Testing clove oil as an anaesthetic for long-distance transport of live fish: the case of the Lake Victoria cichlid Haplochromis obliquidens

Clove oil can be used as an anaesthetic in the handling of marine and freshwater fish. Few studies report on its use for periods up to 48 h, for example, under long‐distance transport conditions. This study tested the effect of different clove oil concentrations for 1–48 h on recovery and survival of the cichlid Haplochromis obliquidens, an ornamental fish species endemic to Lake Victoria. Haplochromis obliquidens were anaesthetized for 1 h using 5–25 μl L^?1 clove oil. There was no correlation between clove oil concentration and post‐anaesthesia recovery time (P = 0.15). On average, fish recovered within 9.5 ± 2 min, and no fish died within 24 h after recovery. Results from exposure of fish to 18–20 μl L^?1 clove oil for up to 48 h suggested a narrow margin of safety as this concentration range induced mortality. At 18 μl L^?1 recovery times ranged from 3 to 43 min between 24 and 36 h exposure, while fish exposed longer than 36 h recovered within 1–10 min, or within 1–2 min after 44–48 h. At the end of a 48‐h transport experiment total ammonia levels were higher in transport water containing anaesthetized fish than for non‐anaesthetized fish (1.65 ± 0.19 and 0.54 ± 0.08 mg L^?1 NH + NH₃, respectively). The combined use of clove oil and the selective ammonium ion exchanger zeolite was considered feasible as ammonia levels could be reduced by up to 82% compared to control bags without zeolite.     

Fish as sources and sinks of nutrients in lakes

1. The release of total phosphorus (TP) and nitrogen (N in ammonium) was measured for the five most abundant fish species (>85% of biomass) in Mouse and Ranger Lakes, two biomanipulated, oligotrophic lakes in Ontario. 2. The specific release rate of both nutrients was significantly related to fish mass; log₁₀ TP release rate (μg h^?1) = 0.793 (±0.109) [log₁₀ wet mass (g)] + 0.7817 (±0.145), and log₁₀ N release rate (μg h^?1) = 0.6946 (±0.079) [log₁₀wet mass (g)] + 1.7481 (±0.108). 3. When fish nutrient release was standardized for abundance (all populations, 1993–95) and epilimnetic volume, fish were estimated to contribute 0.083 (±0.061) μg TP L^?1 day^?1, and 0.41 (±0.17) μg N L^?1 day^?1 in Mouse L., and 0.062 (±0.020) μg TP L^?1 day^?1 and 0.31 (±0.08) μg N L^?1 day^?1 in Ranger L. 4. In comparison, concurrent rates of total planktonic P regeneration were 1.02 (±0.45) μg L^?1 day^?1 (Mouse L.) and 0.85 (±0.19) μg L^?1 day^?1 (Ranger L.). Fish represented 8% of planktonic P release in Mouse L. and 7% in Ranger L. 5. Fish dry mass had mean elemental body compositions of 39.3% carbon, 10.9% nitrogen, and 4.0% phosphorus (all fish combined), with a mean molar C : N : P ratio of 27 : 6 : 1. This comprised about 55% and 23% of the total epilimnetic particulate P and N respectively. 6. Turnover times of P and N in fish were approximately 103 and 48 days respectively. In comparison, planktonic turnover times of particulate P in Mouse and Ranger Lakes were 4.3 and 4.4 days respectively. Given their high P content and low turnover rates, fish appear to be important P sinks in lakes.     

Feed intake and tissue distribution of florfenicol in cod (Gadus morhua) administered feed with different fat contents

This study was performed to examine the appetite and the corresponding plasma and tissue distribution of florfenicol when administered to healthy groups of cod using medicated and non‐medicated salmonid and marine feeds. Marine feed contains approximately 18% fat whereas salmonid feed contains approx. 30% fat. Two groups of fish were medicated with florfenicol at a dosage of 10 mg kg^?1 day^?1 for 10 consecutive days when the drug was administered either via marine or salmonid pellets. Two groups of fish also received either non‐medicated marine or salmonid pellets. Twenty‐four hours after giving the medicated marine feed, 14 out of 20 fish contained detectable concentrations of florfenicol with mean values (n = 14) of 4.67 ± 4.02 μg ml^?1 in plasma, 2.29 ± 2.11 μg g^?1 in muscle and 0.79 ± 0.69 μg g^?1 in the liver. In the fish given medicated salmonid feed, 18 of 20 fish contained detectable concentrations of florfenicol with mean values (n = 18) of 1.77 ± 1.84 μg ml^?1 in plasma, 0.75 ± 0.66 μg g^?1 in muscle and 0.30 ± 0.25 μg g^?1 in the liver. Decreased feed intake of the salmonid feed, both medicated and non‐medicated, was noted when compared to medicated and non‐medicated marine feed. No difference in feed consumption was registered between medicated and non‐medicated marine feed, however a difference was noted between the medicated and non‐medicated salmonid feed.     

Effect of periphyton on growth performance of grey mullet, Mugil cephalus (Linn.), in inland saline groundwater ponds

The present study attempts to assess the potential of artificial substrates to enhance fish production in inland saline groundwater ponds through periphyton production. Grey mullet, Mugil cephalus, was cultured for 100 days in ponds with substrate (treatment ponds) and without substrate (control ponds). To enhance the surface area, bamboo poles were used as substrate. The periphyton population, pigment concentration and hydrobiological characteristics of pond water were monitored. The studies revealed little difference in most of the water quality parameters observed in the two treatments. However, turbidity (27.0 ± 0.1–35.0 ± 0.1 Nephalo Turbidity Unit (NTU)), chlorophyll ‘a’ (6.6 ± 0.6–7.6 ± 0.6 μg L^?1), plankton population (phytoplankton 8.4 × 10³–9.4 ×10³ numbers L^?1; zooplankton 4.0 × 10³–5.1 × 10³ numbers L^?1) and NH₄–N (2.0 ± 0.2–2.3 ± 0.1 mg L^?1) were high in the treatment with no additional substrate; however, in the treatment with substrate the total Kjeldahl nitrogen (9.8 ± 0.8–10.8 ± 0.7 mg L^?1) and o‐PO₄ (0.1 ± 0.01–0.1 mg L^?1) remained significantly (P < 0.05) higher. Highest periphyton biomass in terms of dry matter (DM) (0.8 ± 0.01–1.4 ±0.01 mg cm^?2), ash free DM (0.4 ± 0.0–0.6 ± 0.01 mg cm^?2), chlorophyll ‘a’ (3.1 ± 0.2–8.1 ± 0.8 μg cm^?2) and pheophytin ‘a’ (1.9 ± 0.4–3.9 ± 0.5 μg cm^?2) was observed at 50 cm depth in ponds provided with additional substrate. Fifteen plankton genera showing periphytic affinity colonized the bamboo substrates. Fish growth (mean fish weight 524.3 ± 8.7 g and SGR 2.5 ± 0.1) was significantly (P < 0.05) higher in ponds provided with additional substrate compared with control ponds (387.2 ± 6.0). Length–weight relationship (LWR) (W = cLⁿ) also showed that the exponential value (‘n’) of length was high in substrate‐supported ponds (n = 2.36) in comparison with controls (n = 1.09). These studies suggest that a periphyton‐supported aquaculture system can be used successfully for the culture of herbivorous brackishwater fish species like M. cephalus in inland saline groundwaters and thus could contribute to the development of sound and sustainable aquaculture technology.     

Administration of the antibacterial agents flumequine and oxolinic acid to small turbot (Scophthalmusmaximus L.) by bath

Administration of flumequine and oxolinic acid to turbot, Scophthalmus maximus L., by bath resulted in significant levels of both drugs in the muscle tissue. Bath treatment using 150 mg L^?1 of flumequine and 200 mg L^?1 of oxolinic acid for 72 h gave muscle concentrations of 10.2 and 6.2 μg g^?1, respectively. Excretion of both antibacterials was rapid, reaching concentrations of 0.8 and 0.9 μg g^?1, respectively, for flumequine and oxolinic acid 24 h after the end of treatment. At day 3 post‐treatment the concentration of flumequine was below the limit of quantitation (0.1 μg g^?1) of the analytical method. Based on a minimum inhibitory concentration (MIC) of 0.0625 μg ml^?1 for susceptible strains, bath treatment maintain muscle levels in excess of 0.5 μg ml^?1, corresponding to eight times the MIC‐value for approximately 118 h for oxolinic acid and 104 h for flumequine.     

Effects of human chorionic gonadotropin (hCG) and handling stress on spermiation of silver perch Leiopotherapon plumbeus (Kner, 1864)

This study determined the effect of human chorionic gonadotropin (hCG) and handling stress on the spermiation and milt response of silver perch Leiopotherapon plumbeus based on the measurement of spermatocrit, sperm density, and milt production. Compared to saline‐injected fish, the mean spermatocrit (or packed sperm) of hCG‐treated fish was significantly lower at 18 h (47.9%) and 30 h (40.2%) post‐injection while mean sperm density was significantly lower at 30 h post‐injection (3.6 × 10⁶ cells μl^?1) but not at 18 h. At 18 h (1.8 μl g‐BW^?1) and 30 h (2.5 μl g‐BW^?1) post‐injection, mean milt production of hCG‐treated fish was significantly higher than in the saline group. Milt consistency was also thinner in the hCG‐treated group. Mean sperm density of handled fish (18.0 × 10⁶ cells μl^?1) was significantly lower than control fish (23.4 × 10⁶ cells μl^?1). However, mean sperm density of handled plus saline‐injected (16.2 × 10⁶ cells μl^?1) and handled plus hCG‐treated fish (8.4 × 10⁶ cells μl^?1) was significantly lower than in the control goup. Having thicker milt consistency, mean spermatocrit and milt production of handled (77.5%; 1.1 μl g‐BW^?1, respectively) and handled plus saline‐injected fish (75.4%; 1.1 μl g‐BW^?1, respectively) were not significantly different from the control fish (76.2%; 1.3 μl g‐BW^?1, respectively). Handled plus hCG‐treated fish had the lowest mean sperm density (8.4 × 10⁶ cells μl^?1) and spermatocrit (54.7%), but had the highest mean milt production (5.5 μl g‐BW^?1) among the treatment groups. These results demonstrate that the hCG injection effectively induces spermiation and milt expression and that handling‐related stress negatively affects such responses. The spermatocrit method may be used to assess the spermiation and milt response of silver perch.     

Mitigating stress effects during transportation of matrinxã (Brycon amazonicus Günther, 1869; Characidae) through the application of calcium sulfate

This study verified the effects of CaSO₄ on physiological responses of the tropical fish matrinxãBrycon amazonicus (200.2 ± 51.1 g) in water containing CaSO₄ after a 4‐h transportation at concentrations of: 0, 75, 150, and 300 mg L^?1. Blood samples were collected prior to transportation (initial levels), immediately after packaging, at arrival, and 24 h and 96 h after transportation (recovery). Cortisol levels increased after packaging (118.2 ± 14.2 ng ml^?1), and decreased slightly after transportation in water containing CaSO₄ (106.8 ± 14.1), but remained higher than initial levels (21.0 ± 2.6 ng ml^?1). Fish kept at 150 mg L^?1 CaSO₄ reached the pre‐transportation levels at 24 h of recovery. Blood glucose increased after transportation in all treatments (8.2 ± 0.2 mmol L^?1) and declined after full recovery to values below initial levels (4.8 ± 0.1 mmol L^?1). Chloride levels did not change in CaSO₄ treatments; serum sodium concentrations decreased after packaging and after transportation. Serum calcium levels did not differ among treatments, but decreased after packaging and increased at 96 h of recovery. Hematocrit and the number of red blood cells were higher in all treatments after packaging and arrival, except in fish exposed to 300 mg L^?1 CaSO₄. Mean corpuscular volume increased in 75 mg L^?1 CaSO₄, which reached the higher VCM after transportation. Hemoglobin levels increased only after transportation, regardless of calcium sulfate levels. Handling before transportation and transportation itself were both stressful to fish; calcium sulfate at concentrations tested in the present work had a moderate influence in the reduction of stress responses.     

Experimental evaluation of using calcein and alizarin red S for immersion marking of bighead carp Aristichthys nobilis (Richardson, 1845) to assess growth and identification of marks in otoliths,scales and fin rays

In order to evaluate the effects of immersion marking with calcein (CAL) and alizarin red S (ARS) on growth and mortality of juvenile bighead carp Aristichthys nobilis, and assess mark quality in otoliths, scales, and fin rays, CAL from 50 to 200 mg L^?1 and ARS from 150 to 300 mg L^?1 concentrations were used. With the exception of non‐lateral line scales from 50 mg L^?1 CAL treatments, immersion for 24 h produced detectable marks in sagittae, lateral line and non‐lateral line scales, and fin rays (dorsal, pectoral, ventral, anal, and caudal) at 100 days post‐marking. Detectable fluorescent marks in sagittae were readily observed at concentrations of 150–200 mg L^?1 CAL or 150–300 mg L^?1 ARS. Marks were poorly visible in all non‐lateral line scales from both CAL‐ and ARS‐treated groups. Fluorescent marks were readily detected in lateral line scales at 100–200 mg L^?1 CAL or 150–300 mg L^?1 ARS, and in fin rays at 150–200 mg L^?1 CAL or 150–300 mg L^?1 ARS. In particular, optimal marks were observed at the highest concentrations investigated in sagittae (300 mg L^?1 ARS), lateral line scales (150–200 mg L^?1 CAL or 250–300 mg L^?1 ARS), and fin rays (200 mg L^?1 CAL or 250–300 mg L^?1 ARS). However, fluorescent marks visible to the naked eye were not produced by any of the CAL or ARS treatments in sagittae, scales, or fin rays during this experiment. In addition, there was no significant difference on survival and growth of marked fish compared to controls throughout the experiment (P > 0.05).     

Constructed wetlands with free water surface for treatment of aquaculture effluents

The aim of the study was to determine the reduction of the overall environmental load (in terms of organic and nutrient load) in effluents of a flow‐through trout farm. Effluents of a flow‐through system for rainbow trout (Oncorhynchus mykiss) production passed through constructed wetlands with free water surface. Removal of nutrients was determined in three wetlands of 350 m² each at hydraulic residence times (HRTs) of 3.5, 5.5 and 11 h. The areal load of total suspended solids (TSS), chemical oxygen demand (COD), total phosphorus (TP), and total nitrogen (TN) varied in terms of HRTs from 12.3–36.8 g m^?2 day^?1, 21.7–65.2 g m^?2 day^?1, 0.23–0.70 g m^?2 day^?1, and 1.46–4.37 g m^?2 day^?1. Values for reduction of suspended solids, COD, TP, and TN were 67–72%, 30–31%, 41–53% ,and 19–30%, respectively. Significantly lower nutrient concentrations in the effluent among the wetlands were only found for nitrogen parameters: TN and ammonia concentrations were lower in the wetlands with a HRT of 5.5 h (0.89 mg L^?1, 0.11 mg L^?1) and 11 h (0.81 mg L^?1, 0.11 mg L^?1) compared with the one with 3.5 h (0.96 mg L^?1, 0.16 mg L^?1).     

Comparative Toxicity of Three Organic Acids to Freshwater Organisms and Their Impact on Aquatic Ecosystems

The comparative toxicity of lactic acid, acetic acid, and benzoic acid to tilapia (Oreochromis mossambicus), cladoceran crustacea (Moina micrura), and oligochaete worm (Branchiura sowerbyi) were determined using static bioassay tests. Worms were found most sensitive to all the acids whereas the cladoceran was found most resistant to lactic acid and the fish most resistant to acetic acid and benzoic acid. The 96h LC₅₀ values of lactic acid, acetic acid, and benzoic acid, were, respectively, 257.73, 272.87, and 276.74 mg L^?1 for O. mossambicus; 329.12, 163.72, and 71.65 mg L^?1 for M. micrura and 50.82, 14.90, and 39.47 mg L^?1 for B. sowerbyi. Tilapia lost appetite at sub-lethal concentrations as low as 2.18 mg L^?1 lactic acid, 1.26 mg L^?1 acetic acid, and 13.84 mg L^{? 1} of benzoic acid. Growth and reproduction of the fish were affected following 90-day chronic exposure to sub-lethal concentrations of the acids. Minimum effective concentration of the acids that significantly reduced food conversion efficiency (FCE), percent increase of weight, specific growth rate, yield and fecundity of the fish were 2.18, 1.47, and 3.95 mg · L^?1 of lactic acid, acetic acid, and benzoic acid, respectively. Effects of acetic acid and benzoic acid on FCE, weight increase, and yield were not significantly different from each other whereas lactic acid produced different effects from acetic acid as well as benzoic acid. Mean values of dissolved oxygen, primary productivity, and plankton populations of the test medium significantly reduced from control at 16.94 mg L^?1 lactic acid, 16.79 mg L^?1 acetic acid, and 13.84 mg L^?1 benzoic acid.     

Feeding and growth of juvenile sea bass: the effect of ration and temperature on growth rate and efficiency

The effect of ration on the growth of pairs of juvenile sea bass Dicentrarchus labrax fed squid mantle was recorded at four temperatures: 6, 10, 14 and 18) C, covering the range typical of Welsh coastal waters. Initial weight of the fish ranged from 2.8 to 15.9 g. A predictive model for the maximum meal size (M_max) at temperatures between 10 and 18) C, accounted for 95% of the variance in lnM_max. Even when offered excess food, bass at 6) C had a low rate of food consumption [0.19% body weight (BW) day^?1] and lost weight (G=?0.04% day^?1). Predictive regression models for specific growth rate (G) accounted for 86% of the variance at reduced rations and 70% at maximum meals. The relationship between G (calculated for total biomass per tank) and ration was a decelerating curve. G at maximum meals increased with temperature, at lower rations G decreased with temperature. For a pair of bass with a combined weight of 15 g, predicted maintenance ration ranged between 0.7 and 2.3% BW day^?1 and increased with temperature. Maximum meal size was more sensitive to temperature than maintenance ration. At 18) C optimum ration was 7.4% BW day^?1. At lower temperatures, the optimum ration was the maximum meal. The maximum gross growth efficiency was 17.4% at 18) C. Mean absorption efficiency was 94.8%. Ration level had no significant effect on absorption efficiency, which was lowest at 6) C. Condition indices (Fulton condition factor, wet and dry liver—somatic indices and body depth index) increased with meal size at all temperatures except 6) C. An increase in temperature between 10 and 18) C generally resulted in a decrease in condition indices at a given ration. When comparisons were made at a given standard length, gut and carcass weight increased with ration. Visceral fat and gut weight decreased with increased temperature.     

Effects of clove oil,essential oil of Lippia alba and 2‐phe anaesthesia on juvenile meagre,Argyrosomus regius (Asso, 1801)

The objectives of this experiment were to (i) determine the efficacy of essential oils of clove (CO) and Lippia alba (EOLA) to induce deep anaesthesia in juvenile specimens (49.0 ± 6.2 g body mass, 16.6 ± 0.8 cm; n = 8 per treatment) of meagre (Argyrosomus regius); and (ii) study the feasibility of these substances, together with 2‐phenoxyethanol (2‐PHE), as potential sedatives [low concentration: (i) EOLA: 12 mg L^?1; (ii) CO: 1 mg L^?1; and (iii) 2‐PHE: 33 mg·L ^?1; n = 8 per treatment] for live fish transport of this species. All test were performed at a constant temperature (18°C). Thus, the main primary stress indicator (plasma cortisol) and secondary factors (plasma metabolites) were evaluated. In addition, growth hormone (GH) mRNA expression was also evaluated in the pituitary gland. The results indicated that EOLA is considered to be effective for deep anaesthesia when the concentration is close to 160 mg L^?1, while CO produces the same effect when lower concentrations are added (40–50 mg L^?1). Regarding sedative concentrations, a significant ~3‐fold increase in plasma cortisol levels was detected in the EOLA group when compared to control specimens. In addition, glucose levels were not reduced and significantly increased (~1.6‐fold) for 2‐PHE in relation to the control fish. None of the anaesthetics promoted a significant difference for GH expression with respect to the control group, but a significant ~2‐fold increase for 2‐PHE treatment with respect to the EOLA exposition was found in this gene expression. Results show that none of the anaesthetics analysed, at least in the ranges of concentrations used in this study (EOLA 12 mg L^?1, CO 1 mg L^?1, 2‐PHE 33 mg L^?1), are recommended for live fish transport, as shown by the absence of inhibition on the stress parameters assessed.     

Toxicity of ammonia and nitrite to yellow catfish (Pelteobagrus fulvidraco)

The 96‐h LC₅₀ (median lethal concentration, LC₅₀) tests were conducted using four different sizes of yellow catfish Pelteobagrus fulvidraco to provide primary information on the sensitivity of this species to elevated ammonia and/or nitrite, and to determine if the sensitivity is mediated by size under the same conditions. The results showed that 96‐h LC₅₀ of fish weighing 0.034 ± 0.002, 0.296 ± 0.049, 3.52 ± 0.95 and 32.96 ± 5.75 g to total ammonia nitrogen‐N was 24.96, 35.85, 47.44 and 68.79 mg L^?1, respectively; un‐ionized ammonia nitrogen‐N was 0.34, 0.49, 0.65 and 0.94 mg L^?1 in test conditions of pH 7.42 and 23°C; and that nitrite nitrogen‐N was 69.06, 97.23, 133.61 and 196.05 mg L^?1 in test conditions of pH 7.58 and 23°C, respectively. The NOEL (No Observable Effect Level) of fish (body weight from 0.03 to 30 g) to ammonia and nitrite was 2.25–6.22 mg L^?1 total ammonia nitrogen‐N, 0.03–0.10 mg L^?1 un‐ionized ammonia nitrogen‐N in test conditions of pH 7.42 and 23°C, and 6.27–17.68 mg L^?1 nitrite nitrogen‐N in test conditions of pH 7.58 and 23°C, respectively. These results indicate that the susceptibility of this fish to total ammonia or nitrite was reduced with increasing size, and that a dose‐dependent relationship might exist between them. The 96‐h LC₅₀ and NOEL of different sizes of fish to total ammonia, un‐ionized ammonia and nitrite would be important to know for water quality standards in yellow catfish aquaculture.     

Menthol as an alternative anaesthetic and sedative for rainbow trout,Oncorhynchus mykiss

Menthol is known for its analgesic properties, but relatively little information is available on its potential as an anaesthetic on fish. The purpose of this study was to assess anaesthetic and sedative effectiveness of menthol and its safety in rainbow trout (Oncorhynchus mykiss). Juvenile rainbow trout 180 ± 28 g (mean ± SD) within a range of 152–208 g fish^?1 were individually exposed to menthol concentrations between 10 and 150 mg l^?1 and observed for behavioural responses, induction time to anaesthesia and recovery time. Menthol concentrations of 40–150 mg l^?1 induced anaesthesia with varying exposure times. There was an exponential relationship (p < 0.001) between induction time and menthol concentration. Menthol concentrations of 80–150 mg l^?1 induced anaesthesia within three minutes of exposure and fish recovered within three minutes. Induction and recovery data showed that 80 mg l^?1 was most suitable for anaesthesia in juveniles of this species. Concentrations of 10–20 mg l^?1 had sedative effects. Menthol stock solutions prepared using ethanol and acetone and storage time of stock solutions at room temperature for up to 48 h showed no significant differences in anaesthetic efficiency. When exposure time to menthol was kept constant at three minutes, 22% of fish had temporary cessation of gill ventilation. These fish had longer recovery times than those that did not show that response. Menthol was an effective anaesthetic and could be tested as a sedative for trout.     

A note on copper bioaccumulation in Mozambique tilapia,Oreochromis mossambicus (Osteichthyes: Cichlidae)

Copper (Cu) is one of the most commonly reported metal pollutants in African water bodies, but there are few studies on African freshwater fish species of copper accumulation and copper toxicity. Adult O. mossambicus were exposed to 0mg l^?1 (control) and 0.75mg l^?1 Cu for 96h and 0 (control), 0.11, 0.29 and 0.47mg l^?1 copper for 64 days. Samples of liver and gills were collected after 96h, and after 1, 32 and 64 days, respectively. There were significant differences in the mean Cu accumulation values in the liver and gills between the control and the Cu-exposed fish after the 96-h exposure. In fish exposed to 0.11 and 0.29mg l^?1 Cu for 64 days there was an increase in copper level in the tissues. In fish exposed to 0.47mg l^?1 Cu the concentration in the gill and liver tissue did not increase between Day 1 and Day 32. At this time, Cu accumulation in the liver was higher than for fish exposed to 0.11 and 0.29mg l^?1 Cu for 64 days. Exposure to approximately 0.47mg l^?1 Cu for more than 32 days induced mortality.     

Carbofuran- and cypermethrin-induced histopathological alterations in the liver of Labeo rohita (Hamilton) and its recovery

Alterations in the liver histology of Labeo rohita were examined after exposure to different concentrations of carbofuran (0.06 and 0.15 mg L^?1) and cypermethrin (0.16 and 0.40 μl L^?1) for 28 days. Histological recovery was also studied by maintaining the intoxicated fish in a freshwater system for an additional 28 days. Major damages caused by carbofuran toxicity were diffuse necrosis, cordal disarrangement, individualization of hepatocytes, etc.; significant changes induced by cypermethrin were hyperplasia, disintegration of hepatic mass, focal coagulative necrosis, etc. In both cases, damages were dose‐dependent, with cypermethrin exhibiting more sensitivity than carbofuran. In all cases, recovery was prominent and rate of recovery was faster with carbofuran than when using cypermethrin.     

Effects of stocking density on survival,growth and size variation of juvenile Brachymystax lenok (Pallas, 1773)

In this experiment the effects of stocking density on growth and survival of juvenile Brachymystax lenok were studied. Experimental fishes were reared at different stocking densities (5, 25, 50 and 75 fish L^?1) for 40 days at ambient temperatures (11.2–16.4°C). During the experiment, dissolved oxygen (DO) was above 5.4 mg L^?1 and other major environmental factors were controlled at the same levels in each aquarium (DO 5.4–7.2 mg L^?1, pH 6.6–7.4, and flow‐through rates 0.3–0.4 L s^?1). Mortality data in each group was recorded daily and random samples of 30 juveniles were measured and weighed every 10 days. All statistical analyses were performed by anova . The survival rate was found to be significantly affected by stocking density, but not the condition factor (CF), specific growth rate (SGR) or coefficients of variation (CV).The results demonstrate that lenok juveniles can be reared at higher stocking densities, which can increase survival under intensive conditions.     

Concentration,Distribution, Source,and Risk Assessment of PAHs and Heavy Metals in Surface Water from the Three Gorges Reservoir,China

Fifteen polycyclic aromatic hydrocarbons (PAHs) and heavy metals (Cr, Ni, As, Cd, Pb, and Hg) were quantified in 19 surface water sites of the Three Gorges Reservoir, China. The total concentrations of 15 PAHs and six heavy metals in the 19 sample sites ranged from 130.8 ng L^?1 to 227.5 ng L^?1 and 3.2 μg L^?1 to 6.0 μg L^?1, respectively. The mean concentration of As was the highest among the six heavy metals (2.1 ± 0.3 μg L^?1), followed by Cr (0.5 ± 0.3 μg L^?1), Ni (1.3 ± 0.1 μg L^?1), Cd (0.2 ± 0.01 μg L^?1), Pb (0.07 ± 0.08 μ g L^?1) and Hg (0.05 ± 0.08 μg L^?1). The isomer ratio results suggest that PAHs at most sites were mainly from petroleum combustion, while coal and biomass combustion was the main source at sites 1, 2, 6, 7, 9, 14, and 17. Based on principal component analysis, the main source of heavy metals was anthropogenic activities and weathering of bedrocks. Depending on characteristic of RQ_(NCs) ≥ 1 and RQ_(MPCs) < 1, BaA showed higher potential ecological risk than other PAHs, therefore, all sampling site needed to be paid much more attention, included some remedial actions. Meanwhile, after assessing human health risk of heavy metal, it was unlikely to experience adverse health effects, even exposing through more pathways and six kinds of heavy metals simultaneously.     

Effect of cadmium on survival,osmoregulation and gill structure of the Sunda prawn,Macrobrachium sintangense (de Man), at different salinities

The prawn Macrobrachium sintangense is likely to be subjected to occasional exposure to combined metal and saline stressors in its natural environment. This research evaluated the acute toxicity (96?h LC₅₀) of cadmium (Cd) on the prawn M. sintangense, with respect to the osmoregulatory capacity (OC) of prawns and to document histological changes in the gills after exposure to sublethal Cd concentrations at different salinities. The 96?h LC₅₀ of Cd to M. sintangense decreased with increasing salinity. The 96?h LC₅₀ values were 89.12 (72.53–109.50), 681.26 (554.20–837.46) and 825.37 (676.99–1006.27) μg CdL^?1 at 0, 10 and 20 ppt, respectively. The OC of prawns exposed to 30?μg?CdL^?1 at 0 ppt and to 300?μg?CdL^?1 at10 ppt decreased significantly compared with that of control prawns exposed to 0 and 10 ppt respectively. Swelling, hyperplasia and necrosis of gill lamellae resulting in the loss of marginal canals were observed in the gills of prawns exposed to 30?μg?CdL^?1 at 0 ppt and to 300?μg?CdL^?1 at 10 ppt for 7?days.     

Nonlinear response of stream ecosystem structure to low‐level phosphorus enrichment

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