Insights into Toxic Prymnesium parvum Blooms as a Cause of the Ecological Disaster on the Odra River.

In 2022, Poland and Germany experienced a prolonged and extensive mass fish kill in the Odra River. During the period from the end of July to the beginning of September 2022, a high level of incidental disease and mortality was observed in various fish species (dozens of different species were found dead). The fish mortality affected five Polish provinces (Silesia, Opole, Lower Silesia, Lubuskie, and Western Pomerania) and involved reservoir systems covering most of the river (the Odra River is 854 km long, of which 742 km are in Poland). Fatal cases were investigated using toxicological, anatomopathological, and histopathological tests. Water samples were collected to determine nutrient status in the water column, phytoplankton biomass, and community composition. High nutrient concentrations indicated high phytoplankton productivity, with favorable conditions for golden algal blooms. The harmful toxins (prymnesins secreted by Prymnesium parvum habitats) had not been found in Poland before, but it was only a matter of time, especially in the Odra River, whose waters are permanently saline and still used for navigation. The observed fish mortality resulted in a 50% decrease in the fish population in the river and affected mainly cold-blooded species. Histopathological examinations of fish showed acute damage to the most perfused organs (gills, spleen, kidneys). The disruption to hematopoietic processes and damage to the gills were due to the action of hemolytic toxins (prymnesins). An evaluation of the collected hydrological, meteorological, biological, and physico-chemical data on the observed spatio-temporal course of the catastrophe, as well as the detection of three compounds from the group of B-type prymnesins in the analyzed material (the presence of prymnesins was confirmed using an analysis of the fragmentation spectrum and the accurate tandem mass spectrometry (MS/MS) measurement, in combination with high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS), allowed the formulation and subsequent testing of the hypothesis for a direct link between the observed fish mortality and the presence of prymnesins in the Odra River. This article systematizes what is known about the causes of the fish kill in the Odra River in 2022, based on official government reports (one Polish and one German) and the EU technical report by the Joint Research Centre. A review and critical analysis of government findings (Polish and German) on this disaster were conducted in the context of what is known to date about similar cases of mass fish kills.

A fish kill at the Aposelemis dam (Crete, Greece) caused by heavy parasitism by Ichthyobodo sp.

A fish kill was recorded at the Aposelemis Dam, which is the main reservoir of drinking water for the island of Crete in Greece. Hundreds of goldfish were found dead at a side stream which provides water to the reservoir. The affected fish had been entrapped in a small pond at the side of the stream with practically zero water renewal as the event occurred in August which is a dry season for the island of Crete. The event was alarming for the local community since anthropogenic pollution was initially suspected which could pose a significant human health threat. Following examination of the fish, the mortality was attributed to heavy infection by the parasitic flagellate, Ichthyobodo sp., whilst no pollutants were detected. The parasite was studied through light and scanning electron microscopy and was identified molecularly.

Description of two new species Chattonella tenuiplastida sp. nov. and Chattonella malayana sp. nov. (Raphidophyceae) from South China Sea, with a report of wild fish mortality.

Fisheries damage caused by Chattonella red tide has been recorded in Southeast Asia. Molecular studies have clarified the presence of two species, Chattonella marina complex and Chattonella subsalsa in the region, unlike East Asia that had only C. marina complex. To elucidate the phylogeography of Chattonella in Asia, further phylogenetic and morphological examinations were carried out with 33 additional culture strains, including the strains isolated during a bloom of Chattonella sp. (up to 142 cells mL-1) that was associated with a wild fish mortality along the northeastern coast of Peninsular Malaysia in 2016, and those from Yellow Sea, where the Chattonella genotypes have not been determined. LSU rDNA and ITS2 trees showed five intrageneric clades in the genus Chattonella, which were clades I and II (C. subsalsa), clade III (C. marina complex) and two new clades, namely clade IV from Thailand and Malaysia, and clade V from Peninsular Malaysia. The positions of the two new clades were different in LSU rDNA and ITS2 trees. LSU rDNA divergences of clades IV and V from the other clades were ≥ 4.01% and ≥ 5.70%, while their ITS2 divergences were ≥ 7.44% and ≥ 16.43%, respectively. Three and five compensatory base changes (CBCs) were observed in the clades IV and V, respectively, when compared to each of their closest clade. Cells from clades IV and V showed similar morphology to C. marina complex and C. subsalsa clade II, including the presence of button-like granules on cell surface and oboe-shaped mucocysts. However, cell size, the number and shape of chloroplasts in Chattonella clades IV and V, and the non-stacked thylakoids penetrated the pyrenoid in C. subsalsa clade II, were distinctive. Based on the diagnostic chloroplast shape, we proposed the designation of clades IV and V to two new species, Chattonella tenuiplastida sp. nov. and Chattonella malayana sp. nov.

Assessing the Toxicity and Mitigating the Impact of Harmful Prymnesium Blooms in Eutrophic Waters of the Norfolk Broads.

Prymnesium parvum is a toxin-producing microalga, which causes harmful algal blooms globally, frequently leading to massive fish kills that have adverse ecological and economic implications for natural waterways and aquaculture alike. The dramatic effects observed on fish are thought to be due to algal polyether toxins, known as the prymnesins, but their lack of environmental detection has resulted in an uncertainty about the true ichthyotoxic agents. Using qPCR, we found elevated levels of P. parvum and its lytic virus, PpDNAV-BW1, in a fish-killing bloom on the Norfolk Broads, United Kingdom, in March 2015. We also detected, for the first time, the B-type prymnesin toxins in Broads waterway samples and gill tissue isolated from a dead fish taken from the study site. Furthermore, Norfolk Broads P. parvum isolates unambiguously produced B-type toxins in laboratory-grown cultures. A 2 year longitudinal study of the Broads study site showed P. parvum blooms to be correlated with increased temperature and that PpDNAV plays a significant role in P. parvum bloom demise. Finally, we used a field trial to show that treatment with low doses of hydrogen peroxide represents an effective strategy to mitigate blooms of P. parvum in enclosed water bodies.

Streptococcus iniae associated mass marine fish kill off Western Australia.

Streptococcus iniae causes high mortality in cultured and wild fish stocks globally. Since the first report in captive Amazon river dolphins Inia geoffrensis in 1976, it has emerged in finfish across all continents except Antarctica. In March 2016, an estimated 17000 fish were observed dead and dying along a remote 70 km stretch of the Kimberley coastline north of Broome, Western Australia. Affected species included finfish (lionfish Pterois volitans, angelfish Pomacanthus sp., stripey snapper Lutjanus carponotatus, sand bass Psammoperca waigiensis, yellowtail grunter Amniataba caudavittata, damselfish Pomacentridae sp.), flatback sea turtles Natator depressus, and olive (Aipysurus laevis) and black-ringed (Hydrelaps darwiniensis) sea snakes. Moribund fish collected during the event exhibited exophthalmia and abnormal behaviour, such as spiralling on the surface or within the water column. Subsequent histopathological examination of 2 fish species revealed bacterial septicaemia with chains of Gram-positive cocci seen in multiple organs and within brain tissue. S. iniae was isolated and identified by bacterial culture, species-specific PCR, Matrix-Assisted Laser Desorption Ionisation Time-Of-Flight (MALDI-TOF) and biochemical testing. This is the first report of S. iniae associated with a major multi-species wild marine fish kill in Australia. Extreme weather events in the region including a marked decrease in water temperatures, followed by an extended period of above-average coastal water temperatures, were implicated as stressors potentially contributing to this outbreak.

Prolonged high biomass diatom blooms induced formation of hypoxic-anoxic zones in the inner part of Johor Strait.

The Johor Strait has experienced rapid development of various human activities and served as the main marine aquaculture area for the two countries that bordered the strait. Several fish kill incidents in 2014 and 2015 have been confirmed, attributed to the algal blooms of ichthyotoxic dinoflagellates; however, the cause of fish kill events after 2016 was not clarified and the causative organisms remained unknown. To clarify the potential cause of fish kills along the Johor Strait, a 1-year field investigation was conducted with monthly sampling between May 2018 and April 2019. Monthly vertical profiles of physical water parameters (temperature, salinity, and dissolved oxygen levels) were measured in situ at different depths (subsurface, 1 m, 5 m, and 8 m) depending on the ambient depth of the water column at the sampling stations. The spatial-temporal variability of macronutrients and chlorophyll a content was analyzed. Our results showed that high chlorophyll a concentration (up to 48.8 µg/L) and high biomass blooms of Skeletonema, Chaetoceros, Rhizosolenia, and Thalassiosira were observed seasonally at the inner part of the strait. A hypoxic to anoxic dead zone, with the dissolved oxygen levels ranging from 0.19 to 1.7 mg/L, was identified in the inner Johor Strait, covering an estimated area of 10.3 km2. The occurrence of high biomass diatom blooms and formation of the hypoxic-anoxic zone along the inner part Johor Strait were likely the culprits of some fish kill incidents after 2016.

Hydro-environmental processes governing the formation of hypoxic parcels in an inverse estuarine water body: Assessment of physical controls.

Hypoxia is often thought of as the key factor responsible for fish kill events in coastal areas but fish kill events are too complex to be governed by a single factor. The events are influenced by a combination of chemical, biological and physical processes. Hydrodynamics play a key role in understanding the formation of hypoxia in shallow waters. This study aims to identify the settings of the physical forces that lead to a large-scale depletion of dissolved oxygen in Kuwait Bay at the northwest of the Arabian Gulf. The assessment, made with a validated three-dimensional numerical model (Alosairi and Alsulaiman, 2019), revealed that the pollution from the outfalls leads to nearfield depletion of dissolved oxygen but has only a minor effect on the bay-scale dissolved oxygen. This is a result of the strong dynamics of Kuwait Bay, which mixes the pollutant rapidly before it is transported seawards. Offshore, a low dynamic region has been identified near Jahra Bay which is susceptible to occasional dissolved oxygen depletion. Assessment of the physical forces revealed that the density-driven current and, to a greater extent the wind regime, controlled the formation of a hypoxic parcel near Jahra Bay. The combination of neap tides and low mixed winds reduced mixing and enabled the longer residence times of Kuwait Bay. These are the most critical circumstances, as the average dissolved oxygen can be reduced by 50% during summer. The circumstance resulting in low dynamics near Jahra Bay were also found to be effective in explaining algal blooms.

A large-scale sustained fish kill in the St. Johns River, Florida: A complex consequence of cyanobacteria blooms.

In the summer of 2010, a sustained multispecies fish kill, affecting primarily adult red drum (Sciaenops ocellatus) and Atlantic stingray (Dasyatis sabina), along with various baitfish such as menhaden (Brevoortia spp.) and shad (Dorosoma spp.), was documented for six weeks along 50 km of the Lower St. Johns River (LSJR), Florida. An Aphanizomenon flos-aquae bloom was present in the freshwater reaches before the fish kill. The kill was triggered by a significant reverse-flow event and sudden influx of high-salinity water in late May that contributed to the collapse of the bloom upstream and brought euryhaline fish downstream into the vicinity of the senescing bloom or its by-products. The decomposing bloom led to a sequence of events, including the release of small amounts of cyanotoxins, bacterial lysis of cyanobacterial cells, high organic loading, and changes in the diversity and dominance of the plankton community to include Microcystis spp., Leptolyngbya sp., Pseudanabaena spp., Planktolyngbya spp., and low concentrations of Heterosigma akashiwo. Dissolved oxygen levels were within normal ranges in the reach of the fish kill, although elevated ammonia concentrations and high pH were detected farther upstream. These conditions resulted in complex pathological changes in fish that were not consistent with acute cyanotoxin exposure or with poor water quality but were attributable to chronic lethal hemolysis. Potential sources of hemolytic activity included H. akashiwo, Microcystis spp., and Bacillus cereus, a hemolytic bacterium. The continued presence of A. flos-aquae in the LSJR could have significant environmental repercussions and ideally the causal factors contributing to bloom growth and maintenance should be fully understood and managed.

Predicting fish kills and toxic blooms in an intensive mariculture site in the Philippines using a machine learning model.

Harmful algal blooms (HABs) that produce toxins and those that lead to fish kills are global problems that appear to be increasing in frequency and expanding in area. One way to help mitigate their impacts on people's health and livelihoods is to develop early-warning systems. Models to predict and manage HABs typically make use of complex multi-model structures incorporating satellite imagery and frequent monitoring data with different levels of detail into hydrodynamic models. These relatively more sophisticated methods are not necessarily applicable in countries like the Philippines. Empirical statistical models can be simpler alternatives that have also been successful for HAB forecasting of toxic blooms. Here, we present the use of the random forest, a machine learning algorithm, to develop an early-warning system for the prediction of two different types of HABs: fish kill and toxic bloom occurrences in Bolinao-Anda, Philippines, using data that can be obtained from in situ sensors. This site features intensive and extensive mariculture activities, as well as a long history of HABs. Data on temperature, salinity, dissolved oxygen, pH and chlorophyll from 2015 to 2017 were analyzed together with shellfish ban and fish kill occurrences. The random forest algorithm performed well: the fish kill and toxic bloom models were 96.1% and 97.8% accurate in predicting fish kill and shellfish ban occurrences, respectively. For both models, the most important predictive variable was a decrease in dissolved oxygen. Fish kills were more likely during higher salinity and temperature levels, whereas the toxic blooms occurred more at relatively lower salinity and higher chlorophyll conditions. This demonstrates a step towards integrating information from data that can be obtained through real-time sensors into a an early-warning system for two different types of HABs. Further testing of these models through times and different areas are recommended.

Remote sensing application to estimate fish kills by Saprolegniasis in a reservoir.

Saprolegniasis is one of the most economical and ecologically harmful diseases in different species of fish. Low water temperature is one of the most important factors which increases stress and creates favourable conditions for the proliferation of Saprolegniasis. Therefore, the monitoring of water surface temperature (WST) is fundamental for a better understanding of Saprolegniasis. The objective of this study was to develop a predictive algorithm to estimate the probability of fish kills caused by Saprolegniasis in Río Tercero reservoir (Argentina). WST was estimated by Landsat 7 and 8 imagery using the Single-Channel method. Logistic regression was used to relate WST estimated from 2007 to 2017 with different episodes of fish kills by Saprolegniasis registered in the reservoir during this period of time. Results showed that the algorithm created with the first quartile (25th percentile) of the WST values estimated by Landsat sensors was the most suitable model to estimate Saprolegniasis in the studied reservoir.

Saxitoxin Poisoning in Green Turtles (Chelonia mydas) Linked to Scavenging on Mass Mortality of Caribbean Sharpnose Puffer Fish (Canthigaster rostrata-Tetraodontidae).

Fish within the family Tetraodontidae are potential sources of both endogenous tetrodotoxins (TTXs) and dietary derived saxitoxins (STXs). Ingestion of fish tissues containing these toxins by other vertebrates can lead to severe illness and death. The Caribbean sharpnose puffer (Canthigaster rostrata) is a widespread tetraodontid species within the western Atlantic. Mass settlement of juveniles into foraging habitats have been associated with large-scale puffer fish mortality events. In 2013, 2014, and 2017, puffer mortality events on the southern Caribbean coast of Costa Rica were also associated with strandings of green turtles (Chelonia mydas) found to have fed on C. rostrata. Stranded sea turtles were found dead without apparent cause or alive with severe neurological signs that resolved during short periods of captivity. Puffer fish and turtle organ samples were analyzed for both TTXs and STXs. Concentrations of TTXs were extremely low in the fish (0.5-0.7 µg/g) and undetectable in turtle stomach contents. However, concentrations of STXs in whole fish (16.6-47.5 µg STX-eq/g) exceeded the 0.8 µg STX-eq/g human seafood safety threshold for STXs by orders of magnitude. Saxitoxins were also detected in samples of stomach contents (ingested fish), brain, lung, kidney, and serum from three affected turtles. Study results indicate that saxitoxicosis resulting from opportunistic foraging on C. rostrata during fish mortality events may be a significant factor in episodic stranding of green sea turtles in this region.

First report of a fish kill episode caused by pyrethroids in Italian freshwater.

INTRODUCTION: Fish kills are events of strong emotional impact on the population because of the frequent suspicion that they can be the result of serious pollution accidents. As a matter of fact, they are often due to natural occurrences, such as low levels of dissolved oxygen in the water, but in many cases the causes remain unknown. Fish are particularly sensitive to pesticides and pyrethroids are reported to be the most ecotoxicologically active in the aquatic environment. Nevertheless, the reported cases of massive wild fish mortalities due to these toxicants are very few. This paper describes a fish kill episode occurred in the Padua Province (Veneto Region - North Eastern Italy) which involved several fish species and for which it was possible to identify the cause in the presence of pyrethroids in the water. CASE PRESENTATION: When a whitish liquid coming from the rainwater drain of an industrial area was seen to be spilling into a drainage channel, a fish massive mortality was noticed and investigated. The collected water samples showed the presence of relevant concentrations of cypermethrin, permethrin, deltamethrin and tetramethrin. Analyses on the fish tissues revealed the presence of cypermethrin and permethrin at a concentration range of 476-2834µg/kg and 346-2826µg/kg on a lipid basis, respectively. DISCUSSION: According to the results of the performed analyses, we can reasonably state that the described episode had been caused by the exposure of biota to high concentrations of pyrethroids. The present case report significantly contributes to the limited literature available on pesticides-related fish kills. Moreover, it highlights the importance of sharing protocols for fish kill management at a national level, as this would help to better define the roles of the different institutions involved and to improve the investigation and the reporting of these events.

Kinetics of sulfate reduction and sulfide precipitation rates in sediments of a bar-built estuary (Pescadero, California).

The bar-built Pescadero Estuary in Northern California is a major fish rearing habitat, though recently threatened by near-annual fish kill events, which occur when the estuary transitions from closed to open state. The direct and indirect effects of hydrogen sulfide are suspected to play a role in these mortalities, but the spatial variability of hydrogen sulfide production and its link to fish kills remains poorly understood. Using flow-through reactors containing intact littoral sediment slices, we measured potential sulfate reduction rates, kinetic parameters of microbial sulfate reduction (Rmax, the maximum sulfate reduction rate, and Km, the half-saturation constant for sulfate), potential sulfide precipitation rates, and potential hydrogen sulfide export rates to water at four sites in the closed and open states. At all sites, the Michaelis-Menten kinetic rate equation adequately describes the utilization of sulfate by the complex resident microbial communities. We estimate that 94-96% of hydrogen sulfide produced through sulfate reduction precipitates in the sediment and that only 4-6% is exported to water, suggesting that elevated sulfide concentrations in water, which would affect fish through toxicity and oxygen consumption, cannot be responsible for fish deaths. However, the indirect effects of sulfide precipitates, which chemically deplete, contaminate, and acidify the water column during sediment re-suspension and re-oxidation in the transition from closed to open state, can be implicated in fish mortalities at Pescadero Estuary.

Black liquor and the hangover effect: fish assemblage recovery dynamics following a pulse disturbance.

Anthropogenic perturbations impact aquatic systems causing wide-ranging responses, from assemblage restructuring to assemblage recovery. Previous studies indicate the duration and intensity of disturbances play a role in the dynamics of assemblage recovery. In August 2011, the Pearl River, United States, was subjected to a weak black liquor spill from a paper mill which resulted in substantial loss of fish in a large stretch of the main channel. We quantified resilience and recovery of fish assemblage structure in the impacted area following the event. We compared downstream (impacted) assemblages to upstream (unimpacted) assemblages to determine initial impacts on structure. Additionally, we incorporated historic fish collections (1988-2011) to examine impacts on assemblage structure across broad temporal scales. Based on NMDS, upstream and downstream sites generally showed similar assemblage structure across sample periods with the exception of the 2 months postdischarge, where upstream and downstream sites visually differed. Multivariate analysis of variance (PERMANOVA) indicated significant seasonal variation among samples, but found no significant interaction between impacted and unimpacted assemblages following the discharge event. However, multivariate dispersion (MVDISP) showed greater variance among assemblage structure following the discharge event. These results suggest that 2 months following the disturbance represent a time period of stochasticity in regard to assemblage structure dynamics, and this was followed by rapid recovery. We term this dynamic the "hangover effect" as it represents the time frame from the cessation of the perturbation to the assemblage's return to predisturbance conditions. The availability and proximity of tributaries and upstream refugia, which were not affected by the disturbance, as well as the rapid recovery of abiotic parameters likely played a substantial role in assemblage recovery. This study not only demonstrates rapid recovery in an aquatic system, but further demonstrates the value of continuous, long-term, data collections which enhance our understanding of assemblage dynamics.

The effects of press and pulse disturbance by long and short-term pollution on the fish community in the Sinos River, RS, Brazil / Efeitos de distúrbios contínuos e pulsados da poluição aguda e de longo prazo sobre a comunidade de peixes no Rio dos Sinos, RS, Brasil

The fish fauna of the Sinos River has been subjected to severe pollution since the 1970´s. Continuous discharges of industrial and municipal sewage cause hypoxia and often even fish kills. The objectives of the present study are to assess long-term effects of pollution on the fish community over a time scale of approximately ten years and to investigate recuperation of the fish fauna after a massive fish kill in 2006. To assess the long-term impacts, seasonal sampling was conducted from September 2007 to March 2009 in four sites which were investigated in 1998/99 with the same methodology. The effects of the fish kill were investigated by comparing the present fauna in the affected river stretch with the fauna of an unaffected adjacent river stretch. The collective community properties richness and Shannon diversity changed during the ten year interval in a consistent pattern. Richness and Shannon diversity increased significantly in all sites, abundance values, however, did not. Analysis of species constancy and cluster analysis showed that the differences between the 1998/99 and 2007/09 studies were relatively small. The comparison of the reaches affected by the 2006 fish kills showed a rapid recovery within one year. Probably the Sinos fish fauna suffered the most severe impacts in the 70s of the last century, which could not be documented by this study. After an initial decline, the community displays relatively stable patterns with a tendency of recovery. After a severe fish kill, faunal recovery was rapid, probably favoured by the proximity of unpolluted source areas and physical habitat integrity of the Sinos River.

A fauna de peixes do Rio dos Sinos vem sendo exposta a uma poluição grave desde os anos 70 do século passado. Descargas contínuas de esgotos industriais e urbanos causaram hipóxia e recorrentes mortandades de peixes. Os objetivos do presente estudo são: avaliar os efeitos de longo prazo da poluição sobre a comunidade de peixes e investigar a recuperação da ictiofauna após uma mortandade severa em 2006. Para avaliar os impactos de longo prazo, foram realizados amostragens sazonais entre setembro de 2007 a março de 2009 em quatro locais que foram investigados em 1998/99 com a mesma metodologia. Os efeitos da mortandade de peixes foram investigados comparando a fauna no trecho afetado pela mortandade com o que não foi afetado. As propriedades coletivas da comunidade íctica riqueza e diversidade de Shannon aumentaram durante o intervalo de 10 anos em todos os pontos de amostragem, porém os valores da abundância ficaram estáveis. A análise da constância das espécies e a análise de agrupamento mostraram que as diferenças encontradas entre os estudos 1998-1999 e 2007/09 são pouco expressivas. A comparação dos trechos afetados e não afetados pela mortandade de peixes mostrou uma rápida recuperação da fauna que ocorreu em um ano. A ictiofauna do Rio dos Sinos sofreu provavelmente os impactos mais graves nos anos 70 do século passado, contudo, não documentado por este estudo. Depois de um declínio inicial a comunidade exibiu padrões relativamente estáveis com tendências de recuperação. Após as mortandades de 2006 a recuperação da fauna foi rápida, provavelmente favorecida pela proximidade de áreas de fonte não poluídas e pela integridade física dos habitats do Rio dos Sinos.

The effects of press and pulse disturbance by long and short-term pollution on the fish community in the Sinos River, RS, Brazil

p>The fish fauna of the Sinos River has been subjected to severe pollution since the 1970´s. Continuous discharges of industrial and municipal sewage cause hypoxia and often even fish kills. The objectives of the present study are to assess long-term effects of pollution on the fish community over a time scale of approximately ten years and to investigate recuperation of the fish fauna after a massive fish kill in 2006. To assess the long-term impacts, seasonal sampling was conducted from September 2007 to March 2009 in four sites which were investigated in 1998/99 with the same methodology. The effects of the fish kill were investigated by comparing the present fauna in the affected river stretch with the fauna of an unaffected adjacent river stretch. The collective community properties richness and Shannon diversity changed during the ten year interval in a consistent pattern. Richness and Shannon diversity increased significantly in all sites, abundance values, however, did not. Analysis of species constancy and cluster analysis showed that the differences between the 1998/99 and 2007/09 studies were relatively small. The comparison of the reaches affected by the 2006 fish kills showed a rapid recovery within one year. Probably the Sinos fish fauna suffered the most severe impacts in the 70s of the last century, which could not be documented by this study. After an initial decline, the community displays relatively stable patterns with a tendency of recovery. After a severe fish kill, faunal recovery was rapid, probably favoured by the proximity of unpolluted source areas and physical habitat integrity of the Sinos River. /p>

p>A fauna de peixes do Rio dos Sinos vem sendo exposta a uma poluição grave desde os anos 70 do século passado. Descargas contínuas de esgotos industriais e urbanos causaram hipóxia e recorrentes mortandades de peixes. Os objetivos do presente estudo são: avaliar os efeitos de longo prazo da poluição sobre a comunidade de peixes e investigar a recuperação da ictiofauna após uma mortandade severa em 2006. Para avaliar os impactos de longo prazo, foram realizados amostragens sazonais entre setembro de 2007 a março de 2009 em quatro locais que foram investigados em 1998/99 com a mesma metodologia. Os efeitos da mortandade de peixes foram investigados comparando a fauna no trecho afetado pela mortandade com o que não foi afetado. As propriedades coletivas da comunidade íctica riqueza e diversidade de Shannon aumentaram durante o intervalo de 10 anos em todos os pontos de amostragem, porém os valores da abundância ficaram estáveis. A análise da constância das espécies e a análise de agrupamento mostraram que as diferenças encontradas entre os estudos 1998-1999 e 2007/09 são pouco expressivas. A comparação dos trechos afetados e não afetados pela mortandade de peixes mostrou uma rápida recuperação da fauna que ocorreu em um ano. A ictiofauna do Rio dos Sinos sofreu provavelmente os impactos mais graves nos anos 70 do século passado, contudo, não documentado por este estudo. Depois de um declínio inicial a comunidade exibiu padrões relativamente estáveis com tendências de recuperação. Após as mortandades de 2006 a recuperação da fauna foi rápida, provavelmente favorecida pela proximidade de áreas de fonte não poluídas e pela integridade física dos habitats do Rio dos Sinos. /p>

A fish kill associated with a bloom of Amphidinium carterae in a coastal lagoon in Sydney, Australia.

We report on a dense bloom (~1.80 × 105 cells mL-1) of the marine dinoflagellate species Amphidinium carterae (Genotype 2) in a shallow, small intermittently open coastal lagoon in south eastern Australia. This bloom co-occurred with the deaths of >300 individuals of three different species of fish. The opening of the lagoon to the ocean, as well as localized high nutrient levels, preceded the observations of very high cell numbers. A. carterae is usually benthic and sediment-dwelling, but temporarily became abundant throughout the water column in this shallow (<2 m) sandy habitat. Histopathological results showed that the Anguilla reinhardtii individuals examined had damage to epithelial and gill epithelial cells. An analysis of the bloom water indicated the presence of a compound with a retention time and UV spectra similar to Luteophanol A, a compound known from a strain of Amphidinium. Assays with a fish gill cell line were conducted using a purified compound from cells concentrated from the bloom, and was found to cause a loss of 87% in cell viability in 6 h. The fish deaths were likely due to the low dissolved oxygen levels in the water and/or the presence of Luteophanol A-like compounds released during the bloom.

Ichthyotoxic Karlodinium veneficum (Ballantine) J Larsen in the Upper Swan River Estuary (Western Australia): Ecological conditions leading to a fish kill.

Ichthyotoxic Karlodinium veneficum has become a persistent problem in the eutrophic Swan River Estuary (SRE) near Perth, Western Australia. Karlotoxin (KmTx) concentrations and K. veneficum were sampled from March to July 2005, spanning a bloom confirmed by microscopy and genetics (ITS sequence), and a fish kill coincident with end of the bloom. The objective of this study was to investigate K. veneficum cell and toxin dynamics, and water quality conditions, leading up to the bloom and fish kill in this estuarine system. Abundance of K. veneficum increased as diatom abundance decreased over a 3-month period (Jan-Mar) preceding the bloom. Low freshwater flow to the SRE characterized the bloom initiation period, while elevated seasonal flows altered water quality and preceded the end of the bloom and fish kill. The bloom of K. veneficum was localized over a bottom layer of hypoxic water in a stratified water column. Low nitrate levels, DIN:DIP (mol) near unity, and particulate C:N:P of K. veneficum-rich water samples were consistent with nitrogen limitation of phytoplankton. A KmTx 2 congener was present in the concentration range 0-1052 ng KmTx mL-1, levels that were sufficient to kill larval fish in the laboratory within 4 h. A KmTx cell quota of 2.8 pg KmTx cell-1 was estimated for the bloom, which is moderately high for the species. Gill histopathology of fish from this fish kill showed signs of damage similar to those caused by KmTx in the lab. Results from this study suggest that conditions in the SRE, including elevated K. veneficum abundance and KmTx cell quotas, as well as hypoxia in the upper SRE, likely contribute to seasonal fish kills observed in this system.

Evaluation of techniques used to protect tailrace fishes during turbine maneuvers at Três Marias Dam, Brazil

Turbine dewatering and stop/startup may lead to the death of tons of fish at Brazilian power dams. The Três Marias Dam (TMD) on the São Francisco River has adopted two techniques to reduce the quantity of fish, mostly mandi (Pimelodus maculatus, Pimelodidae), affected by these maneuvers. They are: (i) spill before turbine dewatering to attract fish out of the tailrace, and (ii) fish screens in the stop log slots during turbine stop/startup to prevent fish from entering the draft tube. Here, we investigated whether spill and fish screens reduced the quantity of fish affected by turbine dewatering and stop/startup at TMD. We also determined whether the biomass of mandi trapped during turbine dewatering may be predicted by turbine discharge (Q) and/or catch per unit effort (CPUE) of mandis in the tailrace. Due to insufficient statistical power, our data were inconclusive as to whether spill attracted mandi out of the tailrace. We verified that the presence of fish screens significantly reduced the biomass of dead/moribund fish during turbine stop/startup. The biomass of mandis trapped in the draft tube during turbine dewatering was mainly influenced by Q (r² = 0.67), followed by CPUE (r² = 0.49). Since the trapped fish biomass correlated negatively with Q, we recommend that Q be maximized before turbine dewatering to reduce quantity of mandi trapped in the draft tube. The information presented here may be useful for reducing the quantity of fish affected by turbine maneuvers at TMD, as well as other dams.

Drenagem e parada/partida de turbina podem provocar a morte de toneladas de peixes em usinas hidrelétricas brasileiras. A usina de Três Marias (UTM), rio São Francisco, adotou duas técnicas para reduzir a quantidade de peixes, principalmente do mandi (Pimelodus maculatus, Pimelodidae), afetada durante essas manobras. Essas são: (i) vertimento antes da drenagem de turbina para atrair peixes para fora do canal de fuga, e (ii) grades nas guias das comportas ensecadeiras durante paradas/partidas para prevenir a entrada de peixes no tubo de sucção. Neste estudo, investigamos se o vertimento e as grades reduziram a quantidade de peixes afetados durante drenagem e parada/partida de turbina na UTM. Nós também determinamos se a biomassa de mandis aprisionados em drenagem de turbina pode ser predita pela vazão da turbina (Q) e/ou pela captura por unidade de esforço (CPUE) de mandis no canal de fuga. Devido ao poder estatístico insuficiente, nossos dados foram inconclusivos se o vertimento atraiu mandis para fora do canal de fuga. Verificamos que a presença das grades reduziu significativamente a biomassa de peixes mortos/moribundos em paradas/partidas de turbinas. A biomassa de mandis aprisionada no tubo de sucção nas drenagens foi influenciada principalmente pelo Q (r² = 0.67), seguida da CPUE (r² = 0.49). Como essa biomassa foi negativamente correlacionada com Q, recomendamos que Q seja máxima antes da drenagem para reduzir a biomassa de mandis aprisionada no tubo de sucção. Acreditamos que as informações apresentadas aqui poderão ser úteis para reduzir a quantidade de peixes afetada em manobras de turbinas na UTM e outras usinas hidrelétricas.

Temporal variation in fish community in the tailrace at Três Marias Hydroelectric Dam, São Francisco River, Brazil

Damming rivers to generate hydroelectric energy causes a series of changes in the environment, including impacts on the ichthyofauna. Knowledge of the fish community immediately downstream from a hydroelectric dam can help to reduce the negative effects of dam operation, such as fish entrance into the draft tube during turbines maintenance. We evaluated the temporal variation in fish community composition and abundance, near Três Marias Hydroelectric Dam (TMD), and its relationship with abiotic variables. Samples (n = 18) were carried out using gill nets in the tailrace of the dam, over the course of a hydrological year, at six time points during a 24-hour period. Abiotic data were also sampled to assess the relationship with the biotic data. In the tailrace, Characiformes showed the highest richness, while Siluriformes were the most abundant. Of the 33 species sampled, six were migratory. The fish community was significantly different between the dry and wet seasons, with higher abundances during the wet season. In the wet season, the frequency of migratory species in the community rose from 0.7 to 18.3%, and Pimelodus maculatus accounted for 14.5% of the overall abundance. We observed that Characiformes captures occurred mainly in the morning, with peak activity between 5:00 and 9:00 h. Siluriformes showed greater nocturnal activity and were largely captured between 17:00 and 21:00 h. Synchronizing operational maneuvers that represent high risk to the fish with periods of low abundance in the tailrace, i.e., during months of low precipitation, may be a measure to reduce the impact of the operation on the downstream fish community.

O barramento de rios para implantação de hidrelétricas causa uma série de modificações no ambiente, gerando impactos sobre a ictiofauna. O conhecimento sobre a comunidade de peixes encontrada imediatamente à jusante pode auxiliar na redução de impactos gerados pela sua operação. Assim, avaliamos as variações temporais na comunidade de peixes próxima à Usina Hidrelétrica de Três Marias quanto à composição de espécies, abundância e suas relações com variáveis abióticas. Foram realizadas 18 coletas com redes de emalhar no canal de fuga da usina, durante um ano hidrológico, em seis horários ao longo de 24 h, quando também foram obtidos dados abióticos. Foi observado que no canal de fuga da usina, Characiformes apresentou uma maior riqueza, enquanto os Siluriformes foram os mais abundantes. Das 33 espécies coletadas seis eram migradoras. A comunidade de peixes foi significativamente diferente entre os meses de seca e chuva, com maior abundância no período de chuva. Neste período, a frequência das espécies migradoras na comunidade subiu de 0,7 para 18,3%, sendo que Pimelodus maculatus representou 14,5% da abundância. A maior captura de Characiformes se deu no período da manhã com pico de atividade de 5:00 às 9:00 h. Os Siluriformes apresentaram maior atividade à noite, principalmente das 17:00 às 21:00 h. Conciliar manobras que oferecem mais riscos para os peixes com o período de menor abundância no canal de fuga, ou seja, nos meses de baixa pluviosidade, pode ser considerada medida para reduzir o impacto da operação sobre a comunidade à jusante.