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To better understand potential diet overlap among exotic Asian species of carp and native species of filter-feeding fishes of the upper Mississippi River system, microscopy was used to document morphological differences in the gill rakers. Analysing samples first with light microscopy and subsequently with confocal microscopy, the three-dimensional structure of gill rakers in Hypophthalmichthys molitrix, Hypophthalmichthys nobilis and Dorosoma cepedianum was more thoroughly described and illustrated than previous work with traditional microscopy techniques. The three-dimensional structure of gill rakers in Ictiobus cyprinellus was described and illustrated for the first time. [ABSTRACT FROM AUTHOR]

Non-native, Asian carps bighead Hypophthalmichthys nobilis and silver Hypophthalmichthys molitrix have been present in the Illinois River since the early 1990s. The Long-Term Resource Monitoring Program (LTRMP) has been collecting bighead and silver carps in routine monitoring of the La Grange Reach, Illinois River, since 1995 and 1998, respectively. Despite variable recruitment, Asian carps abundance and biomass have increased since 2000, as evidenced by commercial landings, and Asian carps now dominate the fish community on La Grange Reach. Previous research suggests dietary overlap among bighead and silver carps and two native Illinois River fishes, gizzard shad Dorosoma cepedianum and bigmouth buffalo Ictiobus cyprinellus. Total length and mass data from c. 5000 fishes were used to test for changes in gizzard shad and bigmouth buffalo body condition after Asian carps establishment and investigate potential competitive interactions and changes in fitness. Analyses revealed significant declines in body condition of gizzard shad (−7%) and bigmouth buffalo (−5%) following the Asian carps invasion from 2000 to 2006. Segmented regression analyses showed no significant change in the rate of decline in gizzard shad condition after 2000, whereas the rate of decline in bigmouth buffalo condition increased significantly after 2000. Statistically significant differences in gizzard shad condition after Asian carps establishment (2000–2006) was observed, whereas condition of bigmouth buffalo was significantly lower in all years following Asian carps establishment as compared to 2000. Declines in gizzard shad and bigmouth buffalo condition were significantly correlated with increased commercial harvest of Asian carps and poorly correlated with other abiotic and biotic factors ( e.g. temperature, chlorophyll a and discharge) that may influence fish body condition. These results may suggest that Asian carps are influencing native planktivore body condition, and future research should focus on determining whether food is limited in the Illinois River for native planktivores and other fish species. [ABSTRACT FROM AUTHOR]

The genetic variation, phylogeny and biogeography of catostomid fishes were investigated based on mitochondrial cytochrome b and nuclear 18S-ITS1-5.8S DNA sequences. The pair-wise genetic distance of cytochrome b for 17 catostomids varied considerably, from 1·00% ( Chasmistes brevirostris and Deltistes luxatus) to 23·3% ( Cycleptus elongatus and Moxostoma anisurum). The size of the 18S-ITS1-5.8S sequence ranged from 315 bp ( Moxostoma robustum) to 575 bp ( Ictiobus cyprinellus). The 18S-5.8S region was conservative and the length of ITS1 regions was found to vary considerably among the seven catostomids. It is interesting that the primitive I. cyprinellus and Myxocyprinus asiaticus had longer ITS1 regions than suckers from the Catostominae. Based on the nucleotide substitution model, the nuclear 18S-5.8S gene had a faster evolution rate than the mitochondrial cytochrome b gene. In a phylogenetic analysis, 17 catostomids from 14 genera representing three subfamilies were not distinctly divergent. Nevertheless, three major genetically divergent clades were identified. Clade I (95% bootstrap) included general Catostomus, Thoburnia, Xyrauchen, Chasmistes and Deltistes. Clade II (94% bootstrap) included Hypentelium, Moxostoma and Scartomyzon. Clade III (77% bootstrap) was a monophyletic Ictiobinae containing I. cyprinellus and Carpiodes carpio. The biogeography of old world catostomids followed a disperse event, and the speciation of the extant catostomids was a vicariance event. The earliest catostomid evolved in Asia from one branch of ostariophysans in the early Tertiary. Before the Eocene, catostomids belonging to the genus Amyzon had a wide, trans-Pacific distribution over Asia and North America. Later, oceanic ingression and the Tertiary glacial event forced catostomids to evolve on both mainlands, respectively. The present disjunct distribution pattern of catostomids was presumably due to competitive pressure from cyprinids, geographical events, their Late Cenozoic radiation in North America and glacial events. The divergence time based on the mitochondrial and nuclear DNA sequences suggests that catostomids began to diverge in the early or mid-Miocene, which agrees with the fossil evidence. [ABSTRACT FROM AUTHOR]

The bowfin Amia calva is an amiid (Amiiformes) relict native to North America. It is the last surviving member of the Halecomorphi, a group of fishes that evolved more than 250 million years ago. Despite the phylogenetic significance of the amiids in vertebrate evolution, little has been published about their age and growth. Recreational bowfin harvest is currently unregulated throughout most of the USA, yet new recreational fisheries are emerging. As such, bowfin are increasingly harvested by sport bowfishing without limit, in addition to their growing commercial harvest for caviar. From 2017 to 2021 we studied a total of 81 bowfin from 11 populations across the east–west gradient of Minnesota within a narrow latitudinal margin (<50 km) of the 46th parallel north. We compared the allometry and translucence of bowfin asteriscus, lapillus and sagittal otoliths and found the lapillus otoliths provide consistent readability for age estimation despite being the smallest of the set. Size‐at‐age data derived from otoliths indicated that bowfin are sexually dimorphic in asymptotic length and may live up to 33 years, which is 15 years longer than previously estimated in wild populations, but comparable to what has been reported in captivity. Overall, 28% of the otolith‐aged fish were estimated as older than the previously reported maximum age for wild bowfin populations. Our findings suggest that the bowfin life history may exhibit slower growth, greater longevity, and more variable recruitment than previously recognized, which sets the stage for more otolith‐derived population demographics across their range and age validation study. Our results have direct implications for conservation of bowfin, especially amidst the increasing rates of exploitation during the bowfishing era. [ABSTRACT FROM AUTHOR]

Non‐physical barriers, including the use of underwater strobe lights alone or paired with sound or bubbles, are being considered as a means to prevent the upstream migration of invasive silver carp Hypophthalmichthys molitrix and bighead carp H. nobilis. To optimize potential optical deterrents, it is necessary to understand the visual sensitivity of the fishes. Dark‐adapted H. molitrix and H. nobilis were found to possess broad visual sensitivity between 470 to 620 nm with peak spectral sensitivity at 540 nm for H. molitrix and 560 nm in H. nobilis. To assess the effect of a strobe light on vision, dark‐adapted H. molitrix, H. nobilis and common carp Cyprinus carpio, were exposed to three different 5 s trains (100, 200, or 500 ms on–off flashes) of white light and the recovery of visual sensitivity was determined by measuring the b‐wave amplitude of the electroretinogram (ERG). For all species, the longest recoveries were observed in response to the 500 ms flash trains (H. molitrix mean ± SE = 702.0 ± 89.8 s; H. nobilis 648.0 ± 116.0 s; C. carpio 480 ± 180.0 s). The results suggest that strobe lights can temporarily depress visual sensitivity, which may render optical barriers less effective. [ABSTRACT FROM AUTHOR]

The feeding ecology of the small‐bodied benthic naked goby Gobiosoma bosc, a western Atlantic species that occurs in estuaries and other inshore habitats from Connecticut to Texas U.S.A., was investigated in a total of four estuaries spanning South Carolina, North Carolina, Maryland and New Jersey. Gut content analysis of 391 individuals revealed that G. bosc is a benthic microcarnivore that feeds primarily on polychaetes, gammarid amphipods and harpacticoid copepods. Diet composition varied with body size, tidal creek within an estuary and geographic region. Analyses of gut fullness suggest that G. bosc is a daytime visual predator and that nest and egg guarding during the reproductive season reduce foraging activity in mature males. Additionally, G. bosc infected with adult digenean parasites of the gut foraged more intensely than uninfected individuals, a relationship that was strongest for reproductively mature males. Regionally, significant variation in dietary breadth was documented and may reflect a foraging response to a decrease in prey diversity moving from estuaries of higher salinity and lower latitude to estuaries of lower salinity and higher latitude. These results contribute to an understanding of the life history of G. bosc and the role played by this common species in estuarine food webs. [ABSTRACT FROM AUTHOR]

The objectives of this study were (1) to determine whether the presence or absence of prairie fishes can be modelled using habitat and biotic characteristics measured at the reach and catchment scales and (2) to identify which scale ( i.e. reach, catchment or a combination of variables measured at both scales) best explains the presence or absence of fishes. Reach and catchment information from 120 sites sampled from 1999 to 2004 were incorporated into tree classifiers for 20 prairie fish species, and multiple criteria were used to evaluate models. Fewer than six models were considered significant when modelling individual fish occurrences at the reach, catchment or combined scale, and only one species was successfully modelled at all three scales. The scarcity of significant models is probably related to the rigorous criteria by which these models were evaluated as well as the prevalence of tolerant, generalist fishes in these stochastic and intermittent streams. No significant differences in the amount of reduced deviance, mean misclassification error rates ( MER), and mean improvement in MER metrics was detected among the three scales. Results from this study underscore the importance of continued habitat assessment at smaller scales to further understand prairie-fish occurrences as well as further evaluations of modelling methods to examine habitat relationships for tolerant, ubiquitous species. Incorporation of such suggestions in the future may help provide more accurate models that will allow for better management and conservation of prairie-fish species. [ABSTRACT FROM AUTHOR]

This study tested the hypothesis that the most common gear type used to sample fishes in wadeable systems, electrofishing, was more effective than another commonly used gear type, seining, for sampling fish species at risk. Five predictions were tested. At sites where species at risk were detected, (1) the probability of detecting the species at risk, (2) the probability of only one gear type detecting the species at risk and (3) the estimated catch per unit effort of the species at risk, was as high as, or higher, when using electrofishing than when using a seine. (4) The number of sample sites required to detect a species at risk within a watershed and (5) the number of subsections required to detect a species at risk within a site, were as low as, or lower, using electrofishing than the number required using a seine. Based on analyses of these measurements, electrofishing was a more effective gear type than seining for sampling fish species at risk, irrespective of the unit (presence or absence or catch per unit effort) or scale of measurement (watershed or site level). Dissolved oxygen, turbidity, specific conductivity and nitrate concentrations were measured at each site and did not account for the between gear differences. Selection of sampling gear can be a fundamental consideration for the assessment of fish species at risk, where, unlike common species, they may be particularly influenced by small population sizes, restricted geographic ranges and narrow habitat preferences. Resource managers must weigh differences in the risks of injury of fish species at risk against differences in the effectiveness of each gear type when deciding between gear types and the utility of the assessments they represent. [ABSTRACT FROM AUTHOR]