Allen F. Mensinger

The partial reinforcement extinction effect (PREE) occurs when a conditioned response is more resistant to extinction when reinforced unpredictably versus continuously. The PREE has been observed in many species; however, our knowledge of the PREE in fishes is limited. In this study, we investigated two different reinforcement methods, continuous and partial, while using Pavlovian conditioning to acoustically condition common carp ( Cyprinus carpio ), a highly invasive species, to swim into a feeding ring (conditioned behaviour) where they would receive a food reward at the onset of a 400 Hz sound stimulus. The extinction rates of the conditioned behaviour were compared following cessation of the food reward. Using binomial generalized linear mixed-effect regressions we showed that tanks subjected to partial reinforcement were expected to have a higher proportion of carp exhibiting the conditioned behaviour up to two times longer than tanks subjected to continuous reinforcement, consistent with the PREE. Carp in partial reinforcement tanks continuously responded for up to 30 days, while responses in continuous reinforcement tanks typically ceased by day 9. Our findings support common carp management strategies that use baiting to train carp to form feeding aggregations that can be removed en masse from lakes and suggest that such baiting strategies may benefit from partial conditioning protocols, saving on both labour and bait.

Understanding the phenotypic consequences of naturally occurring genetic changes, as well as their impact on fitness, is fundamental to understanding how organisms adapt to an environment. This is critical when genetic variants have pleiotropic effects, as determining how each phenotype impacted by a gene contributes to fitness is essential to understand how and why traits have evolved. Here, we characterized the effects of mutations in the oca2 gene, which underlie albinism and reductions of sleep in the blind Mexican cavefish Astyanax mexicanus, on larval prey capture. We found that when surface A. mexicanus with engineered mutations in oca2 are hunting, they use cave-like, wide-angle strikes to capture prey. However, unlike cavefish or surface fish in the dark, which utilize the lateral line when hunting, oca2 mutant (oca2Δ2bp/Δ2bp) surface fish can use vision when striking at prey from wide angles. We found that when raised under lighted conditions, pigmented surface fish outcompete albino oca2Δ2bp/Δ2bp surface fish when hunting in lighted conditions. In contrast, when surface fish are reared in darkness, oca2Δ2bp/Δ2bp surface fish outcompete their wild type siblings in the dark. This raises the possibility that albinism is detrimental to larval feeding in a surface-like lighted environment, but may confer an advantage to fish in cave-like, dark environments. Together, these results demonstrate that oca2 plays a role in larval feeding behavior in A. mexicanus, and expand our understanding of the pleiotropic phenotypic consequences of oca2 in cavefish evolution.

There are increasing concerns from scientists and policymakers regarding the potential effects of sound on aquatic life. While mobile species can move away from sound sources, slow-moving or sessile organisms are unable to escape. Many species of elasmobranchs are oviparous and deposit egg cases that remain in a fixed position on or near the seabed with development times ranging from months to over a year. The auditory sensitivity of elasmobranchs has been relatively understudied compared with that of marine mammals and teleost fish, with little known about the effect of sound on adults and almost nothing reported on how sound may impact developing embryos. Therefore, the effect of sound on the behavior of late-stage embryonic little skates (Leucoraja erinacea) and chain catsharks (Scyliorhinus retifer) in their egg case was monitored. Both species reacted to sound prior to hatching. Little skates interrupted tail movements in response to 300 and 400 Hz pure tones as well as playbacks of boat sound, while chain catsharks ceased respiratory movements during boat sound playbacks. Thus, late-stage embryos can detect and are affected by sound, and fisheries managers may need to account for the impact of anthropogenic sound near oviparous elasmobranch breeding grounds.

The round goby (Neogobius melanostomus) is an invasive benthic fish first introduced to the Laurentian Great Lakes in 1990 that has negatively impacted native fishes through increased competition for food and habitat, aggressive interactions, and egg predation. While complete eradication of the round goby is currently not possible, intensive trapping in designated areas during spawning seasons could potentially protect critical native fish spawning habitats. Baited minnow traps were spaced 10 meters apart in shallow water along a 100-meter stretch of shoreline within the Duluth-Superior Harbor during the round goby breeding period (June to October) with captured round gobies removed from interior traps (N = 10) every 48 hours. These traps were bracketed by two pairs of reference traps deployed weekly for 48 hours, from which round gobies were also tagged and released. The number of round gobies captured in the interior traps declined by 67% compared to reference traps over the course of the study, with extended periods of no captures. The tagged round gobies showed high site affinity, with 82.8% of tagged fish recaptured at the previous release site. The results indicate that even at open water sites, which allow natural migration of round gobies into the area, extensive trapping could reduce local population numbers.

Fish bioacoustics, or the study of fish hearing, sound production, and acoustic communication, was discussed as early as Aristotle. However, questions about how fishes hear were not really addressed until the early 20th century. Work on fish bioacoustics grew after World War II and considerably in the 21st century since investigators, regulators, and others realized that anthropogenic (human-generated sounds), which had primarily been of interest to workers on marine mammals, was likely to have a major impact on fishes (as well as on aquatic invertebrates). Moreover, passive acoustic monitoring of fishes, recording fish sounds in the field, has blossomed as a noninvasive technique for sampling abundance, distribution, and reproduction of various sonic fishes. The field is vital since fishes and aquatic invertebrates make up a major portion of the protein eaten by a signification portion of humans. To help better understand fish bioacoustics and engage it with issues of anthropogenic sound, this special issue of The Journal of the Acoustical Society of America (JASA) brings together papers that explore the breadth of the topic, from a historical perspective to the latest findings on the impact of anthropogenic sounds on fishes.