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Animals play an important and sometimes overlooked role in nutrient cycling. The role of animals in nutrient cycling is spatially and temporally variable, but few studies have evaluated the long-term importance of animal-mediated nutrient cycling in meeting nutrient demand by primary producers. We quantified the proportion of phytoplankton nutrient (phosphorus, P) demand met by excretion by gizzard shad (Dorosoma cepedianum) in a eutrophic reservoir where this species dominates fish biomass. From 2000 to 2014, gizzard shad excretion supported a variable proportion of phytoplankton P demand, averaging 7–27% among years over the growing season (spring and summer). Temporal patterns emerged, as gizzard shad consistently supported a higher proportion of demand during summer (mean 31%) than spring (8%). In spring, the proportion of demand met from gizzard shad excretion was best predicted by gizzard shad population biomass, stream discharge, and temperature. In summer, this proportion was best predicted only by biomass of the young-of-year (YOY) gizzard shad. Thus, variation in YOY shad biomass significantly alters nutrient supply, and future studies should explore the long-term role of animal population dynamics in nutrient cycling. Our study shows that several years of data are needed to perform a critical evaluation of the importance of animals in meeting ecosystem nutrient demand.

Microplastics (MPs) and heavy metals are significant pollutants affecting aquatic ecosystems in Bangladesh, with potential ecological and human health implications. This study investigates the occurrence and characteristics of MPs and heavy metal contamination in Tenualosa ilisha (riverine shad) from the Meghna River Estuary in the northern Bay of Bengal. MPs abundance varied from 17 to 38 particles/fish sample with a mean of 10 items/fish sample. MPs show variations in shape, size, and color. The occurrence of 189 MPs from the visually identified 210 microplastic-like particles were confirmed by µ-Fourier Transformed Infrared Spectroscope (µ-FTIR). In addition, 12 heavy metals, including arsenic (As), lead (Pb), cadmium (Cd), and iron (Fe), were quantified in different body parts (head, flesh, and bones). The concentration was found as As ˃ Fe ˃ Mn ˃ Cu ˃ Ni ˃ Pb ˃ Mg ˃ Se ˃ Co ˃ Zn ˃ Cd ˃ Hg in all parts (head, flesh and bones) of the fish samples. Significant differences in MPs and metal concentrations were observed based on fish size and body part. PCA analysis revealed distinct patterns of metal accumulation across different body parts and fish sizes, with larger fish showing higher levels of Pb and Cu, indicating prolonged exposure. Hierarchical clustering further highlighted similarities in metal distribution, grouping metals such as Pb and Cd due to common sources or pathways of accumulation. The results emphasize the potential health risks associated with consuming larger Hilsa fish due to the occurrence of elevated levels of heavy metal and MPs. To tackle this, the need for regular monitoring of both MPs and heavy metals in anadromous fish species in Bangladesh's aquatic environments is quite apparent.

We examined trends in abundance of four pelagic fish species (delta smelt, longfin smelt, striped bass, and threadfin shad) in the upper San Francisco Estuary, California, USA, over 40 years using Bayesian change point models. Change point models identify times of abrupt or unusual changes in absolute abundance (step changes) or in rates of change in abundance (trend changes). We coupled Bayesian model selection with linear regression splines to identify biotic or abiotic covariates with the strongest associations with abundances of each species. We then refitted change point models conditional on the selected covariates to explore whether those covariates could explain statistical trends or change points in species abundances. We also fitted a multispecies change point model that identified change points common to all species. All models included hierarchical structures to model data uncertainties, including observation errors and missing covariate values. There were step declines in abundances of all four species in the early 2000s, with a likely common decline in 2002. Abiotic variables, including water clarity, position of the 2‰ isohaline (X2), and the volume of freshwater exported from the estuary, explained some variation in species' abundances over the time series, but no selected covariates could explain statistically the post-2000 change points for any species.

Focusing on metadiscourse markers during EFL writing classes has garnered research attention, yet few studies were conducted on online expository writing. This study explores the effect of metadiscourse markers instruction on expository writing of 80 male and female EFL learners in the school context, selected through convenience sampling and an interview followed with a smaller number of participants. Initially, the eighty participants were assigned to experimental (n=40) and control (n=40) groups after checking homogeneity in terms of English proficiency level. The participants in the experimental group received explicit instruction of markers, whereas the control group received the conventional curriculum-based writing instruction that included similar material/topics, except for the explicit focus on metadiscourse markers, all through a uniform digital platform mandated in the state-run schools. The frequency/use of metadiscourse markers in the writing assignments of the participants per session and the total was noted, and then a corpus of 80 collected essays was analyzed by a trained rater and researcher to both analyze whether metadiscourse markers instruction had any significant effect on expository writings and to determine which metadiscourse markers showed up in the texts written by students more. Finally, a semi-structured interview was conducted with eight EFL instructors to explore their attitudes. Statistical test of Analysis of Covariance showed a significant effect of metadiscourse markers instruction on EFL learners’ expository writing. Another finding was that participants employed interactional metadiscourse markers frequently. Implications for policy-makers, students, and teachers indicate that free access to online writing resources improves learning perceptions/outcomes.

Four species of pelagic fish of particular management concern in the upper San Francisco Estuary, California, USA, have declined precipitously since ca. 2002: delta smelt ( Hypomesus transpacificus ), longfin smelt ( Spirinchus thaleichthys ), striped bass ( Morone saxatilis ), and threadfin shad ( Dorosoma petenense ). The estuary has been monitored since the late 1960s with extensive collection of data on the fishes, their pelagic prey, phytoplankton biomass, invasive species, and physical factors. We used multivariate autoregressive (MAR) modeling to discern the main factors responsible for the declines. An expert-elicited model was built to describe the system. Fifty-four relationships were built into the model, only one of which was of uncertain direction a priori. Twenty-eight of the proposed relationships were strongly supported by or consistent with the data, while 26 were close to zero (not supported by the data but not contrary to expectations). The position of the 2‰ isohaline (a measure of the physical response of the estuary to freshwater flow) and increased water clarity over the period of analyses were two factors affecting multiple declining taxa (including fishes and the fishes' main zooplankton prey). Our results were relatively robust with respect to the form of stock-recruitment model used and to inclusion of subsidiary covariates but may be enhanced by using detailed state-space models that describe more fully the life-history dynamics of the declining species.

This study aimed to evaluate the growth, mortality parameters, and exploitation rate of Pontic shad, Alosa immaculata Benett, 1835, in the Danube River, Romania (km 169–197). The sampling collection started with the first signs of Pontic shad migration, on 4 March 2023, and continued weekly until the beginning of June 2023, when the last specimens were caught in the nets. The estimation of the growth, mortality parameters, and exploitation rate was done in FiSAT (FAO-ICLARM Stock Assessment Tools). The von Bertalanffy growth equation was estimated at L[sub.∞] = 36.75 cm, the growth coefficient was k = 0.68 year[sup.−1] , and the theoretical initial age was t[sub.0] = −0.67 year[sup.−1] . The total mortality rate (Z) estimated was 2.76 year[sup.−1] , with a natural mortality rate (M) and fishing mortality rate (F) of 0.89 year[sup.−1] and 1.87 year[sup.−1] , respectively. The Z/k ratio was found to be 4.11 and the exploitation rate (E) was estimated at 0.68 year[sup.−1] , indicating the overexploitation of Alosa immaculata stocks. In conclusion, this study provides valuable insights into the population dynamics of Pontic shad in the Danube River, Romania. The assessments of the growth parameters, mortality rates, and exploitation rates highlight a level of overexploitation of Alosa immaculata stocks. These findings underscore the importance of applying effective fishery management strategies to ensure the sustainability and conservation of this valuable fish species in the Danube River ecosystem.

Objective The objectives of this study were to investigate potential shift in the phenology of spawning for the Hudson River American Shad Alosa sapidissima and to identify factors contributing to the decline of the Hudson River shad population. Methods This study utilized American Shad eggs collected from the Long River Ichthyoplankton Survey. Logistic models were employed to estimate spawning phenology metrics, including the onset, peak, cessation, and duration of the spawning season. Additionally, we investigated the effects of biotic and abiotic variables on spawning timing. Result This study suggests that temporal changes in the spawning onset exhibited high variation and were not significant. However, a significantly delayed spawning peak and cessation, along with an extended spawning season, were observed. Additionally, the findings of this study revealed a correlation between the timing of spawning onset and water temperature, indicating that a 1°C increase in water temperature was associated with a 3.66‐day earlier initiation of spawning. Smaller female spawner size was associated with delayed peak and cessation of the spawning season. With a 1‐cm decrease in the average female spawner size, the peak of the spawning season was delayed by 1.79 days and the cessation of the spawning season was delayed by 2.87 days. Conclusion The findings indicate that water temperature may be a crucial trigger for initiating spawning in Hudson River American Shad, with higher water temperatures associated with earlier spawning onset. Moreover, the findings indicate that the timing of spawning peaks and cessations has been progressively delayed over time, and this is linked to the size of female spawners. Impact statement Given the global decline and potential extinction risks faced by diadromous fish populations, including American Shad, our study enhances understanding of the complex relationship between shad spawning timing and environmental variability, revealing that water temperature and spawner size are linked to the timing of the spawning season. The comprehensive insights from our research provide valuable contributions to management and conservation strategies for diadromous fish populations.

We examined the status of diadromous (migratory between saltwater and freshwater) fishes within the North Atlantic basin, a region of pronounced declines in fisheries for many obligate marine species. Data on these 24 diadromous (22 anadromous, 2 catadromous) species are sparse, except for a few high-value forms. For 35 time series, relative abundances had dropped to less than 98% of historic levels in 13, and to less than 90% in an additional 11. Most reached their lowest levels near the end of the observation period. Many populations persist at sharply reduced levels, but all species had suffered population extirpations, and many species are now classified as threatened or endangered. Habitat loss (especially damming), overfishing, pollution, and, increasingly, climate change, nonnative species, and aquaculture contributed to declines in this group. For those diadromous fishes for which data exist, we show that populations have declined dramatically from original baselines. We also discuss the consequences of these changes in terms of lost ecosystem services.

Gut microbiota of invasive Asian silver carp (SVCP) and indigenous planktivorous gizzard shad (GZSD) in Mississippi river basin were compared using 16S rRNA gene pyrosequencing. Analysis of more than 440 000 quality-filtered sequences obtained from the foregut and hindgut of GZSD and SVCP revealed high microbial diversity in these samples. GZSD hindgut (GZSD_H) samples ( n =23) with >7000 operational taxonomy units (OTUs) exhibited the highest alpha-diversity indices followed by SVCP foregut ( n =15), GZSD foregut ( n =9) and SVCP hindgut (SVCP_H) ( n =24). UniFrac distance-based non-metric multidimensional scaling (NMDS) analysis showed that the microbiota of GZSD_H and SVCP_H were clearly separated into two clusters: samples in the GZSD cluster were observed to vary by sampling location and samples in the SVCP cluster by sampling date. NMDS further revealed distinct microbial community between foregut to hindgut for individual GZSD and SVCP. Cyanobacteria, Proteobacteria , Actinobacteria and Bacteroidetes were detected as the predominant phyla regardless of fish or gut type. The high abundance of Cyanobacteria observed was possibly supported by their role as the fish’s major food source. Furthermore, unique and shared OTUs and OTUs in each gut type were identified, three OTUs from the order Bacteroidales , the genus Bacillariophyta and the genus Clostridium were found significantly more abundant in GZSD_H (14.9–22.8%) than in SVCP_H (0.13–4.1%) samples. These differences were presumably caused by the differences in the type of food sources including bacteria ingested, the gut morphology and digestion, and the physiological behavior between GZSD and SVCP.

The nutritional needs of anadromous fish species must be met for successful annual spawning migration and reproduction. Despite its widespread distribution throughout Europe, little is known about the composition of the twaite shad, Alosa fallax , diet in freshwater ecosystems. To redress this, we studied the composition of stomach contents extracted from 287 A. fallax sampled during their spawning migration from the Baltic Sea to the Curonian Lagoon (Lithuania). We found that the diet comprised 32 types of prey, with Insecta (unknown Order), Chironomidae and Daphniidae being the most prevalent taxonomic categories consumed. Our analyses revealed significant differences in the abundance of prey categories (Chironomidae, Insecta—unknown order, and Mysidae) among several size groups of A. fallax , associated with stage of maturity inferred from body length. Despite this being a spawning aggregation, juveniles were also present among the A. fallax we collected. The results imply that feeding behavior and morphometry may be responsible for the differences observed, and further investigation of this topic is warranted.