The effects of temperature and salinity on the endocrinology in two life stages of juvenile rainbow/steelhead trout (Oncorhynchus mykiss).

The San Francisco Bay Delta is experiencing seasonally warmer waters and saltwater intrusion into historically freshwater ecosystems due to climate change. Steelhead/rainbow trout (Oncorhynchus mykiss) are resident in the Bay-Delta from juvenile development through the smoltification process. Due to increases in sea level, premature seawater (SW) acclimation may co-occur with increased temperatures on pre-smolt juveniles. To evaluate the interactive effects of salinity and temperature on juvenile life stages of salmonids, rainbow trout alevin (3 days post-hatching) were exposed to 13, 16.4 and 19°C for 10 days and then challenged for 24 h to 18 parts per thousand SW. Similarly, fry (4 weeks post-hatching) were exposed to 13, 16.4 and 19°C for 2 weeks (14 days) and then challenged to SW. Estradiol-17ß (E2 ), cortisol, triiodothyronine (T3 ) and thyroxine (T4 ) were measured in whole animal homogenates and muscle tissue using enzyme-linked immunosorbent assays. Transcripts of gill Na+ /K+ ATPase ß (NKAα1b), brain growth hormone I (gh1) and brain gonadotropin-releasing hormone receptor 2 (gnrh2) were also measured. Alevin exhibited a significant temperature-dependent decrease in survival, and fry showed a temperature-dependent decrease in condition factor. The gene expression of NKAα1b, gh1 and gnrh2 significantly decreased in all SW-challenged alevin, and a significant decrease in gnrh2 expression was observed in fry with temperature. Alevin T3 and T4 concentrations significantly increased with increasing temperature. There was a temperature-dependent increase in E2 of fry but not of alevin. The results of this study demonstrate that increasing temperature and SW exposure may adversely affect the survival and SW acclimation of alevin and fry stages of salmonids and that the tolerances of younger juvenile stages should be considered when assessing the response of salmonid populations to climate change stressors.

Alteration of neuro-dopamine and steroid hormone homeostasis in wild Bank voles in relation to tissue concentrations of PFAS at a Nordic skiing area.

Perfluoroalkyl substances (PFAS) are contaminants that are applied in a wide range of consumer products, including ski products. The present study investigated the neuro-dopamine (DA) and cellular steroid hormone homeostasis of wild Bank voles (Myodes glareolus) from a skiing area in Norway (Trondheim), in relation to tissue concentrations of PFAS. We found a positive association between brain DA concentrations and the concentration of several PFAS, while there was a negative association between PFAS and dopamine receptor 1 (dr1) mRNA. The ratio between DA and its metabolites (3,4-dihydroxyphenylacetic acid: DOPAC and homovanillic acid: HVA) showed a negative association between DOPAC/DA and several PFAS, suggesting that PFAS altered the metabolism of DA via monoamine oxidase (Mao). This assumption is supported by an observed negative association between mao mRNA and PFAS. Previous studies have shown that DA homeostasis can indirectly regulate cellular estrogen (E2) and testosterone (T) biosynthesis. We found no association between DA and steroid hormone levels, while there was a negative association between some PFAS and T concentrations, suggesting that PFAS might affect T through other mechanisms. The results from the current study indicate that PFAS may alter neuro-DA and steroid hormone homeostasis in Bank voles, with potential consequences on reproduction and general health.

Mechanisms behind interactive effects of temperature and bifenthrin on the predator avoidance behaviors in parr of chinook salmon (Oncorhynchus tshawytscha).

Many coastal systems have been experiencing the effects of non-chemical and chemical anthropological stressors through respective increases in surface water temperatures and rainstorm-derived runoff events of pyrethroid pesticide movement into waterways such as the San Francisco Bay-Delta. Salmonid populations in the Bay-Delta have been dramatically declining in recent decades. Therefore, the aim of this study was to investigate the interactive effects of bifenthrin, a pyrethroid insecticide, and increasing water temperatures on targeted neuroendocrine and behavioral responses in Chinook salmon (Oncorhynchus tshawytscha) parr (10- month post-hatch). Parr were reared at 11 °C, 16.4 °C, or 19 °C for 14 days and, in the final 96 h of rearing, exposed to nominal concentrations of 0, 0.15, or 1.5 µg/L bifenthrin. A predatory avoidance Y-Maze behavioral assay was conducted immediately following exposures. Parr were presented a choice of clean or odorant zones, and locomotive behavior was recorded. Thyroid hormones (T3 and T4), estradiol, and testosterone were quantified within plasma using ELISAs, and the expression of brain hormone and dopamine receptor genes were also evaluated by qPCR. Brain dopamine levels were analyzed by LC/MS. No significant changes were observed in brain transcripts or plasma hormone concentrations with bifenthrin or increasing temperature. However, temperature did significantly lower brain dopamine levels in fish reared at 19 °C compared to 11 °C controls, but was unaltered by bifenthrin treatment. In contrast, parr reared at 11 °C and exposed to 1.5 µg/L bifenthrin spent significantly less time avoiding a predatory odorant compared to vehicle controls reared at 11 °C. The 16.4 °C and 1.5 µg/L-treated fish spent significantly more time in the neutral arm compared to the odorant and clean arms, as well as spending significantly less time in the clean arm compared to the 11 °C control fish. These results suggest that the interaction of temperature and bifenthrin may be adversely impacting predator-avoidance behavior, which may not be related to dopaminergic responses.

Effects of bifenthrin on sex differentiation in Japanese Medaka (Oryzias latipes).

Bifenthrin (BF) is a pyrethroid insecticide used in urban and agricultural applications. Previous studies in early life stages of fish have indicated anti-estrogenic activity; however, estrogenic activity has been observed in adults. To test the hypothesis that BF impairs sex differentiation, larval Japanese Medaka were exposed to BF during a critical developmental window for phenotypic sexual differentiation. Fish were exposed to environmentally relevant concentrations of BF (0.15 µg/L and 1.5 µg/L), a single concentration (0.3 mg/L) of an estrogen receptor (ER) antagonist (ICI 182,780), and an ER agonist (0.2 ug/L) (17ß-estradiol). Fish were exposed at 8 days post hatch (dph) larvae for 30 days. Phenotypic sex, secondary sexual characteristics (SSC) and genotypic sex were investigated at sexual maturity (8 weeks). A trend towards masculinization (p = 0.06) based on the presence of papillary processes in anal fin rays of Japanese Medaka was observed in fish exposed to the lowest concentration of BF. However, genotypic gender ratios were not altered. These results show sex differentiation was not significantly altered by larval exposure to BF in Japanese medaka.

Effects of Chlorpyrifos on Cholinesterase and Serine Lipase Activities and Lipid Metabolism in Brains of Rainbow Trout (Oncorhynchus mykiss).

Chlorpyrifos is an organophosphorus insecticide that elicits acute toxicity through inhibition of acetylcholinesterase (AChE), leading to acetylcholine accumulation and prolonged stimulation of cholinergic receptors throughout the central and peripheral nervous systems. Previous studies have indicated that neurodevelopment may also be impaired through alternative pathways, including reduction of cyclic adenosine monophosphate (cAMP)-catalyzed downstream events. The upstream initiating events that underlie noncholinergic neurological actions of chlorpyrifos and other organophosphorus compounds remain unclear. To investigate the potential role of fatty acid signaling disruption as a mechanism of toxicity, lipid metabolism and fatty acid profiles were examined to identify alterations that may play a critical role in upstream signaling in the central nervous system (CNS). Juvenile rainbow trout were treated for 7 days with nominal chlorpyrifos concentrations previously reported to diminish olfactory responses (10, 20, and 40 µg/l). Although lethality was noted higher in doses, measured chlorpyrifos concentrations of 1.38 µg/l (nominal concentration 10 µg/l) significantly reduced the activity of AChE and two serine lipases, monoacylglycerol lipase, and fatty acid amide hydrolase in the brain. Reductions in lysophosphatidylethanolamines (16:0, 18:0, 18:1, and 22:6) derived from the phosphatidylethanolamines and free fatty acids (palmitic acid 16:0, linolenic acid 18:3, eicosadienoic acid 20:2, arachidonic acid 20:4, and docosahexaenoic acid 22:6) were also noted, suggesting that chlorpyrifos inhibited the metabolism of select phospholipid signaling precursors at sublethal concentrations. These results indicate that in addition to AChE inhibition, environmentally relevant chlorpyrifos exposure alters serine lipase activity and lipid metabolites in the trout brain, which may compromise neuronal signaling and impact neurobehavioral responses in aquatic animals.

The effects of bifenthrin and temperature on the endocrinology of juvenile Chinook salmon.

The San Francisco Bay delta (USA) is experiencing seasonally warmer waters attributable to climate change and receives rainstorm runoff containing pyrethroid pesticides. Chinook salmon (Oncorhynchus tshawytscha) inhabit the affected waterways from hatch through smoltification, and thus juvenile fish may experience both pyrethroid and warmer water exposures. The effects of higher temperatures and pesticide exposure on presmolt Chinook are unknown. To improve understanding of the potential interaction between temperature and pesticide exposure on salmonid development, juvenile alevin and fry were reared in 11, 16.4, and 19 °C freshwater for 11 d and 2 wk, respectively, and exposed to nominal concentrations of 0, 0.15, and 1.5 µg/L bifenthrin for the final 96 h of rearing. Estradiol-17ß (E2), testosterone, triiodothyronine, and thyroxine levels were measured in whole-body homogenates using hormone-specific enzyme-linked immunosorbent assays. Brain gonadotropin-releasing hormone receptor (GnRH2), dopamine receptor 2A, and growth hormone 1 (GH1) mRNA levels were measured using quantitative PCR. Results showed significantly decreased survival and condition factors observed with increasing temperature in alevin. Alevin thyroid hormones increased significantly with temperature, but fry thyroid hormones trended toward a decrease at lower temperatures with increasing bifenthrin exposure. There were significant reductions in fry testosterone and E2 at 11 °C with increasing bifenthrin treatments and significant changes in GnRH2 and GH1 gene expression in both alevin and fry, indicating potential disruption of hormonal and signaling pathways. Environ Toxicol Chem 2019;38:852-861. © 2019 SETAC.