Recent identification of 6PPD-quinone as the chemical causing acute toxicity in coho salmon has led to substantial concern regarding the toxicity of this contaminant for other aquatic species. Environmental occurrence of 6PPD-quinone is probably high, because it is an oxidation product of a common tire rubber additive. Research on 6PPD-quinone toxicity in fish has revealed a rather unusual pattern, with closely related species exhibiting responses ranging from extreme sensitivity to no effect. Of 11 previously studied fish species, 6PPD-quinone was toxic to four. The species-specific toxicity of 6PPD-quinone complicates urgently needed environmental risk assessment. We investigated the acute toxicity of 6PPD-quinone in Atlantic salmon and brown trout alevins (sac fry). These species have previously not been tested for sensitivity to 6PPD-quinone. The fish were exposed in static conditions in eight treatments with initial concentrations ranging from 0.095 to 12.16 µg/L. Fish were observed for 48 h, and changes in concentrations of 6PPD-quinone were monitored throughout the experiment. No mortalities or substantial changes in behavior were recorded in either Atlantic salmon or brown trout. This provides an important first step in assessing effects of 6PPD-quinone on these economically and culturally highly important species. Environ Toxicol Chem 2022;41:3041–3045. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine-quinone (6PPD-quinone) is a widespread contaminant of emerging concern resulting from oxidation of 6PPD, which is an antidegradant substance added to tires. The recent identification of 6PPD-quinone as the cause of acute mortality in coho salmon has quickly motivated studies on 6PPD-quinone toxicity to other species. Subsequent findings have shown that 6PPD-quinone toxicity is highly species specific. Closely related species can differ widely in response to 6PPD-quinone from extremely sensitive to tolerant. Hence toxicity testing is currently the only way to establish whether a species exhibits 6PPD-quinone toxicity. We investigated the acute toxicity of 6PPD-quinone in pink salmon alevins (sac fry). This species has is the only Pacific salmon that so far has not been tested for 6PPD-quinone sensitivity. Fish were exposed in static water in eight treatments with initial concentrations ranging from 0.1 to 12.8 μg/L. Fish were observed for 48 h, and changes in concentrations of 6PPD-quinone were monitored throughout the experiment. No mortalities or substantial changes in behavior were recorded. Environ Toxicol Chem 2024;43:1332–1338. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Passive integrated transponder (PIT) tags are widely used in studies of various aspects of fish survival, movement and behaviour. Quality of such studies depends on the fish retaining the tags over the study period and that the tagging procedure or the tag does not influence behaviour or survival. Here we document PIT tag retention rates in hatchery-reared Atlantic salmon over a 533-day period from the late juvenile freshwater stage (pre-smolts) to young adults after 1 year in seawater. Fish were marked with 12-mm PIT tags, injected into their body cavity, as age 1+ pre-smolt and scanned for presence of PIT tags five times during the study. Tag retention for the entire period was 91% and varied between periods (96.09–99.89%). For individual time steps, daily retention rate was lowest in the first period following tagging (days 0–49). After this period retention rate increased substantially, before again dropping close to initial levels at the two last periods (days 173–533). Length of fish was only significantly related to retention during the first period. No difference in retention rates was found between males and females. A subset of fish without detected tags was X-rayed to verify that lack of PIT detection was due to tag loss. The retention rates observed in this study clearly show that tag loss needs to be accounted for when analysing PIT tag data on Atlantic salmon. Further, the temporal changes in retention rate clearly challenge previous assertions that tag loss is something that primarily occurs shortly after tagging or during spawning.

Sedimentation is one of the main eco-morphological and technological challenges associated with reservoirs. Sedimentation not only reduces the functional capacity of a reservoir by filling it, but also changes downstream sediment dynamics and habitat availability for the aquatic biota. Additionally, dams hinder free bi-directional fish passage, emerging as a major threat to species of migratory fish. In the past decades, mitigation measures aimed at reducing such environmental and technological impacts have been developed. Sediment bypass tunnels (SBTs) have been shown to successfully help prevent reservoir sedimentation, whereas fish passages have been found to be potential solutions to facilitate bi-directional passage of fish. However, the construction of such structures, in particular of SBT, can be extremely costly. The development of design solutions that can function both for downstream sediment transport and up- and downstream fish passage should be considered as they can mitigate ecological deficiencies of reservoir operations while accounting for economic feasibility. Possibilities and challenges of combining SBT and fish passage were explored by bringing together a team of interdisciplinary specialists on hydraulics, sediment transport and continuity, bypassing, hydraulic structures, hydropower engineering, aquatic biology, and fish passage in a two-day workshop. Here, we present potential solutions identified during the workshop for integrating SBT and fish passage.

While effects of acidification on salmonid fish are well studied and documented, effects of episodic high pH have rarely received attention. In the present study, we investigate effects of high pH events on Atlantic salmon (Salmo salar) using both field and laboratory data. Effects of an episodic high pH event on juvenile densities in a Norwegian river were studied using data from several electrofishing surveys conducted both before and after the event. Effects of high pH on survival of eggs were studied by exposing eggs to a range of high pH treatments for different durations. Juvenile densities from the field study showed that the high pH event had little or no effect on the cohort that had been exposed to pH 9.7-10.3 during the egg stage. This finding was in accordance with the laboratory experiment that showed no excess mortality on eggs until pH was above 12. The high pH event occurred in March during low winter flows, and densities of older juveniles in May were significantly lower in the affected area compared to controls upstream. In June and September the difference was not significant, but there was a clear spatial trend indicating that the event had a negative effect on densities of older juvenile salmon.