American Shad Research Articles

Restoring Genetic Resource through In Vitro Culturing Testicular Cells from the Cryo-Preserved Tissue of the American Shad (Alosa sapidissima).

Simple SummaryCryopreservation and in vitro culture of germ cells are key techniques for the genetic resource preservation of the declining population of American shad. Two types of cryopreserved samples, namely testis pieces and testicular cells of American shad, were comparatively analyzed for cell viability. The results showed that the cell viability of the cryopreserved testis pieces was much higher than that of the cryopreserved testicular cells. The viability of the cells from the cryopreserved testis pieces ranged from 65.2 ± 2.2 (%) to 93.8 ± 0.6 (%), whereas the viability of the dissociated cells after cryopreservation was 38.5 ± 0.8 (%) to 87.1 ± 2.6 (%). Moreover, the testicular cells isolated from the post-thaw testicular tissue could be cultured and propagated in vitro. Our findings would benefit further investigations on genetic resource preservation and other manipulations of germ cells in a commercially and ecologically important fish species.Germ cells, as opposed to somatic cells, can transmit heredity information between generations. Cryopreservation and in vitro culture of germ cells are key techniques for genetic resource preservation and cellular engineering breeding. In this study, two types of cryopreserved samples, namely testis pieces and testicular cells of American shad, were comparatively analyzed for cell viability. The results showed that the cell viability of the cryopreserved testis pieces was much higher than that of the cryopreserved testicular cells. The viability of cells from the cryopreserved testis pieces ranged from 65.2 ± 2.2 (%) to 93.8 ± 0.6 (%), whereas the viability of the dissociated cells after cryopreservation was 38.5 ± 0.8 (%) to 87.1 ± 2.6 (%). Intriguingly, the testicular cells from the post-thaw testicular tissue could be cultured in vitro. Likewise, most of the cultured cells exhibited germ cell properties and highly expressed Vasa and PCNA protein. This study is the first attempt to effectively preserve and culture the male germ cells through freezing tissues in the American shad. The findings of this study would benefit further investigations on genetic resource preservation and other manipulations of germ cells in a commercially and ecologically important fish species.

Effect of Reproductive Status on Some Biochemical Parameters in American Shad

The pattern of some blood biochemical parameters of adult American shad (Alosa sapidissima) was investigated during their reproductive cycle. A total of 288 sub adult broodstocks were captured between October 2015 and September 2016, in which ten brood stock for each developmental stage were selected based on similar length and weight to evaluate the overall health status of the fishes. The results showed that the serum levels of total protein (TP), albumin (Alb), globulin (Glb), glutamic-oxaloacetic transaminase (GOT), glutamic-pyruvic transaminase (ALT), low-density lipoprotein (LDL), high-density lipoprotein (HDL), plasma glucose (Glu), triglycerides (TG), total cholesterol (TC), Ca2+ and P of the American shad brood stock (females and males) significantly increased as their gonads developed, reaching the highest at stages IV and V, after which that the above mentioned parameters substantially decreased at stage VI. The TC and TG levels in females significantly increased from stage II to stage V, and then the levels began to decrease after spawning (stage VI), but there was no significant difference between TC and TG levels in male shad. With the development of the gonads, the plasma glucose (Glu), superoxide dismutase (SOD), catalase (CAT), and lysozyme (LZM) levels in both male and female brood stocks showed different degrees of decline, especially, in stages V (spawning period) and VI (postnatal period), these parameters significantly decreased. The results of this study indicate that the physiological parameters, such as blood glucose level, blood lipid level and antioxidant capacity, of American shad brood stocks, especially females, show varying degrees of reduction during reproduction, which suggests that nutritional imbalance significantly reduces immunity during the postnatal period.

Long‐term exposure to enrofloxacin increases body weight and alters the metabolism of American shad ( Alosa sapidissima ) in indoor aquaculture

Enrofloxacin (ENR) is widely used in animal husbandry, medical treatment and aquaculture, resulting in its discharge into various water environments. Although the toxicity effects of ENR on aquatic animal metabolism have been studied, there is still little information on the long-term toxic hazard on the metabolism of cultured American shad. In this study, American shad juveniles were exposed to 0.1 mg/kg ENR for 10 months. The results showed that ENR could induce body weight gain in American shad. Alterations in metabolic pathways were found in pyrimidine metabolism, arginine and proline metabolism, the calcium signalling pathway and the arachidonic acid metabolism pathway. However, the alteration of neuroactive ligand–receptor interaction pathways was speculated to be related to weight gain through the regulation of the nervous system. The metabolomic and transcriptomic analysis suggested a similar pattern of pathway alterations. The multiomic data revealed that the specific metabolism alteration resulting from ENR exposure was associated with nutrition quality and predation ability in fish. Furthermore, previous works showed that ENR residues in fish tissue and the water environment would ultimately threaten human health and safety through food consumption. In sum, this study, for the first time, reveals that ENR exposure increases body weight in American shad and induces metabolic alteration. The ecotoxicity of antibiotic occurrences in indoor aquaculture systems should be further evaluated.

A phylogeny based on cytochrome-c oxidase gene sequences identifies sympatric Ichthyophonus genotypes in the NE Pacific Ocean.

In recent decades, evidence has accumulated to suggest that the widespread and highly variable parasite Ichthyophonus hoferi is actually a species complex. Highly plastic morphology and a general lack of defining structures has contributed to the likely underestimate of biodiversity within this group. Molecular methods are a logical next step in the description of these parasites, but markers used to date have been too conserved to resolve species boundaries. Here we use mitochondrial encoded cytochrome-c oxidase (MTCO1) gene sequences and phylogenic analysis to compare Ichthyophonus spp. isolates from several marine and anadromous fish hosts. The resulting phylogeny displays lineage separation among isolates and possible host/niche segregation not previously described. The parasite type that infects Pacific herring Clupea pallasii, Atlantic herring C. harengus, Atlantic salmon Salmo salar, and Pacific staghorn sculpin Oligocottus maculosus (Clade A) is different from that which infects Chinook salmon Oncorhynchus tshawytscha, walleye pollock Gadus chalcogrammus, Greenland halibut Reinhardtius hippoglossoides, and Pacific halibut Hippoglossus stenolepsis (Clade B). MTCO1 sequences confirmed the presence of a more divergent Ichthyophonus sp. isolated from American shad Alosa sapidissima in rivers of eastern North America (Clade C), while American shad introduced to the Pacific Ocean are infected with the same parasite that infects Pacific herring (Clade A). Currently there are no consensus criteria for delimiting species within Ichthyophonidae, but MTCO1 sequences hold promise as a potential species identifying marker and useful epizootiological tool.

What Have We Lost? Modeling Dam Impacts on American Shad Populations Through Their Native Range

American shad (Alosa sapidissima) are native to the east coast of North America from the St. Johns River, Florida, to the St. Lawrence River region in Canada. Since the 1800s, dams have reduced access to spawning habitat. To assess the impact of dams, we estimated the historically accessed spawning habitat in coastal rivers (485,618 river segments with 21,113 current dams) based on (i) width, (ii) distance from seawater, and (iii) slope (to exclude natural barriers to migration) combined with local knowledge. Estimated habitat available prior to dam construction (2,752 km2) was 41% greater than current fully accessible habitat (1,639 km2). River-specific population models were developed using habitat estimates and latitudinally appropriate life history parameters (e.g., size at age, maturity, iteroparity). Estimated coast-wide annual production potential was 69.1 million spawners compared with a dammed scenario (41.8 million spawners). Even with optimistic fish passage performance assumed for all dams (even if passage is completely absent), the dam-imposed deficit was alleviated by fewer than 3 million spawners. We estimate that in rivers modeled without dams, 98,000 metric tons of marine sourced biomass and nutrients were annually delivered, 60% of which was retained through carcasses, gametes and metabolic waste. Damming is estimated to have reduced this by more than one third. Based on our results, dams represent a significant and acute constraint to the population and, with other human impacts, reduce the fishery potential and ecological services attributed to the species.

Survival and spawning success of American shad (Alosa sapidissima) in varying temperatures and levels of glochidia infection.

Temperature fluctuations and climate change impacts may substantially affect spawning success of fish, especially migratory species with a limited spawning window. Factors affecting American shad (Alosa sapidissima) spawning success and survival were investigated at different temperatures and periods (peak- and late-spawning periods) during the Connecticut River, USA, spawning migration in 2017. Wild caught American shad were exposed to constant temperatures regimes of 15, 18, 21, 24 and 27°C for 2weeks. During the peak-spawning period, an increase in temperature (15-24°C) was shown to increase spawning success factors, including spawning probability, number of eggs, and fertilization success, but decreased egg size. Temperatures between 18 and 27°C did not affect these factors during the late-spawning period. Glochidia infection by the alewife floater (Anodonta implicata) was much higher in the late-spawning period and significantly decreased the survival of American shad. Further research should investigate the parasite-host relationship between the alewife floater and American shad to determine annual variability of glochidia infections and how they affect American shad from physiological and passage perspectives. Higher temperatures were shown to increase spawning success of American shad during the peak-spawning period, but temperature had no effect during the late-spawning period. However, any effect during the late-spawning period may have been masked by a high level of glochidia infection.

Enrofloxacin induces intestinal disorders of metabolome and microbiome in American shad ( Alosa sapidissima )

Enrofloxacin (ENR) has been often detected in the environment and organisms due to its widespread use in aquaculture, medical cosmetology and animal husbandry. Though the effects of ENR exposure on the gut microbiome of aquaculture fish have been reported, there is little information on the long-term impact on adult American shad. In this study, ENR (100 mg/kg) exposed to American shad for 30 days. Then, we monitored the alterations in the gut microbiome, the responses on metabolomic and the change in the body weight. ENR exposure affected the composition of the gut microbiota community and altered community diversity. The LC-MS analysis showed the changes in several metabolic pathways, including lipid metabolism, the cellular process pathways, immune system and amino acid metabolism pathway. These metabolic pathways were related to increasing body weight gain through fat accumulation. In conclusion, this study provides evidence that ENR exposure can increase the body weight in American shad and yield new information on the effects of ENR exposure on the aquatic system.

Metabolic and transcriptional disruption of American shad (Alosa sapidissima) by enrofloxacin in commercial aquaculture

Antibiotics, including enrofloxacin (ENR), are widely used for bacterial disease treatment in aquaculture in China, resulting in their discharge into various aquatic environments. Therefore, researchers have focused their attention on the harmful effects of antibiotics on aquatic animal metabolism. To understand the impacts of ENR on the metabolism of cultured American shad, the guts of these fish were sampled to test the toxicity of ENR through the combined results of metabolomics and transcriptomics analyses. In this study, adult American shad were exposed to ENR (200 mg/kg) for 30 days. The results showed that ENR could significantly (p< 0.05) increase the body weight of American shad. ENR exposure also contributed to the dysregulation of intestinal metabolism (approximately 49 metabolites and 963 genes). Multiomics analyses of the responses indicated that the specific metabolic dysregulation caused by ENR affects many signaling pathways, such as the glycolysis/gluconeogenesis and pentose phosphate pathways, which are known to be linked with body weight gain through protein and lipid accumulation. In conclusion, ENR treatment affected the metabolic system in the gut of American shad. The transcriptomics and metabolomics analysis results provide essential data for evaluating antibiotic hazards in the guts of aquatic organisms.

Contrasting fishing effort reduction and habitat connectivity as management strategies to promote alewife (Alosa pseudoharengus) recovery using an ecosystem model

AbstractSmall pelagics, or forage fish, link lower and higher trophic levels in marine food webs. Recently, attention has been given to the management of forage fish, including anadromous river herring (Alewife Alosa pseudoharengus, blueback herring A. aestivalis) and American shad (A. sapidissima) due to their current depleted status and historically important ecological and economic roles. Little is known about the impact of changes in their biomass on marine food webs and what management practices will promote their recovery. Estimated historical riverine productivity was utilized to evaluate potential ecosystem impacts of the increasing river to ocean connectivity to resemble 19th‐century conditions. The Ecopath with Ecosim modeling framework was used to simulate management strategies, focused on anadromous forage fish, by creating scenarios of fisheries reduction (mixed fishery effort reduction) and river to ocean habitat connectivity (75% of historical connectivity achieved). Sixty‐year simulations covered the entire time series including a 36‐year forecast period to evaluate the ecosystem impacts of management strategies. Results suggest nonlinear relationships and large changes in biomass flows from forage fish to upper trophic levels in the Gulf of Maine ecosystem. Increases in biomass were observed for pelagic sharks, demersal piscivores, and species of conservation concern such as pinnipeds and seabirds, although overall results were strongly influenced by indirect trophic effects. Promoting anadromous forage fish recovery through increased connectivity resulted in the redundancy of marine ecosystem niches that would increase resilience to climate, fisheries, and other perturbations. This study highlights the value of employing ecosystem models for testing management scenarios to contrast different approaches to recover anadromous forage fish towards its former ecological prominence.

Effect of backwatering a streamgage weir on the passage performance of adult American Shad (Alosa sapidissima)

Streamgage designs often include a full-width artificial hydraulic control (e.g., concrete weir) to aid in the computation of streamflow. While important to water resource managers, these weirs also tend to act as full or partial barriers to fish migration, effectively hindering the health and survival of these populations. In this study, we conducted experiments to quantify the effect of head drop and submergence of a common streamgage weir on the passage performance of an important migratory fish species, the American Shad. Three treatment conditions were selected based on the tailwater surface elevation (ElTW ): unsubmerged (ElTW = 1.05 m; head drop = 0.46 m), equal to the weir crest (ElTW = 1.20 m; head drop = 0.31 m), and submerged (ElTW = 1.36 m; head drop = 0.15 m). Fish movements were recorded via passive integrated transponder telemetry techniques. Results revealed that the backwatered Columbus-type weir was not a complete barrier at any of the three treatments, but passage was shown to be significantly impaired when the weir was unsubmerged. Passage efficiency for the unsubmerged, equal, and submerged treatments was 20.2 ± 6.2, 49.2 ± 7.2, and 64.2 ± 7.4%. Backwatering a weir, rather than removal or other major alterations that would affect weir calibration, may be an acceptable retrofit to increase fish passage.

Environmental and anthropogenic influences on spatiotemporal dynamics ofAlosain Chesapeake Bay tributaries

AbstractAmerican Shad (Alosa sapidissima), Hickory Shad (A. mediocris), and river herrings (AlewifeA. pseudoharengusand Blueback HerringA. aestivalis) are anadromous pelagic fishes, which as adults spend most of the annual cycle at sea, but enter the coastal rivers in spring to spawn. Once as one of the most valuable fisheries along the Atlantic coast,Alosapopulations have declined in recent decades and current populations are at historic lows. Various management actions have been conducted to restore the populations, and stocks in different river systems display different demographic trends. Demonstration of synthetic diagnostics on the factors impacting these populations is important to better conserve this species group. We developed a Bayesian hierarchical spatiotemporal model to identify the population trends of these species among rivers in the Chesapeake Bay based on results of surveys conducted by the Virginia Department of Game and Inland Fisheries and Maryland Department of Natural Resources and to identify environmental and anthropogenic factors influencing their distribution and abundance. The hierarchical model structure helped to diagnose river‐specific population trends and impacts of surrounding factors, and decrease uncertainties in rivers with less samples available. The results demonstrate river‐specific heterogeneity of spatiotemporal dynamics of these species and indicate river‐specific impacts of multiple factors, including water temperature, river flow, chlorophyllaconcentration, and total phosphorus concentration, on their population dynamics. Atlantic Multidecadal Oscillation and Gulf Stream meanders displayed significant influence on the inter‐annual trends ofAlosaspecies in rivers with more data available. The results would help to develop river‐ and species‐specific management strategies to recover these species.

Risks from mercury in anadromous fish collected from Penobscot River, Maine

Levels of total mercury were measured in tissue of six species of migratory fish (alewife, American shad, blueback herring, rainbow smelt, striped bass, and sea lamprey), and in roe of American shad for two consecutive years collected from the Penobscot River or its estuary. The resultant mercury levels were compared to reference doses as established in the U.S. Environmental Protection Agency (EPA) Integrated Risk Information System and wildlife values. Mercury concentrations ranged from 4 μg/kg ww in roe to 1040 μg/kg ww in sea lamprey. Sea lamprey contained the highest amounts of mercury for both seasons of sampling. Current health advisories are set at sufficient levels to protect fishers from harmful consumption of the fish for mercury alone, except for sea lamprey. Based upon published wildlife values for mink, otter, and eagle, consumption of rainbow smelt, striped bass, or sea lamprey poses a risk to mink; striped bass and sea lamprey to otter; and sea lamprey to eagle. For future consideration, the resultant data may serve as a reference point for both human health and wildlife risk assessments for the consumption of anadromous fish. U.S. EPA works with federally recognized Tribes across the nation greatly impacted by restrictions on sustenance fishing, to develop culturally sensitive risk assessments.

Using Partnerships and Community Science to Protect Wild and Scenic Rivers in the Eastern United States

The Musconetcong (New Jersey) and the Sudbury-Assabet-Concord (Massachusetts) are federally-designated Partnership Wild and Scenic Rivers, a model for river conservation under the Wild and Scenic Rivers Act. These two rivers are embedded in a patchwork of private and public land ownership. The Act has been used to facilitate partnerships among municipal, state, federal and local non-profit actors to implement river conservation plans. These partnerships have supported community science-based monitoring to make the case for dam removal and stricter water pollution controls. Two case studies examine using community science to provide actionable data to decision-makers. In New Jersey, a documented increase in macroinvertebrates post-dam removal supported additional dam removals, leading to the return of American shad to the river. Quality controls and training proved to be key components. In Massachusetts, stricter effluent discharge permits reduced instream Total Phosphorus from 0.8 mg/L in 1999 to the eutrophication threshold of 0.023–0.05 mg/L. Community engagement in river science and stewardship was an important co-benefit. As many US rivers evolve from generating hydropower and conveying waste into major recreational resources, local organizations are uniquely positioned to engage the public and generate quality-controlled data to use in advocating for major improvements in water and habitat quality. Useful policy and regulatory frameworks for broader applicability are suggested.

Commentary on a Successful Spawning of American Shad in a Novel Recirculating Aquaculture System

American shad is one of the most vulnerable and sensitive fish species to disturbance. Any handling may cause serious lesion or death, and suspend gonad maturation and ovulation, eventually leading to difficulties in its culture and reproduction. How to avoid disturbance and reduce stress would be very important measures to be successful in inducing spawning for this species. Recently, we reported a successful integration of maturation and natural reproduction of American shad for the first time in a novel Recirculating Aquaculture System (RAS) without any handling for hormone administration.

Brood-stock management and natural spawning of American shad (Alosa sapidissima) in a recirculating aquaculture system

American shad (Alosa sapidissima) is one of the most vulnerable and overreacting fish to disturbance. Any handling may cause serious lesion or death, and suspend gonad maturation and ovulation, eventually resulting in failure in hormone induced reproduction. In this study, we first reported a specially designed dual-drain recirculating aquaculture system (RAS), which leads to a successful integration of maturation and natural reproduction of anadromous American shad without any handling for hormone administration. The results illustrate the relationships among the change of seasonal temperature, gonadal maturation and spawning behavior of American shad in the freshwater environment. A total of 300 one-year-old fish were selected as brookstock (495.8 g for females and 441.1 g for males) with a sex ratio of 1:1. Fish grew, matured and naturally spawned in each of the RAS tank under two temperature manipulation regimes. The gonadosomatic indices increased significantly in two months before the start of spawning from 1.46% in females and 0.82% in males in January, to 5.19% in females and 2.73% in males in March. Fish at different temperature regimes started mating in early February and spawning in late March when the water temperature reached 19.3 °C. On average, females produced 65,930 eggs per kg body weight during the 2-month spawning period, resulting in 77.5% fertilization rate and 41.0% hatching rate. This study reports the first successful case of natural spawning on American shad in a specially designed RAS through temperature manipulation.

Prey-Related Asphyxiation in Harbor Porpoises (Phocoena phocoena) along the U.S. West Coast: Importance of American Shad (Alosa sapidissima) on Adult Female Harbor Porpoise Mortality

Harbor porpoise (Phocoena phocoena) diets are predominantly comprised of small fish species (&lt;30 cm) and squid. However, predation on larger species (up to 63 cm) occurs, raising the question of increased risk of asphyxiation associated with this behavior. Literature was reviewed and stranding data from 1983 to 2020 from the U.S. West Coast (including California, Oregon and Washington) were searched for cases of prey-related asphyxiation of harbor porpoises and analyzed in relation to age, sex, reproductive status and prey species. Twenty-nine cases were documented. Twenty-seven cases involved large prey; non-native American shad caused the asphyxiation in 87% of the cases where the prey species was identified. The majority (92%) of harbor porpoises were females, and at least 83.3% were pregnant or recently post-partum. Reproductively active females may be more likely to attempt potentially risky behavior in order to compensate for their increased energetic needs. Increasing numbers of non-native American shad may pose a unique danger in this region for harbor porpoises not adapted to deal with the challenges of that prey. This may be a cause for concern, as there is likely an interaction between location, age and reproductive status on the diet composition and foraging strategies of harbor porpoises.

Balancing fish-energy-cost tradeoffs through strategic basin-wide dam management

Dam management often involves tradeoffs among hydropower generation capacity, environmental impacts, and project costs. However, our understandings of such tradeoffs under a full range of dam management options remain limited, which hinders our ability to make sound and scientifically defensible dam management decisions. In order to assess the scope for theoretical tradeoffs, a dynamic model of hydropower production, important fish populations, and project costs was developed using the system dynamics modeling technique. Three dam management options investigated the likely outcomes from: dam removal, fishway installation (e.g., pool-and-weir, Denil, and fish lift), and no action. The model was applied to the Penobscot River located in Maine, United States as a proof of concept, where recent actions (i.e., dam removal and fishway construction) have been undertaken. We modeled theoretical influence of these actions on four significant sea-run fish (alewife Alosa pseudoharengus, American shad Alosa sapidissima, Atlantic salmon Salmo salar, and sea lamprey Petromyzon marinus) by developing an index of spawner population potential based on population models for each species. Optimal dam management solutions may maximize spawner population potential and energy production to 60-62% of maximum achievable values while limiting the project cost to US$17 million (44% of the maximum value). Our results demonstrate that basin-scale management strategies may increase the migratory fish restoration while preserving hydropower generation capacity. Diversification of management options (e.g., combination of fishway installations, dam removals, and generation capacity) may increase the efficacy of strategic fish-energy-cost tradeoffs.

Examining Retention-at-Length of Pelagic Fishes Caught in the Fall Midwater Trawl Survey

The Fall Midwater Trawl Survey has provided data on aquatic organisms in the San Francisco Estuary for over five decades. In 2014–2015, a study was conducted to investigate and quantify the efficiency of this trawl for catching the endangered fish species Delta Smelt (Hypomesus transpacificus). In an analysis based on that study, we calculated retention probability—the probability that a Delta Smelt is retained in the cod end of the trawl—as a function of fish length and fit a selectivity curve reflecting the relationship between size and retention. Here we return to the same gear efficiency study and further utilize the data set by (1) fitting selectivity curves for three additional pelagic fish species: Threadfin Shad (Dorosoma petenense), American Shad (Alosa sapidissima), and Mississippi Silverside (Menidia beryllina), (2) refitting the selectivity curve for Delta Smelt to incorporate between-haul variability, and (3) calculating the lengths of 50% and 95% retention in order to characterize and compare the resulting selectivity curves. We also present retention data on age-0 Striped Bass (Morone saxatilis), all of which were retained in the cod end. We found that Threadfin Shad, American Shad, and Delta Smelt are 95% retained at 45, 49, and 61 mm fork length, respectively. Because data were limited for Mississippi Silverside, American Shad, and age-0 Striped Bass, we used body shape, in conjunction with retention data, to develop hypotheses about selectivity based on whether each species’ body shape resembles that of Threadfin Shad, which are more deep-bodied and laterally compressed, or Delta Smelt, which are more fusiform. We also found that retention-at-length was more variable for Delta Smelt than for Threadfin Shad, potentially because length is a good predictor of retention in deep-bodied, laterally compressed fish whereas maximum girth is a better predictor of retention in fusiform fish.

Oropharyngeal morphology related to filtration mechanisms in suspension‐feeding American shad (Clupeidae)

To assess potential filtration mechanisms, scanning electron microscopy was used in a comprehensive quantification and analysis of the morphology and surface ultrastructure for all five branchial arches in the ram suspension-feeding fish, American shad (Alosa sapidissima, Clupeidae). The orientation of the branchial arches and the location of mucus cells on the gill rakers were more consistent with mechanisms of crossflow filtration and cross-step filtration rather than conventional dead-end sieving. The long, thin gill rakers could lead to a large area for the exit of water from the oropharyngeal cavity during suspension feeding (high fluid exit ratio). The substantial elongation of gill rakers along the dorsal-ventral axis formed d-type ribs with a groove aspect ratio of 0.5 and a Reynolds number of approximately 500, consistent with the potential operation of cross-step filtration. Mucus cell abundance differed significantly along the length of the raker and the height of the raker. The mucus cell abundance data and the observed sloughing of denticles along the gill raker margins closest to the interior of the oropharyngeal cavity suggest that gill raker growth may occur primarily at the raker tips, the denticle bases, and the internal raker margins along the length of the raker. These findings will be applied in ongoing experiments with 3D-printed physical models of fish oral cavities in flow tanks, and in future ecological studies on the diet and nutrition of suspension-feeding fishes.

Diversity, abundance and size structure of fishes and invertebrates captured by an intertidal fishing weir at Bramber, Minas Basin, Nova Scotia

Capturing fish using a weir or trap on the intertidal flats of the Bay of Fundy was developed by native Mi’kamaq who later taught the method to the European settlers. Between 1800-1910 fish weirs were a significant part of the important American shad fishery in the inner Bay of Fundy before the collapse of the northwest Atlantic population from pollution and damming of major spawning rivers in the United States. Weirs remain an important segment of the Minas Basin fisheries but now the largest commercial catches consist of Atlantic herring, gaspereau and flounders. Studies on the fishes captured in Minas Basin weirs were published in 1852, 1924, 1984 and 2014, but all lacked a sampling intensity which would fully describe the diversity, abundance and size structure of the catch. An intertidal weir at Bramber, Minas Basin was surveyed during April-July, 2017 where catches were examined at each low tide. The weir was constructed on the intertidal flat during early April after Minas Basin cleared of drift ice. During the study period mean daily tide range was 10.46 m with a maximum spring tide range of 13.72 m. A total of eight neap and eight spring tide cycles were observed. Daily water temperature of Minas Basin was 8.0 C° during late May and increased to a maximum of 21.4 C° in late July. Fish and invertebrate collections began on April 10 and continued daily until July 22 when water temperatures in the trap became too warm for by-catch species to survive (+25 C°). During the study period an estimated total of 674,402 fishes consisting of 45 species were captured and of these 57,950 were measured. The most abundant fishes observed were gaspereau (alewife and blueback herring 51.9%), rainbow smelt (13.9%), Atlantic herring (13.0%) and tomcod (10.1%). Other commonly captured fishes were American shad, skate (little and winter), winter flounder, windowpane flounder, striped bass, mackerel and Atlantic sturgeon. A total of 18,511 invertebrates were captured and counted. The most abundant were long-fin squid (13.8%) and crustaceans (rock crab, lady crab; 84.0%). Keywords: Bay of Fundy; Canada; Clupeidae; commercial fishing; temperatures; tides