We performed two controlled experiments to determine the amount of mass-dependent and mass-independent fractionation (MDF and MIF) of methylmercury (MeHg) during trophic transfer into fish. In Experiment 1, juvenile yellow perch (Perca flavescens) were raised in captivity on commercial food pellets and then their diet was either maintained on un-amended food pellets (0.1 µg/g MeHg), or was switched to food pellets with 1.0 µg/g or 4.0 µg/g of added MeHg, for a period of 2 months. The difference in δ202Hg (MDF) and Δ199Hg (MIF) between fish tissues and food pellets with added MeHg were within the analytical uncertainty (δ202Hg; 0.07 ‰, Δ199Hg; 0.06 ‰) indicating no isotope fractionation. In Experiment 2, lake trout (Salvelinus namaycush) were raised in captivity on food pellets, and then shifted to a diet of bloater (Coregonus hoyi) for 6 months. The δ202Hg and Δ199Hg of the lake trout equaled the isotopic composition of the bloater after 6 months, reflecting re-equilibration of the Hg isotopic composition of the fish to new food sources and a lack of isotope fractionation during trophic transfer. We suggest that the stable Hg isotope ratios in fish can be used to trace environmental sources of Hg in aquatic ecosystems.

The bowfin (Amia calva) is a ray-finned fish that possesses a unique suite of ancestral and derived phenotypes, which are key to understanding vertebrate evolution. The phylogenetic position of bowfin as a representative of neopterygian fishes, its archetypical body plan and its unduplicated and slowly evolving genome make bowfin a central species for the genomic exploration of ray-finned fishes. Here we present a chromosome-level genome assembly for bowfin that enables gene-order analyses, settling long-debated neopterygian phylogenetic relationships. We examine chromatin accessibility and gene expression through bowfin development to investigate the evolution of immune, scale, respiratory and fin skeletal systems and identify hundreds of gene-regulatory loci conserved across vertebrates. These resources connect developmental evolution among bony fishes, further highlighting the bowfin’s importance for illuminating vertebrate biology and diversity in the genomic era.

Perspectives of white males have overwhelmingly dominated fisheries science and management in the USA. This dynamic is exemplified by bias against "rough fish"-a pejorative ascribing low-to-zero value for countless native fishes. One product of this bias is that biologists have ironically worked against conservation of diverse fishes for over a century, and these problems persist today. Nearly all U.S. states retain bag limits and other policies that are regressive and encourage overfishing and decline of native species. Multiple lines of evidence point towards the need for a paradigm shift. These include: (1) native species deliver critical ecosystem services; (2) little demonstration that native fish removals deliver intended benefits; (3) many native fishes are long-lived and vulnerable to overfishing and decline; and (4) fisher values and demographics shifting towards native fish conservation. Overall, existing native fish policies are unacceptable and run counter to the public trust doctrine where government agencies manage natural resources for public use. We encourage agencies to revisit their policies regarding native fishes and provide suggestions for developing more holistic, protective, and inclusive conservation policy.

Abstract. Empirically understanding spatial variation in secondary production rates is central to ecology. Yet for most taxa, such patterns are rarely examined, especially at different levels of ecological organization (e.g., species-vs. community-level patterns). We compiled data on biomass, production, and P/B rates of freshwater fish communities and species across latitudes and contrast patterns observed at the community level with those observed for species. At the community level, and at two distinct spatial scales (global vs. continental-North American), negative or neutral relationships were apparent between biomass, production, and P/B with latitude; however, there was substantial scatter in these data. Yet at the species level in North America, production was often closely linked to latitude, but in the opposite direction: Many species showed improved production with latitude. Latitudinal increases in species-level production rates were strongest for cool-and cold-water species, and species rarely showed the opposite trend. Species-level increases in production with latitude strengthened when production rates were normalized by the thermal opportunity for production, suggesting potential adaptations of individuals and populations to shorter growing seasons (i.e., "countergradient" production) at high latitudes. At the global scale, there were apparent unimodal relationships between community fish production measures and species richness; however, these patterns became linearized or non-significant at the continental scale. Decreased interspecific competition at northern latitudes combined with genetic adaptations (e.g., countergradient growth) could explain a tendency for increased species production in northern populations, while total community production remains reduced. Latitude has contrasting effects on fish production at different spatial scales and levels of biological organization. Thus while freshwater fish communities are somewhat more productive and diverse at lower latitudes, species production in northern populations is often surprisingly high.