Direct and circulatory paths of Permethrin (NRDC-143) causing histopathological changes in the gills of rainbow trout, Salmo gairdneri Richardson

Rainbow trout were exposed to sublethal concentrations of Permethrin in water (0.09, 0.18 and 0.35 μg l⁻¹) and in food (85, 180 and 350 μg kg⁻¹ dry diet) in 20–0 day experiments. Histological changes in the gills included epithelial separation or necrosis, mucus cell hyperplasia, clubbing of epithelial cells or hyperplasia and fusion of adjacent secondary lamellae. These changes were noted in all fish, suggesting that the pesticide or its metabolites reached the gills not only directly through the water, but also indirectly via the circulation.     

Mercury and chlorinated hydrocarbons in the food chain of Lake Päijänne, Finland

The sediments and various organisms in Lake Päijänne were examined for contaminants. The average mercury content of water plants was 9, of plankton 14, of sediment 114, of zoobenthic predators 83, of fish 332–1510 and of birds 240–13685 μg kg⁻¹ (wet weight). The average PCB content of plants was 3, of plankton 21, of the zoobenthos 44, of fish 36-117 and of birds 219–13490 μg kg⁻¹. The average ΔDDT content of plants was 0.5, of plankton 6, of the zoobenthos 14, of fish 7–42 and of birds 144-8262 μg kg⁻¹. Regional differences in mercury content were most pronounced in sediment and fish. PCB concentration was highest near a town. ΔDDT was quite evenly distributed. Water plant species did not differ from each other, nor did the plankton fractions. The zoobenthic predators contained more chlorinated hydrocarbons than did the herbivores. There were clear differences between most species of fish and the chlorinated hydrocarbon content was highest in vendace. In adult birds levels of all residues were significantly higher than in juveniles.
In most cases PCB content was positively correlated with ΔDDT and in birds PCB, ΔDDT and mercury levels were correlated. DDT residues occurred mostly as DDE, but in vendace the proportion of DDT was high. At most trophic levels, ΔDDT/PCB was 0.15-0.40 but in birds it reached 1–2.     

Seasonal Variation of Boron and Fluoride in Tilapia nilotica from an Egyptian Fish Farm in Relation to Human Health Hazard Assessment

This study evaluated the seasonal accumulation of boron and fluoride in different tissues of a common edible fish, Tilapia nilotica, from an Egyptian fish farm as well as their hazard to human health. Among all the determined fish tissues, brain, liver, and bone were the ones that accumulated the highest boron and fluoride contents. Interestingly, flesh tissue showed the lowest boron and fluoride concentrations (0.30 ± 0.06 and 2.50 ± 1.57 μg/g, respectively). Statistical analyses using Pearson correlation matrix and multiple regression procedures indicated that boron accumulation was highest amongst flesh, liver, brain, and bone tissues. Additionally, fluoride content in water affects its abundance in the different fish tissues: flesh, gills, bone, and skin. Human hazard assessment of fluoride and boron from water, sediment, and fish flesh tissue was studied using calculations that considered chronic daily intake from water, sediment, and fish; chronic exposure from dermal contact and ingestion of water; and fish as well as a single acute human dose. These calculations indicated that the consumption of Tilapia nilotica is still safe as regards boron intake, but for fluoride, it may pose a hazard to human health in the long term.     

Reproductive biology, length-weight relationship and relative condition of pond raised Tilapia zilli (Gervais)

In 'runted' populations of Tilapia zilli positive correlations were found between maturation stages and the following: gonadosomatic index, gonad weight, fish weight and fish length. The minimum size at maturity was 9·0 cm in males and 11·0 cm in females. The mean fecundity in the 'stunted' females was 2359 eggs and it increased with length ( L ) weight (HO and depth ( D ) of the fish. There was, however, no correlation between fecundity and egg size. The results indicated that growth in this 'stunted' T. zilli population was not isometric. The relative condition factor ( Kn ) which approached one indicates good condition.     

Induced spawning by LHRHa and pimozide in the Asian catfish Clarias macrocephalus (Gunther)

Experiments were conducted to determine the optimum dose of luteinizing hormone-releasing hormone analogue (LHRHa) and pimozide (PIM) injected simultaneously to yield a high ovulation rate and produce sufficient eggs in the Asian catfish Clarias macrocephalus . In June 1990, injection of 0.05 or 0.10 μg LHRHa/g body weight (BW) + 1 μg PIM/g resulted in 100% ovulation, while only 80% of gravid catfish injected 0.025 μg LHRHa + 1 μg PIM/g ovulated. Most of the eggs stripped from 6 out of 8 control fish were not mature. Fertilization and hatching rates of LHRHa + PIM-induced fish (75–90% and 39–51%, respectively) were higher than those of control fish (36–39% and 0–1% respectively). In August and September 1990, at gravid catfish ovulated after injection of 0.05–0.10 μg LHRHa + 1 μg PIM/g BW. However, only 20% of the fish given 0.025 μg LHRHa/g + 1 μg PIM/g BW in August ovulated. No eggs could be striped from any of the control fish in August and September 1990. Techniques developed in this study, showed a simple and effective way of spawning captive catfish, C. macrocephalus . A simultaneous intramuscular injection of 0.05 μg LHRHa + 1 μg PIM/g and stripping of eggs at 16–20 h post-injection have been tested to yield high ovulation, fertilization and hatching rates.     

Some effects of low pH and calcium on the growth and tissue mineral content of yearling brown trout, Salmo trutta

Yearling brown trout, Salmo trutta , were exposed to low mineral content water (nominal concentrations of 20μmol 1⁻¹ magnesium, 7.7 μmol 1⁻¹ potassium, 44 μmol 1⁻¹ sodium) over a pH range of 4.0–5.2 with ambient calcium concentrations of 2.5–60 μmol 1⁻¹. All fish died at pH 4.0 and 4.2 irrespective of ambient calcium concentration and also at pH 4.4 with only 2–3 μmol 1 ⁻¹ calcium (that is calcium-free water except for that leached from the diet or excreted by the fish). Good growth rates were obtained over the remaining treatments which extended down to pH 4.4 with as little as 7 μmol 1⁻¹ calcium. When starved, weight loss was inversely correlated with pH. Effects on plasma chloride, percentage dry weight and calcium, potassium sodium, and phosphorus contents of skin, muscle and bone tissue were also investigated. These demonstrated pH effects on mineral metabolism in starved fish, but no effects were detected in fed fish.     

Tissue distribution and residue depletion of thiamphenicol after multiple oral dosing in seabass (Dicentrarchus labrax L.) and seabream (Sparus aurata L.)

The distribution and residue depletion of thiamphenicol (TAP) were studied in seabass ( Dicentrarchus labrax L.) and seabream ( Sparus aurata L.) reared in field conditions at temperatures of 20–28 °C. The drug was administered orally as medicated feed at the rate of 40 mg active ingredient (a.i.) kg⁻¹ of biomass once a day for 5 days. Samples of muscle, liver, skin and vertebrae from 10 fishes were collected on the 2nd and 4th day of treatment and 1, 2, 3, 5, 7, 9, 12, 15, 18, 21, 24, 27 and 30 days after the last administration of the drug, and were stored at −20 °C. Quantitative analysis of TAP was performed by high performance liquid chromatography (HPLC) after liquid-liquid extraction; the quantification limits of the HPLC method were 0.02 μg/g for muscle, and 0.05–0.10 μg/g for the other tissues. In seabass, TAP concentrations during treatment were higher in liver and muscle than in skin and vertebrae, and rapidly decreased after the end of medication. Three days after treatment ceased, TAP was still detectable in liver (0.41 ± 0.23 μg/g), vertebrae (0.09 ± 0.03 μg/g) and in three out of 10 samples of muscle (0.03 μg/g), but not in skin. All tissues were below the limits of quantification on the 5th day of withdrawal. In seabream the highest TAP concentrations during treatment were measured in liver and skin, and their reduction after the end of medication was as rapid as that of seabass: on the 3rd day after treatment ceased traces were found in only four out of 10 samples of muscle (0.03 ± 0.00 μg/g) and vertebrae (0.08 ± 0.02 μg/g).     

Toxicity in Tilapia zilli and Clarias lazera (Pisces) induced by zinc, seasonally

Subadult teleosts, Tilapia zilli and Clarias lazera, were exposed in laboratory bioassays to lethal and sublethal concentrations of zinc, seasonally (at range of temperature between 9.3 +/- 1.5 and 25 +/- 1 degree C). It appears that Tilapia is more susceptible to Zn than Clarias and both species are more resistant to Zn toxicity at lower temperature (during winter). To determine the uptake and tissue distribution of Zn in the two species, gill, liver and muscles were analysed at moderate temperature (during spring). After a 96 hr exposure period, Zn was decreased in the following order: gill greater than liver greater than muscle.     

Susceptibility of Kenyan Wheat Varieties to Head Blight, Fungal Invasion and Deoxynivalenol Accumulation Inoculated with Fusarium graminearum

Fifteen wheat varieties commercially grown in Kenya were tested for their susceptibility to head blight and mycotoxin accumulation after inoculation with Fusarium graminearum in pot experiments. The strains of the pathogen used had been isolated from wheat collected in different growing areas of Kenya. Head blight susceptibility was assessed as the percentage of spikelets bleached and area under disease progress curve; kernel colonization by fungal mycelium was determined as ergosterol content. All varieties were found to be moderately to highly susceptible. However, the varieties differed in head blight susceptibility (29–68% of spikelets bleached; mean 54%), fungal colonization (67–187  μ g/g ergosterol content; mean 111  μ g/g) and the resulting mycotoxin contamination [deoxynivalenol (DON) 5–31  μ g/g; mean 13.5  μ g/g]. Grain weight reductions due to head blight ranged from 23 to 57% (mean 44%). The varieties could be therefore divided into partially resistant and highly susceptible genotypes. The kernels of highly susceptible varieties had higher mycotoxin and ergosterol contents. However, the kernels of some varieties contained more fungal mycelium (ergosterol) without the corresponding high amounts of DON, suggesting that they possess some resistance to DON accumulation. Less susceptible varieties showed resistance to fungal spread, as indicated by a slow disease development and lower content of fungal biomass.     

Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) chemical control: residues associated with the three consecutive spray strategy

Abstract  Chemical control of western flower thrips Frankliniella occidentalis requires three consecutive applications of the same pesticide, 3–6 days apart. Initially, pesticides recommended for western flower thrips control were based on established maximum residue limits (MRLs) from previously established use on pests other than F. occidentalis , rather than product efficacy against F. occidentalis . Moreover, MRLs were based on a single application rather than three consecutive sprays. Chemical residues associated with the three-spray strategy were not quantified. Here those residues are quantified and the scope for rate increases is further tested, as laboratory bioassays suggest that some current permit rates may be too low to be effective. At established withholding periods (WHPs), current permit rate applications of abamectin (0.018 g/L) on strawberry and tomato, and methidathion (0.5 g/L) and endosulfan (0.666 g/L) on lettuce produced residues above the current Australian MRL. Results indicated that a higher than the current permit rate for endosulfan (2.0 g/L) could be sustained on cucumber and strawberry at established WHPs, but would require an extension to the current WHP. Similarly, a modest increase in methidathion (1.0 g/L) rate on tomato could be practical, again with a WHP extension. In each instance additional supporting data are required to accurately quantify the proposed WHP extensions.     

Amount and distribution of biochemical-genetic variation among wild populations and a hatchery stock of Atlantic salmon, Salmo salar L., from north-east Ireland

The effects of tributyltin (TBT) compounds on gill morphology were examined in the mummichog, Fundulus heteroclitus , in 96-h LC50 and 6-week sublethal exposures. Morphometry was used for the identification and quantification of effects with the light microscope. A 96-h LC50 of 17.2 μg 1 ¹ was determined. Morphometric analysis of gill tissues revealed hypertrophy of the lamellar epithelium in fish exposed to 17.2 μg 1–1. Relative diffusing capacity was significantly decreased (−41 %); ( P <0.05, ANOVA, Bonferroni t -test). At 35.6 μg 1⁻¹, TBT exposure resulted in a significant reduction (− 40%) in the volume of the lamellar blood channels. Both of these observations occurred in fish that showed signs of acute poisoning including loss of equilibrium. In fish exposed to sublethal concentrations of 0.105–2.000 μg TBT 1⁻¹ for 6 weeks, there were no pathological changes in the gill. There were no treatment-related changes in the surface morphology of the gills of fish from both experiments upon scanning electron microscopic examination. Although gill pathology was observed in acutely toxic exposures, it does not appear to be a major mechanism of TBT toxicity.     

Sulphide tolerance and adaptation in the California killifish, Fundulus parvipinnis, a salt marsh resident

Hydrogen sulphide is a toxicant naturally produced in hypoxic marine sediments, hydrocarbon and brine seeps and hydrothermal vents. The California killifish, a salt marsh resident, is remarkably tolerant of sulphide. The 50% lethal concentration is 700 μM total sulphide in 96 h, and 5 mM in 8 h (determined in flow-through, oxygenated sea water). Killifish exposed to sulphide produce thiosulphate which accumulates in the blood. The cytochrome c oxidase (a major site of toxicity) of the killifish is 50% inhibited by <1 μM sulphide. Killifish liver mitochondria are poisoned by 50–75 μM sulphide but can oxidize 10–20 μM sulphide to thiosulphate. Sulphide causes sulphhaemoglobin formation (and impairment of oxygen transport) at 1–5 mM in vitro and to a small extent at 2 mM in vivo . Killifish blood neither catalyses sulphide oxidation significantly nor binds sulphide at environmental (low) sulphide concentrations. Exposure to 200 μM and 700 μM sulphide over several days causes significant increases in lactate concentrations, indicating shift to anaerobic glycolysis. However, individuals with the most lactate die. In terms of diffusible H₂S, the killifish can withstand concentrations two to three orders of magnitude greater than would poison cytochrome c oxidase. The high sulphide tolerance of the killifish, particularly of concentrations typical of salt marshes, can be explained chiefly by mitochondrial sulphide oxidation. Sulphide tolerance and mitochondrial sulphide oxidation in the killifish have a constitutive basis, i.e. do not diminish in fish held in the laboratory in sulphide-free water for 1–2 months, and are improved by prior acclimation.     

The reaction of young coho Oncorhynchus kisutch to declining oxygen levels during long-term exposure

The respiration of coho salmon, Oncorhynchus kisutch , weighing between 20 and 45 g was measured at gradually declining oxygen levels and at temperatures ranging between 14 and 17 °C. The maximum and minimum oxygen concentrations tested were 235 and 41 μmol/L, respectively. Respiration rates were measured for 24 h at 235 μmol/L before the oxygen concentration was lowered stepwise to 157 and 81 μmol/L. In one single trial, the oxygen level was lowered to 66, 53, and 41 μmol/L. Respiration was highly variable in time. Peak activities always occurred during the night. The standard metabolic rate at normoxic conditions was estimated to be around 4 μmol oxygen/g/h. The highest rates reached values close to 15 μmol oxygen/g/h. At reduced oxygen levels the standard oxygen demand slightly increased to 4.5 μmol oxygen/g/h, indicating a higher demand for vital metabolic functions. Due to the decrease of swimming activity, the maximum oxygen uptake rates dropped to < 8 μmol oxygen/g/h below 81 μmol/L oxygen concentration. Under long-term conditions, physiological and behavioural adaptations play an important role for survival and need to be considered for the design and operation of fish farm facilities.     

Hormonal sex reversal of wild-spawned tilapia in India

The effectiveness of methyltestosterone (MT) for sex reversal and growth promotion in Oreochromis mossambicus was studied in culture experiments in India. Wild-spawned fry were treated with 30 μg MT g⁻¹ diet for 30 or 60 days at two feeding levels (initially 20% or 10% of body weight daily). The fish were grown on for 66–96 days after the hormone treatment period in fertilized cement ponds without supplementary feeding. Tilapia treated with MT for 60 days attained an average weight of 29.0 g compared to 18.8 g for untreated fish reared under similar conditions. The percentage of males among the untreated tilapia was 58%, MT treatment for 30 days significantly increased this percentage at the higher feeding level (79% male), but not at the lower feeding level (51%). More than 90% of the tilapia in both 60 day MT treatment groups were male; 3% of all the fish reared showed an intersex condition. The experiments demonstrated that the anabolic and sex reversal effects of MT on tilapia are proportional to the duration of treatment and quantity of hormone administered. The possible application of monosex tilapia culture in tropical countries is noted.     

What do dung beetles eat?

Abstract.  1. Most adult coprophagous beetles feed on fresh dung of mammalian herbivores, confining ingestion to small particles with measured maximum diameters from 2–5 to 130 μm, according to body size and kind of beetle. This study explores benefits and costs of selective feeding in a 'typical' dung beetle with a maximum diameter of ingested particles (MDIP) of 20 μm.
2. Examined dung types (from Danish domestic sheep, cattle and horse, and African wild buffalo, white rhino and elephant) contained 76–89% water. Costs of a 20 μm MDIP were often low, since 69–87% of the total nitrogen in bulk dung other than that of elephant and rhino (40–58%) was available to selective feeders.
3. Nitrogen concentrations were high – and C/N ratios low – in most types of bulk dung compared with the average food of terrestrial detritivores or herbivores. Exceptions were elephant and rhino dung with low nitrogen concentrations and high C/N ratios.
4. Estimated C/N ratios of 13–39 in bulk dung (sheep–elephant) were decreased by selective feeding to 7.3–12.6 in the ingested material. In assimilated food, ratios are probably only 5–7, as most assimilable nitrogen and carbon may be of microbial origin. If so, the assimilable food contains a surplus of nitrogen relative to carbon.
5. The primary advantage of selective feeding, particularly in dung with a high C/N ratio, may be to concentrate assimilable carbon in the ingested food. Effects of changing the MDIP within 20–106 μm are modest, especially in dung with a low C/N ratio.     

The effect of humic substances on the toxicity of aluminium to adult rainbow trout, Oncorhynchus mykiss (Walbaum)

Some physiological parameters were measured in adult rainbow trout during a 10-day exposure to 180 μg Al_total l⁻¹ in acid water (pH 4.7) with or without humic substances (10 mg l⁻). The fish were acclimatized to pH 5.0 for 7 days prior to the experimental treatments.
Chemical analyses revealed that, in the presence of human substances, 74–80% of the A1 was organic bound, while in the absence of humic substances most of the Al(987percnt;) occurred in the inorganic form.
Al bound to humic substances (13–150 μg l⁻¹) did not alter the plasma NaCl-concentration, nor the haematocrit value, of rainbow trout during an exposure period of 10 days. This contrasts with the high death rate obtained within 2–3 days when most of the A1 (175 μg l⁻¹) was in the inorganic form. The lethality was accompanied by a 25% decrease in the plasmaconcentration of NaCl and a doubling of the haematocrit value. Bulk analysis revealed that when the metal was present in inorganic forms the total Al content of the gills (75 μg A1 g⁻¹ wet weight) was 15 times higher than when it was present as bound to the humic substances. These experiments showed that the accumulation of A1 at the gills was accompanied by physiological disturbances, both being a function of the chemical speciation of Al.     

Light and Electron Microscopy of the Spore of Myxobolus heckelii n. sp. (Myxozoa), Parasite from the Brazilian Fish Centromochlus heckelii (Teleostei, Auchenipteridae)

ABSTRACT. A myxosporean parasitizing the gill filaments of the freshwater teleost fish Centromochlus heckelii collected in the Tocantins River (Lower Amazonian Region, Brazil) is described using light and electron microscopy. This parasite produces spherical to ellipsoidal cyst-like plasmodia up to 250 μm in diameter, with a thick wall strengthened by several stratified juxtaposed crossed collagen layers, whose thickness varies according to the number of the layers. Several compressed fibroblasts are observed among the collagen fibrils. Deposits of spherical dense material are scattered at the internal periphery of the cysts. Plasmodia and different developmental stages, including immature and mature spores, filled the central region of the cysts. The spore body is ellipsoidal in valvar view and biconvex in sutural view. It is formed by two equal-sized and symmetric valves measuring 12.7 μm long (12.2–13.1) ( n =50), 6.6 μm wide (6.3–6.9) ( n =25), and 4.0 μm (3.7–4.4) ( n =20) thick. A thin layer formed by fine and anastomosed microfibrils is observed at the spore surface. Two equal, elongated pyriform polar capsules measure 2.9 μm (2.7–3.3) × 1.7 μm (1.4–2.0) ( n =25), each containing four or five oblique polar filament coils. The binucleated sporoplasm contains numerous spherical sporoplasmosomes, glycogen particles, and a large vacuole with fine granular matrix. Based on the morphological and ultrastructural differences and specificity of the host, we describe this isolate as a new myxosporidian, Myxobolus heckelii n. sp. (Myxozoa, Myxosporea).     

Haematological changes in fish following aerial spraying with endosulfan insecticide for testse fly control in Botswana

Endosulfan, an insecticide highly toxic to fish, is currently applied from the air for tsetse fly control in the Okavango Delta, Botswana. Although dosages are very ow (6–12 g a.i. ha⁻¹), they cause some fish mortality and affects the behaviour of survivors. In order to determine how quickly fish recover from sublethal poisoning, four haematological characteristics (erythrocyte count, leucocyte count, haemoglobin concentration and plasma protein concentration) were monitored in several species during and after six sequential applications of endosulfan (July–October 1978). In all cases, blood cel counts were significantly elevated during spraying (by up to a factor of four), while plasma protein levels were often disturbed. Total haemogobin (Hb) did not change, but the mean weight of Hb per erythrocyte declined significantly in Tilapia spp. from 59 to 39 pg. Im most instances these quantities began returning to normal before spraying ceased and reached prespray levels within six months.     

Effects of waterborne complexing agents on silver uptake and depuration in rainbow trout

Rainbow trout Oncorhynchus mykiss ( c . 60 g) were exposed for 1 week to 0·1 μM silver as AgNO₃ in ion poor water (Ca c . 150 μM, pH c . 8, water temperature 13° C) with or without waterborne organic matter (27 mg C l⁻¹ as Aldrich humic acid), thiosulphate (5 μM Na₂S₂O₃) or chloride (4 mM KCl). Organic matter decreased Ag accumulation by the gills initially, but did not decrease Ag accumulation by plasma or liver. Thiosulphate decreased the amount of Ag accumulated by the gills for the entire 1 week exposure but had no effect on Ag concentrations in the plasma, liver or bile. Chloride had no effect on Ag uptake in any of the tissues examined. All three complexing agents reduced the decreases in plasma Na and Cl concentrations caused by Ag. To study the effects of waterborne complexing agents on Ag depuration, rainbow trout were exposed to 0·1 μM AgNO₃ for 1 week then placed for 8 days in Ag‐free, ion poor water with or without waterborne organic matter (55 mg C l⁻¹) or thiosulphate (5 μM). These complexing agents did not alter depuration of Ag from the gills, plasma, liver or bile. Thus, once Ag has entered a fish, subsequent elimination of internal Ag is not affected by external complexing agents.