Captive propagation can lead to phenotypic change in fish populations, but the broader community‐level consequences of captive phenotypes remain largely unknown. We investigate the degree to which captive propagation alters the phenotypes and ecological roles of fish stocked into wild communities. We focus on captive propagation of western mosquitofish (Gambusia affinis) for biocontrol, which represents one of the largest scale production efforts for any fish released into the wild. Captive propagation in mosquitofish consistently generated novel mixtures of morphological and behavioural traits that deviate from those of wild populations. A mesocosm experiment showed that mosquitofish from captive propagation facilities differ from wild fish in their effects on aquatic community structure by shifting their consumption to less‐mobile, benthic prey. Synthesis and applications. Captive‐propagated and translocated wild fish stocks not only differ in phenotype, but can have substantially different ecological effects on the communities into which they are introduced. Therefore, captive propagation programmes involving continual release should expand their concerns beyond altered phenotypes and fitness to include whether propagated fish actually provide the intended ecological roles and services associated with their wild counterparts. Infusions of wild alleles and captive environments that mimic wild conditions are recommended strategies to retain the desired ecological role of captive‐propagated fish.

Eco-evolutionary feedbacks may determine the outcome of predator–prey interactions in nature, but little work has been done to quantify the feedback effect of short-term prey adaptation on predator performance. We tested the effects of prey availability and recent (less than 100 years) prey adaptation on the feeding and growth rate of largemouth bass ( Micropterus salmoides ), foraging on western mosquitofish ( Gambusia affinis ). Field surveys showed higher densities and larger average body sizes of mosquitofish in recently introduced populations without bass. Over a six-week mesocosm experiment, bass were presented with either a high or low availability of mosquitofish prey from recently established populations either naive or experienced with bass. Naive mosquitofish were larger, less cryptic and more vulnerable to bass predation compared to their experienced counterparts. Bass consumed more naive prey, grew more quickly with naive prey, and grew more quickly per unit biomass of naive prey consumed. The effect of mosquitofish history with the bass on bass growth was similar in magnitude to the effect of mosquitofish availability. In showing that recently derived predation-related prey phenotypes strongly affect predator performance, this study supports the presence of reciprocal predator–prey trait feedbacks in nature.

Background Acoustic telemetry is a widely used tool to study the movement and survival of juvenile fish and often requires a surgical procedure to implant the transmitter, which may impact overall fitness and survival following release. This is an important consideration when implementing large-scale acoustic telemetry projects aimed at estimating outmigration survival. The objective of this study was to examine the effects of water temperature, tag type, size at tagging, and surgeon experience on tag retention and growth rate of juvenile Chinook salmon (Oncorhynchus tshawytscha). We tagged 128 spring-run Chinook salmon (81–97 mm fork length, 5.2–10.0 g, tag burden 2.4–6.0%) with one of two types of acoustic transmitters; a shorter, heavier model (‘standard’) and a longer, lighter model (‘injectable’). Fish were tagged by either a novice or experienced surgeon. An additional 64 untagged fish served as a control group and were split between temperature treatments. Fish were reared in either cool (mean 13.4 °C) or warm (mean 17.8 °C) water for 60 days, prior to being euthanized, weighed and measured. Results Tag retention was similar for both transmitter types, but varied with water temperature, with significantly higher tag loss in the warm treatment (21.9%, 14 tags expelled), compared to the cold treatment (7.8%, 5 tags expelled). In the warm treatment, fish growth in the injectable tag group was significantly lower compared to the control group, and lower than the standard tag group, but not significantly lower. There was no significant difference between the control and standard tag groups for the warm treatment. In the cool temperature treatment, fish growth was not significantly different among any of the factors tested. Surgery time differed between surgeons; however, surgeon experience did not significantly affect tag shedding or growth. Conclusion Total tag loss was 14.8% over the 60-day trial, with higher and earlier loss in the warmer treatment. Tag length may be a more important factor than tag weight in smaller size fish. This suggests that tag shedding is a significant factor to consider when estimating survival, as the actual survival rate may be higher than estimates based solely on receiver detections.

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