Massive Fish Kills Research Articles

Giant Hydrogen Sulfide Plume in the Oxygen Minimum Zone off Peru Supports Chemolithoautotrophy

In Eastern Boundary Upwelling Systems nutrient-rich waters are transported to the ocean surface, fuelling high photoautotrophic primary production. Subsequent heterotrophic decomposition of the produced biomass increases the oxygen-depletion at intermediate water depths, which can result in the formation of oxygen minimum zones (OMZ). OMZs can sporadically accumulate hydrogen sulfide (H2S), which is toxic to most multicellular organisms and has been implicated in massive fish kills. During a cruise to the OMZ off Peru in January 2009 we found a sulfidic plume in continental shelf waters, covering an area >5500 km2, which contained ∼2.2×104 tons of H2S. This was the first time that H2S was measured in the Peruvian OMZ and with ∼440 km3 the largest plume ever reported for oceanic waters. We assessed the phylogenetic and functional diversity of the inhabiting microbial community by high-throughput sequencing of DNA and RNA, while its metabolic activity was determined with rate measurements of carbon fixation and nitrogen transformation processes. The waters were dominated by several distinct γ-, δ- and ε-proteobacterial taxa associated with either sulfur oxidation or sulfate reduction. Our results suggest that these chemolithoautotrophic bacteria utilized several oxidants (oxygen, nitrate, nitrite, nitric oxide and nitrous oxide) to detoxify the sulfidic waters well below the oxic surface. The chemolithoautotrophic activity at our sampling site led to high rates of dark carbon fixation. Assuming that these chemolithoautotrophic rates were maintained throughout the sulfidic waters, they could be representing as much as ∼30% of the photoautotrophic carbon fixation.Postulated changes such as eutrophication and global warming, which lead to an expansion and intensification of OMZs, might also increase the frequency of sulfidic waters. We suggest that the chemolithoautotrophically fixed carbon may be involved in a negative feedback loop that could fuel further sulfate reduction and potentially stabilize the sulfidic OMZ waters.

Osmotic stress does not trigger brevetoxin production in the dinoflagellate Karenia brevis.

With the global proliferation of toxic harmful algal bloom species, there is a need to identify the environmental and biological factors that regulate toxin production. One such species, Karenia brevis, forms nearly annual blooms that threaten coastal regions throughout the Gulf of Mexico. This dinoflagellate produces brevetoxins, which are potent neurotoxins that cause neurotoxic shellfish poisoning and respiratory illness in humans, as well as massive fish kills. A recent publication reported that a rapid decrease in salinity increased cellular toxin quotas in K. brevis and hypothesized that brevetoxins serve a role in osmoregulation. This finding implied that salinity shifts could significantly alter the toxic effects of blooms. We repeated the original experiments separately in three different laboratories and found no evidence for increased brevetoxin production in response to low-salinity stress in any of the eight K. brevis strains we tested, including three used in the original study. Thus, we find no support for an osmoregulatory function of brevetoxins. The original publication also stated that there was no known cellular function for brevetoxins. However, there is increasing evidence that brevetoxins promote survival of the dinoflagellates by deterring grazing by zooplankton. Whether they have other as-yet-unidentified cellular functions is currently unknown.

Dispatches

Dispatches

Brevisulcenal-F: A Polycyclic Ether Toxin Associated with Massive Fish-kills in New Zealand

A novel marine toxin, brevisulcenal-F (KBT-F, from karenia brevisulcata toxin) was isolated from the dinoflagellate Karenia brevisulcata. A red tide of K. brevisulcata in Wellington Harbour, New Zealand, in 1998 was extremely toxic to fish and marine invertebrates and also caused respiratory distress in harbor bystanders. An extract of K. brevisulcata showed potent mouse lethality and cytotoxicity, and laboratory cultures of K. brevisulcata produced a range of novel lipid-soluble toxins. A lipid soluble toxin, KBT-F, was isolated from bulk cultures by using various column chromatographies. Chemical investigations showed that KBT-F has the molecular formula C(107)H(160)O(38) and a complex polycyclic ether nature. NMR and MS/MS analyses revealed the complete structure for KBT-F, which is characterized by a ladder-frame polyether scaffold, a 2-methylbut-2-enal terminus, and an unusual substituted dihydrofuran at the other terminus. The main section of the molecule has 17 contiguous 6- and 7-membered ether rings. The LD(50) (mouse i.p.) for KBT-F was 0.032 mg/kg.

Mortality of mackerel ( Scomber scombrus L.) after pursing and slipping from a purse seine

A new method was used to study the effect of crowding and subsequent slipping from a purse seine on the mortality of Atlantic mackerel ( Scomber scombrus L.). Mackerel were allowed to swim from a purse seine through a transfer channel into two identical large floating net-pens. One pen was used as a control and was left floating in the sea without further treatment. The other was used to simulate crowding and slipping. The volume of the pen was gradually decreased by hoisting the bottom of the pen using a crane until the fish started to show panic reactions, and this volume was maintained for 15 min (2006) or 10 min (2007). The volume was then allowed to return to normal and the net-pens were left to drift freely in the open sea for 3–6 days. Five repeat experiments were performed, all of which showed that crowding has a major effect on survival rates. In all five experiments, mortality was higher among the crowded fish (80–100% mortality) than the controls (0.1–46% mortality), and the difference was significant ( p = 0.01). The experiments demonstrate that excessive crowding before slipping mackerel from purse seines should be avoided, if possible, in order to avoid massive fish kills.

Reassessing the ichthyotoxin profile of cultured Prymnesium parvum (golden algae) and comparing it to samples collected from recent freshwater bloom and fish kill events in North America

Within the last two decades, Prymnesium parvum (golden algae) has rapidly spread into inland waterways across the southern portion of North America and this organism has now appeared in more northerly distributed watersheds. In its wake, golden algae blooms have left an alarming trail of ecological devastation, namely massive fish kills, which are threatening the economic and recreational value of freshwater systems throughout the United States. To further understand the nature of this emerging crisis, our group investigated the chemical nature of the toxin(s) produced by P. parvum. We approached the problem using a two-pronged strategy that included analyzing both laboratory-grown golden algae and field-collected samples of P. parvum. Our results demonstrate that there is a striking difference in the toxin profiles for these two systems. An assemblage of potently ichthyotoxic fatty acids consisting primarily of stearidonic acid was identified in P. parvum cultures. While the concentration of the fatty acids alone was sufficient to account for the rapid-onset ichthyotoxic properties of cultured P. parvum, we also detected a second type of highly labile ichthyotoxic substance(s) in laboratory-grown golden algae that remains uncharacterized. In contrast, the amounts of stearidonic acid and its related congeners present in samples from recent bloom and fish kill sites fell well below the limits necessary to induce acute toxicity in fish. However, a highly labile ichthyotoxic substance, which is similar to the one found in laboratory-grown P. parvum cultures, was also detected. We propose that the uncharacterized labile metabolite produced by P. parvum is responsible for golden algae's devastating fish killing effects. Moreover, we have determined that the biologically-relevant ichthyotoxins produced by P. parvum are not the prymnesins as is widely believed. Our results suggest that further intensive efforts will be required to chemically define P. parvum's ichthyotoxins under natural bloom conditions.

Effects of Karenia brevis harmful algal blooms on nearshore fish communities in southwest Florida

Blooms of the toxic alga Karenia brevis, commonly referred to as 'Florida red tides,' occur along Florida's west coast on a near-annual basis, causing massive fish kills. However, few quantitative data on the ecological effects of red tides on fish communities exist. We surveyed fish communities in 5 habitats within Sarasota Bay and the adjacent Gulf of Mexico during the summers of 2004 to 2007 using a purse seine. We collected contemporaneous data on fish densities, fish spe- cies composition, K. brevis cell densities, water temperature, salinity, dissolved oxygen, and turbid- ity. Fish density (catch per unit effort (CPUE)) and species richness were significantly lower in all habitats during red tides. Shannon-Wiener diversity indices were significantly lower in 4 of 5 habitats during red tides. Classification and regression tree analysis showed significant negative relationships between K. brevis density and non-clupeid CPUE, and between K. brevis density and species rich- ness. Fish community structure differed significantly between red tide and non-red tide conditions. Canonical correspondence analysis showed that of all the environmental factors investigated, K. bre- vis density had the greatest influence on community structure. Most trophic guilds were negatively associated with K. brevis density, whereas the guild that included clupeids was positively associated with K. brevis density. Florida's fish kill database showed that 96% of local fish kills during 2003 to 2007 occurred during red tides. We concluded that red tides caused the observed changes in fish abundance and community structure. Harmful algal blooms occur throughout the world and may play an important, yet little understood, role in regulating fish communities.

Harmful algal toxins of the Florida red tide (Karenia brevis): natural chemical stressors in South Florida coastal ecosystems.

The Florida red tide is a descriptive name for high concentrations of the harmful marine alga, Karenia brevis. Although most prevalent along the south-west Florida coast, periodic blooms have occurred throughout the entire US and Mexico Gulf coasts and the Atlantic coast to North Carolina. This dinoflagellate produces a suite of polyether neurotoxins, called brevetoxins, that cause severe impacts to natural resources, as well as public health. These naturally produced biotoxins may represent one of the most common chemical stressors impacting South Florida coastal and marine ecosystems. Impacts include massive fish kills, marine mammal, sea turtle and sea bird mortalities, benthic community die-off and public health effects from shellfish contamination and inhalation of air-borne toxins. The primary mode of action is binding to voltage-gated sodium channels causing depolarization of nerve cells, thus interfering with nerve transmission. Other effects include immune depression, bronchial constriction and haemolysis. Parent algal toxins are synthesized within the unicellular organism, others are produced as metabolic products. Recent studies into the composition of brevetoxins in cells, water, air and organisms have shown PbTx-2 to be the primary intracellular brevetoxin that is converted over time to PbTx-3 when the cells are ruptured, releasing extracellular brevetoxins into the environment. Brevetoxins become aerosolized by bubble-mediated transport of extracellular toxins, the composition of which varies depending on the composition in the source water. Bivalved molluscs rapidly accumulate brevetoxins as they filter feed on K. brevis cells. However, the parent algal toxins are rapidly metabolized to other compounds, some of which are responsible for neurotoxic shellfish poisoning (NSP). These results provide new insight into the distribution, persistence and impacts of red tide toxins to south-west Florida ecosystems.

Geographic distribution of Karlodinium veneficum in the US east coast as detected by ITS-ferredoxin real-time PCR assay

Karlodinium veneficum is an ichthyotoxic dinoflagellate suspected to be responsible for massive fish kills. Because it is morphologically similar to Pfiesteria and related dinoflagellates, accurate abundance data of K. veneficum in the natural environment are difficult to obtain using light microscopy. In this study, species-specific real-time PCR assays were developed using the ferredoxin gene (KvFERR) and rDNA locus (partial internal transcribed spacer regions and 5.8S rDNA, KvITS). These assays were used to investigate the geographic and temporal distribution of K. veneficum from various estuaries and coastal regions of the Pacific and West Atlantic Oceans. In general, both genes gave similar quantitative results, detecting down to 0.1–1 K. veneficum cells mL−1. The higher occurrence frequency and abundance of K. veneficum were observed in Neuse River, North Carolina, Narragansett Bay, Rhode Island and Chesapeake Bay, MD, USA. Most of the KvITS sequences from North Carolina to Maine were identical to that of K. veneficum strain CCMP1975 (initially isolated from Chesapeake Bay), with 1–2 nucleotide substitutions occurring in sequences from Texas and Narragansett Bay samples. This result suggests the same origin and recent separation of K. veneficum populations living in this wide geographic range. In this study, K. veneficum was more abundant at 5–15°C and 4–20 psu.

Comparative analysis of two algicidal bacteria active against the red tide dinoflagellate Karenia brevis

The red tide dinoflagellate Karenia brevis blooms annually along the eastern Gulf of Mexico, USA, and is often linked to significant economic losses through massive fish kills, shellfish harvest closures, and the potential threat to humans of neurotoxic shellfish poisonings as well as exposure to aerosolized toxin. As part of an effort to enhance the strategies employed to manage and mitigate these events and their adverse effects, several approaches are being investigated for controlling blooms. Previous studies have established the presence of algicidal bacteria lethal to K. brevis in these waters, and we aim to characterize bacterial–algal interactions, evaluate their role as natural regulators of K. brevis blooms, and ultimately assess possible management applications. Herein, the algicidal activity of a newly isolated Cytophaga/ Flavobacterium/ Bacteroidetes (CFB)-bacterium, strain S03, and a previously described CFB-bacterium, strain 41-DBG2, was evaluated against various harmful algal bloom (HAB) and non-HAB species (23 total), including multiple clones of K. brevis, to evaluate algal target specificity. Strains S03 and 41-DBG2, which employ direct and indirect modes of algicidal lysis, respectively, killed ∼20% and ∼40% of the bacteria-containing isolates tested. Interestingly, no bacteria-free algal cultures were resistant to algicidal attack, whereas susceptibility varied occasionally among bacteria-containing isolates of a single algal taxon originating from either the same or different geographic location. The dynamics of K. brevis culture death appeared to differ according to whether the algicidal bacterium did or did not require direct contact with algal cells, with the former most rapidly affecting K. brevis morphology and causing cell lysis. Both bacterial strains promoted the formation of a small number of cyst-like structures in the K. brevis cultures, possibly analogous to temporary cysts formed by other dinoflagellates exposed to certain types of stress. Results were also consistent with earlier work demonstrating that bacterial assemblages from certain cultures can confer resistance to attack by algicidal bacteria, again indicating the complexity and importance of microbial interactions, and the need to consider carefully the potential for using such bacteria in management activities.

Acute Hypoxia–Reperfusion Triggers Immunocompromise in Nile Tilapia

Inadequate dissolved oxygen in the aquatic environment is a well-established cause of fish morbidity and mortality. The specific effects of hypoxia on immune function in fish, however, are not well characterized. In this study, the effects of acute hypoxia followed by reoxygenation (rapid tissue reperfusion) as a source of immunocompromise in Nile tilapia Oreochromis niloticus were investigated. Using a precision apparatus developed in our laboratory for hypoxia exposures, a series of assays of increasing specificity for immune function were performed on acutely hypoxia-stressed Nile tilapia: tier I consisted of histopathology, tier II of hematology, plasma chemistry, and determining cortisol concentration, and tier III of determining the phagocytic index and analyzing the expression of the cytokines transforming growth factor-beta (TGF-beta) and interleukin-1beta (IL-1beta). Nile tilapia were exposed to 7% oxygen saturation for 96 h, then tank water was rapidly reoxygenated. Sampling intervals were 48 and 96 h during hypoxia and 12 and 84 h during reperfusion. Histopathology showed no remarkable microscopic abnormalities in lymphoid or other tissues. Lymphopenia and neutrophilia were observed in peripheral blood. Plasma total protein, partial pressure of oxygen, and oxygen saturation were decreased in response to hypoxia. Plasma lipase decreased in response to hypoxia but returned to normal during reperfusion. Phagocytic capability and the phagocytic index decreased during hypoxia and 12 h reperfusion, whereas these values were recovered by 84 h reperfusion. The TGF-beta transcription continued to increase during the exposures, the greatest production being at 12 h reperfusion, whereas IL-1beta transcription decreased in response to hypoxia and reperfusion. We conclude that acute hypoxia triggered an overall downregulation of the immune system in the test fish. This suggests a possible factor in the pathogenesis of disease outbreaks in fish in which repeated, sublethal bouts of environmentally induced hypoxia lead to increased disease susceptibility and individual mortalities rather than massive fish kills.

Transfer of brevetoxins to a tellinid bivalve by suspension- and deposit-feeding and its implications for clay mitigation of Karenia brevis blooms

Blooms of the brevetoxin-producing Karenia brevis in the Gulf of Mexico cause massive fish kills, food poisoning and adverse respiratory effects in humans. Sedimentation of toxic cells following inert clay application could reduce toxin incorporation by commercially important suspension-feeding bivalves and thus prevent direct public health impacts, but could potentially lead to brevetoxin (PbTx) accumulation by benthic deposit-feeders. The goal of this study was therefore to compare suspension- and deposit-feeding as pathways for brevetoxins. We investigated: (1) the effect of toxic K. brevis on both feeding modes using a facultative deposit-suspension feeding tellinid bivalve, the clam Macoma balthica, as a model species and (2) the relative effectiveness of brevetoxin transfer via suspension- and deposit-feeding over 24-h exposure. Sedimentation of K. brevis was achieved by treatment with 0.25 g phosphatic clay l−1 and brevetoxin concentrations were measured by ELISA. Karenia brevis reduced both suspension- and deposit-feeding activity. This study demonstrates that brevetoxins can be rapidly accumulated by a surface deposit-feeding bivalve from sedimented K. brevis cells and that comparable toxin levels can be attained by both suspension- and deposit-feeding modes [1.2–1.6 μg PbTx (g tissue wet weight)−1]. Deposit-feeding clams generally do not pose a direct threat to humans but may provide a pathway for brevetoxin food web transfer.

Real time observations of coastal algal blooms by an early warning system

In eutrophic sub-tropical coastal waters around Hong Kong, phytoplankton or unicellular microalgae can grow rapidly to very high concentrations under favourable environmental conditions. These harmful algal blooms (HABs) have led to massive fish kills, hypoxia, and beach closures. However, to date the causality and mechanism of coastal algal blooms are still poorly understood. A remotely controlled autonomous real time field monitoring system has been developed to continuously track the changes in chlorophyll fluorescence, dissolved oxygen and other hydro-meteorological variables at two representative mariculture zones. The system can give an alarm when a bloom is detected, so that timely manual water quality sampling can be carried out to supplement the telemetric data. During 2000–2003, the system has successfully tracked 19 algal blooms. In the shallow weakly flushed coastal water (depth 7–10 m, tidal current 5–19 cm s −1), the bloom is short-lived, typically lasting a few days to over a week, with chlorophyll and DO concentrations in the range of 20–40 mg m −3 and 2–15 g m −3, respectively. It is found that: (1) the chlorophyll concentration is strongly correlated with its past values in the previous week, suggesting an auto-regressive type of algal dynamics; (2) the dissolved oxygen can reach highly super-saturated levels (12 g m −3) during a diatom bloom, and decreases to below 4 g m −3 at the tail of the growth phase; (3) in contrast, a dinoflagellate bloom is characterized by a much more pronounced vertical structure. Diel vertical migration and aggregation to dense layers are clearly observed. Significant dissolved oxygen consumption is associated with the migration, resulting in DO drops by as much as 6 g m −3 during the bloom; (4) the predominance of diatoms and dinoflagellates at the two sites can be explained in terms of the different hydrographic and nutrient conditions (the N:P ratio). Net algal growth rate, sinking and swimming velocities are derived from the in situ bloom data. The 4-year high frequency data set provides a basis for development of models for forecast of harmful algal blooms.

The effect of brevenal on brevetoxin-induced DNA damage in human lymphocytes

Brevenal is a nontoxic short-chain trans-syn polyether that competes with brevetoxin (PbTx) for the active site on voltage-sensitive sodium channels. The PbTxs are highly potent polyether toxins produced during blooms of several species of marine dinoflagellates, most notably Karenia brevis. Blooms of K. brevis have been associated with massive fish kills, marine mammal poisoning, and are potentially responsible for adverse human health effects such as respiratory irritation and airway constriction in beach-goers. Additionally, the consumption of shellfish contaminated with PbTxs results in neurotoxic shellfish poisoning (NSP). The purpose of the present study was to determine whether PbTx could induce DNA damage in a human cell type, the lymphocyte, and if so, whether the damage could be antagonized or ameliorated by brevenal, a brevetoxin antagonist. The DNA damage may occur through both endogenous and exogenous physiological and pathophysiological processes. Unrepaired or erroneously repaired DNA damage may result in gene mutation, chromosome aberration, and modulation of gene regulation, which have been associated with immunotoxicity and carcinogenesis. A single-cell gel electrophoresis assay, or comet assay, was used to determine and compare DNA damage following various treatments. The data were expressed as tail moments, which is the percentage of DNA in the tail multiplied by the length between the center of the head and center of the tail (in arbitrary units). The negative control tail moment was 29.2 (SE=+/-0.9), whereas the positive control (hydrogen peroxide) was 72.1 (1.5) and solvent (ethanol) was 24.2 (2.1). The PbTx-2 (from Sigma, St. Louis, MO, USA), 10(-8) M was 41.3 (3.6), PbTx-9 (Sigma), 10(-8) M was 57.0 (5.3), PbTx-2 (from University of North Carolina at Wilmington, UNCW), 10(-8) M was 49.4 (9.9), and PbTx-3 (UNCW), 10(-8) M was 64.0 (6.4). 1.0 microg/ml brevenal applied 1 h before the PbTxs protected the lymphocytes from DNA damage; PbTx-2 (Sigma), 31.3 (2.1); PbTx-9 (Sigma), 35.5 (2.9); PbTx-2 (UNCW), 33.9 (1.4); PbTx-3 (UNCW), 34.9 (1.25). The tail moment for 1.0 mug/ml brevenal alone was 30.8 (2.6). The results indicate that extensive genotoxic damage is induced by PbTx-2 and 9 (Sigma), and PbTx-2 and 3 (UNCW) in normal human lymphocytes, which is fully antagonized by brevenal. This suggests that the immune systems of individuals exposed to PbTx during harmful algal bloom (HAB) events may be at risk.

Brevenal is a natural inhibitor of brevetoxin action in sodium channel receptor binding assays.

1. Florida red tides produce profound neurotoxicity that is evidenced by massive fish kills, neurotoxic shellfish poisoning, and respiratory distress. Red tides vary in potency, potency that is not totally governed by toxin concentration. The purpose of the study was to understand the variable potency of red tides by evaluating the potential for other natural pharmacological agents which could modulate or otherwise reduce the potency of these lethal environmental events. 2. A synaptosome binding preparation with 3-fold higher specific brevetoxin binding was developed to detect small changes in toxin binding in the presence of potential antagonists. Rodent brain labeled in vitro with tritiated brevetoxin shows high specific binding in the cerebellum as evidenced by autoradiography. Synaptosome binding assays employing cerebellum-derived synaptosomes illustrate 3-fold increased specific binding. 3. A new polyether natural product from Florida's red tide dinoflagellate Karenia brevis, has been isolated and characterized. Brevenal, as the nontoxic natural product is known, competes with tritiated brevetoxin for site 5 associated with the voltage-sensitive sodium channel (VSSC). Brevenal displacement of specific brevetoxin binding is purely competitive in nature. 4. Brevenal, obtained from either laboratory cultures or field collections during a red tide, protects fish from the neurotoxic effects of brevetoxin exposure. 5. Brevenal may serve as a model compound for the development of therapeutics to prevent or reverse intoxication in red tide exposures.

A Comparative Study of the Harmful Dinoflagellates Cochlodinium polykrikoides and Gyrodinium impudicum Using Transmission Electron Microscopy, Fatty Acid Composition, Carotenoid Content, DNA Quantification and Gene Sequences

The massive growth of the dinoflagellate alga Cochlodinium polykrikoides in Korean coastal waters was first observed in 1982. Thereafter the blooms associated with massive fish kills have been occurring annually, and C. polykrikoides is now regarded a harmful red tide organism in Korea. Recently, a new chain-forming Gyrodinium impudicum, usually occurring with Cochlodinium polykrikoides, was observed. Thus, we need to identify the toxic C. polykrikoides from the non-toxic Gyrodinium impudicum. Because of a similarity in morphology, it is difficult to distinguish the two species under the light microscope. In this study, comparisons were made using fine-scale features of transverse sections and biochemical analysis including rDNA sequencing targeted ITS regions. The observation of cellular arrangement and structure by transmission electron microscopy showed a similar distribution of the main components in both species, but location of the nucleus and distribution of the chloroplasts were different. Fatty acid composition showed that the long-chain polyunsaturated fatty acid docosahexanoic acid was not present in Cochlodinium polykrikoides. These data suggest that fatty acid composition may be a useful biochemical indicator to distinguish the microalgae. The amount of total carotenoids in Gyrodinium impudicum was approximately 10 times higher than in Cochlodinium polykrikoides. The nuclear DNA content in Cochlodinium polykrikoides was twice as high as that in Gyrodinium impudicum (p < 0.06). Sequence analyses coding for the 5.8S rDNA and ITS regions showed quite different nucleotide alignments with only 55% similarity, the length of the ITS regions also differed. The genetic differences between the two microalgae will allow the development of species specific DNA probes for species differentiation.

Haidadinium ichthyophilumgen.nov. et sp.nov. (Phytodiniales, Dinophyceae), a freshwater ectoparasite on stickleback (Gastetosteus aculeatus) from the Queen Charlotte Islands, Canada

The dinoflagellate Haidadinium ichthyophilum gen.nov. et sp.nov. is associated with the threespine stickleback, Gasterosteus aculeatus L., in freshwater. This new genus differs from all previously described dinoflagellates in the morphology and ultrastructure of its complex life history stages and in the ecology of its interaction with G. aculeatus. Distinguishing characters included (i) the absence of thecal plates and the occurrence of chloroplastes in the short-lived swarmer (=dinospore) stage; (ii) the development of four distinct amoeboid stages including a spheroidal, rolling amoeba unknown in any other species; and (iii) the fact that this dinoflagellate causes epithelial hyperplasia in the stickleback and does not result in massive fish kills. Haidadinium ichthyophilum is known only from two acidic lakes in the Queen Charlotte Islands, British Columbia, Canada. Haidadinium is tentatively assigned to the family Phytodiniaceae of the order Phytodiniales. Key words: dinoflagellates, Dinophyceae, Gasterosteus, Haidadinium ichthyophilum gen.nov. et sp.nov., Queen Charlotte Islands, Phytodiniales, symbiosis, taxonomy, ultrastructure.

Winter Mass Mortality of Animals in Texas Bays

The Texas coast experienced three unusually cold weather periods in the 1980's, one in 1983 and two in 1989, that caused massive fish kills. Identification of organisms killed and estimation of the number of estuarine fishes and invertebrates killed was accomplished through a systematic standardized approach utilizing airplanes, ground qualitative observations and quantitative counts, and trawling. Of 159 species identified, 103 were fishes, 45 were invertebrates, and 11 were vertebrates other than fishes. About 14 million fishes were killed in December 1983, 11 million in February 1989 and 6 million in December 1989; number of invertebrates killed ranged from 13,000 in February 1989 to 1,000,000 in 1983. These assessments are the largest in area and most comprehensive to be documented in the literature with known levels of precision. Methodology used provides reasonably precise estimates which managers can use to assess extensive widespread kills and subsequent impacts on affected populations. It is recommended that managers consider reducing fishing mortality on the remaining economically important populations after extensive kills to speed recovery of those populations.

Massive fish kills within the Nyanza Gulf of Lake Victoria, Kenya

The morphometry and hydrology of the Nyanza Gulf of Lake Victoria can be greatly affected by violent storms. This can result in a condition in which nutrient-rich bottom mud is mixed with the sediment-laden runoff water from neighbouring marshes and rivers. This situation can lead to massive fish kills. It is such an event in 1984 which will be described that caused the sudden death of over 400 000 fish weighing over 2400 tonnes. The unusually low precipitation in the catchment area during that year resulted in a drop in the lake level from 12.4 to 11.8 m. This low water level, combined with a severe storm created the conditions which caused this large fish kill. The species affected were Lates niloticus and Oreochromis niloticus. Mortality was attributed to several factors which included high levels of suspended material in the water column (detritus and algae) which clogged the gills of the fish, low dissolved oxygen, low pH, and high concentrations of algae.

Impact of Municipal Wastewater on the Quality of the River Sava

The River Sava is very polluted in certain sections. At times, the dissolved oxygen is completely exhausted (1.0 to 3.0 mg O2/l) resulting in frequent massive fish kills. The water quality has significantly deteriorated during the past few decades, due to the industry developed in the watershed and the increased population in the area. Especially heavy pollution loads come from the greater Zagreb area (153 t BOD5/day). Treating the wastewater from Zagreb could upgrade the water quality of the Sava, and 68 to 72% oxygen saturation could be achieved even under the most unfavourable conditions. Particular attention should be given to the choice of the treatment process, due to the planned construction of multi-purpose reservoirs along the Sava.