Drifting Fish Eggs Research Articles

Effects of Flow Turbulence on the Entire Development Process of Drifting Fish Eggs

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.

Metabarcoding of ichthyoplankton communities associated with a highly dynamic shelf region of the southwest Indian Ocean.

Drifting fish eggs and larvae (ichthyoplankton) can be identified to species using DNA metabarcoding, thus allowing for post hoc community analyses at a high taxonomic resolution. We undertook a regional-scale study of ichthyoplankton distribution along the east coast of South Africa, focused on the contrasting environments of the tropical Delagoa and subtropical Natal Ecoregions, and on exposed and sheltered shelf areas. Zooplankton samples were collected with tow nets at discrete stations along cross-shelf transects (20-200 m depth) spaced along a latitudinal gradient that incorporates a known biogeographical boundary. Metabarcoding detected 67 fish species, of which 64 matched prior distribution records of fishes from South Africa, with the remaining three known from the Western Indian Ocean. Coastal, neritic and oceanic species were present, from epi- and mesopelagic to benthopelagic and benthic adult habitats. By family, Myctophidae (10 species), Carangidae, Clupeidae, Labridae (each with 4 species) and Haemulidae (3 species) were most speciose. Ichthyoplankton community composition varied significantly with latitude, distance to coast, and distance to the shelf edge. Small pelagic fishes had the highest frequency of occurrence: Engraulis capensis, Emmelichthys nitidus and Benthosema pterotum increased in frequency towards the north, whereas Etrumeus whiteheadi increased towards the south. Chub mackerel Scomber japonicus accounted for most variability related to distance from the coast, whilst African scad Trachurus delagoa correlated with distance to the shelf edge. Dissimilarity between communities in the Delagoa and Natal Ecoregions was 98-100%, whereas neighbouring transects located within the sheltered KwaZulu-Natal Bight had lower dissimilarity (56-86%). Onshore transport of ichthyoplankton by Agulhas Current intrusions plausibly explained the abundance of mesopelagic species over the shelf. Metabarcoding followed by community analysis revealed a latitudinal gradient in the ichthyoplankton, associations with coastal and shelf-edge processes, and evidence of a spawning area in the sheltered KwaZulu-Natal Bight.

An annual profile of the impacts of simulated oil spills on the Northeast Arctic cod and haddock fisheries.

We simulate the combined natural and pollutant-induced survival of early life stages of NEA cod and haddock, and the impact on the adult populations in response to the time of a major oil spill in a single year. Our simulations reveal how dynamic ocean processes, controlling both oil transport and fate and the frequency of interactions of oil with drifting fish eggs and larvae, mediate the magnitude of population losses due to an oil spill. The largest impacts on fish early life stages occurred for spills initiated in Feb-Mar, concomitant with the initial rise in marine productivity and the earliest phase of the spawning season. The reproductive health of the adult fish populations was maintained in all scenarios. The study demonstrates the application of a simulation system that provides managers with information for the planning of development activities and for the protection of fisheries resources from potential impacts.

Oscillation and dispersion of live grass carp egg settlement in static water: Laboratory experiments and theoretical models

AbstractFull understanding of the settling process of drifting fish eggs in static water is crucial for improving predictions of fish egg drift in rivers, which can inform reservoir operations by incorporating the ecological requirements of fish. However, current understanding of the settling process remains limited. Observations and analysis of live grass carp egg settlement in static water, with a video capture technology and wavelet analysis, have improved understanding. Results reveal that microscale oscillation and dispersion occur during the settling process. The oscillating velocities of eggs had periods of 0.113 s in longitudinal and 0.135 s in vertical, with oscillating angles around 1.13°. The maximum position differences among eggs after stably settling for 14 s were 25.0 mm in vertical and 4.2 mm in longitudinal. Mechanical models were then established and employed to elucidate two settling phenomena. Simulated results revealed that microscale oscillation was related to biological attributes (the egg specific gravity and diameters of the egg and embryo), special inner structure of the live egg and random hydraulic disturbance of the surroundings. Dispersion was mainly caused by the difference between eggs (diameter and specific gravity). This work furthers understanding and forecasts of fish egg drift in rivers, from which river engineers and managers can better estimate the locations of fish spawning sites, calculate ecological water requirement, and designate ecological conservation areas.

DNA barcoding reveals the temporal community composition of drifting fish eggs in the lower Hongshui River, China.

Determining the temporal community composition of fish eggs in particular regions and understanding the reproductive times of regional fish taxa are key aspects of the management and regulation of regional fish stocks. However, it is extremely difficult to accurately identify fish eggs due to the absence of diagnostic morphological characters. We sampled fish eggs in the lower Hongshuihe River (an upper mainstem of the Pearl River) between May and September 2020. We then used DNA barcoding to determine the species composition of the egg pool and to predict the spawning periods of the identified species. A total of 641 eggs and 17 larvae were chosen for molecular identification; 397 eggs and 17 larvae yielded high‐quality barcoding sequences. The high failure rate (~38%) was most likely due to long‐term storage in low concentrations of ethanol prior to molecular analysis. We successfully classified 392 eggs into 10 species and 13 larvae into four species using public databases. Most of the species identified in the egg pool were small and/or benthic, and migratory species were rare. This may partially reflect the adverse effects of hydropower cascade development in this river section. We also found that spawning periods tended to be species‐specific. Our study provides a reference for the conservation and management of regional fishery stocks.

Editorial: Green or red: Challenges for fish and freshwater biodiversity conservation related to hydropower

Editorial: Green or red: Challenges for fish and freshwater biodiversity conservation related to hydropower

Species diversity of drifting fish eggs in the Yangtze River using molecular identification.

The dam constructions greatly changed the hydrologic conditions in the Yangtze River, and then significantly affected the spawning activities of indigenous river fish. Monitoring the species composition of drifting eggs during spawning season is important for protection issues. In this study, we have sampled drifting fish eggs in nine locations from 2014 to 2016. Eggs were identified using the mitochondrial cyt b gene sequence. A total of 7,933 fish eggs were sequenced successfully and blasted into the NCBI database. Thirty-nine fish species were identified, and were assigned to four families and two orders. Approximately 64% of the species identified, and 67% of the eggs, were classified in the Family Cyprinidae. Abundance and Shannon–Wiener diversity index of species were higher in the main river than in tributaries of the river. However, tributaries may be important spawning grounds for some fish species. The Jaccard’s similarity index and river-way distances among sampled stations were negatively correlated suggesting the environment shapes species composition in the sampled spawning grounds. These results showed that mitochondrial DNA sequence is a powerful and effective tool for fish egg identification in Yangtze River and these data are useful for conservation efforts.

STUDIES ON THE DRIFT PATTERN OF DRIFTING FISH EGGS WITH TRACERS IN UPPER YANGTZE RIVER

Investigation of fish early life history is an important technique to calculate spawning sites and estimate spawning size for fish with drifting eggs.But,drift patterns of drifting eggs are greatly different for the diverse hydrological condition in different river reach.The drift pattern of drifting fish eggs was studied in this experiment with drifting tracers,and the classic estimate method of spawning size was tested to evaluate the applicability in upper Yangtze River.The experiment was conducted in the 31 km river reach in the upper Yangtze River from Jiangjin city to Luohuang town on 7th April 2008.A total of 485800 tracers were separated into 6 groups and dyed into red,green,white,black,blue and yellow respectively,the total number of tracers of every group was 80966,80968,80966,80966,80968 and 80966 in turn.Two releasing sites were set up to test the influence of configuration of river channel on the drifting speed.A total of 58 tracers were collected in the collecting site.The results showed that the mean drifting speeds of tracers released in the same releasing site were significantly different.Drift density of tracers showed a pattern of alternate with peak and low density,and the peak density showed gradual decline as drift time increase.All the 58 tracers were collected in the main stream,it reflected that drift density in the main stream was higher than the slow flow region.So we advise the main stream should be surveyed in the fish early life history investigation.Mean drifting speeds were 1.19 m/s,1.03 m/s,1.05 m/s and 1.22 m/s for red,green,white and black tracers respectively.There was no significantly difference for mean drifting speeds released in the two releasing sites.Estimated releasing numbers of red,green,white and black tracers were 8356,11141,12533 and 48741,and corresponding for 10.3%,13.8%,15.5% and 60.2% of the total number released respectively,so the accuracy of estimation showed greatly declining as drift time increasing.No blue and yellow tracers were collected for the low drift density in the slow flow region.The total estimated number was 16.6% of the real releasing number only.So a coefficient should be added into the calculation formula to compensate the decline of accuracy caused by drift time increase when estimate spawning size in the upper Yangtze River.