Causes and consequences of the success of bream in Dutch eutrophic lakes

In the last decennia eutrophication has caused a shift in the species composition of fish communities in Dutch fresh waters. The changes have led to the disappearance of vegetation in lakes and ponds; zooplankton and chironomids are now the most abundant food organisms for fish. In the turbid, open waters bream and pikeperch are the dominant fish species. Only small bream is vulnerable to predation, but because bream grows much faster than the other cyprinids the time span in which the fish is vulnerable is the shortest. The large bream (>20 cm) can coexist with pikeperch since it is not vulnerable to predation and still utilizes the food organisms efficiently. Eutrophication is accelerated if both bream populations are composed of small-sized specimens preventing large-sized zooplankton to develop, and if they are composed of large-sized individuals which can efficiently stir up the bottom sediments.     

The proteomic study of Danio rerio embryos using one-dimensional electrophoresis and mass-spectrometry

Using one-dimensional proteomic mapping (combination of one-dimensional gel electrophoresis (1DE) with subsequent mass spectrometry MALDI-TOF-PMF) the protein profile of Danio rerio embryos has been investigated. The fish species Danio rerio is the most effective alternative model of vertebrates used for studies of drug toxicity (e.g. doxorubicin) due to its high degree of homology with human genome. The proteomic profiling resulted in identification of 84 proteins, including 15 vitellogenins. Using the procedure of preparation of homogenates of Danio rerio embryos optimized by ultrasonic treatment promoting removal of yolk basic proteins (vitellogenin) we have registered changes in the proteome profile of D. rerio embryos induced by doxorubicin (DOX). Growth D. rerio embryos in the medium with DOX caused the decrease in the number of vitellogenins, disappearance of cardiac troponins, and induction of caspase-3. All these observations are consistent with the literature data on doxorubicin-induced cardiotoxicity. The proposed method of 1D proteomic mapping may be used not only for protein identification but also for registration of changes in embryonic proteomic profile caused by drugs or any toxic compound for studying the mechanisms underlying induced toxicity.     

基于在线生物监测系统的氨氮胁迫下斑马鱼行为响应

研究基于四级阻抗技术的在线生物监测系统, 参照国家地表水环境质量标准(GB3838-2002)中对 Ⅰ 类和 Ⅳ 类地表水氨氮质量标准的限值分类, 探究 0.15和1.5 mg/L氨氮胁迫下 15d 内斑马鱼(Danio rerio)行为响应, 为环境胁迫下斑马鱼的行为响应提供数据支撑。实验采用斑马鱼游动强度和速率综合行为强度来反映其行为变化, 对实验数据进行 SPSS 差异性分析、自相关分析(Autocorrelation)和自组织神经网络(Self-organization mapping net, SOM)分析。研究结果: (1)在对照组中, 行为强度数据平均值为0.69±0.13, 光周期行为强度数据(0.73±0.13)高于暗周期(0.66±0.14; P<0.01), 且光暗周期差异值为10.61%; 在氨氮胁迫组(NH₃-N, 0.15和 1.5 mg/L)实验中, 斑马鱼行为强度平均值分别为0.68±0.09和0.64±0.09, 差异值分别为 7.6%和 18.64%, 与对照组相同, 光周期行为强度明显高于暗周期(P<0.01), 证明斑马鱼的昼夜节律性。(2)在氨氮胁迫下斑马鱼行为响应最显著的特点是行为活动遭到抑制。低浓度胁迫轻微抑制, 高浓度胁迫严重抑制。在有效氨氮浓度下, 浓度越高, 抑制作用越明显(P<0.001)。(3)斑马鱼行为响应具有显著的昼夜节律现象。Autocorrelation 中正负相关峰值交替性出现, 总体表现出较为良好的对称性和以 24h 循环的周期性, 通过SOM 分析, 大部分行为强度数据与光暗周期时间分布相匹配, 说明斑马鱼的昼夜节律现象。研究表明斑马鱼行为响应具有明显的昼夜节律现象, 光周期行为强度高于暗周期, 周期为 24h 左右; 在氨氮胁迫下斑马鱼行为强度遭到抑制, 在有效氨氮浓度下浓度越高, 抑制作用越明显, 出现时间节点延迟和聚类分析异常的现象。研究使用第三代在线生物行为监测系统, 其灵敏性和精确度显著提高, 能够实时准确反映氨氮胁迫下斑马鱼的行为响应变化, 也表明在线生物监测技术在水生生物行为学研究中发挥着不可或缺的作用。     

原油和消油剂对鱼类毒性的研究进展

原油对鱼类的毒性主要来自其水溶性成分,可导致鱼卵死亡或发育畸形,并造成鱼类麻痹、发炎、粘膜受损和死亡。消油剂的使用在分散了油膜的同时也带来二次污染,其活性剂对鱼类产生新的毒性影响。消油剂将原油分散为乳化颗粒并能进入鱼体内,加大了原油的毒性并延长其作用时间。综述了原油和消油剂对鱼类毒性的研究进展,展望了鱼类在相关毒性试验领域的应用及发展方向。     

Histological process and dynamics of germ cell degeneration in pejerrey Odontesthes bonariensis larvae and juveniles during exposure to warm water

Elevated temperature causes degeneration and disappearance of the germ cells in the males of scrotal mammals. It was recently shown that heat-induced germ cell degeneration occurs also in fish but, unlike in mammals, it occurs not only in males but also in females. The purpose of this study was to clarify the histological process and dynamics of heat-induced germ cell disappearance in pejerrey Odontesthes bonariensis larvae and juveniles. Monosex and mixed-sex fish produced by thermal manipulation of sex (temperature-dependent sex determination) were subjected to 29 degrees C for periods between 1 and 12 weeks, and used to analyze, by histological methods, the changes in gonadal size and the number of normal and degenerating germ cells. Groups exposed to 29 degrees C for 8-12 weeks were subsequently transferred to 24 degrees C to verify if any gonadal damage would be permanent. Germ cell degeneration, histologically characterized by nuclear pyknosis or eosinophilia and cytoplasmic eosinophilia, was observed with increasing frequency at higher temperatures (29>24> 17 degrees C) and more in males than in females. Clear degenerative changes in the germinal epithelium usually began within one week of exposure to 29 degrees C and appeared clearer in females than in males. Complete loss of germ cells was observed only in individuals exposed for periods of 8-12 weeks to 29 degrees C but no treatment produced 100% sterile fish. Germ cells that remained in the gonads after exposure to 29 degrees C retained the capacity to rapidly recolonize germ cell-depleted areas, suggesting that the associated somatic cells in the gonads are little or not affected by this temperature.     

Dimethylthiourea prevents hydrogen peroxide and neutrophil mediated damage to lung endothelial cells in vitro and disappears in the process

Dimethylthiourea (DMTU) progressively disappeared following reaction with increasing amounts of hydrogen peroxide (H2O2) in vitro. DMTU disappearance following reaction with H2O2 was inhibited by addition of catalase, but not aminotriazole-inactivated catalase (AMT-catalase), superoxide dismutase (SOD), mannitol, benzoate or dimethyl sulfoxide (DMSO) in vitro. By comparison, DMTU disappearance did not occur following addition of histamine, oleic acid, elastase, trypsin or leukotrienes in vitro. Addition of DMTU also decreased H2O2-mediated injury to bovine pulmonary artery endothelial cells (as reflected by LDH release) and DMTU disappeared according to both added amounts of H2O2 and corresponding degrees of injury. DMTU disappearance was also relatively specific for reaction with H2O2 in suspensions of endothelial cells where it was prevented by addition of catalase, but not AMT-catalase or SOD and did not occur following sonication or treatment with elastase, trypsin or leukotrienes. Addition of washed human erythrocytes (RBC) also prevented both H2O2 mediated injury and corresponding DMTU decreases in suspensions of endothelial cells. In addition, phorbol myristate acetate (PMA) and normal neutrophils, but not O2 metabolite deficient neutrophils from patients with chronic granulomatous disease (CGD), caused DMTU disappearance in vitro which was decreased by simultaneous addition of catalase, but not SOD, sodium benzoate or DMSO. Finally, addition of normal neutrophils (but not CGD neutrophils) and PMA caused DMTU disappearance and increased the concentrations of the stable prostacyclin derivative (PGF1 alpha) in supernatants of endothelial cell suspensions. In parallel, DMTU also decreased PMA and neutrophil-mediated PGF1 alpha increases in supernatants from endothelial cell monolayers. Our results indicate that DMTU can decrease H2O2 or neutrophil mediated injury to endothelial cells and that simultaneous measurement of DMTU disappearance can be used to improve assessment of the presence and toxicity of H2O2 as well as the H2O2 inactivating ability of scavengers, such as RBC, in biological systems.     

Correlation of the aquarium goldfish toxicities of some phenols,quinones, and other benzene derivatives with their inhibition of autooxidative reactions

Hydroquinone when added to the aquarium water was found to be about a hundred times more toxic than phenol, to goldfish (and to Daphnia magna), but is only about twice as toxic when injected into fish or mammals. Tertiarybutyl catechol shows a similar high toxicity in the aquarium, while the toxicity of catechol, resorcinol, and pyrogallol approaches more closely that of phenol. As the substances of high aquarium toxicity are known to inhibit many oxidative and polymerizing autocatalytic "chain reactions," rank correlations were tabulated between the recorded inhibitory potency of various substances in these processes, and their aquarium toxicity for goldfish. The correlation between aquarium fish toxicity and electric oxidation potential (P 0.09) is more than suggestive, and becomes still more so if explainable discrepancies are excluded. Antioxidant fat stabilizers show suggestive correlation with fish toxicity (0.20), and better with electric oxidation potential (0.10). The photographic reduction potential gives suggestive correlation with fish toxicity (0.20) and somewhat better with the oxidation potential (0.15). The gasoline induction period correlation is more than suggestive with the oxidation potential (0.099), but rather poor for fish toxicity (0.265). The rubber anti-aging potency gives only poor correlation (0.39) with fish toxicity. The reasons for these divergencies are not clear; they may perhaps be connected with the solvent properties of the substrate. As an example, Lea (p. 175) cites that 0.01 per cent of maleic acid prevents rancidity of fats, but is rendered ineffective by the presence of water. Taken by themselves, no one of the P values is entirely convincing of the relationships stressed in this paper. However, the consistent finding of relatively small values of P lends considerable weight to the hypothesis that these chemicals act in a related manner; and that the chemical activity of a substance may furnish useful suggestions of its biologic potency, perhaps more so than the chemical constitution as such. The aquarium toxicity, for goldfish is a convenient means of classifying the biologic potency.     

Selenium:mercury molar ratios in freshwater fish from Tennessee: individual, species, and geographical variations have implications for management

Vertebrates, including humans, can experience adverse effects from mercury consumed in fish. Humans often prefer large predatory fish that bioaccumulate high mercury levels. Recent attention has focused on the role of selenium countering mercury toxicity, but there is little research on the selenium:mercury molar ratios in freshwater fish. We examine selenium:mercury molar ratios in freshwater fish from Tennessee at Poplar Creek which receives ongoing inputs of mercury from the Department of Energy's Oak Ridge Y-12 facility. Our objective was to determine variation of the ratios within species that might affect the protectiveness of selenium against mercury toxicity. Within species, the ratio was correlated significantly and positively with fish length only for two species. There was great individual variation in the selenium:mercury molar ratio within each species, except striped bass. The lack of a clear relationship between the selenium:mercury molar ratio and fish length, and the intraspecific variation, suggests that it would be difficult to use the molar ratio in predicting either the risk from mercury toxicity or in devising consumption advisories.     

Actin-containing cables within anchorage-dependent rat embryo cells are dissociated by plasmin and trypsin

The distribution of intracellular actin has been examined by specific immunofluorescence in a series of normal and SV40-transformed cell lines of rat origin. A consistent correlation was found between the presence of large thick sheathes of actin-containing material and anchorage-dependent growth control. Anchorage-independent growth by these cells has been shown to be associated with the production and secretion of a plasminogen activator, and dependent upon the presence of the active protease plasmin. We have found that these phenomena can be linked as follows. First, treatment with plasmin, but not urokinase or plasminogen, reversibly removes the actin-containing cables from normal rat embryo fibroblasts, and similar results are obtained with trypsin. Thrombin and chymotrypsin are relatively ineffective in causing the disappearance of the cables. Second, sera such as dog or monkey, which permit high levels of plasmin formation and activity, support cell growth in semi-solid media better than sera in which plasminogen is activated poorly or that are plasminogen-deficient; concomitantly, cables disappear in the former but not in the latter sera. The addition of a plasmin inhibitor prevents the disappearance of actin-containing cables.     

Comparative culture and toxicity studies between the toxic dinoflagellate Pfiesteria piscicida and a morphologically similar cryptoperidiniopsoid dinoflagellate

A series of fish bioassays using cultures of the toxic dinoflagellate, Pfiesteria piscicida and a cryptoperidiniopsoid dinoflagellate indicated various degrees of toxicity for Pfiesteria piscicida and no toxicity by the cryptoperidiniopsoid. P. piscicida maintained toxicity in the presence of live fish, and this toxicity was perpetuated following a series of inoculations to other culture vessels. Differences in the onset and magnitude of the fish deaths occurred, requiring 16 days for the initial fish death when using P. piscicida from a culture that had previously been maintained on algal cells, to kills within hours when using a culture that had recently (previous day) killed fish. Autopsies of moribund fish from the test and control fish bioassays indicated a general lack of bacterial infection, which ensued following death of other autopsied fish. Moreover, bacterial comparisons of waters in the fish bioassay and control fish cultures indicated that similar bacterial concentrations were present. Neither oxygen or ammonia levels were determined to be factors in the fish death. Life stages of a cryptoperidiniopsoid dinoflagellate from Virginia estuaries were also identified, including motile zoospore, gametes, planozygote, amoebae, and cyst stages. The cryptoperidiniopsioid did not initiate fish deaths in bioassays conducted over a 14-week period at zoospore concentrations of ca. 700-800 cells ml(-1). Elemental X-ray analysis of the scales from cysts of this dinoflagellate and P. piscicida indicate that they both contain silicon. Overall, the data from this study demonstrate that the cryptoperidiniopsoid possesses several similar life stages and feeding patterns as P. piscicida, but was not toxic to fish.     

A food web based hypothesis for the survival vs. weight relationship of rainbow trout in an experimental stream study with bleached kraft mill effluent

A series of experimental streams studies carried out with biologically treated bleached kraft mill effluent (BKME) and rainbow trout Oncorhynchus mykiss included a variety of fish health parameters. There was a pattern of larger but fewer fish in BKME exposed streams. To determine if reduced fish numbers was a detrimental effect, we examined the relationship between number and weight for control and BKME exposed streams for the 9‐month effluent exposures of 1.3–5.1% v/v. A regression analysis indicated that fish numbers decreased at a similar rate for corresponding fish size in both control and BKME‐exposed streams. A dose‐response relationship for effluent and fish number was not found, indicating that reduced fish number was not a direct expression of toxicity. The factors which induced BKME‐exposed fish populations to tend toward fewer but larger fish were not determined but are hypothesized to relate to BKME food web stimulation, a related enhancement in trout growth, and a corresponding reduction in fish number.     

The population biology of two species of eyefluke, Diplostomum gasterostei and Tylodelphys clavata, in perch

Incidence, intensity and frequency distributions of infections in perch, Perca fluviatilis , with the eyeflukes Tylodelphys clavata and Diplostomum gasterostei were studied in a lake at monthly intervals over a period of two years. T. clavata had appeared in the lake immediately prior to the study, and its levels of infection continued to rise throughout the period of investigation whereas those of D. gasterostei remained relatively steady. The main period of infection of fish by both species of parasites was late summer, but a second and minor infection took place in spring. In the first year after its introduction T. clavata exhibited a seasonal cycle in incidence and intensity of infection and disappeared from fish in summer, but in the second year this cycle was masked by increased variation in development times and lack of synchrony throughout the parasite population. It is concluded that T. clavata has a life span of one year or less and that the parasites die within the fish, mainly in summer. D. gasterostei in contrast has a life span of at least one year, and disappearance of the parasite from the population is probably due to death of some heavily infected fish, although it was not possible to determine if this was due directly to the presence of the parasite.     

Disappearance of koaro,Galaxias brevipinnis,from Lake Rotopounamu,New Zealand,following the introduction of smelt,Retropinna retropinna

Synopsis Koaro, Galaxias brevipinnis, were once the only fish present in Lake Rotopounamu but, after a comprehensive survey in 1990, none were found in the lake or its tributary streams. Introduced native fish, specifically smelt, Retropinna retropinna, and the common bully, Gobiomorphus cotidianus, now occur in this lake. As koaro co-exist with bullies in other lakes, but have declined in landlocked lakes containing smelt, the disappearance of koaro in Lake Rotopounamu is attributed to the introduction of smelt alone. Interspecific competition for food between 0 + year old koaro and smelt, combined with predation by 2 + year old smelt on koaro larvae, are thought to be responsible. Such a mechanism would be consistent with theoretical predictions of predator-prey regulation systems within same chain food webs. Rainbow trout, Oncorhynchus mykiss, which were introduced into a number of local lakes before smelt, and which preyed on the koaro, have been blamed for the decline of the koaro populations. However, the disappearance of koaro in Lake Rotopounamu shows that smelt can reduce koaro populations independently of trout predation.     

Invited Debate/Commentary: Selenium — A Potential Time Bomb or Just Another Contaminant?

Environmental issues related to selenium are complex and not universally understood. This paper provides detailed information regarding selenium and associated aquatic environmental issues, and then introduces and comments on five debate/commentary papers discussing selenium in the context of the title of this paper. Selenium has a complex and not fully understood biogeochemistry in the aquatic environment as well as an unusual mode of toxicity (acute via water column exposure; chronic via food chain exposure). It has the narrowest range between nutritional requirements and toxicity of any essential element, and chronic toxicity is not readily predictable. Selenium contamination of waters or even of tissues does not necessarily indicate a ticking time bomb; there are no generally accepted or universally accepted threshold values for chronic toxicity. Assessing risk must be done site-specifically in a risk assessment framework, focusing on reproductive effects to sensitive exposed fish and waterfowl and on “worst case” hydrologic units. Unless selenium inputs decrease or site-specific biogeochemistry can be shown not to change, continued biological monitoring and testing are required. Provided the necessary investigative and monitoring studies are done, any potential selenium time bombs can be defused.     

Kinetics of the absorption of amino acids by the rat intestine in vivo

The kinetics of l-phenylalanine and l-lysine absorption by the rat small intestine in vivo have been studied by perfusing intestinal segments and monitoring simultaneously the uptake of the substrate into the intestinal tissue and its disappearance from the perfusate.The rate of phenylalanine disappearance is a linear function of the substrate concentration. Its uptake into the tissue is rapid and obeys saturation kinetics, but is not concentrative. Both tissue uptake and disappearance rate can be inhibited by leucine or methionine, but are not influenced by hydrophilic neutral or dibasic amino acids.Lysine disappearance from the perfusate and its uptake into the tissue both display saturation kinetics. Lysine transport is quantitatively smaller than that of phenylalanine. Both uptake and disappearance are inhibited by arginine and leucine, but are unaffected by other neutral amino acids or sugars.To analyse the kinetic results, integrated equations were developed to express the final concentration in the perfusate in terms of the original concentration. The disappearance rate was considered as a mixed process (saturable and non-saturable in parallel) in a one-compartment system, and the uptake by the tissue was treated as a two-compartment system in which the amino acid entered the cells by a mixed process but left them by a pure non-saturable mechanism.The results concerning disappearance from the lumen are compatible with the one-compartment model. Phenylalanine absorption can be described by a major non-saturable component and a minor saturable one, while lysine absorption occurs almost entirely by a saturable process. The two-compartment model does not adequately describe the tissue uptake results.     

Toxicity studies of nonylphenol on rosy barb (Puntius conchonious): a biochemical and histopathological evaluation

Acute and subacute toxicity of the nonylphenol (NP) on fish was investigated in laboratory toxicity tests with rosy barb (Puntius conchonious). The acute toxicity of NP to rosy barb was determined in semi-static bioassays. Median lethal concentration (LC50) for 96 h was 1.72 microM. The effects of sublethal concentrations of NP (0.17, 0.34 and 0.68 microM) on the structures and biochemical parameters [alkaline phosphatase (ALP), aspartate aminotransferase (AST) and alanin aminotransferase (ALT)] in gills, liver and kidney of rosy barb were studied after 14 days. The results showed that NP caused alteration of the structure in organs, as evidenced by the hyperplasia of epithelium and the fusion of secondary lamellae in the gills, the disappearance of the cell membrane and the cell necrosis in the liver as well as haemorrhages in the kidney. In addition, the functional enzyme activities were also changed. The increase trend in ALP activity in organs of fish treated with NP was recorded. The levels of AST and ALT in gills, liver and kidney were stimulated to rise at the lower concentration and fall at the higher concentration NP treatment compared to controls. This study suggests that NP can alter of the structures and biochemical parameters within non-endocrine tissue of fish and these changes may be mediated via destroying membrane structure and inducing cell necrosis.     

Modulation in hepatic and head kidney parameters of carp (Cyprinus carpio L.) induced by copper and chitosan

Copper is used in treatment mixtures to control fungal diseases in vineyards plants. High concentrations of copper are inducing antioxidant stress in some aquatic ecosystems, and potential bioaccumulation in aquatic organisms has prompted the demand for alternative use of low toxic molecules in culture treatments. Chitosan is a biomolecule with antifungal and heavy metal ion chelating properties that may be used as a biopesticide. In this study, we investigate the potential toxicity of chitosan for aquatic animal health, alone or associated with copper. Carp (Cyprinus carpio L.) were exposed to different chitosan concentrations (from 37.5 to 375 mg/l) or to two sublethal copper concentrations (0.1 and 0.25 mg/l) or to chitosan and copper (75 and 0.1 mg/l, respectively). Antioxidant enzyme activities were enhanced in chitosan treated fish after 4 days and depressed after 8 days. This phenomenon indicated a non-negligible toxicity of chitosan in fish physiology. However, the mixture copper-chitosan seems to induce a lower degree of oxidative stress than each fungicide alone. These observations show that chitosan is a potentially noxious molecule for some fish and any industrial and/or agricultural uses of this compound will have to address this problem.     

A review of karenia mikimotoi: Bloom events,physiology, toxicity and toxic mechanism

Karenia mikimotoi is a worldwide bloom-forming dinoflagellate in the genus Karenia. Blooms of this alga have been observed since the 1930s and have caused mass mortalities of fish, shellfish, and other invertebrates in the coastal waters of many countries, including Japan, Norway, Ireland, and New Zealand. This species has frequently bloomed in China, causing great financial losses (more than 2 billion yuan, Fujian Province, 2012). K. mikimotoi can adapt to various light, temperature, salinity, and nutrient conditions, which together with its complex life history, strong motility, and density-dependent allelopathy, allows it to form blooms that are lethal to almost all marine organisms. However, its toxicity differs between subspecies and some target-species-specific toxicity has also been recorded. Significant gill disorder is observed in affected fish, to which the massive fish kills are attributed, rather than to the hypoxia that occurs in the fading stage of a bloom. However, although this species is haemolytic and cytotoxic, and generates reactive oxygen species, none of the isolated toxins or lipophilic extracts have toxic effects as extreme as those of the intact algal cells. The toxic effects of K. mikimotoi are strongly related to contact with intact cells. Several reasonable hypotheses of how and why this species blooms and causes mass mortalities have been proposed, but further research is required.     

Biological degradation of resin acids in wood chips by wood-inhabiting fungi.

Resin acids in many pulp mill effluents are primary sources of toxicity to fish. Inconsistent biological detoxification of chlorinated and nonchlorinated resin acids in secondary treatment of pulp mill effluents is a continuing source of concern. An alternative approach to effluent detoxification is to remove or modify the toxic compounds present in wood chips prior to pulping. Results from experiments in which lodgepole pine sapwood chips were inoculated with several fungal candidates indicate that the total resin acid content can be reduced by up to 67% after fungal growth. Such a treatment could be an efficient and environmentally acceptable way for deresinating wood chips and so decreasing the toxicity of pulp mill effluents.     

Intermittent exposure to aquatic pollutants: assessment,toxicity and sublethal responses in fish and invertebrates

Aquatic animals are often exposed to intermittent, variable poison concentrations during pollution incidents. However, current understanding of ecotoxicology has evolved primarily from continuous exposure studies. This review summarises the relatively dispersed toxicity literature on intermittent exposures. Methodologies used in existing continuous exposure toxicity tests may be adapted to intermittent regimes provided the exposure profile is known and “poison concentration” is defined to give toxicologically relevant lethality estimate. Such tests rely on assuming that continuous and intermittent exposures of equivalent dose have the same toxicity. This assumption is untrue for some chemicals. The toxicity of intermittent events may be assessed by correlating mortality with poison accumulation, biochemical, haematological or physiological response syndromes. Such bioassays can be performed without knowledge of the exposure profile, and are often sufficiently rapid to record short pollution events. Intermittent and continuous exposures of equivalent dose may not have the same toxicities. Intermittent exposures are less toxic than continuous events, but only when peak concentrations of pollutant are the same in each regime. Exceptionally, sulphuric acid, acid/Al and ammonia are much more toxic to fish when administered intermittently. Variations in intermittent exposure frequency or duration do not produce proportional changes in lethality, since apparently large changes in exposure dose may not significantly alter toxicity. The short-lived nature of intermittent exposures suggests that equilibriums in poison concentrations between the external environment and the body compartments of the test species are not achieved. The overall accumulation response depends particularly on the duration of peak concentrations and any “recovery periods” between multiple episodes relative to poison uptake and depuration rates respectively. Transient biochemical and physiological disturbances occur during intermittent exposures. Latent effects include reduced post-exposure growth and reproductive failure in the F₁ generation, or increased deformities in the F₂ generation of fish.