Visual, spectral, and microchemical quantification of crystalline anomalies in otoliths of wild and cultured delta smelt.

Developmental abnormalities in otoliths can impact growth and survival in teleost fishes. Here, we quantified the frequency and severity of developmental anomalies in otoliths of delta smelt (Hypomesus transpacificus), a critically endangered estuarine fish that is endemic to the San Francisco Estuary. Left-right asymmetry and anomalous crystalline polymorphs (i.e., vaterite) were quantified and compared between wild and cultured populations using digital image analysis. Visual estimates of vaterite were validated using X-ray diffraction, Raman spectroscopy, laser ablation ICPMS, and electron probe microanalysis. Results indicated that cultured delta smelt were 80 times more likely to contain a vateritic otolith and 18 times more likely to contain relatively large (≥ 15%) amounts of vaterite. Similarly, cultured fish exhibited 30% greater asymmetry than wild fish. These results indicate that cultured delta smelt exhibit a significantly higher frequency of vestibular abnormalities which are known to reduce fitness and survival. Such hatchery effects on otolith development could have important implications for captive culture practices and the supplementation of wild fish populations with cultured individuals.

Temperature and salinity preferences of endangered Delta Smelt (Hypomesus transpacificus, Actinopterygii, Osmeridae).

Temperature and salinity often define the distributions of aquatic organisms. This is at least partially true for Delta Smelt, an imperiled species endemic to the upper San Francisco Estuary. While much is known about the tolerances and distribution of Delta Smelt in relation to these parameters, little is known regarding the temperature and salinity preferences of the species. Therefore, the temperature and salinity preferences of sub-adult Delta Smelt were investigated across a wide range of thermal (8-28 °C) and salinity (0-23 ppt) conditions. Replicates of ten fish were allowed to swim between two circular chambers with different temperature or salinity, and the distribution of fish between the chambers was recorded. We found that Delta Smelt showed no temperature preference below 15 °C, a modest aversion to the warmer tank from 15 to 28 °C, and a strong aversion to the warmer tank with elevated mortality at temperatures above 28 °C. Delta Smelt also preferred lower salinities, and this preference became more pronounced as salinity increased toward 23 ppt. These results indicate that Delta Smelt can tolerate high temperatures and salinities for a short time, and that their preferences for lower temperature and salinity strengthens as these variables increase.

Reproductive strategy of Delta Smelt Hypomesus transpacificus and impacts of drought on reproductive performance.

Understanding reproductive biology and performance of fish is essential to formulate effective conservation and management programs. Here, we studied reproductive strategies of female Delta Smelt Hypomesus transpacificus, an endangered fish species in the State of California, the United States, focusing on (1) better understanding their distribution pattern during the winter and spring spawning season at very fine scale to predict their possible spawning grounds and (2) assessing impacts of a recent, severe drought on their reproductive performance. We formulated our hypotheses as follows; (1) female Delta Smelt migrate to particular locations for spawning so that mature females can be frequently found in those locations throughout the spawning season and (2) reproductive performance of individual female fish declined during the drought. To test the first hypotheses, we analyzed relationships between water quality parameters and maturity/distribution pattern of Delta Smelt. Salinity better explained the distribution pattern of Delta Smelt at subadult and adult stages compared with water temperature or turbidity. Although there are some freshwater locations where mature Delta Smelt can frequently be found during the spawning season, Delta Smelt at the final maturation stage (Stage 5: hydration) and post spawners appeared to be widespread in the area where salinity was below 1.0 during the spawning season. Therefore, Delta Smelt could theoretically spawn in any freshwater locations, with more specific spawning requirements in the wild (e.g., substrate type and depth) still unknown. Delta Smelt, which experienced dry and critically dry conditions (the 2013 and 2014 year-classes), showed smaller oocytes, and lower clutch size and gonadosomatic index compared with the fish caught in a wet year (2011 year-class) at the late vitellogenic stage (Stage 4 Late), suggesting reproductive performance was negatively affected by environmental conditions during the drought.

Plasma Linoleate Diols Are Potential Biomarkers for Severe COVID-19 Infections.

Polyunsaturated fatty acids are metabolized into regulatory lipids important for initiating inflammatory responses in the event of disease or injury and for signaling the resolution of inflammation and return to homeostasis. The epoxides of linoleic acid (leukotoxins) regulate skin barrier function, perivascular and alveolar permeability and have been associated with poor outcomes in burn patients and in sepsis. It was later reported that blocking metabolism of leukotoxins into the vicinal diols ameliorated the deleterious effects of leukotoxins, suggesting that the leukotoxin diols are contributing to the toxicity. During quantitative profiling of fatty acid chemical mediators (eicosanoids) in COVID-19 patients, we found increases in the regioisomeric leukotoxin diols in plasma samples of hospitalized patients suffering from severe pulmonary involvement. In rodents these leukotoxin diols cause dramatic vascular permeability and are associated with acute adult respiratory like symptoms. Thus, pathways involved in the biosynthesis and degradation of these regulatory lipids should be investigated in larger biomarker studies to determine their significance in COVID-19 disease. In addition, incorporating diols in plasma multi-omics of patients could illuminate the COVID-19 pathological signature along with other lipid mediators and blood chemistry.

The health and condition responses of Delta Smelt to fasting: A time series experiment.

There is an extensive literature establishing, validating, and quantifying a wide range of responses of fishes to fasting. Our study complements this work by comparing fed and unfed treatments of hatchery-raised Delta Smelt (Hypomesus transpacificus)-an imperiled fish that is endemic to the San Francisco Estuary and its tributaries in California, USA-across a diverse suite of endpoints over a two-month time series. The experiment was conducted at 15.9°C, and individuals were sampled at 12 time points as starvation became increasingly severe. We found that hepatosomatic index and condition factor were relatively sensitive to starvation, becoming significantly depressed at Day 4 and 7, respectively. Histological analysis of liver showed elevated cytoplasmic inclusion bodies at Day 7, followed by increased glycogen depletion, single cell necrosis, and hydropic vacuolar degeneration at Day 14, 21, and 28, respectively. Of four antioxidants measured, glutathione decreased at Day 4, superoxide dismutase increased at Day 14, catalase increased at Day 56, and glutathione peroxidase was not affected by starvation. The net result was a ~2-fold increase in lipid peroxidation (malondialdehyde) in fasted fish that was highly inconsistent through time. RNA to DNA ratio and triglycerides in muscle were relatively insensitive to starvation, only consistently decreasing with fasting after mortality began increasing in the 'No Feeding' treatment, at Day 21. Together, these results suggest that Delta Smelt mobilize hepatic energy stores far more rapidly than lipids in muscle when subjected to fasting, leading to rapid atrophy of liver and the development of cytoplasmic inclusion bodies-possibly autophagosomes-in hepatocytes.

Histopathological assessment of seven year-classes of Delta Smelt.

The Delta Smelt (Hypomesus transpacificus) is an imperiled, annual fish endemic to the Sacramento-San Joaquin Delta and San Francisco Estuary. This study examined the severity and prevalence of liver and gill lesions of juvenile through adult Delta Smelt from 2011 through 2017 collected from five regions throughout its habitat (n = 1,053). The first and last years of the study were wet, but bracketed an extreme drought in CA (2012-2016), during which the Delta Smelt population reached historical lows. Overall, the three most common lesions were gill ionocyte hyperplasia, liver lipidosis, and gill aneurysm. Individuals with higher fork lengths exhibited increased gill and liver lesion score (summations of the severity scores), suggesting that Delta Smelt accumulate lesions through their lives, and that larger individuals were more tolerant of liver and gill lesions. Liver lesion score showed significant regional differences, while salinity was a better predictor of gill lesions than region, with lower gill lesion scores associated with higher salinities. Largely consistent with previously reported histopathology patterns, Delta Smelt collected from the Confluence and Suisun Marsh had the lowest liver lesion score, while Delta Smelt collected from Cache Slough and Suisun Bay had the highest lesion scores, and Suisun Marsh had the lowest glycogen depletion, suggesting heterogeneous levels of exposure to environmental stressors across regions. Gill and liver lesion score also varied significantly with year-class. The highest gill lesion score occurred in the 2015/16 year-class, and the lowest occurred in the 2017/18 year-class, a 2.8-fold difference. Controlling for size and regional effects, individuals with comparatively high liver lesion scores were prevalent in the population until the 2014/15 year-class. In the two subsequent year-classes, Delta Smelt livers were in the best condition, coinciding with peak drought conditions and record low abundances.

Analysis of Covalently Bound Microcystins in Sediments and Clam Tissue in the Sacramento-San Joaquin River Delta, California, USA.

Harmful cyanobacterial blooms compromise human and environmental health, mainly due to the cyanotoxins they often produce. Microcystins (MCs) are the most commonly measured group of cyanotoxins and are hepatotoxic, neurotoxic, and cytotoxic. Due to MCs ability to covalently bind to proteins, quantification in complex matrices is difficult. To analyze bound and unbound MCs, analytical methods were optimized for analysis in sediment and clam tissues. A clean up step was incorporated to remove lipids, improving percent yield. This method was then applied to sediment and clam samples collected from the Sacramento-San Joaquin River Delta (Delta) in the spring and fall of 2017. Water samples were also tested for intracellular and extracellular MCs. These analyses were used to quantify the partitioning of MCs among sediment, clams, and water, and to examine whether MCs persist during non-summer months. Toxin analysis revealed that multiple sediment samples collected in the Delta were positive for MCs, with a majority of the positive samples from sites in the San Joaquin River, even while water samples from the same location were below detection limit. These data highlight the importance of analyzing MCs in complex matrices to accurately evaluate environmental risk.

Toxicity of herbicides to cyanobacteria and phytoplankton species of the San Francisco Estuary and Sacramento-San Joaquin River Delta, California, USA.

The herbicides glyphosate, imazamox and fluridone are herbicides, with low toxicity towards fish and invertebrates, which are applied to waterways to control invasive aquatic weeds. However, the effects of these herbicides on natural isolates of phytoplankton and cyanobacteria are unknown. Three species of microalgae found in the San Francisco Estuary (SFE)/Sacramento-San Joaquin River Delta (Delta) (Microcystis aeruginosa, Chlamydomonas debaryana, and Thalassiosira pseudonana) were exposed to the three herbicides at a range of concentrations in 96-well plates for 5-8 days. All three algal species were the most sensitive to fluridone, with IC50 of 46.9, 21, and 109 µg L-1 for M. aeruginosa, T. pseudonana and C. debaryana, respectively. Imazamox inhibited M. aeruginosa and T. pseudonana growth at 3.6 × 104 µg L-1 or higher, and inhibited C. debaryana growth at 1.0 × 105 µg L-1 or higher. Glyphosate inhibited growth in all species at ca. 7.0 × 104 µg L-1 or higher. Fluridone was the only herbicide that inhibited the microalgae at environmentally relevant concentrations in this study and susceptibility to the herbicide depended on the species. Thus, the application of fluridone may affect cyanobacteria and phytoplankton community composition in water bodies where it is applied.

Toxic effects of fluridone on early developmental stages of Japanese Medaka (Oryzias latipes).

The herbicide fluridone is intensively applied to control invasive aquatic plants globally, including in the Sacramento and San Joaquin Delta (the Delta), California, USA. Our previous study revealed that the adult stage of Delta Smelt showed acute and sub-lethal adverse effects following 6 h of exposure to environmentally relevant concentrations of fluridone. To further investigate mechanisms of toxicity of fluridone and to assess its toxicity to early life stages of fish, we performed additional exposures using the fish model Japanese Medaka (Oryzias latipes). Male and female Medaka embryos were exposed to concentrations of fluridone for 14 d and showed reduced hatching success in a dose dependent manner. The half maximal effective concentration for the hatching success was 2.3 mg L-1. In addition, male and female Medaka larvae were acute exposed to fluridone for 6 h to assess their swimming behavior and gene expression patterns. Fish exposed to fluridone at 4.2 mg L-1 or higher became lethargic and showed abnormal swimming behavior. The response to the stimuli was significantly impaired by fluridone at 21 mg L-1 and above in males, and at 104 mg L-1 in females. Transcriptome analysis identified a total of 799 genes that were significantly differentially expressed, comprising 555 up-regulated and 244 down-regulated genes in males exposed to 21 mg L-1 of fluridone. The gene set enrichment analysis indicated a number of biological processes altered by fluridone. Among the genes involved in those biological processes, the expression of the genes, acetylcholinesterase, retinoic acid receptor, insulin receptor substrate, glutathione reductase, and glutathione S transferase, exhibited dose- and sex-dependent responses to fluridone. The study indicated that fluridone exposure led to detrimental toxic effects at early developmental stages of fish, by disturbing the biological processes of growth and development, and the nervous system, inducing oxidative stress and endocrine disruption.

Hydrodynamic Modeling Coupled with Long-term Field Data Provide Evidence for Suppression of Phytoplankton by Invasive Clams and Freshwater Exports in the San Francisco Estuary.

The San Francisco Estuary (California, USA) had abundant pelagic fish in the late 1960s, but has few pelagic fish today. A primary cause for this decline in fish is thought to be a trophic cascade, triggered by declining phytoplankton. Here, we describe the changes in pelagic community structure of the San Francisco Estuary. Then, we examine whether changes in hydrodynamics due to freshwater exports, which increased exponentially beginning in 1967, in addition to the 1986 invasion by the clam Potamocorbula amurensis, explain the phytoplankton loss. Hydrodynamic variables were reconstructed back to 1956 using statistical models fit to, and cross-validated against, output from a hydrodynamic model. Then, we regressed mean summer/fall chlorophyll a-the season with the largest phytoplankton decline-against the reconstructed hydrodynamic variables and the presence/absence of P. amurensis for 1969-2014. The regression model, which explained 78% of the interannual variation in chlorophyll a, was then used to quantify the influence of P. amurensis and exports on chlorophyll a. Based on monitoring data, chlorophyll a declined 22-fold from 1969-2014, zooplankton declined 32-fold from 1972-2014, and pelagic fish declined 92-fold from 1968-2014. Averaged over 1990-2014, the chlorophyll a model ascribed an 88% decline in chlorophyll a to P. amurensis, a 74% decline to exports (at minimum), and a 97% decline to the combined influence of P. amurensis and exports (at minimum). Thus, the decline in pelagic productivity in the San Francisco Estuary has occurred largely due to the combined impacts of the P. amurensis invasion and increased freshwater exports.

Biodiversity of cyanobacteria and other aquatic microorganisms across a freshwater to brackish water gradient determined by shotgun metagenomic sequencing analysis in the San Francisco Estuary, USA.

Blooms of Microcystis and other harmful cyanobacteria can degrade water quality by producing cyanotoxins or other toxic compounds. The goals of this study were (1) to facilitate understanding of community structure for various aquatic microorganisms in brackish water and freshwater regions with emphasis on cyanobacteria, and (2) to test a hypothesis that Microcystis genotypes that tolerate higher salinity were blooming in brackish water environments during the severe drought, 2014. Shotgun metagenomic analysis revealed that cyanobacteria dominated the brackish water region while bacteria dominated the freshwater region. A group of cyanobacteria (e.g., Aphanizomenon, Microcystis, Planktothrix, Pseudanabaena), bacteria (e.g., Bacillus, Porphyrobacter), and diatoms (Phaeodactylum and Thalassiosira) were abundant in the brackish water region. In contrast, Hassallia (cyanobacteria) and green algae (Nannochloropsis, Chlamydomonas, and Volvox) were abundant in the landward freshwater region. Station variation was also apparent. One landward sampling station located downstream of an urbanized area differed substantially from the other stations in terms of both water chemistry and community structure, with a higher percentage of arthropods, green algae, and eukaryotes. Screening of the Microcystis internal transcribed spacer region revealed six representative genotypes, and two of which were successfully quantified using qPCR (Genotypes I and VI). Both genotypes occurred predominantly in the freshwater region, so the data from this study did not support the hypothesis that salinity tolerant Microcystis genotypes bloomed in the brackish water region in 2014.

Tracking pyrethroid toxicity in surface water samples: Exposure dynamics and toxicity identification tools for laboratory tests with Hyalella azteca (Amphipoda).

Pyrethroid insecticides are commonly used in pest control and are present at toxic concentrations in surface waters of agricultural and urban areas worldwide. Monitoring is challenging as a result of their high hydrophobicity and low toxicity thresholds, which often fall below the analytical methods detection limits (MDLs). Standard daphnid bioassays used in surface water monitoring are not sensitive enough to protect more susceptible invertebrate species such as the amphipod Hyalella azteca and chemical loss during toxicity testing is of concern. In the present study, we quantified toxicity loss during storage and testing, using both natural and synthetic water, and presented a tool to enhance toxic signal strength for improved sensitivity of H. azteca toxicity tests. The average half-life during storage in low-density polyethylene (LDPE) cubitainers (Fisher Scientific) at 4 °C of 5 pyrethroids (permethrin, bifenthrin, lambda-cyhalothrin, cyfluthrin, and esfenvalerate) and one organophosphate (chlorpyrifos; used as reference) was 1.4 d, and piperonyl butoxide (PBO) proved an effective tool to potentiate toxicity. We conclude that toxicity tests on ambient water samples containing these hydrophobic insecticides are likely to underestimate toxicity present in the field, and mimic short pulse rather than continuous exposures. Where these chemicals are of concern, the addition of PBO during testing can yield valuable information on their presence or absence. Environ Toxicol Chem 2018;37:462-472. © 2017 SETAC.

Foraging and metabolic consequences of semi-anadromy for an endangered estuarine fish.

Diadromy affords fish access to productive ecosystems, increasing growth and ultimately fitness, but it is unclear whether these advantages persist for species migrating within highly altered habitat. Here, we compared the foraging success of wild Delta Smelt-an endangered, zooplanktivorous, annual, semi-anadromous fish that is endemic to the highly altered San Francisco Estuary (SFE)-collected from freshwater (<0.55 psu) and brackish habitat (≥0.55 psu). Stomach fullness, averaged across three generations of wild Delta Smelt sampled from juvenile through adult life stages (n = 1,318), was 1.5-fold higher in brackish than in freshwater habitat. However, salinity and season interacted, with higher fullness (1.7-fold) in freshwater than in brackish habitat in summer, but far higher fullness in brackish than freshwater habitat during fall/winter and winter/spring (1.8 and 2.0-fold, respectively). To examine potential causes of this interaction we compared mesozooplankton abundance, collected concurrently with the Delta Smelt, in freshwater and brackish habitat during summer and fall/winter, and the metabolic rate of sub-adult Delta Smelt acclimated to salinities of 0.4, 2.0, and 12.0 psu in a laboratory experiment. A seasonal peak in mesozooplankton density coincided with the summer peak in Delta Smelt foraging success in freshwater, and a pronounced decline in freshwater mesozooplankton abundance in the fall coincided with declining stomach fullness, which persisted for the remainder of the year (fall, winter and spring). In brackish habitat, greater foraging 'efficiency' (prey items in stomachs/mesozooplankton abundance) led to more prey items per fish and generally higher stomach fullness (i.e., a higher proportion of mesozooplankton detected in concurrent trawls were eaten by fish in brackish habitat). Delta Smelt exhibited no difference in metabolic rate across the three salinities, indicating that metabolic responses to salinity are unlikely to have caused the stomach fullness results. Adult migration and freshwater spawning therefore places young fish in a position to exploit higher densities of prey in freshwater in the late spring/summer, and subsequent movement downstream provides older fish more accessible prey in brackish habitat. Thus, despite endemism to a highly-altered estuary, semi-anadromy provided substantial foraging benefits to Delta Smelt, consistent with other temperate migratory fish.

Developmental effects of fipronil on Japanese Medaka (Oryzias latipes) embryos.

Pesticides in urban runoff are a major source of pollutants in aquatic ecosystems. Fipronil, a phenylpyrazole insecticide, found in structural pest control products, turf grass control, and home pet flea medication, has recently increased in use and is commonly detected in urban runoff. However, little is known about the effects of fipronil on aquatic organisms at early developmental stages. Here, we evaluated toxicity of fipronil to embryos of Japanese Medaka (Oryzias latipes, Qurt strain) using a high-throughput 96-well plate toxicity test. Male and female embryos (<6 h post fertilization) were exposed to concentrations of fipronil ranging from 0.1 to 910 µg L-1 for 14 days or until hatching. Embryos were subjected to gross and microscopic examinations of developmental adverse effects as well as transcriptome analysis using RNA-seq. Results indicated a positive dose-response in reduced hatching success, increased gross deformity (tail curvature) at a lowest-observed-effect concentration (LOEC) of 200 µg L-1 and delayed hatching (∼1 day at the highest concentration, LOEC = 600 µg L-1). The transcriptome analysis indicated that fipronil exposure enhanced expression of titin and telethonin, which are responsible for muscle development. It is therefore possible that the formation of a tail curvature is due to asymmetrical overgrowth of muscle. Our results indicate that sub-lethal effects occur in embryonic stages of an aquatic vertebrate following exposure to high concentrations of fipronil, although no adverse effects at the highest published environmentally relevant concentration (6.3 µg L-1) were observed.

A novel and versatile flash-freezing approach for evaluating the health of Delta Smelt.

A common approach used to assess environmental impacts in aquatic environments is to measure indicators of stress (biomarkers) and condition of fish within ecosystems. Particularly in estuarine ecosystems with multiple stressors, it is often desirable to quantify a suite of biological endpoints that (1) reflect fish condition at several levels of biological organization and time scales and (2) are sensitive to a range of environmental stressors. However, established methods of preservation and processing of fish for specific endpoints are often incompatible. Here, we developed a novel flash-freezing approach for assessing the health of a small, sensitive fish, the endangered Delta Smelt (Hypomesus transpacificus) after collections from the San Francisco Estuary (SFE). We assess whether flash-freezing the entire fish ensures effective preservation of multiple tissues for subsequent biomarker analyses by comparing measurements of fresh to frozen tissue. Tissues included brain, gill, and liver for enzyme activity, kidney and spleen for pathogens, and gills, liver, and gonads for histopathology and reproduction. Although flash-freezing in liquid nitrogen altered the length, weight, and condition factor of Delta Smelt, the percent changes were small (<1.5%). Histological analyses of the cellular morphology of gills, liver, and gonads were similar between both methods. Freezing artefacts were observed in ovaries, but did not hinder the identification and interpretation of cell types and oocyte stages. Freezing did not alter bacterial isolation or the activities of ethoxyresorufin-0-deethylase (EROD) or acetylcholinesterase (AChE), but had a small, negative influence on sodium potassium adenosine triphosphatase (ATPase) activity. Thus, flash-freezing in the field is a versatile preservation method for Delta Smelt, allowing for multiple tissue collections and bioassays from an individual tiny fish exposed to a wide range of natural and anthropogenic stressors. Similar methodology may be applicable to other species for which a range of biological endpoints and histopathology data are needed.

Contaminant and food limitation stress in an endangered estuarine fish.

The abundance of Delta Smelt (Hypomesus transpacificus), a fish species endemic to the upper San Francisco Estuary (SFE), is declining. Several causes for the population decline have been proposed, including food limitation and contaminant effects. Here, using juvenile Delta Smelt collected from throughout their range, we measured a suite of indices across three levels of biological organization (cellular, organ, individual) that reflect fish condition at temporal scales ranging from hours to weeks. Using these indices, the relative conditions of fish collected from five regions in the SFE were compared: Cache Slough, Sacramento River Deep Water Ship Channel, Confluence, Suisun Bay and Suisun Marsh. Fish sampled from Suisun Bay and, to a lesser extent the Confluence, exhibited relatively poor short-term nutritional and growth indices and morphometric condition, while fish from the freshwater regions of the estuary, and Cache Slough in particular, exhibited the most apparent histopathological signs of contaminant exposure. In contrast, fish from the Suisun Marsh region exhibited higher short-term nutrition and growth indices, and better morphometric and histopathological condition. For instance, fish collected from Suisun Marsh had a mean stomach fullness, expressed as a percentage of fish weight, that was 3.4-fold higher than fish collected from Suisun Bay, while also exhibiting an incidence of histopathological lesions that was 11-fold lower than fish collected from Cache Slough. Thus, our findings support the hypothesis that multiple stressors, including food limitation and contaminants, are contributing to the decline of Delta Smelt, and that these stressors influence Delta Smelt heterogeneously across space.

Trout reverse the effect of water temperature on the foraging of a mayfly.

Climate change is likely to increase the metabolisms of ectothermic animals living below their thermal optimum. While ectothermic top predators may compensate by increasing foraging, ectothermic prey may be unable to increase foraging because of increased predation risk from ectothermic predators. We examined how the diurnal drift behavior (i.e., the downstream movement associated with foraging) of the mayfly Baetis, an ectothermic herbivore, responds to changing temperature in the implied presence and absence of trout, an ectothermic predator. In an experiment replicated at the catchment scale, water temperature and trout presence strongly interacted to affect the diurnal drift of Baetis from artificial channels lacking periphyton over a water temperature range of 4.2-14.8 °C. In fishless streams, daytime drift increased with increasing water temperature, likely because of increased metabolic demand for food. However, in trout-bearing streams, daytime drift decreased with increasing water temperature. Our interpretation is that the perceived threat of trout rose with increasing water temperature, causing mayflies to reduce foraging despite heightened metabolic demand. These results suggest that anticipated increases in stream temperature due to climate change may further escalate divergence in structure and process between fishless and trout-bearing streams. Similar dynamics may occur in other ecosystems with ectothermic predators and prey living below their thermal optima.

An omega-3 epoxide of docosahexaenoic acid lowers blood pressure in angiotensin-II-dependent hypertension.

Mediators of antihypertensive actions of docosahexaenoic acid (DHA) are largely unknown. The omega-3 epoxide of DHA, 19, 20-EDP (epoxy docosapentaenoic acid), is metabolized by soluble epoxide hydrolase (sEH), which also metabolizes the anti-inflammatory and antihypertensive arachidonic acid epoxides, epoxyeicosatrienoic acids (EETs). Based in part on plasma levels of EDPs after a DHA-rich diet, we hypothesized that 19, 20-EDP contributes to the antihypertensive actions of DHA in angiotensin-II (Ang-II)-dependent hypertension. Treatment individually with 19, 20-EDP and a potent sEH inhibitor TPPU (1-trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl) urea) significantly lowered blood pressure (BP) as compared with Ang-II-infused animals. The largest reduction in BP was obtained with the combination of 19, 20-EDP and TPPU, which was more efficacious than the combination of 14, 15-EET and TPPU. Oxylipin profiling revealed that 19, 20-EDP and 14, 15-EET infusion affected not only most metabolites of the P450 pathway but also renal levels of prostaglandin-E2. Our findings suggest that 19, 20-EDP is a mediator of the antihypertensive effects of DHA in Ang-II-dependent hypertension. It seems that 19, 20-EDP requires metabolic stabilization with a sEH inhibitor to be most effective in lowering BP, although both TPPU and 19, 20-EDP are so effective on their own that demonstrating additive or synergistic interactions is difficult.