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Cisco (Coregonus artedi Lesueur, 1818) in the Laurentian Great Lakes declined throughout the 19th and 20th centuries. Managers are attempting to restore Great Lakes cisco and other coregonines using multiple approaches, including stocking. A potential obstacle to these efforts is that artificially reared coregonines can display deformities and morphological differences compared to wild fish, but the impacts of artificial rearing on cisco morphology are not well understood. We compared morphologies of wild cisco to their artificially reared offspring, including one family that was exposed to three rearing temperature treatments. We found that artificially reared cisco had smaller eyes, shallower bodies, fewer gill rakers, and longer paired fins than their wild parents. We also found that artificially reared cisco were pugheaded, and this result held for another cisco population and rearing facility. Across the temperature treatments we tested, rearing temperatures did not impact the degree of pugheadedness or other morphological differences. Our results have important implications for coregonine restoration efforts. Future work should evaluate whether morphological differences that arise through artificial rearing affect cisco fitness in the wild. [ABSTRACT FROM AUTHOR]

Objective: Here we determine how traditional morphometrics (TM) compares with geometric morphometrics (GM) in discriminating among morphologies of four forms of ciscoes of the Coregonus artedi complex collected from Lake Huron. Methods: One of the forms comprised two groups of the same deepwater cisco separated by capture depth, whereas the other three forms were shallow‐water ciscoes. Result: Our three groups of shallow‐water ciscoes were better separated (3% vs. 19% overlap) in principle component analysis (PCA) with TM data than with GM data incorporating semilandmarks (evenly spaced nonhomologous landmarks used to bridge between widely separated homologous landmarks). Our two deepwater cisco groups, comprising a putatively single form collected from different depths, separated more in PCAs with GM data (33% overlap) than in PCAs with TM data (66% overlap), an anomaly caused by greater decompression of the swim bladder and deformation of the body wall in the group captured at greater depths. Separation of the two deepwater cisco groups captured at different depths was not affected by the removal of semilandmarks. Assignment of forms using canonical variate analysis accurately assigned 86% of individuals using TM data, 98% of individuals using GM data incorporating semilandmarks, and 100% of individuals using GM data without semilandmarks. However, we considered assignments from the same form of deepwater cisco into separate groups as misassignments resulting from different capture depths, which reduced the accuracy of assignments with GM data incorporating semilandmarks to 66%. Conclusion: Our study implies that TM will continue to have an important role in morphological discrimination within Coregonus and other fishes similarly shaped. Impact StatementThis research showed that a nearly antiquated method of describing shapes of fish was, in fact, as good, if not better than newer methods that use sophisticated mathematical treatments. [ABSTRACT FROM AUTHOR]

Deepwater sculpin (Myoxocephalus thompsonii) were considered extirpated from Lake Ontario prior to the 1990s but have since resurged and are now an abundant offshore demersal species. As deepwater sculpin reproduction is poorly described, an investigation of their gonadal development and fecundity was conducted to better understand their reproductive biology. To evaluate spawning period duration and if females spawn multiple times during their spawning period, we compared deepwater sculpin gonadosomatic index (GSI), gonadal development, and fecundity using individuals collected in fall and spring from 2018 to 2021. Our analysis revealed female GSI was greater in fall (8.1 ± 6.2 %) than spring (4.4 ± 4.3 %). Absolute fecundity averaged 763 ± 246 oocytes and relative fecundity averaged 19 ± 6 oocytes per gram of fish. Histological analysis revealed the presence of only one batch of developing oocytes in the ovary (n = 60), indicating group-synchronous ovarian organization. Our findings suggest deepwater sculpin spawn once annually but have a protracted spawning season indicated by prolonged elevated GSI values. Therefore, protracted spawning in deepwater sculpin likely results in an extended period of larval emergence rather than the majority occurring in late spring as previously suggested. A longer timeframe for deepwater sculpin larval emergence may increase reproductive success and contribute to their population's recovery. [ABSTRACT FROM AUTHOR]

Although diel vertical migration (DVM) in aquatic systems may account for the largest daily migration of biomass globally, our understanding of this process under ice cover is limited, particularly in fresh water. The date of lake ice onset and duration of ice cover is declining globally, therefore determining the extent of plankton migrations under ice is imperative to inform our baseline understanding of seasonal differences in community structure and function, and how conditions may change over time. We investigated whether plankton exhibit DVM under ice and explored interactions between phytoplankton and zooplankton at highly resolved space–time scales across 24 h in a eutrophic system. Despite the dominance of motile taxa, phytoplankton remained vertically segregated based on morpho-functional groups throughout the sampling period. Daphnia mendotae exhibited size-structured DVM with an upward migration at sunset and sunrise, and midnight sinking, presumably to avoid the rise of predatory Chaoborus. We hypothesize that because overwintering daphnids require rich lipid stores, D. mendotae migrated to access small, lipid-rich phytoplankton that were limited to surface waters. Given our study took place during an unusually warm winter in a eutrophic system, our results may represent future under-ice dynamics under increasing eutrophication pressure and climate warming in shallow lakes. [ABSTRACT FROM AUTHOR]

Morphometric data from fish are typically generated using one of two methods: direct measurements made on a specimen or extraction of distances from a digital picture. We compared data on 12 morphometrics collected with these two methods on the same collection of Cisco Coregonus artedi from Lake Ontario, North America, to assess the degree of bias in measurements made directly on a specimen- vs. an image-based method. We also assessed the degree of reproducibility within the image-based method by evaluating the amount of variation between different analysts for each morphometric method. Our results indicate specific morphometrics may be more prone to bias across the two methods and between analysts. Four of 12 morphometrics evaluated showed significant deviation from a 1:1 relationship that would be expected if the imaged-based method produced accurate specimen-based measurements. Pelvic fin length and pelvic–anal fin distance had the highest between-analyst variation for image-based landmarks, indicating low reproducibility for these metrics, compared with pectoral fin or total length, which had lower between-analyst variation. Although some morphometric measurements can be accurately obtained with either method, and therefore potentially used interchangeably in studies on Cisco morphology, our findings highlight the importance of considering method bias in morphometric studies that use data collected by different methods. [ABSTRACT FROM AUTHOR]

The article pays tribute to the late Norris Church Mailer, a novelist and widow of U.S. author Norman Mailer.