21 research outputs found
Ontogeny influences sensitivity to climate change stressors in an endangered fish.
Coastal ecosystems are among the most human-impacted habitats globally, and their management is often critically linked to recovery of declining native species. In the San Francisco Estuary, the Delta Smelt (Hypomesus transpacificus) is an endemic, endangered fish strongly tied to Californian conservation planning. The complex life history of Delta Smelt combined with dynamic seasonal and spatial abiotic conditions result in dissimilar environments experienced among ontogenetic stages, which may yield stage-specific susceptibility to abiotic stressors. Climate change is forecasted to increase San Francisco Estuary water temperature and salinity; therefore, understanding the influences of ontogeny and phenotypic plasticity on tolerance to these critical environmental parameters is particularly important for Delta Smelt and other San Francisco Estuary fishes. We assessed thermal and salinity limits in several ontogenetic stages and acclimation states of Delta Smelt, and paired these data with environmental data to evaluate sensitivity to climate-change stressors. Thermal tolerance decreased among successive stages, with larval fish exhibiting the highest tolerance and post-spawning adults having the lowest. Delta Smelt had limited capacity to increase tolerance through thermal acclimation, and comparisons with field temperature data revealed that juvenile tolerance limits are the closest to current environmental conditions, which may make this stage especially susceptible to future climate warming. Maximal water temperatures observed in situ exceeded tolerance limits of juveniles and adults. Although these temperature events are currently rare, if they increase in frequency as predicted, it could result in habitat loss at these locations despite other favourable conditions for Delta Smelt. In contrast, Delta Smelt tolerated salinities spanning the range of expected environmental conditions for each ontogenetic stage, but salinity did impact survival in juvenile and adult stages in exposures over acute time scales. Our results underscore the importance of considering ontogeny and phenotypic plasticity in assessing the impacts of climate change, particularly for species adapted to spatially and temporally heterogeneous environments
Spatiotemporal Models of an Estuarine Fish Species to Identify Patterns and Factors Impacting Their Distribution and Abundance
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Physiological stress biomarkers reveal stocking density effects in late larval Delta Smelt (Hypomesus transpacificus)
Suboptimal fish stocking densities in experimental systems may elicit stress responses that can affect experimental results. Fish species, age and size, water chemistry and flow, and physical characteristics of the experimental system (e.g., tank, cage) are among the parameters to be considered when determining stocking densities. However, systematic studies to define fish densities minimizing stress in experimental systems are rarely performed. This is particularly true when working with species of low aquaculture value or a non-model test species such as the Delta Smelt (. Hypomesus transpacificus). The aim of this study was to use physiological stress biomarkers to determine suitable fish densities for specific experimental vessels routinely used for this species. We maintained late larval Delta Smelt (60. days post-hatch; dph) over a period of 24. h, at five different densities: 7, 14, 28, 42, and 56 fish per 8. L circular fish tank. We assessed whole body cortisol and transcriptomic biomarkers that lead to cortisol production to quantify stress levels. Both marker types delivered similar results. Cortisol levels were lowest at densities of 28 and 42 fish per tank, whereas lowest fish densities (7 and 14 fish per tank) evoked the highest stress levels. Genes such as Mineralocorticoid Receptor 1 and Glucocorticoid Receptor 2, as well as 11-Beta-Hydroxysteroid-Dehydrogenase-2 depicted the lowest expression levels at stocking densities 28 and 42, and elevated expression levels for stocking densities 7 and 14. Our data support the observations that late larval Delta Smelt should be exposed, acclimated, and cultured in groups rather than as individuals or in low numbers. This study indicates the importance of adequately defining experimental conditions that minimize stress, specifically when stress is measured as an endpoint. In addition to classical cortisol measurements, responses of the transcriptome also appear suitable in assessing stress responses in fish, and in determining optimal holding conditions, particularly if short-term responses are the study focus.Statement of relevance. The study highlights the importance of evaluating stress in order to determine species-specific stocking densities. The results are thus relevant to a wide audience in the field of aquaculture and experimental biology