Fish Kills Research Articles

Toxic effects, mechanisms, and ecological impacts of harmful algal blooms in China

Over the last 30 years, harmful algal blooms (HABs) have occurred frequently in the coastal waters of China, resulting in financial losses of over 5.9 billion yuan (about 0.87 billion US dollars) due to massive fish and shellfish mortalities and negative impacts on tourism. To better understand HABs in China, herein we summarized bloom events with massive fish/shellfish mortalities and/or economic losses. Our results suggest that the diversity of HAB species has increased over the last 30 years, with the main causative species shifting from the raphidophyte Chattonella marina and dinoflagellates Gymnodinium spp. to various other species, including the dinoflagellates Karenia mikimotoi and Prorocentrum donghaiense, the haptophyte Phaeocystis globosa, and the pelagophyte Aureococcus anophagefferens. In addition, new types of HABs, such as macroalgal blooms, emerged with severe ecological impacts. We also reviewed the toxic effects, mechanisms, and ecological impacts of common HAB causative species in China. Analysis of the toxic effects of three types of harmful algae (toxin-producing, fish killing, and ecosystem disruptive algae) on marine organisms commonly found in China at different trophic levels revealed that HABs often had toxic effects on multiple organisms in addition to fish or shellfish, with species-specific impacts. Common mechanisms of intoxication include shifting environmental parameters, shellfish poisoning, reactive oxygen species, and haemolytic/cytotoxic toxins. The main mechanism appears to vary with the type of HAB species, and for some notorious algae such as K. mikimotoi and C. marina, further investigations are needed to identify their intoxication mechanism.

Predator selection and predator-prey interactions for the biological control of mosquito dengue vectors in northern Vietnam.

Predators and their interactions with target prey influence the efficiency of control strategies. In the present study, we demonstrate the implementation of natural predator selection for controlling dengue vectors in northern Vietnam through field-based observation of aquatic insect predators in natural habitats and lab-based assessment of predatorial capacities for several aquatic insect predators. The selected species was then used to evaluate the predatory-prey interaction using functional responses (FRs) toward 3rd- and 4th-instar larvae of four major medical mosquito species (Aedes aegypti, Aedes albopictus, Culex quinquefasciatus, and Anopheles minimus). The preference of selected predators for Ae. aegypti larvae over other mosquito larvae was also investigated. Both field observation and lab experiments indicated that the giant water bug Diplonychus rusticus was abundant and exhibited the highest predatory capacity for mosquito larvae. The predator exhibited type II FRs when offered each of the four prey species, and the greatest attack rates were observed for Ae. aegypti and Ae. albopictus, with only negligible differences observed in the handling times of the prey species. Further, Manly's selectivity (α) values calculated from the prey choice experiments showed that Ae. aegypti was preferred over both Cx. quinquefasciatus and An. minimus. Together, these findings indicate that D. rusticus could be successfully used to facilitate the biological control of both Ae. aegypti and Ae. albopictus within the species' distributional overlap in Southeast Asia.

NGHIÊN CỨU MÔI TRƯỜNG SỐNG TỰ NHIÊN CỦA LOÀI CÀ CUỐNG Lethocerus indicus (LEPELETIER ET SEVILLE, 1775) (HEMIPTERA: BELOSTOMATIDAE) GÓP PHẦN BẢO TỒN LOÀI CÔN TRÙNG NƯỚC QUÝ HIẾM CÓ TÊN TRONG SÁCH ĐỎ VIỆT NAM

The study was focused on the natural habitats and distribution of the giant water bug Lethocerus indicus in Lao PDR, with the aims to conserve and breed this rare water insect. The following conclusions were given: Adult giant water bugs were distributed in 5 main natural habitat types, including SC1. Habitat with flowing water such as rivers, streams and canals; SC2. Habitat type with standing or less flowing water such as ponds, lakes and lagoons; SC3. Habitat types such as water rice fields or aquatic plants; SC4. Habitat of standing water or puddles on the edge or inside the rice field; and SC5; and other Habitats include terrestrial, drifting with water, hiding in earthen caves near aquatic habitats. The number of adult giant water bugs decreased in the order of natural habitats studied, as follows SC3 >SC4 >SC2 >SC5 >SC1. The weter rice fields were the most suitable habitat for adult giant water bug. Research results showed that, there are similarities in the distribution of adult male and female in the studied natural habitats. The ratio of adult male to female giant water bug found in the above five studied natural habitats was 1.0 versus 2.3, respectively.

"What's This Bug?" Questions from the Public Provide Relevant Information on Species Distribution and Human-Insect Interactions.

Simple SummarySince its opening in 1990, the Montreal Insectarium has offered an entomological information service, allowing the public to send questions, photographs, and specimens for identification. All requests are answered by entomologists. Over the years, almost 14,000 requests have been received. We wanted to know which species have been seen over the years, which subjects were frequently asked about, and where requests came from. We analyzed the 4163 requests received in 2010–2011 and 2017–2018. Requests received during those four years came from 35 countries, and most of those requests came from Canada. Butterflies and moths were the most popular group. The five most frequent species were the eastern dobsonfly, the masked hunter, the giant water bug, the western conifer-seed bug, and the Japanese beetle. A comparison with the data from the citizen science platform iNaturalist shows that the EIS is a valuable tool to detect invasive species. Frequent subjects included school projects, entomophagy (eating insects), and wasp and bee nests.In general, insects and arthropods polarizing: they either fascinate people, disgust people, or both, and they generate lots of questions. Museums are perceived as reliable sources of information and, as such, a go-to destination for the public to receive answers. Since its opening in 1990, the Montreal Insectarium has offered an entomological information service, allowing the public to send questions, photographs, and specimens for identification. All requests are answered by entomologists. Spatiotemporal variations in taxonomic, geographic, and thematic profiles of the 4163 requests received in 2010–2011 and 2017–2018 were analyzed. Requests came from 35 countries, and most of those requests came from Canada. The majority of requests were identification requests. Representing 25% of identification requests, the five most frequent species were the eastern dobsonfly Corydalus cornutus, the masked hunter Reduvius personatus, the giant water bug Lethocerus americanus, the western conifer-seed bug Leptoglossus occidentalis, and the Japanese beetle Popillia japonica. A comparison with the data from the citizen science platform iNaturalist shows that the EIS can be a valuable tool for invasive species detection. Frequent subjects included school projects, entomophagy (eating insects), and wasp and bee nests. Finally, we discuss the role of entomologists in providing scientific information but also in addressing common concerns regarding cohabitation with arthropods.

Effectiveness of phosphorus control under extreme heatwaves: implications for sediment nutrient releases and greenhouse gas emissions

Eutrophication has been identified as the primary cause of water quality deterioration in inland waters worldwide, often associated with algal blooms or fish kills. Eutrophication can be controlled through watershed management and in-lake measures. An extreme heatwave event, through its impact on mineralization rates and internal nutrient loading (phosphorus—P, and nitrogen—N), could counteract eutrophication control measures. We investigated how the effectiveness of a nutrient abatement technique is impacted by an extreme heatwave, and to what extent biogeochemical processes are modulated by exposure to heatwaves. To this end, we carried out a sediment-incubation experiment, testing the effectiveness of lanthanum-modified bentonite (LMB) in reducing nutrients and greenhouse gas emissions from eutrophic sediments, with and without exposure to an extreme heatwave. Our results indicate that the effectiveness of LMB may be compromised upon exposure to an extreme heatwave event. This was evidenced by an increase in concentration of 0.08 ± 0.03 mg P/L with an overlying water volume of 863 ± 21 mL, equalling an 11% increase, with effects lasting to the end of the experiment. LMB application generally showed no effect on nitrogen species, while the heatwave stimulated nitrification, resulting in ammonium loss and accumulation of dissolved oxidized nitrogen species as well as increased dissolved nitrous oxide concentrations. In addition, carbon dioxide (CO2)-equivalent was more than doubled during the heatwave relative to the reference temperature, and LMB application had no effect on mitigating them. Our sediment incubation experiment indicates that the rates of biogeochemical processes can be significantly accelerated upon heatwave exposure, resulting in a change in fluxes of nutrient and greenhouse gas between sediment and water. The current efforts in eutrophication control will face more challenges under future climate scenarios with more frequent and intense extreme events as predicted by the IPCC.

ОЦЕНКА ЭФФЕКТИВНОСТИ РАБОТЫ ПРУДОВЫХ ЭЛЕКТРОНЕВОДОВ

The article considers the problem of low productivity of many fish farms, especially non-drainage ponds against the background of a growing increase in the volume of fish farming, which is typical for pond fish farming in Russia. It has been found that one of the main factors of low productivity (1–5 c/ha) is the imperfection of existing tools and methods of fishing. With significant costs of manual labor and time, the catch of farmed fish is no more than 50%. The remaining fish die mostly during winter fish kills. To reduce the proportion of manual labor and improve the efficiency of fishing in non-drainage ponds, many countries are looking for the methods to modernize existing or develop new fishing gear. The most promising in this respect are electric breeders for fishing in the non-drainage ponds, small lakes and water reservoirs. The advantages of this method are the coverage of a large fishing zone, the possibility of catching fish leaving ordi-nary seines, and work in silted and tied water bodies. Studying the regularities of the electric field impact on fish is necessary to explain and predict its behavior in electric fields, to develop technical means that provide the necessary control activity, to develop measures to protect ichthyofauna from the harmful effects of electric fields, etc.

Key steps to improve the assessment, evaluation and management of fish kills: lessons from the Murray–Darling River system, Australia

Fish kills are very visible, with high levels of public scrutiny and major effects on populations. In 2018–19, extensive fish kills in the lower Darling River, south-eastern Australia, resulted in the deaths of millions of fish, including threatened and popular, iconic angling and important cultural species. This distressed local communities and the broader Australian society, who questioned the competence of fish and water management. Fish kills are increasing in frequency and severity, exacerbated by climate change. This paper reports on eight major fish-kill case studies across the Murray–Darling Basin that were examined to assess management adequacy. Field assessments and reporting have been poor, not documenting all species or numbers affected. Few values of fishes (cultural, conservation, recreational, social, ecological, economic) have been assessed and replacement or management costs not determined. There is a need to philosophically change our approach to take fish kills more seriously. More comprehensive approaches to assessment, evaluation and management are needed. Responsibilities for fish kills should be clarified and include water and habitat management agencies. Post-kill recovery plans that include the replacement of lost ecological assets should be published and enacted. This paper provides a fresh perspective on fish kills, with 15 key recommendations applicable to improve future management worldwide.

How fish kills affected traditional (Baakandji) and non-traditional communities on the Lower Darling–

In the summer of 2018–19 mass fish kills occurred in the Lower Darling (Baaka) River in south-eastern Australia. The fish kills received national and international attention and have been the focus of numerous government agency and independent assessments. Although fish kills have previously been recorded in the Lower Darling region, the size and rapid succession of the 2018–19 ‘Menindee’ fish kills made them unprecedented in the Murray–Darling Basin, placing significant pressure on the native fish community. Although the deaths of millions of fish were documented, the significant negative effect that the fish kills had on local communities, particularly the traditional Baakandji people, was largely ignored. The social and cultural aspects of such events can have major non-economic effects on local communities. In this paper we document heart-felt feelings conveyed by local community members. Their sense of loss, despair and helplessness is compounded by frustration regarding water management and policy decision making in the Murray–Darling Basin. However, these tragic events have increased understanding of traditional Baakandji connection to the river and its fish and, together with local recovery efforts, now provide prospects for enhanced community and agency cooperation to improve the health of the lower Darling Baaka River and restore its native fish populations.

Genome-wide molecular phylogenetic analyses and mating experiments which reveal the evolutionary history and an intermediate stage of speciation of a giant water bug.

The intermediate stages of speciation are important for understanding the processes involved in the creation of biodiversity, and also comprise a number of interesting phenomena. However, difficulties are associated with dividing clear speciation stages because speciation is a continuous process. Therefore, the elucidation of speciation is an interesting and important task in evolutionary biology. We herein present an example of a species in an intermediate stage of speciation using the giant water bug Appasus japonicus (Heteroptera, Belostomatidae) that was investigated using mating experiments and phylogenetic analyses of the mtDNA COI (658bp) and 16S rRNA (435bp) regions, and nDNA SSR (13loci) and its genome-wide SNPs (11,241 SNPs). The results of our phylogenetic analyses based on their mtDNA data set and the genome-wide SNPs data set strongly supported the paraphyly of the Japanese populations. Therefore, it is suggested that their ancestral lineage which being distributed in the Japanese Archipelago subsequently migrated to the Eurasian Continent (i.e., back-dispersal occurred). Furthermore, the results of the mating experiments suggested that among A. japonicus, even between closely related lineages, premating reproductive isolation has been established by the differentiation of copulatory organ morphologies. In contrast, premating reproductive isolation is not established in the absence of the differentiation of copulatory organ morphologies, even if genetic differentiation is prominent. These results suggested that their phylogenetic distance does not predict premating reproductive isolation. Furthermore, in the present study, we present a clear example of premating reproductive isolation driving speciation between closely related lineages.

Kills in the Darling: assessing the impact of the 2018–20 mass fish kills on the fish communities of the Lower Darling–

Understanding the impacts of extreme events is essential to effective fisheries management. During the summer of 2018–19 millions of native fish died in Lower Darling–Baaka River adjacent to Menindee, New South Wales, Australia. Hypoxia during a period of protracted low flow, triggered by climatic events, was responsible for the fish kills. From June 2019 to March 2020, further broader-scale fish kills occurred throughout ~600 km of the Darling–Baaka River as disconnected refuge pools contracted and water quality deteriorated. This study examined the status of the remnant fish populations, compared the fish assemblage of the Menindee fish death reach with an unaffected reach and monitored change of the fish community over 18 months after the initial fish kills. Significantly lower abundances of Murray cod (Maccullochella peelii), bony herring (Nematalosa erebi), carp gudgeon (Hypseleotris spp.) and freshwater prawn (Macrobrachium australiense) were captured within the Menindee fish death reach compared with the unaffected reach. Varied responses were observed in species abundances within the affected reach in the 18 months after the initial fish kills, attributed to the various life-history traits and reproductive strategies. The results presented highlight a fish community in continued stress. Continued monitoring will guide and track the effectiveness of recovery management interventions in the region.

Temperature and Patterns of Occurrence and Abundance of Key Copepod Taxa in the Northeast Pacific

The Northeast Pacific is a highly heterogeneous and productive ecosystem, yet it is vulnerable to climate change and extreme events such as marine heat waves. Recent heat wave induced die-offs of fish, marine mammals, and seabirds in the Gulf of Alaska were associated with the loss of large, lipid-rich copepods, which are a vital food resource for forage fishes. The critical and temperature sensitive role of copepods in this ecosystem motivates our investigation into the impacts of temperature on copepod occurrence, abundance, and phenology. Here, we pair long term in situ copepod data from Continuous Plankton Recorder surveys with satellite temperature data to determine the influence of water temperature on three key copepod taxa: Neocalanus plumchrus, Calanus pacificus, and Oithona spp. Through the use of linear models and thermal threshold methods, we demonstrate that N. plumchrus is most vulnerable to warming and future marine heat waves in this region. Linear models demonstrate that N. plumchrus abundance is negatively related to temperature, and thermal threshold methods reveal that N. plumchrus has an upper thermal threshold of 11.5°C for occurrence, and 10.5°C for abundance. Additionally, examining N. plumchrus abundance before and during the 2014–2016 marine heat wave demonstrates reduced species abundance during past warming events. Oithona spp. and C. pacificus appear to be less vulnerable to warm temperatures. However, their presence will not be sufficient to supplement the loss of the larger-bodied and lipid-rich N. plumchrus. Our findings demonstrate the power of using long-term in situ data to determine thermal tolerances, and suggest the need to further examine the potential resilience of N. plumchrus to climate change.

Population demographics of golden perch (

An understanding of population demographics and life history processes is integral to the rehabilitation of fish populations. In Australia’s highly modified Murray–Darling Basin, native fish are imperilled and fish deaths in the Darling River in 2018–19 highlighted their vulnerability. Golden perch (Macquaria ambigua) is a long-lived percichthyid that was conspicuous in the fish kills. To guide population rehabilitation in the Darling River, pre-fish kill age structure, provenance and movement of golden perch were explored using otolith microstructure and chemistry (87Sr/86Sr). Across the Lower and Mid-Darling River, recruitment was episodic, with dominant cohorts associated with years characterised by elevated discharge. There was substantial variability in age structure, recruitment source and movement patterns between the Lower and Mid-Darling River. In the Mid-Darling River, tributaries were an important recruitment source, whereas in the Lower Darling fish predominantly originated in the Darling River itself. Downstream movement of juveniles, upstream migration of adults and return movements to natal locations were important drivers of population structure. Restoring resilient golden perch populations in the Darling River will be reliant on mitigating barriers to movement, promoting a connected mosaic of recruitment sources and reinstating the hydrological and hydraulic factors associated with spawning, recruitment and dispersal. Globally, increasing water resource development and climate change will necessitate such integrated approaches to the management of long-lived migratory riverine fishes.

Effects of habitat complexity on giant water bug (Belostoma) functional response to rams-horn snail prey (Helisoma)

Effects of habitat complexity on giant water bug (Belostoma) functional response to rams-horn snail prey (Helisoma)

An Unusual Fish Kill in Chandragiri River, Kasaragod District, Kerala, India

An Unusual Fish Kill in Chandragiri River, Kasaragod District, Kerala, India

Combining Imaging Flow Cytometry and Molecular Biological Methods to Reveal Presence of Potentially Toxic Algae at the Ural River in Kazakhstan

Algal blooms occur in freshwater bodies throughout the world, often leading to fish kills. Cases of these kills along the Ural River were reported in 2018–2019, involving significant amount of sturgeon in fish farming areas. In this study, the analysis of algal samples from the delta of the Ural River up to 100 km inland was carried out from August to December 2019 using imaging flow cytometry (IFC), molecular biological, and microscopic techniques. We identified the filamentous cyanobacteriaCuspidothrix issatschenkoi,Dolichospermumcf.flos-aquae,Dolichospermumcf.macrosporum,Pseudanabaena limnetica, andPlanktothrixspp. as the dominant potentially toxic phytoplankton species, and we also found minor quantities ofCylindrospermopsis raciborskii. For the first time, molecular phylogenetic investigations of field clones of cyanobacteria from Ural River were carried out to establish the taxa of the dominant species and to identify the presence of genes encoding toxins. The complementary analysis with nanopore-based next-generation sequencing overlapped with the results of IFC and was instrumental in revealing minor cyanobacteria taxa. Real-time PCR analysis and sequencing indicated the presence ofMicrocystisand ADA-clade spp. as well as genes associated with the production of microcystin (mcyE) and the algal neurotoxin saxitoxin (sxtA) originating from cyanobacteria. These findings suggest that toxin-producing cyanobacteria could become a threat in the Ural River near Atyrau, which can significantly affect aquaculture in the region.

LSTM Networks to Improve the Prediction of Harmful Algal Blooms in the West Coast of Sabah.

Harmful algal bloom (HAB) events have alarmed authorities of human health that have caused severe illness and fatalities, death of marine organisms, and massive fish killings. This work aimed to perform the long short-term memory (LSTM) method and convolution neural network (CNN) method to predict the HAB events in the West Coast of Sabah. The results showed that this method could be used to predict satellite time series data in which previous studies only used vector data. This paper also could identify and predict whether there is HAB occurrence in the region. A chlorophyll a concentration (Chl-a; mg/L) variable was used as an HAB indicator, where the data were obtained from MODIS and GEBCO bathymetry. The eight-day dataset interval was from January 2003 to December 2018. The results obtained showed that the LSTM model outperformed the CNN model in terms of accuracy using RMSE and the correlation coefficient r as the statistical criteria.

Mass mortality of Giant Water Bug <i>Lethocerus indicus</i> (Lepeletiler & Serville, 1825) [Heteroptera: Belostomatidae] in Thiruvananthapuram, Kerala State, South India

Mass mortality of Giant Water Bug, Lethocerus indicus (Lepeletiler & Serville, 1825) was reported for the first time from India from Thiruvananthpuram district, Kerala. As many as 700 specimens were found dead around the locality. The high intensity of floodlight, the less availability of the water in the vicinity and the lunar phase are the possible reasons for the mass movement and the mortality, are discussed in the present paper.

Mesocosm Experiments to Quantify Predation of Mosquito Larvae by Aquatic Predators to Determine Potential of Ecological Control of Malaria Vectors in Ethiopia.

Malaria parasites are transmitted to humans by infectious female Anopheles mosquitoes. Chemical-insecticide-based mosquito control has been successful in reducing the burden of malaria. However, the emergence of insecticide resistance in malaria vectors and concerns about the effect of the chemicals on the environment, human health, and non-target organisms present a need for new or alternative vector control intervention tools. Biocontrol methods using aquatic invertebrate predators have emerged as a potential alternative and additional tool to control mosquito populations. Ecological control specifically makes use of species insights for improving the physical habitat conditions of competitors and predators of vectors. A first step towards this is to gain knowledge on the predation potential of several typically present macroinvertebrates. Hence, this study aimed at (1) examining the influence of the predation of hemipterans on the number of emerging adult mosquitoes and (2) detecting Anopheles mosquito DNA in the gut of those predators. The prey and predators were collected from a range of water bodies located in the Gilgel Gibe watershed, southwest Ethiopia. A semi-field study was carried out using mesocosms which were constructed using plastic containers mimicking the natural aquatic habitat of immature Anopheles mosquitoes. Adult mosquitoes that emerged from the mesocosms were collected using a mechanical aspirator. At the end of the experiment, predators were withdrawn from the mesocosms and identified to genus level. Polymerase Chain Reaction (PCR) was employed to identify sibling species of Anopheles gambiae s.l. and to detect Anopheles mosquito DNA in the gut of the predators. Data were analysed using R software. Giant water bugs (belostomatids) were the most aggressive predators of Anopheles larvae, followed by backswimmers (notonectids) and water boatmen (corixids). All female Anopheles gambiae s.l. emerged from the mesocosms were identified as Anopheles arabiensis. Anopheles arabiensis DNA was detected in the gut content of hemipteran specimens analysed from the three families. The number of the adult mosquitoes emerging from the mesocosms was affected by the presence of predators. The findings of this study provide evidence of the potential use of aquatic macroinvertebrate predators as biocontrol agents against immature Anopheles mosquitoes and their potential to be considered as a component of integrated vector management for insecticide resistance and the combined restoration of aquatic ecosystems via smart ecological engineering.

Convolutional Neural Network-Based Fish Posture Classification

Fish killing machines can effectively relieve the workers from the backbreaking labour. Generally, it is necessary to ensure the fish to be in unified posture before being input into the automatic fish killing machine. As such, how to detect the actual posture of fish in real time is a new and meaningful issue. Considering that in the actual situation, we only need to determine the four postures which are related to the head, tail, back, and belly of the fish, and we transfer this task into a four-kind classification problem. As such, the convolutional neural network (CNN) is introduced here to do classification and then to detect the fish’s posture. Before training the network, all sample images are preprocessed to make the fish be horizontal on the image according to the principal component analysis. Meanwhile, the histogram equalization is used to make the grey distribution of different images be close. After that, two kinds of strategies are taken to do classification. The first is a paired binary classification CNN and the second is a four-category CNN. In addition, three kinds of CNN are adopted. By comparison, the four-kind classification can obtain better results with error less than 1/1000.

Contrasting natal origin and movement history informs recovery pathways for three lowland river species following a mass fish kill

Understanding the spatial and temporal scales over which key population processes occur is fundamental to effective fisheries management, especially when informing recovery actions following extreme events. In 2018–19, hypoxia-induced fish kills occurred in the lower Darling River, south-eastern Australia. We collected carcasses of three potamodromous species that perished during these events to reconstruct their lifetime movements and identify potential recovery mechanisms. Golden perch Macquaria ambigua, Murray cod Maccullochella peelii and silver perch Bidyanus bidyanus otolith 87Sr/86Sr profiles were compared with water 87Sr/86Sr ratios to better understand natal provenance and movement history, and to identify the scale at which migration influences population processes. Golden perch were predominantly locally spawned (Darling River), although we found some evidence of emigration into the nearby Murray River early in life and return movements into the Darling River. Murray cod were mainly locally spawned and thereafter lifelong residents, with some evidence of stocking supplementing populations. Silver perch were mostly immigrants, with the Murray River (>500 km away) the principal source of fish. For recovery of native fish populations to be effective in the Darling River, recovery actions are required that incorporate knowledge on the relevant spatial and temporal scales over which life history processes occur.