Australian mullet in the contemporary diets of the predatory fishes demonstrates a shift towards the newly available prey which may benefit the native mullet populations. These findings improve the understanding of food web dynamics in contemporary Hawaiian fishponds and provide an example of native predatory fishes consuming an invasive species as part of their diets.

Estuarine fishes feeding on benthic invertebrates and small fishes: Evidence of fine resource partitioning in a tropical coastal lagoon

The main goal of the present study was to carry out an integrated analysis of the feeding habits of a set of species which use the same general food source (benthic invertebrates and small fishes) in a coastal lagoon of the Mexican Pacific. The specific objectives were to explore the patterns of diet overlap among the 12 species included; to relate the differences in diet composition with differences in species morphology and to measure the predator-prey size relationship across the whole set of species. Original primary data on diet composition were obtained from former research whose results were already published in five separated papers dealing with different species or groups of species. Data included information on stomach content (percentage weight) from a total of 2138 individuals pertaining to 12 species (nine of them further split in size groups) and 3953 pairs of prey's size vs predator's size measurements. Eight prey categories made 74% of all food consumed, namely non-identified fishes, penaeids, gobiids, polychaeta, alpheids, upogebiids and engraulids. Using a combination of diet overlap testing based on a null model approach, multivariate methods and regression analyses (linear and quantile), it is concluded that the existence of a relatively homogenous functional group of 12 fish species consuming invertebrates and small fishes is not a realistic assumption. Indeed, several species-size group subsets are clearly identifiable based on the percentage of different prey categories in their diets. The most plausible explanation for the observed patterns of diet composition are the differences in morphological characteristics of the species involved. Other factors allowing the sharing of food resources are the ontogenic change in the size of main prey consumed, notable differences in the abundance of fish species with higher diet overlap values and, perhaps, a high abundance of food resources.

Environmental influences, particularly river flow alteration, on larval fish assemblages in the Douro Estuary, Portugal

Larval stages of fishes are highly vulnerable to environmental shifts and anthropogenic pressures can pose additional stress to such a critical phase. The present study aimed to investigate environmental controls on the larval fish assemblages of the Douro Estuary, a heavily modified water body with several anthropogenic pressures. Monthly sampling surveys were conducted over two years along the estuarine horizontal gradient. The estuarine larval fish assemblage was dominated by a few very abundant taxa. Resident Pomatoschistus microps and members of the marine Clupeidae and Soleidae families were the most abundant taxa, accounting for 87.5% of the total catch. Canonical correspondence analysis identified e.g., river flow and salinity as the main environmental variables regulating the larval fish assemblages in the Douro Estuary. River flow had a significant impact on larval fish abundances with the lowest abundances observed when river flow surpassed 900 m3 s−1. Overall, the Douro larval fish assemblage exhibited similar features to other less impacted temperate estuaries. However, the results of this study highlighted the negative impact of regulating river flows that can compromise the connectivity of estuaries with adjacent coastal areas and, ultimately, their nursery function for the early life stages of fishes.

Response of the Sirtuin/PXR signaling pathway in Mugilogobius chulae exposed to environmentally relevant concentration Paracetamol.

Paracetamol (APAP) is one of the most widely used non-steroidal anti-inflammatory drugs, which is frequently detected in various water bodies. Studies are limited about its toxic effects and mechanisms on non-target aquatic organisms. In this study, an estuarine bottom-dwelling fish named Mugilogobius chulae, distributed in southern China, was selected as experimental species and the changes of PXR signaling pathway, a key signaling pathway of detoxification metabolic system in liver, were investigated under APAP exposure (0.5 μg·L-1, 5 μg·L-1, 50 μg·L-1 and 500 μg·L-1) for 24 h, 72 h and 168 h. Results showed that the key genes (e.g., P-gp, MRP1, CYP1A, CYP3A, GST and SULT) and the enzymatic activities of GST, EROD and ERND in PXR signaling pathway were induced to meet the requirements of detoxification metabolism. By up-regulating the expression of GCLC gene, the reductive small molecule GSH can be rapidly synthesized to counteract the attack of free radicals produced by APAP exposure. The expressions of SIRT1 and SIRT2 proteins decreased, while the expressions of most genes in PXR signaling pathway increased. It was speculated that the expression of PXR and its downstream target genes may be regulated epigenetically by SIRT1 and SIRT2. Studies showed that the exposure to environmental relevant concentrations of APAP can affect the detoxification metabolism of non-target organisms such as Mugilogobius chulae.

Osmoregulatory strategies of estuarine fish Scatophagus argus in response to environmental salinity changes

BackgroundScatophagus argus, an estuarine inhabitant, can rapidly adapt to different salinity environments. However, the knowledge of the molecular mechanisms underlying its strong salinity tolerance remains unclear. The gill, as the main osmoregulatory organ, plays a vital role in the salinity adaptation of the fish, and thus relative studies are constructive to reveal unique osmoregulatory mechanisms in S. argus.ResultsIn the present study, iTRAQ coupled with nanoLC-MS/MS techniques were employed to explore branchial osmoregulatory mechanisms in S. argus acclimated to different salinities. Among 1,604 identified proteins, 796 differentially expressed proteins (DEPs) were detected. To further assess osmoregulatory strategies in the gills under different salinities, DEPs related to osmoregulatory (22), non-directional (18), hypo- (52), and hypersaline (40) stress responses were selected. Functional annotation analysis of these selected DEPs indicated that the cellular ion regulation (e.g. Na+-K+-ATPase [NKA] and Na+-K+-2Cl− cotransporter 1 [NKCC1]) and ATP synthesis were deeply involved in the osmoregulatory process. As an osmoregulatory protein, NKCC1 expression was inhibited under hyposaline stress but showed the opposite trend in hypersaline conditions. The expression levels of NKA α1 and β1 were only increased under hypersaline challenge. However, hyposaline treatments could enhance branchial NKA activity, which was inhibited under hypersaline environments, and correspondingly, reduced ATP content was observed in gill tissues exposed to hyposaline conditions, while its contents were increased in hypersaline groups. In vitro experiments indicated that Na+, K+, and Cl− ions were pumped out of branchial cells under hypoosmotic stress, whereas they were absorbed into cells under hyperosmotic conditions. Based on our results, we speculated that NKCC1-mediated Na+ influx was inhibited, and proper Na+ efflux was maintained by improving NKA activity under hyposaline stress, promoting the rapid adaptation of branchial cells to the hyposaline condition. Meanwhile, branchial cells prevented excessive loss of ions by increasing NKA internalization and reducing ATP synthesis. In contrast, excess ions in cells exposed to the hyperosmotic medium were excreted with sufficient energy supply, and reduced NKA activity and enhanced NKCC1-mediated Na+ influx were considered a compensatory regulation.ConclusionsS. argus exhibited divergent osmoregulatory strategies in the gills when encountering hypoosmotic and hyperosmotic stresses, facilitating effective adaptabilities to a wide range of environmental salinity fluctuation.

Length–weight relationships of three fish species from the Yangtze River Estuary

The present study provides the length–weight relationships (LWRs) for common estuarine fish species collected from the Yangtze River Estuary by bottom trawl from 2017 to 2021. The net port width of bottom trawl net was 6 m, and the mesh size was 20 mm. This study provides new information on LWRs for three species in FishBase. Also, this study updates the information on the maximum length for three species.

Too Much Freshwater, Not Enough, or Just Right? Long-Term Trawl Monitoring Demonstrates the Impact of Canals that Altered Freshwater Flow to Three Bays in SW Florida

Understanding the impact of anthropogenically altering freshwater flow to estuaries is a growing information need for coastal managers. Due to differences in watershed development, drainage canals, and water control structures, the Ten Thousand Islands area of southwest Florida provides an ecosystem-scale opportunity to investigate the influence of both more, and less, freshwater flow to coastal bays compared to locations with more natural hydrology. Bottom trawl and water quality data spanning 20 years were used to investigate how environmental and hydrological differences among three bays affect community structure of small estuarine fishes. Relationships between fish community structure and salinity and temperature variables were evaluated over timescales from 1 day to 3 months prior to each trawl. Longer-term aspects of temperature (i.e., 2–3 months) exhibited the highest correlations in all bays, suggesting that spawning cycles are the main cause of seasonal changes in fish communities, rather than differences in freshwater flow. Despite major contrasts in watershed manipulation and the seasonal salinity of one bay being much less than the others, the bays differed primarily based on relative abundances of more common species rather than due to unique suites of species being present. Truly freshwater conditions were never detected, and high salinity conditions were experienced in all bays during dry seasons. This likely prevents a community shift to freshwater species. The range in flow characteristics among bays and general similarity in fish communities suggest that conditions will remain within the tolerance of most fishes in all three bays following restoration to more saline conditions.

Chronic toxicity of tire crumb rubber particles to mummichog (Fundulus heteroclitus) in episodic exposures

Microrubber (MR) encompasses all tire-related particles in the micro-scale and has recently drawn increased attention as a subclass of the broader group of microplastics. While tire particles entered the environment since the introduction of rubber tires for vehicles, the concern regarding tire wear particles (TWP) as an environmental contaminant is relatively new. Recent studies have examined physical and chemical toxicity of MR particles and leachates to a variety of organisms. However, there is a lack of information on the long-term effects of tire particle exposure under environmentally realistic conditions. The current study examined the chronic toxicity of crumb rubber (CR) particles to the estuarine fish species, mummichog (Fundulus heteroclitus) under episodic exposures at environmentally relevant concentrations. Immunohistochemistry (IHC) of fish gill, intestine, and liver was performed to assess CYP1A induction in these organs. Bile fluorescence was measured as an indicator of exposure to polycyclic aromatic hydrocarbons (PAHs) from CR. DNA damage was measured through the formation of 8-hydroxy-2′-deoxyguanosine (8-OHdG) together with other oxidative stress measures as lipid peroxidation (TBARS assay), free glutathione (GSH), and oxidized glutathione (GSSG) concentrations. Upregulation of CYP1A in gill, intestine, and liver was observed especially in gill filaments and general vasculature. Increased bile fluorescence demonstrated exposure to aromatic compounds, especially pyrene-like PAHs. Data for DNA damage indicated greater plasma 8-OHdG concentrations as a result of increased DNA repair. There was a decrease in malondialdehyde (MDA) production and an increase in total GSH at higher concentrations of CR. It appeared that under long-term repeated dosing, antioxidant systems in mummichog were upregulated to deal with exogenous stressors released by the CR particles. Combined, these data demonstrate that fish exposed to tire crumb rubber particles illicit significant biomarker responses under environmentally relevant CR concentrations, but induced antioxidant and detoxification pathways may prevent mortality and serious physiological effects in F. heteroclitus when exposed to environmentally relevant concentrations of CR.

Sea‐surface temperature anomalies mediate changes in fish richness and abundance in Atlantic and Gulf of Mexico estuaries

AbstractAimAnthropogenic warming of marine systems has caused biological and physiological responses that are fundamentally altering ecosystem structure. Because estuaries exist at the land‐ocean interface, they are particularly vulnerable to the effects of ocean warming as they can undergo rapid biogeochemical and hydrological shifts due to climate and land‐use change. We explored how multiple components of estuarine fish diversity—turnover, richness, and abundance—have changed in the North Atlantic and Gulf of Mexico estuaries across space and time and the drivers of change.LocationNorth Atlantic and Gulf of Mexico.TaxaFish.MethodWe compiled long‐term (>30 years), continent‐wide fisheries independent trawl surveys conducted in estuaries—from the Gulf of Maine to the Gulf of Mexico (U.S. waters)—and combined these with climate and land‐use‐land‐cover data to examine trends and ecological drivers of fish richness, abundance and turnover using mixed‐effect models.ResultsSpecies richness, abundance and turnover have increased in North Atlantic and Gulf of Mexico estuaries in the last 30 years. These changes were mediated largely by sea‐surface temperature anomalies, especially in more northern estuaries where warming has been relatively pronounced.Main ConclusionThe increasing trajectory of turnover in many estuaries suggests that fish communities have changed fundamentally from the baselines. A fundamental change in community composition can lead to an irreversible trophic imbalance or alternative stable states among other outcomes. Thus, predicting how shifting community structures might influence food webs, ecosystem stability, and human resource use remain a pertinent task.

Early life-stage Deepwater Horizon crude oil exposure induces latent osmoregulatory defects in larval red drum (Sciaenops ocellatus)

Crude oil is known to induce developmental defects in teleost fish exposed during early-life stages (ELSs). A recent study has demonstrated that zebrafish (Danio rerio) larvae acutely exposed to Deepwater Horizon (DHW) crude oil showed transcriptional changes in key genes involved in early kidney (pronephros) development and function, which were coupled with pronephric morphological defects. Given the osmoregulatory importance of the kidney, it is unknown whether ELS effects arising from short-term crude exposures result in long-term osmoregulatory defects, particularly within estuarine fishes likely exposed to DWH oil following the spill. To address this knowledge gap, an acute 72 h exposure to red drum (Sciaenops ocellatus) larvae was performed using high-energy water-accommodated fractions (HEWAFs) of DWH weathered oil to analyze transcriptional changes in genes involved in pronephros development and function by quantitative PCR. To test the latent effects of oil exposure on osmoregulation ability, red drum larvae were first exposed to HEWAF for 24 h. Larvae were then reared in clean seawater for two weeks and a 96 h acute osmotic challenge test was performed by exposing the fish to waters with varying salinities. Latent effects of ELS crude oil exposure on osmoregulation were assessed by quantifying survival during the acute osmotic challenge test and analyzing transcriptional changes at 14 dpf. Results demonstrated that ELS crude oil exposure reduced survival of red drum larvae when challenged in hypoosmotic waters and that latent transcriptional changes in some target pronephric genes were evident, indicating that an affected kidney likely contributed to the increased mortality.

Estimation of population parameters and fishery status of spotted scat, Scatophagus argus (Scatophagidae) in Pabean Bay, Indramayu, West Java, Indonesia

Abstract. Manangkalangi E, Pertami ND, Asriansyah A, Aditriawan RM, Sala R, Rahardjo MF. 2022. Estimation of population parameters and fishery status of spotted scat, Scatophagus argus (Scatophagidae) in Pabean Bay, Indramayu, West Java, Indonesia. Biodiversitas 23: 3480-3487. Pabean Bay is a fishing ground for various types of estuarine fish, including spotted scat, Scatophagus argus. This study aims to describe this type of fish population and its level of exploitation by using length-frequency distribution data for one year (January to December 2015). Fish samples were obtained from the catch of fishers using sero fishing gear and gill nets. Analysis of first caught size, growth parameters, mortality, recruitment pattern, and fishery status used FiSAT II program and some empirical formulas. The results of this study indicate that the length of the first time caught (Lc) is 100.195 mm and is smaller than the size of the first maturity (Lm). The asymptotic length (L?) and growth coefficient (K) were 191.65 mm and 0.18 year-1. Recruitment took place throughout the year with a peak in two periods (February-March and August-September). Total mortality, natural mortality, and catch mortality were 0.84 year-1, 0.37 year-1, and 0.47 year-1.The exploitation rate (E) of this fish was 0.56 year-1. The condition of this fish resource showed slow growth and was indicated to experience overfishing conditions. This information is expected to be considered, especially the use of sero and gillnet fishing gears with small mesh sizes and the frequency of catching it so that the fishing activities will not negatively impact the sustainability of this fish resource in the area.

Foodways of the Late Archaic people of St. Catherines Island, Georgia: an analysis of vertebrate remains from two shell rings

ABSTRACT The results of a large study of vertebrate remains from two shell rings on St. Catherines Island, Georgia, are presented: the St. Catherines (9LI231) and McQueen (9LI1648) Shell Rings. The vertebrate archaeofaunal collections are used to infer foodways of Late Archaic people on St. Catherines Island, which centered on a limited suite of small-bodied, estuarine fishes. Given the prevalence of small-bodied fishes, Late Archaic people deployed a number of mass-capture fishing technologies which may have necessitated shared labor and community cooperation. Although there are similarities in the vertebrate assemblages at these two rings, suggesting a shared foodways tradition, differences are notable. These differences may indicate that the occupants of the two rings had unique preferred or controlled fishing grounds. The zooarchaeological collections also are used to contextualize the vertebrate data within the current formational models proposed for Late Archaic shell rings. Vertebrate remains align with models that interpret shell rings as the result of Late Archaic people living in circular villages, discarding refuse from daily meals; however, these animals were also featured in a ritualized event highlighting their relevance and meaning beyond food.

Trophic guild structure and dietary patterns of a juvenile-dominated demersal fish community in a tropical mangrove estuarine system

Community-wide understanding of food web dynamics in species-rich tropical estuaries are generally lacking, exacerbating the challenges of managing these valuable coastal habitats. To address this gap, trophic guilds and dietary patterns were elucidated for 39 species of a juvenile-dominated demersal estuarine fish community in the Matang Mangrove Forest Reserve, an Important Marine Mammal Area. Fishes were sampled monthly for a year using otter trawl, and stomach contents were analyzed. Of the seven trophic guilds identified from clustering analysis, the three most speciose ones were shrimp feeders (12 species), zooplanktivores (9), and generalist crustacivores (7). Copepods occurred in diets of 50% of all fish species and were the most important food item volumetrically for specialist zooplanktivores. Diverse shrimp and prawn taxa, including commercially valuable Acetes and juvenile penaeids, showed highest frequency of occurrence in stomachs and supported the shrimp feeder and crustacivore guilds that contained relatively more diet generalists. Biomass-dominant annelidivore guild members are known to be a vital food resource for highly threatened coastal cetaceans. Ontogenetic diet shift, wide intra-guild diet breadth, seasonality in major resource use, and prevalence of detritus in diet were feeding strategies that reduced niche overlap and competition among fish species sharing common food resources. Future fisheries management must consider the bottom-up trophic impacts from excessive removal of valuable prey resources such as shrimps on equally valuable fish consumers that depend on them.

Pyrene drives reduced brain size during early life exposure in an estuarine fish, the red drum (Sciaenops ocellatus)

Crude oil and the constituent polycyclic aromatic hydrocarbons (PAHs) induce a consistent suite of sub-lethal effects in early life stage fishes. It has been suggested that 3-ring PAHs drive cardiotoxicity and that all other impacts are downstream consequences of these cardiac effects. However, recent studies have documented behavioral alterations that may not be linked to cardiotoxicity. This raises the question of whether the 3-ring PAHs that drive cardiotoxicity are also responsible for the observed neurological impairments. To explore this question, we exposed embryonic red drum (Sciaenops ocellatus) – a species that exhibits greater sensitivity to craniofacial malformations than cardiotoxicity – to individual 2-ring, 3-ring, and 4-ring PAHs for 48 h after which they were assessed for sub-lethal developmental malformations. No effects were observed following exposure to naphthalene, anthracene, dibenzothiophene, phenanthrene and fluorene at doses equivalent to the ΣPAH50 effective concentration 50 for craniofacial malformation in red drum. Conversely, pyrene caused complete lethality at the original dose, and a 5× diluted dose resulted in significantly reduced brain size and spine length. Similar sub-lethal effects were also observed in chrysene at the 1× dose. These results indicate that 4-ring PAHs are driving malformations in developing red drum and suggest oil induced impairments in this species are not a downstream consequence of 3-ring PAH induced cardiac malformations.

ULTRASTRUCTURE AND CYTOCHEMISTRY OF LATE EMBRYOS AND COTYLOCIDIUM LARVAE OF ROHDELLA AMAZONICA (TREMATODA: ASPIDOGASTREA), FROM THE TROPICAL ESTUARINE FISH, COLOMESUS PSITTACUS.

Developmental ultrastructure of late embryos and cotylocidium larval morphogenesis of Rohdella amazonica, an aspidogastrean parasite of fish, were studied to reveal the functional aspects of larvigenesis within the egg as well as phylogenetically relevant characteristics of the embryos and larvae in this basal trematode group. Gravid worms were removed from the intestine of naturally infected banded puffer fish Colomesus psittacus, collected from the Bay of Marajó, Paracauari River (Pará, Brazil) and processed by standard methods of transmission electron microscopy (TEM) and cytochemistry. During late cleavage and rearrangement of the blastomeres, the vitelline syncytium that plays a role in eggshell formation and nutrient provision to the embryo completes its apoptotic degeneration as the embryonic mass grows substantially. Early larval morphogenesis involves cellular positioning that defines the anteroposterior polarity of the differentiating larva. Progressing through larvigenesis, the anterior end forms a muscular oral sucker surrounding the mouth, which leads inward into the pharynx and expanding digestive cavity. At the posterior end, a large disc forms as a precursor to the eventual ventral disc. The fully formed cotylocidium, still within the eggshell, is flexed ventrally, bringing the 2 poles into near juxtaposition. The neodermatan tegument with outwardly projecting small microvilli becomes fully formed, as myocytons, a protonephridial system, and 2 glandular regions occupy the body's interior. The ultrastructural features described here are very similar to those reported for Aspidogaster limacoides from fish and somewhat similar to those reported for Cotylogaster occidentalis from molluscs, but differ from the more diverse larvae of neodermatan taxa that have been studied more extensively.

Categorizing estuarine fish assemblages in the Warm Temperate Southwestern Atlantic Province: The case of Patos Lagoon Estuary, Brazil

Classifying organisms into guilds is a good strategy to deal with taxonomic differences, and possibly to compare systems worldwide to address ecosystemic questions. Functional guilds have been used to classify organisms; however different classifications frequently are used for the same species, depending on each author. In order to standardize the guild classification for the Patos Lagoon Estuary, South Brazil, we evaluated its fish assemblage using historical dataset (1979 through 2016). Fish species were classified into guilds covering estuarine use, feeding mode and reproductive strategy. We found 140 Osteichthyes species for this estuary, in that most of the species are marine (58.5%), followed by freshwater (31.4%), estuarine (6.3%), and diadromous (3.8%) species. Concerning feeding mode, most species were classified as zoobenthivores, followed by piscivores and zooplanktivores, with some species presenting ontogenetic variation in their feeding habits. The average trophic level of this fish assemblage was estimated in three. Regarding reproduction, oviparity was the main reproductive mode, with pelagic eggs in the marine species, and settled eggs in the freshwater species. We provided an updated and unified list of Osteichthyes from Patos Lagoon Estuary, with all species classified in standardized guilds, assisting future studies that aim at analyzing estuarine assemblages in the Warm Temperate Southwestern Atlantic Province, as well as worldwide.

Identifying Environmental Factors Limiting Recovery of an Imperiled Estuarine Fish

Correctly identifying the environmental factors that limit population growth and recovery of imperiled species is an essential element of any targeted conservation program. Abundance index values for delta smelt (Hypomesus transpacificus), an imperiled fish in the upper San Francisco Estuary, have exhibited substantial inter-annual variation and the population is now at historically low numbers. Drawing from conceptual ecological models, we developed and applied a new multivariate analytical technique that incorporates a fundamental characteristic of limiting environmental factors– recognition that certain factors influence abundance in certain seasons or years, but they may have no influence on the species’ performance at other times. We observe that delta smelt occasionally experience years with population size increases, despite their ongoing long-term downward trajectory in numbers. The differences in environmental conditions that occur in years that prompt different population responses can provide insight into the environmental factors that limit species recovery. Nine temporally and spatially explicit covariates emerged from analyses that explain changes in inter-annual delta smelt abundance indices. We contrast those environmental factors with the factors that influence occupancy because distinguishing and focusing conservation actions on factors affecting delta smelt performance, rather than occupancy, should lead to the implementation of management and habitat-restoration actions that are more likely to benefit the fish. We think that the approach taken in this study can be a model for other species where salient data are limited and information needs are pressing.

Polygenic discrimination of migratory phenotypes in an estuarine forage fish.

Migration is a complex phenotypic trait with some species containing migratory and nonmigratory individuals. Such life history variation may be attributed in part to plasticity, epigenetics, or genetics. Although considered semianadromous, recent studies using otolith geochemistry have revealed life history variation within the critically endangered Delta Smelt. Broadly categorizable as migratory or freshwater residents, we examined Restriction site Associated DNA sequencing data to test for a relationship between genetic variation and migratory behaviors. As previously shown, we found no evidence for neutral population genetic structure within Delta Smelt; however, we found significant evidence for associations between genetic variants and life history phenotypes. Furthermore, discriminant analysis of principal components, hierarchical clustering, and machine learning resulted in accurate assignment of fish into the freshwater resident or migratory classes based on their genotypes. These results suggest the presence of adaptive genetic variants relating to life history variation within a panmictic population. Mechanisms that may lead to this observation are genotype dependent habitat choice and spatially variable selection, both of which could operate each generation and are not exclusive. Given that the population of cultured Delta Smelt are being used as a refugial population for conservation, as a supply for wild population supplementation, and currently represent the majority of all living individuals of this species, we recommend that the hatchery management strategy consider the frequencies of life history-associated alleles and how to maintain this important aspect of Delta Smelt biological variation while under captive propagation.

Estuarine fish diversity as indicator of natural environmental gradients

Estuarine fish diversity as indicator of natural environmental gradients