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Withdrawal of fish eggs and larvae through a river intake (entrainment) may damage the river's early fish resources. To investigate how the hydraulics (flow velocities, directions, and magnitudes) around and within the water intake structure influence entrainment, this study focused on a typical river‐pump intake. A turbulence model was developed based on the Euler‐Lagrange method and the variable of helicity was introduced to define the zone of the river from which water is withdrawn and organisms are entrained. The process of simulated hydraulics on organism withdrawal was validated by physical experiments using artificial fish eggs under various river flow and intake flow conditions. The simulated results indicated that when the intake‐to‐river flow ratio ranged from 3 to 7‰, the width of the planar entrainment area was approximately 1.2 to 1.4 times the width of the intake structure, and the entrainment quantity of fish eggs and larvae accounted for 0.12% to 0.49% of the incoming flux. The entrainment quantity increased with the intake flow to the river flow ratio. The absolute helicity threshold under different conditions ranged from 0.004 to 0.047 m/s2, which was inversely proportional to the intake flow rate and unaffected by river flow and water depth. An optimized intake structure design with stepped side walls was promoted, which can minimize the impact of river sedimentation and reduce the fish entrainment quantity by an average of 11%. This research provides valuable insights for water intake safety and fish resource protection.

Drifting fish eggs are a type of fish egg with a slightly higher density than water, requiring floating for successful hatching. While it is acknowledged that interaction with the riverbed surface can cause mortality of the eggs, the impact of this process on their downstream transport remains unclear. In this paper, we theoretically explore the transport of drifting fish eggs in turbulent open channel flows, taking into account both gravitational settling and riverbed mortality effects. This is done by incorporating a vertical drift term in the governing advection‐diffusion equation and an absorbing boundary condition for the riverbed surface, respectively. For the first time, we derive an analytical solution by the method of separation of variables for the vertical distribution of eggs during transport. Our analysis shows that in principle, settling can lead to egg accumulation near the riverbed, reducing the population's mean velocity, while conversely, riverbed mortality can decrease near‐bed accumulation and accelerate drifting to some extent. However, by estimating values of the mortality rate parameter in the real rivers, we conclude that while it can significantly affect the population size, it has a negligible effect on the vertical concentration distribution in practice, allowing for a considerable simplification of the analytical solution. Furthermore, we deduce an analytical solution for the mean velocity of the egg population, indicating variations of the deceleration rate compared to mean flow velocity, which is capable of assisting in the identification of spawning grounds. The obtained analytical solutions are validated by various numerical and experimental results.

There is urgent need for effective and efficient monitoring of marine fish populations. Monitoring eggs and larval fish may be more informative than that traditional fish surveys since ichthyoplankton surveys reveal the reproductive activities of fish populations, which directly impact their population trajectories. Ichthyoplankton surveys have turned to molecular methods (DNA barcoding & metabarcoding) for identification of eggs and larval fish due to challenges of morphological identification. In this study, we examine the effectiveness of using metabarcoding methods on mock communities of known fish egg DNA. We constructed six mock communities with known ratios of species. In addition, we analyzed two samples from a large field collection of fish eggs and compared metabarcoding results with traditional DNA barcoding results. We examine the ability of our metabarcoding methods to detect species and relative proportion of species identified in each mock community. We found that our metabarcoding methods were able to detect species at very low input proportions; however, levels of successful detection depended on the markers used in amplification, suggesting that the use of multiple markers is desirable. Variability in our quantitative results may result from amplification bias as well as interspecific variation in mitochondrial DNA copy number. Our results demonstrate that there remain significant challenges to using metabarcoding for estimating proportional species composition; however, the results provide important insights into understanding how to interpret metabarcoding data. This study will aid in the continuing development of efficient molecular methods of biological monitoring for fisheries management. We examine the effectiveness of using metabarcoding methods on mock communities of known fish egg DNA using six mock communities with known ratios of species and two samples from a large field collection of fish eggs. We examine the ability of our metabarcoding methods to detect species and relative proportion of species identified in each mock community. We found that our metabarcoding methods were able to detect species at very low input proportions; however, levels of successful detection depend on the markers used in amplification suggesting that the use of multiple markers is desirable.

Identifying fish eggs and understanding fish reproductive periods are necessary for informed fishery management. However, accurate the identification of fish eggs is difficult because eggs have few distinct characters, and their morphology varies ontogenetically. Using cytochrome c oxidase subunit I, we identified fish eggs from ichthyoplankton samples collected in the summer and autumn of 2021 from southwestern Daya Bay, China. Of 567 fish eggs, 498 high-quality cytochrome c oxidase subunit I sequences were obtained, of which 116 eggs (23.3%) could be identified to species; 364 (73.1%) to genus, family and/or order; and 18 (3.6%) could not be assigned. Of 51 apparent taxa, 46 were identified to 6 orders, 19 families, and 30 genera; 20 to the species and 25 to the genus and/or family, and 1 to the order. Among these 51 taxa, 35 occurred in summer, 29 occurred in autumn, and 13 occurred in both seasons; 22 occurred only in summer and 16 only in autumn, indicating species-specific spawning periods. High-resolution photographs of eggs are provided to facilitate subsequent identification based on morphology. These results will facilitate the identification of spawning grounds and their protection, to more holistically manage fishery resources in Daya Bay, China.

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 2 weeks. 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.

Excessive flow turbulence poses a threat to the development of drifting fish eggs, leading to mortality or developmental malformations and ultimately depleting early fish resources. Currently, there is a scarcity of quantitative studies investigating the effects of flow turbulence on the entire process of drifting fish egg development, from fertilized egg division to hatching. In this paper, the effects of different flow turbulence conditions (FTCs), including turbulent kinetic energy and shear stress, and action times on different stages of fish egg development were quantitatively explored using a transverse-oscillating-grids turbulence tank. Empirical formulas were established to predict the proportion of normal fish egg development under different FTCs within a selected range. The research findings provide a quantitative basis for protecting early fish resources, mitigating the biological invasion of specific fish, constructing fish-breeding facilities, and ensuring safe transfer and transportation.

The distribution of fish eggs and larvae (ichthyoplankton) reflects spawning and nursery areas as well as dispersal routes. This study’s goal is to demonstrate how the identification of ichthyoplankton species and stages and their spatial distribution among natural reefs (NRs) and artificial reefs (ARs) may serve as decision-making tools in conservation and fishery management. Natural reefs exhibited an eight-times higher abundance of eggs, as well as the highest abundance of larvae in the yolk-sac and preflexion phases. In contrast, ARs had the highest abundance of larvae in the flexion and postflexion phases. Natural reefs may serve as breeding grounds for Scaridae, Labridae, and Mugilidae; whereas, ARs may serve as breeding sites for Lutjanidae, Synodontidae, Carangidae, Fistularidae, and Haemulidae. Our study revealed differences between ARs and NRs, which demonstrate the potential of artificial reefs to expand the supply and settlement options of reef fishes and consequently can lead to increased fish production with potential benefits to adjacent fishing areas through connectivity. Thus, ARs as no-take sites can be effective tools for both fishery management and biodiversity conservation. The findings highlight the potential use of ichthyoplankton tools and the importance of considering both types of reefs in marine conservation and management efforts.

Fish eggs have a wide range of predators. However, observing these predators is challenging, as is identifying fish eggs based on morphological traits. In this study, we observed hydroids, which are sessile organisms, consuming pelagic fish eggs. We conducted cytochrome c oxidase I (COI) metabarcoding to identify both the predator and the prey species. Massive COI reads were de novo assembled and nine representative sequences were constructed. The predator, identified from the representative sequences and its morphological features, was determined as Ectopleura crocea. The fish eggs that had been preyed upon belonged to two species: Sillago japonica and Parajulis poecilepterus. Additionally, four arthropod species (Labidocera rotunda, Oithona similis, Paracalanus parvus, and Pseudevadne tergestina) were consumed, and their morphological traits could not be observed, due to digestion. COI metabarcoding was an effective tool for studying the feeding activity of these small predators.

The life cycles of fishes are complex and varied, and knowledge of the early life stages is important for understanding the biology, ecology, and evolution of fishes. InEarly Life History of Marine Fishes,Bruce S. Miller and Arthur W. Kendall Jr., bring together in a single reference much of the research available and its application to fishery science-knowledge increasingly important because for most fishes, adult populations are determined at the earliest stages of life. Clear and well written, this book offers expert guidance on how to collect and analyze larval fish data and on how this information is interpreted by applied fish biologists and fisheries managers.

Sansha Bay (26.40−27.00°N, 119.50−120.20°E) is a typical semi-enclosed bay, located in northern Fujian Province, China, and adjacent to the East China Sea. The ichthyoplankton species composition and assemblage structure were investigated based on monthly sampling at 25 stations in April−September 2019, covering the important spring and summer spawning seasons in the region. Sampling was conducted in the first 3−5 days of the full moon or new moon phases using a standard plankton net through horizontal and vertical tows during daytime. In total, 25,819 ichthyoplankton samples were collected, of which 25,449 samples (i.e., 24,757 eggs and 692 larvae) were from horizontal tows. For horizontal tow samples, the ichthyoplankton were classified into 58 taxa in 15 orders and 23 families with a combination of external morphology and DNA barcoding analyses, from pelagic to demersal and benthic species. The dominant order was the Gobiiformes, including 23 species (39.7% of all species). The dominant taxa, in terms of relative abundance and frequency of occurrence, consisted of commercially important fishes, such as Setipinna tenuifilis (Valenciennes, 1848) (Engraulidae), Epinephelus akaara (Temminck and Schlegel, 1842) (Serraenidae), Collichthys lucidus (Richardson, 1844), Nibea albiflora (Richardson, 1846) (Sciaenidae), Acanthopagrus schlegelii (Bleeker, 1854), and Pagrus major (Temminck and Schlegel, 1843) (Sparidae), accounting for 78.9% of the horizontal tow samples. Low-valued and small-sized fishes, such as Stolephorus commersonnii Lacepède, 1803 (Engraulidae), Solea ovata Richardson, 1846 (Soleidae), Nuchequula nuchalis (Temminck and Schlegel, 1845), and Photopectoralis bindus (Valenciennes, 1835) (Leiognathidae), were also dominant species, accounting for 11.4% of the horizontal tow samples. The ichthyoplankton assemblage was categorized into five different temporal assemblages based on the cluster and nonmetric multidimensional scaling analysis, namely, April, May, June, July, and August−September (ANOSIM, Global R = 0.656, p < 0.01) with the highest density and richness of ichthyoplankton occurred in May. The spatial distribution pattern showed that the high density (ind./m 3 ) of ichthyoplankton occurred mainly in S12–S25 in Guanjingyang and along the Dongchong Peninsula coastline into Dongwuyang, while low density occurred mainly in S01–S11 in the northwest waters of Sandu Island (ANOVA, F = 8.270, p < 0.05). Temperature, salinity, and chlorophyll a were key factors structuring the ichthyoplankton assemblages in Sansha Bay. In addition, this study revealed the changes of the ichthyoplankton composition, density, and spatial distribution in Sansha Bay over the past three decades.