Most sources of stress in aquaculture, fish salvage, stocking programs, and commercial and sport fisheries may be unavoidable. Collecting, handling, sorting, holding, and transporting are routine practices that can have significant effects on fish physiology and survival. Nevertheless, an understanding of the stressors affecting fish holding can lead to practices that reduce stress and its detrimental effects. The stress-related effects of short-term holding are influenced by water quality, confinement density, holding container design, and agonistic and predation-associated behaviors. Physiological demands (e.g., resulting from confinement-related stresses) exceeding a threshold level where the fish can no longer compensate may lead to debilitating effects. These effects can be manifested as suppressed immune systems; decreased growth, swimming performance, or reproductive capacity; even death. Furthermore, holding tolerance may depend upon the species, life stage, previous exposure to stress, and behavior of the held fish. Water quality is one of the most important contributors to fish health and stress level. Fish may be able to tolerate adverse water quality conditions; however, when combined with other stressors, fish may be quickly overcome by the resulting physiological challenges. Temperature, dissolved oxygen, ammonia, nitrite, nitrate, salinity, pH, carbon dioxide, alkalinity, and hardness are the most common water quality parameters affecting physiological stress. Secondly, high fish densities in holding containers are the most common problem throughout aquaculture facilities, live-fish transfers, and fish salvage operations. Furthermore, the holding container design may also compromise the survival and immune function by affecting water quality, density and confinement, and aggressive interactions. Lastly, fishes held for relatively short durations are also influenced by negative interactions, associated with intraspecific and interspecific competition, cannibalism, predation, and determining nascent hierarchies. These interactions can be lethal (i.e., predation) or may act as a vector for pathogens to enter (i.e., bites and wounds). Predation may be a significant source of mortality for fisheries practices that do not sort by size or species while holding. Stress associated with short-term holding of fishes can have negative effects on overall health and well-being. These four aspects are major factors contributing to the physiology, Ó Springer Science+Business Media B.V. 2006behavior, and survival of fishes held for a relatively short time period.

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The societal benefits of hydropower systems (e.g., relatively clean electrical power, water supply, flood control, and recreation) come with a cost to native stream fishes. We reviewed and synthesized the literature on hydropower-related pulsed flows to guide resource managers in addressing significant impacts while avoiding unnecessary curtailment of hydropower operations. Dams may release pulsed flows in response to needs for peaking power, recreational flows, reservoir storage adjustment for flood control, or to mimic natural peaks in the hydrograph. Depending on timing, frequency, duration, and magnitude, pulsed flows can have adverse or beneficial short and long-term effects on resident or migratory stream fishes. Adverse effects include direct impacts to fish populations due to (1) stranding of fishes along the changing channel margins, (2) downstream displacement of fishes, and (3) reduced spawning and rearing success due to redd/nest dewatering and untimely or obstructed migration. Beneficial effects include: (1) maintenance of habitat for spawning and rearing, and (2) biological cues to trigger spawning, hatching, and migration. We developed a basic conceptual model to predict the effects of different types of pulsed flow, identified gaps in knowledge, and identified research activities to address these gaps. There is a clear need for a quantitative framework incorporating mathematical representations of field and laboratory results on flow, temperature, habitat structure, fish life stages by season, fish population dynamics, and multiple fish species, which can be used to predict outcomes and design mitigation strategies in other regulated streams experiencing pulsed flows.

Otolith stable carbon isotope ratios provide a unique and widely applicable environmental record. Unfortunately, uncertainty regarding the proportion of otolith carbon that derives from metabolized food versus dissolved inorganic carbon (DIC) in the water currently limits utilization of this marker. We manipulated the δ13C of food and ambient DIC in a factorial design with juvenile rainbow trout (Oncorhynchus mykiss). At the activity levels and total metabolic rates characteristic of fish in this study, 17% (±3% standard error, SE) of otolith C was metabolically derived, while >80% was derived from DIC in ambient water. We also estimated isotopic enrichment factors associated with physiological carbon transformations by measuring δ13C of blood and endolymph (which closely tracked otolith δ13C). There was substantial depletion in 13C of blood relative to C sources (εblood–sources = –16.9‰ ± 1.1‰ SE), but substantial enrichment in 13C in otolith relative to blood (εoto–blood = 13.3‰ ± 1.3‰ SE). Net isotopic enrichment between sources and the otolith was therefore slightly negative. Most of the isotopic enrichment between the blood and the otolith was associated with the movement of C from blood to endolymph, while enrichment associated with the precipitation of otolith aragonite from the endolymph was small.

Intensive water management and frequent drought cycles can increase water temperatures, thereby decreasing habitat quality for Chinook salmon Oncorhynchus tshawytscha inhabiting streams of California's Central Valley. We studied the incremental effects of chronic exposure (Ͼ60 d; effects measured bimonthly) to three temperature regimes typical of the range of conditions experienced by Sacramento River fall-run Chinook salmon during juvenile rearing and smoltification (13-16ЊC, 17-20ЊC, and 21-24ЊC; diel fluctuations of 0.5-3ЊC were allowed within these limits). Our laboratory experiments demonstrated that Chinook salmon can readily survive and grow at temperatures up to 24ЊC. However, juveniles reared at 21-24ЊC experienced significantly decreased growth rates, impaired smoltification indices, and increased predation vulnerability compared with juveniles reared at 13-16ЊC. Fish reared at 17-20ЊC experienced similar growth, variable smoltification impairment, and higher predation vulnerability compared with fish reared at 13-16ЊC. These results improve our understanding of the range of juvenile Chinook salmon responses to elevated temperatures and should assist biologists and resource decision makers in coordinating water management and salmon conservation decisions.