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    Ichthyology V

    2021-07-23   13:45 - 15:15

    Moderator: Adam Summers

    1.  13:45  VIRTUAL    Tagging Reveals Stock Specific Behaviours and Habitat Partitioning of Atlantic Bluefin Tuna Thunnus thynnus. Simon Dedman*, Stanford University; Emil Aalto, Stanford University; Mike Stokesbury, Acadia University; Robbie Schallert, Stanford University; Mike Castleton, Stanford University; Barbara Block, Stanford University

    We use twenty years of tag data to compare movement and diving behaviours of Atlantic bluefin tuna (ABT) during their annual cycles of movement around the NW Atlantic. Stock-of-origin was assigned by spawning ground visitation. Both the Gulf of Mexico (GOM) and Mediterranean (Med) stocks use central area of the US eastern seaboard similarly in fall and winter, but diverge in summer. GOM fish expand their latitudinal range as they age, shifting to a ‘high effort, high reward’ strategy, spawning in the GOM then moving rapidly a long distance to the productive grounds of the Gulf of St Lawrence (GSL). In contrast, Med fish occupy a smaller latitudinal range along the NW Atlantic coast. Med fish arrive from their temperate spawning grounds into the NW Atlantic as juveniles and visit the rich foraging grounds of North Carolina, New England, and Canada. GOM fish display less expansive offshore migrations given that their spawning and feeding grounds are on the same coast. Within the GSL, GOM fish mostly conduct shallow dives within warmer inshore waters, while Med fish dive deeper, in colder offshore water. Using tracks of the assigned-stock fish (118 fish), we use a probabilistic analysis of depth and movement behaviours to assign many of the unknown-stock fish to a stock (190 of 290 fish). By comparing dive behaviours and thermal use of habitats, we can better understand habitat partitioning by the two ABT stocks, and use more of the unassigned portion of our dataset for research and management purposes.

    2.  14:00  IN-PERSON    Zebrafish Pose Estimation, Tracking, and Behavioral Classification: Illuminating the Role of the Lateral Line in Rheotaxis. Kyle Newton*, Washington University School of Medicine; Dovi Kacev, Scripps Instituion of Oceanography; Simon Nilsson, University of Washington; Lavinia Sheets, Washington University School of Medicine

    Sensory hair cells of the lateral line transduce and transmit water flow stimuli and mediate rheotaxis in fishes, or the ability to orient with respect to flowing water. The zebrafish lateral line is an established model for understanding the cellular mechanisms of hair cell organ damage and repair; however, few studies link mechanistic disruptions to observable changes in biologically relevant behavior. Therefore, we used larval zebrafish to model how ototoxic drugs damage hair-cell organs and determine how this damage impacts rheotaxis. Fish were exposed to neomycin or CuSO4 then allowed to recover for two hours. Then we exposed drug treated and control fish to water flow stimuli of constant velocity and recorded their swimming behavior with a high-speed camera. DeepLabCut software was used to estimate and track the body pose and orientation angles of fish then SimBA behavioral analysis software was used to annotate and classify rheotaxis behavior. Fish exposed to drugs performed rheotaxis in flowing water, but their rheotactic responses were significantly different in number, latency, duration, interval between events, spatial use, total distance traveled, and mean relative velocity and acceleration compared to controls. We posit that the lateral line fine tunes rheotaxis dependent behaviors, such as foraging, schooling, and predator evasion, where the accurate detection and response to water flow is critical for individual fitness. Future studies integrating this behavioral assay with molecular and physiological studies on the same individual larvae will directly link sensory hair cell organ damage to differences in the natural behaviors of live fish.

    3.  14:15  VIRTUAL    Northern Redbelly Dace Recovery Project. Mikki McComb-Kobza*, Ocean First Institute; Robert Kobza, Boulder County Parks & Open Space; Boyd Wright, Colorado Parks & Wildlife

    In 2013, a 100-year flood occurred in Boulder County, Colorado that severely altered the regional watersheds. The recovery and restoration efforts that followed provided an opportunity to restore Webster Pond, a county-owned fishing pond, into a native fish nursery site. Boulder County Parks & Open Space, Colorado Parks & Wildlife, Ocean First Institute and the St. Vrain Valley School District began collaborating in 2019 to create the restoration framework for a state endangered species, the northern redbelly dace (Chrosomus eos). The high school students were able to aquaculture and release several thousand dace into a private pond as a pilot study in 2020, with plans to release into Webster Pond in 2021. Students have subsequently conducted monitoring to document the effectiveness of the recovery effort. Several methods are being used to determine the success of the introduction including environmental DNA, camera and minnow traps, and PIT tagging. We will be assessing these methods in order to select the most efficient and least invasive techniques for continued monitoring. Reintroduction of endangered native freshwater fish is an increasingly important conservation goal amidst persistent anthropogenic pressures and new threats related to climate change.

    4.  14:30  IN-PERSON    Poachers as models for understanding armor in fishes. Adam Summers*, Friday Harbor Labs; Matt Kolmann, University of Michigan

    Poachers (Agonidae) are a heavily armored clade nested in the sculpins. The mineral invested in armor ranges from 3-10 times the mineral in the axial skeleton. With eight rows of overlapping scales, the group presents a useful opportunity for probing the function of armor that is variable but shares an underlying structure and clear homologies. Viewed as a network of connected plates the armor is usually six-connected, but there are variations with less connectivity, and a set of lateral line plates with more connectivity. Ornamentation ranged from very large hooked excrescences in Hypsagonus to flat plates in Anoplagonus. The role fo the armor is not purely defensive. In some species it is used in male-male combat, and bears the sharp breakage patterns of impact damage. We propose that the prominent hook in some species acts as protection from thin penetrators as well as mediating combat. We will present 3D models of the armor plates, showing their complex internal structure, as well as the armoring of the head. We have imaged 40 species of poachers using uCT and have made these models available open access.

    5.  14:45  IN-PERSON    Does Dis-integration of Brain Modules Facilitate Functional Specialization in Gymnotiform Electric Fishes? Shannon Kuznar*, University of Louisiana; James Albert, University of Louisiana

    The degree of integration among phenotypic modules has recently been shown to affect rates and directions in the evolution of skull morphology of several vertebrate clades. Although the skull and brain are developmentally coupled, studies on the degree of integration among brain modules are a still in their infancy. Here we examine patterns of brain evolution using landmark-based 3-D geometric morphometrics of contrast-stained computer tomography (CT) scans in 87 brains representing 24 gymnotiform species and 17 genera, among brain regions defined by functional, structural, and developmental criteria. We then use multivariate statistical and phylogenetic comparative methods to test alternative hypotheses in the literature of teleost brain evolution. We expect to find similar patterns of evolution in the morphology of the gymnotiform brain and braincase region of the neurocranium, greater integration of brain regions in dolichocephalic than brachycephalic taxa associated with generalized habitat and trophic utilization, and less integration (i.e. sub-functional partitioning) of brain regions associated with habitat and trophic specialization.

    6.  15:00  IN-PERSON    Population structure of the gafftopsail catfish (Bagre marinus) in the U.S. Atlantic and Gulf of Mexico. DAVID PORTNOY*, Texas A&M University - Corpus Christi; Shannon O'Leary, St, Anselm College; Erin Pulster, University of South Florida; Steve Murawski, University of South Florida; Douglas Adams, Florida Fish and Wildlife Conservation Commission; R. Dean Grubbs, Florida State University

    Gafftopsail catfish, Bagre marinus, are an ecologically important coastal predator, found seasonally in great abundance in nearshore habitats of the U.S. Atlantic and Gulf of Mexico. The species engages in a reproductive strategy in which males carrying broods of eggs, and subsequently fry, and occupy bays and estuaries in the spring and summer months. This means that dispersal is limited to juvenile and adult phases, suggesting a greater potential for population structuring than seen in marine species with dispersive larval phases. Further, if individuals show site fidelity across estuarine systems that are environmentally heterogenous, there may be localized adaptation. Here SNP-containing loci were used to assess partitioning of genetic variation in gafftopsail catfish sampled in eight localities through the Gulf of Mexico and on the Atlantic Coast of Florida. Analyses based on neutral loci indicated that the Atlantic, northern Gulf and southern Gulf (Campeche Mexico) represent clear genetic units, and that the northern Gulf can be further subdivided into an eastern genetic unit (Florida) and a central/western genetic Unit. Analyses with outlier loci, potentially associated with selection, recovered the same groupings but the relationships among groups changed and some comparison within regions were significant. Results of redundancy analysis indicated the environmental variables, as well spatial proximity were important for explaining components of genomic variation in the northern Gulf of Mexico. Results will be compared to recent population genomic studies of other estuarine-obligate fishes in the northern Gulf of Mexico.

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