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1.
In the present study, we investigate the short‐term adaptive physiological strategies to polycyclic aromatic hydrocarbon (PAH) of Pacific oysters, Crassostrea gigas, by exposing the oysters to varying levels of PAH (0, 50, 100 and 200 μg L−1) for 7 days with a 3‐day acclimation period under laboratory conditions. The filtration rate (FR) and respiration rate (R) increased significantly at 50 μg L−1 PAH and decreased at 100 and 200 μg L−1 compared with the control. The absorption efficiency (Abs. eff.) was significantly impaired at 200 μg L−1 PAH. Ammonia excretion (E) increased with increasing PAH levels, with a significant elevation at 200 μg L−1. Although a significantly elevated FR was observed, oysters exposed to 50 μg L−1 PAH showed scope for growth (SFG) similar to the control. This indicates that even at nominal levels, PAH contamination is a possible cause of reduced oyster production because of increased food demand. The oysters exposed to 200 μg L−1 PAH showed negative SFG values, which could be a possible cause of growth stagnation or even mortality when the exposure is chronic.  相似文献   

2.
《水生生物资源》1998,11(4):289-295
An experimental small scale partial recirculating system for rainbow trout was assembled. The system components were two 1.3-m3 fish tanks with sloping bottoms, each connected to a sedimentation column and containing 50 kg rainbow trout biomass, an anaerobic up-flow digester (total volume 0.424 m3, available volume 0.382 m3) connected to the funnel shaped bottom of the sedimentation column by means of a peristaltic pump, an aerobic submerged plug-flow filter (total volume 1 m3; filled with 0.83 m3 plastic rings with a specific surface of 194 m2·m−3) and a submerged pump. Aeration was provided through porous stones. The anaerobic digester was filled with 35 mm cubes of expanded polyurethane foam (25 pores·cm−2, specific surface 1.375 m2·m−3, filtering volume 0.291 m3) and kept at a temperature of 24–25 °C using an electric heater. The gas chamber at the top of the anaerobic digester was connected to a gas meter and to an infrared continuous gas analyser. Measures on system performance with a recirculation rate of 60 % were done following three feeding levels (1, 1.5 and 2 % live weight). At the highest feeding rate, 2.8 L of faecal sludge collected from the trout tanks were pumped every four hours in the anaerobic digester. Slurry characteristic were: total N 0.197 g·L−1, TAN 0.014 g·L−1, volatile solids (VS) 16.91 g·L−1, suspended solids (SS) 21.39 g·L−1 and pH 6.9. Biogas production was 144 L·d−1 (mean value) with a methane content higher than 80 %. Methane volumetric production was 0.3 m3·m−3·d−1 and methane daily yield was 0.4 and 0.32 m3·kg−1 VS and SS respectively. After passing through the anaerobic digester, effluents were characterized by a total N content of 0.243 g·L−1, TAN 0.222 g·L−1, VS 1.1 g·L−1, SS 1.32 g·L−1 and pH 6.8. The anaerobic digester was able to significantly reduce VS and SS content of wastewater and the zeolite ion-exchange column significantly improved water quality of effluent produced by the digester. The aerobic biofilter significantly reduced the ammonia content of the water leaving the fish tanks.  相似文献   

3.
The toxicity of formalin and trifluralin to the larval stages of the mud crab Scylla serrata was compared in a static bioassay. Prophylactic doses of 5, 10, 15, 20 and 25 μg L−1 formalin and 0.05, 0.1, 0.2, 0.4 and 0.8 μg L−1 trifluralin were used. Toxicity was assessed on the basis of survival of larvae after 24, 48, 72 and 96 h exposure to the test chemicals and metamorphosis to the next larval stage. Result shows that larval survival in all stages was significantly reduced at concentrations of 20 and 25 μg L−1 formalin whereas larvae were able to tolerate all trifluralin treatments. However, larvae became more tolerant to high formalin concentrations as the larval stage progressed. Survival was better at 5, 10 and 15 μg L−1 formalin and in all trifluralin treatments than the control in almost all the larval stages. Faster metamorphosis was observed at 5 and 10 μg L−1 formalin and 0.05, 0.1 and 0.2 μg L−1 trifluralin concentrations. Doses of formalin and trifluralin obtained from the toxicity experiments were applied as prophylaxis to newly hatched larvae in white plastic basins. Prophylactic doses of 5 and 10 μg L−1 formalin and 0.05 and 0.1 μg L−1 trifluralin applied every other day were found to be effective in enhancing survival and larval development to megalopa compared with control. However, no megalopae survived to crab instar in all formalin treatments. Although the use of fungicides in rearing systems resulted in higher survival compared with controls, other strategies (i.e. maintenance of good water quality and hygienic practices in the hatchery) should be further investigated as an alternative to the use of chemicals in hatcheries.  相似文献   

4.
1. Recreational and subsistence angling in South African estuaries is a small, but relevant, sector of South Africa's diverse coastal fisheries. This paper reviews these fisheries and their effects in two estuaries. 2. The composition of angler's catches in two large Eastern Cape Province estuaries has hardly changed over a period of nearly 20 years. 3. Gill-net catches (in terms of CPUE) indicate a decline in the abundance of the most popular angling fish species, especially the spotted grunter Pomadasys commersonnii. 4. Regular freshwater inputs into estuaries are required to ensure a salinity gradient which is crucial for the maintenance of an abundant and diverse estuarine ichthyofaunal assemblage. 5. Present management and conservation policies are poorly defined, and the philosophy and principles of ecosystem preservation, rather than that of species preservation, should be seriously considered. © 1996 by John Wiley & Sons, Ltd.  相似文献   

5.
Thibault I, Hedger RD, Dodson JJ, Shiao J‐C, Iizuka Y, Tzeng W‐N. Anadromy and the dispersal of an invasive fish species (Oncorhynchus mykiss) in Eastern Quebec, as revealed by otolith microchemistry. Ecology of Freshwater Fish 2010: 19: 348–360. © 2010 John Wiley & Sons A/S Abstract – Rainbow trout (Oncorhynchus mykiss) is invading rivers bordering the St. Lawrence Estuary (Quebec, Canada). Some rivers in Eastern Quebec support self‐sustaining populations while adult vagrants are frequently captured in rivers where no reproduction has been confirmed. We hypothesised that the development of anadromy has promoted the species dispersal. Otolith Sr:Ca analyses revealed that although all fish captured in the upstream stocking region were freshwater residents, both anadromous and freshwater resident phenotypes were found downstream in Eastern Quebec. The proportion of fish exhibiting the anadromous life cycle increased with the distance from the stocking zone. Eastern Quebec steelhead migrated to sea at the same age but at a larger size than steelhead within their native range. Age at first reproduction was similar to that observed in native populations. The development of the anadromous life cycle enables this species to colonise new rivers following long‐distance migrations along the St. Lawrence Estuary corridor.  相似文献   

6.
Survival rate, growth and feed intake were determined for late juveniles (4.31 ± 0.18 g) of river prawn Macrobrachium rosenbergii in freshwater with total ammonia‐N (NH3‐N+NH4‐N) concentrations of 0.015 (control), 0.5, 1.0 and 1.5 mg L−1 for 60 days at pH 7.53 ± 0.04 and temperature 24.0 ± 2.5°C. Survival rate was significantly (P<0.05) lower (54 ± 4.2–70 ± 5.4%) for total ammonia concentrations from 0.5 to 1.5 mg L−1 [0.0139–0.0419 mg L−1 of unionized ammonia (NH3)]. Growth (0.026–0.030 g day−1 range) of the prawns did not differ for the different NH3 levels but were significantly (P<0.05) lower compared with control (0.056 g day−1). Feed intake rates also diminished significantly (P<0.05) from 77.60 ± 2.45% at control (0.015 mg L−1 NH3‐N) to 48.69 ± 2.13% at 1.5 mg L−1 NH3‐N (0.0419 mg L−1 of unionized NH3).  相似文献   

7.
In this study, the efficacy of biofloc system was assessed for culturing Indian major carps, e.g., rohu (Labeo rohita), catla (Catla catla), and mrigal (Cirrihinus mrigala) at varied stocking densities (STD) from 4.28, 8.57, and 12.85 fish m−3 of tank volume. Biofloc system could efficiently remove inorganic nitrogen from culture water and substantially improved the growth parameters of fishes as compared to the control system without the application of biofloc. Among different STDs in biofloc system, water quality and floc formation were noted to be higher with a STD of 4.28 fish m−3 and the average concentration of NH4 – N, NO2 – N and NO3 – N of 0.61 mg L−1, 0.35 mg L−1 and 1.8 mg L−1, respectively was recorded lowest as compared to the other STD. As a result, catla and rohu could achieve a specific growth rate of 1.1 % day−1 and 0.98 % day−1, respectively. However, in the other two STDs, the respective concentrations were noted in the range of acceptable water quality, and the growth rates were satisfactory. It can be concluded that the biofloc system is efficient to culture IMC in polyculture mode amd therefore, can be directly applied in scaled-up culture modules.  相似文献   

8.
  • 1. Ecological water reserves are part of the new water management philosophy in South Africa. The estuaries are threatened by excessive water abstraction from their rivers and the consequent reduction in freshwater input. This study was conducted to further improve our understanding of freshwater requirements in terms of nutrients for South African estuaries.
  • 2. The Gamtoos Estuary was sampled between November 1996 and November 1998 to determine its nutrient status and freshwater input rates. Furthermore, the possible existence of a distinct river‐estuarine interface (REI) in terms of nutrients has been investigated. Nutrients analysed included phosphate, nitrate, nitrite, ammonia, dissolved organic nitrogen (DON), dissolved organic carbon (DOC), particulate organic nitrogen (PON) as Kjieldahl nitrogen, total particulate phosphorus and total particulate carbon.
  • 3. The Gamtoos River was found not to be the ultimate source of nutrients to the estuary, but non‐point sources such as the seepage of fertilisers from adjacent agricultural fields determined to a great extent the nutrient status of the estuary.
  • 4. Results showed that it was not possible to identify a defined river‐estuarine interface region for all nutrients. Most were measured in higher concentrations in the lower salinity reaches (<17‰) where we observed the combined effect of inputs from the Gamtoos River, an agricultural drainage pipe, and fertilizer seepage from non‐point sources on nutrient concentration.
  • 5. Prolonged water withdrawal for human use impacts the continuous renewal of the nutrient pool so important to other South African estuaries with relative pristine catchment areas. However, reduced fresh water inputs could enhance eutrophication in polluted estuaries due to a decreased flushing potential of the estuary. In this case the Gamtoos Estuary has a freshwater requirement for freshets and floods to “clean” the estuary of accumulated nutrients and other organic material.
  • 6. This should be a consideration in further freshwater abstraction policies. Conservation issues arise since the Gamtoos Estuary is one of the few permanently open estuaries along the South African coast and serve in this study as an example and as a first attempt to relate freshwater requirements to nutrient dynamics in a South African context.
Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

9.
In the present study, the efficacy of Letrozole, a potent nonsteroidal aromatase inhibitor (AI), on gonadal sex differentiation and sex reversal was examined in bluegill sunfish (Lepomis macrochirus). In Experiment 1, using AI diet treatments (50, 150, 250 and 500 mg kg−1) from 30 to 90 days posthatch (dph), AI interrupted ovarian cavity formation at a dose of 500 mg kg1 diet and one intersex fish was identified in this group. The proportions of males in all the treated groups were significantly higher than those in the control group. In Experiment 2, using AI immersion treatments (250, 500 and 1000 μg L−1) during 30–50 dph, the treated groups of 500 and 1000 μg L−1 produced significantly more males than the control and 250 μg L−1 groups. Histological examination revealed no differences in ovary or testis tissue between control and AI‐treated fish. There were no significant differences detected in body weight and length among the AI treated and control groups (P>0.05) for both experiments. The results from these two experiments suggest that inhibition of aromatase activity by AI could influence sex differentiation in bluegill sunfish.  相似文献   

10.
1. The effect of riparian ecotone functional complexity and stream hydraulics on an upland river ecosystem has been analysed. 2. The amount of nutrients retained by bottom sediment was lowest on a sandy substrate (range: 26–104 mg m−2 P-PO4) and highest in wetland bays (range: 558–5368 mg m−2 P-PO4). A stream bed covered by Berula erecta had about three times higher retentive nutrient capacity ( x̄ = 584 mg m−2 day−1) than did a sandy substrate( x̄ = 205 mg m−2 day−1). 3. The amount of allochthonous organic matter (CPOM) deposited on the stream bed decreased with current velocity. The trophic potential of CPOM, measured as total protein, was significantly correlated with the amount of deposited CPOM (r = 0.863; p<0.00001) and depended on stream order. 4. Both invertebrate and fish biomass in the upland river were significantly correlated with calcium/bicarbonate (benthos: r = 0.858; p<0.006; fish: r = 0.918; p<0.001). 5. Fish biomass, diversity and species richness were highest in pools, lower in riffles and lowest in the run/transition zone. 6. Macroinvertebrate biomass was highest at an intermediate riparian ecotone complexity with an adequate supply of organic matter and incident light. Fish biomass followed the same trend, being lowest in heavily shaded areas and in open channels without riparian vegetation (range: 1–4.5 g m−2), but highest in ecotones of intermediate complexity (range: 1.6–92.8 g m−2). The ‘cascading effect’ of invertebrate density depletion, which was inversely related to fish biomass, was observed seasonally. 7. The above results indicate that riparian ecotone structure and the heterogeneity of the stream channel may regulate biodiversity, productivity and nutrient retention in the fluvial corridor. These quantitative data help to create alternative scenarios for sustainable river basin management. © 1998 John Wiley & Sons, Ltd.  相似文献   

11.
Aquaculture development in Kenya has been hampered by lack of targeted feeds. Chemical fertilizers can enhance natural food production and thus indirectly provide protein to complement energy-rich cereal brans used as feed. Consequently, an experiment was conducted at Sagana Fish Farm in central Kenya to realize least-cost combinations of rice bran and fertilizer. Twelve 800 m2 (0.08 ha) ponds were stocked with juvenile (32 g) Oreochromis niloticus L. at 2 m−2 and Clarias gariepinus (Burchell 1822) (fingerlings of 4.6 g) at 0.2 m−2. Four treatments, calculated to approximate isonitrogenous conditions, were applied in triplicate as follows: (1) urea and diammonium phosphate (DAP) to provide 16 kg of N ha−1 week−1 and 4 kg of P ha−1 week−1; (2) urea and DAP applied to give 8 kg of N ha−1 week−1 and 2 kg of P ha−1 week−1, plus rice bran fed at 60 kg ha−1 day−1; (3) rice bran fed at 120 kg ha−1 day−1; (4) rice bran as in treatment 3 and fertilizer as in treatment 2. Ponds were sampled monthly to measure fish growth, and drained completely after 20 weeks. A partial economic analysis indicated minimal net profits of K.Sh. 18 851 (US$ 251), K.Sh. 9895 (US$ 132), K.Sh. 3299 (US$ 44) and K.Sh. 7015 (US$ 94) for treatments 1–4, respectively, because of high feed and seed costs.  相似文献   

12.
Aquaculture of Spinibarbus denticulatus (Oshima, 1926), a fish species indigenous to North Vietnam and Eastern China, is constrained by lack of fingerlings for stocking ponds and cages. As these fish do not naturally breed in captivity, carp pituitary extract (CPE), luteinizing hormone-releasing hormone analogue (LHRHa) with domperidone (DOM) and human chorionic gonadotropin (HCG) were administered at various doses to induce ovulation. A first set of experiments evaluated the response to LHRHa (30, 40 and 50 μg kg−1) with or without DOM (10 mg kg−1), CPE (20, 30 and 40 mg kg−1) and HCG (3000, 4000 and 5000 IU kg−1). A second set of experiments evaluated the dose response to LHRHa (30, 35, 40 and 50 μg kg−1) primed with 6 mg kg−1 of CPE, and HCG (3000, 3500, 4000, 5000 IU kg−1) primed with 6 mg kg−1 of CPE. The treatment groups were compared with each other and the control (injected with 0.9% saline solution). Only 25% and 50% ovulation resulted when treated with LHRHa at 40 and 50 μg kg−1, whereas 100% ovulation was achieved with an addition of DOM to LHRHa. Both 30 and 40 mg kg−1 CPE induced 100% ovulation. However, HCG (4000 and 5000 IU kg−1) induced ovulation in only 33% of females. When primed with CPE, the minimum dose of LHRHa required was 35 μg kg−1 to achieve 70% ovulation. Priming HCG with CPE also resulted in 100% ovulation, and the minimum effective dose of HCG to induce ovulation was 3500 IU kg−1 with 60% ovulation. Fertilization and hatch rates observed in this study with different hormonal stimulation were high (80–93%). The results indicate that while the use of combined hormone strategy has no apparent advantage over a single hormone strategy, LHRHa+DOM (40 μg kg−1+10.0 mg kg−1) and CPE (30 mg kg−1) are most effective in consistently inducing ovulation and thus can be used for commercial hatchery production of S. denticulatus larvae.  相似文献   

13.
1. A diatom-phosphorus (P) transfer function was applied to fossil diatom assemblages in sediment cores from three Anglesey lakes of conservation importance, in order to reconstruct quantitatively the recent history of total P (TP) concentrations for each lake. The results indicate that all three lakes have been eutrophic throughout the period represented by the cores. 2. The model suggests that Llyn Coron and Llyn Dinam experienced gradual increases in TP concentration (core base to 20 cm), followed by marked, rapid increases from the time represented by a sediment depth of 20 cm (early 1970s for Llyn Coron), most probably associated with agricultural intensification. 3. A recent decline in TP concentration at Llyn Coron and Llyn Dinam, associated with reductions in external P loading, is indicated by the model, although current levels are still considerably higher than those estimated for the base of the cores (Dinam: current=112 μg L−1; base=65 μg L−1, and Coron: current=156 μg L−1; base=70 μg L−1). 4. No clear changes in diatom-inferred TP concentration were observed for Llyn Penrhyn over the 70 year period represented by the core. However, the reconstruction for this lake is inaccurate because: (a) the sediment record appears to be disturbed, and (b) unlike Llyn Coron and Llyn Dinam, diatom preservation and modern analogues are poor, and the present TP concentration (>1 mg L−1) is beyond the TP range of the model. 5. Continued control of the external TP loads from agricultural sources is essential to prevent further increases in lake TP concentrations at Llyn Coron and Llyn Dinam. Given the problems with the Llyn Penrhyn data, it is not possible to draw any firm conclusions regarding future site management. However, the impact of the recent installation of a phosphate stripping plant at the local sewage works should be monitored, to identify whether a reduction in external P loading results in a decrease in epilimnetic TP concentrations, and in turn whether this causes changes to the biological community structure of the lake.  相似文献   

14.
  1. Fish assemblages in estuaries have a much lower species richness (number of taxa) when compared with the combined numbers of freshwater and marine species from adjacent aquatic ecosystems. This is primarily because of the relatively harsh and fluctuating physico-chemical conditions in estuaries compared with the more stable freshwater and marine environments.
  2. A comprehensive fish survey of estuaries in South Africa is used as a basis to determine fish species richness in subtropical, warm temperate, and cool temperate systems along the coast, and to assess the degree of redundancy in the different biogeographic regions.
  3. In general, only one or two species belonging to each of the detritivorous, piscivorous, zoobenthivorous, and zooplanktivorous fish guilds are numerically well represented in the larger cool temperate estuaries, but between four and 10 species in each of these guilds are usually recorded in the larger subtropical estuaries.
  4. Although the overall low redundancy of fish species groups in estuaries has already been formally recognized in the literature, this short note highlights the sensitivity of certain trophic guilds in temperate South African estuaries to any form of redundancy, a characteristic that may be equally applicable, based on declining species richness with increasing latitude, to temperate estuaries in other parts of the world.
  相似文献   

15.
The performance of the Pacific white shrimp Litopenaeus vannamei (Boone) under various stocking strategies was evaluated in earthen ponds filled with freshwater amended with major ions. Six 0.1‐ha earthen ponds located in Pine Bluff, AR, USA, were filled with freshwater in 2003 and 2004, and potassium magnesium sulphate added to provide 50 mg K+ L?1 and stock salt added to provide 0.5 g L?1 salinity. In 2003, three ponds either were stocked with PL15 shrimp (39 PL m?2) for 125 days of grow out or with PL25 shrimp for 55 days (23 PL m?2) followed by a 65‐day (28 PL m?2) grow‐out period. In 2004, ponds were stocked with 7, 13 or 30 PL15 m?2 for 134 days of grow out. Salinity averaged 0.7 g L?1 during both years, and concentration of SO4?2, K+, Ca2+ and Mg2+ was higher, and Na+ and Cl? was lower in amended pond water than in seawater at 0.7 g L?1 salinity. Potassium concentration in amended water was 52–61% of the target concentration. Shrimp yields ranged from 3449 kg ha?1 in 2003 to 4966 kg ha?1 in 2004 in ponds stocked with 30–39 PL15 m?2 for a 125–134‐day culture period. At harvest, mean individual weight ranged from 17.1 to 19.3 g shrimp?1. In ponds stocked with PL25 shrimp, yields averaged 988 and 2462 kg ha?1 for the 1st and 2nd grow‐out periods respectively. Gross shrimp yield in 2004 increased linearly from 1379–4966 kg ha?1 with increased stocking rate. These experiments demonstrated that L. vannamei can be grown successfully in freshwater supplemented with major ions to a final salinity of 0.7 g L?1.  相似文献   

16.
A feeding experiment was conducted to determine the dietary calcium (Ca) requirement for juvenile hybrid tilapia, Oreochromis niloticus × O. aureus reared in nature water. Purified diet supplemented with 0, 1, 2, 3, 4, 5, 7 and 10 g Ca kg−1 diet providing of 0.6, 1.6, 2.6, 3.7, 4.7, 5.5, 7.5 and 10.7 g Ca kg−1 diet, respectively, were fed to tilapia (mean initial weight: 0.52 ± 0.01 g, n = 3) for 8 weeks. Each diet was fed to three replicate groups of fish in a closed, recirculating fresh water rearing system. The rearing water contained 27.1–33.3 mg L−1 Ca. The tilapia fed the diets supplemented with ≥3.7 g Ca kg−1 had significantly (P < 0.05) higher weight gain, when compared with fish fed the diet with ≤1.6 g Ca kg−1. Fish fed the unsupplemented control showed significantly lower weight gain when compared with the other groups (P < 0.05). Bone Ca concentration was highest in fish fed the diets with ≥4.7 g Ca kg−1, intermediate in fish fed the diet with 2.6 g Ca kg−1 and lowest in fish fed the control diet. Scale Ca concentration was higher in fish fed the diets with ≥3.7 g Ca kg−1 than in fish fed the diets with ≤2.6 g Ca kg−1. Serum alkaline phosphatase activity was 36% increased in fish fed the diets with ≥2.6 g Ca kg−1 than fish fed the diets with <1.6 g Ca kg−1. Analysis by broken‐line regression of weight gain, bone and scale Ca concentrations indicated that the adequate dietary Ca concentration for tilapia in water containing 27.1–33.3 mg Ca L−1 was 3.5, 4.3 and 4.2 g Ca kg−1 diet, respectively, supplied as Ca‐lactate.  相似文献   

17.
A 7-week experimental study was performed to evaluate the effect of five concentrations of adult live Artemia (0, 1, 2, 3 and 4 L−1) as exogenous natural feed on the water quality and production parameters of juvenile (0.2 ± 0.01 g) shrimp (Litopenaeus vannamei) pre-grown intensively (125 organism m−2) under laboratory conditions (80 L plastic tanks). No significant differences were observed in the environmental variables among treatments. Total ammonium nitrogen, nitrates and phosphates recorded higher concentrations in all the treatments using artemia, as compared with the treatment without Artemia. In all the cases, the levels remained within or close to the ranges considered necessary for the farming of the species. The highest weight gain and biomass were obtained in the treatments with 3 and 4 Artemia L−1. The best feed conversion ratio were recorded using 2 Artemia L−1 and the highest with 0 Artemia L−1. No differences in survival were detected among treatments. The greatest concentrations of nitrogenous metabolites achieved at the highest densities of Artemia were lower than the LC50 for penaied shrimp and no negative effect was observed on the survival of the shrimp. These results clearly indicate that the use of adult live Artemia as exogenous natural feed significantly increased the production parameters of the Pacific white shrimp.  相似文献   

18.
The current study combined P and N removal using organic flocculant chemicals and woodchip bioreactors in both freshwater and brackish water (7 ppm) recirculating aquaculture systems (RAS). The use of carbon (C) containing flocculant chemicals in the process was hypothesized to further stimulate C-demanding N removal (denitrification) in bioreactors. The trial of combined P and N removal consisted of four treatments: freshwater and brackish water RAS with and without the addition of supernatant from flocculation process to the woodchip reactor. Duplicate woodchip reactors were used per treatment and the trial was run for six weeks. 56% and 49% of P was removed from fresh and brackish sludge water, respectively. The nitrate-N (NO3-N) removal rate was improved in the treatment when supernatant from flocculation process was used together with RAS discharge water when compared against the control. In brackish water RAS, the improvement was more pronounced (from 6.6–16.5 g NO3-N m−3 d-1) than in freshwater RAS (from 5.1–6.5 NO3-N m−3 d-1). In the freshwater bioreactors using supernatant, N was largely discharged as a nitrite-N (NO2-N). High NO2-N concentrations in freshwater reactors allude to incomplete denitrification reactions taking place. The results suggest that the organic flocculants did provide an additional C source for denitrification, which improved the N-removal process. However, in freshwater RAS this might have been partly due to untargeted processes such as DNRA (dissimilatory nitrate reduction to ammonium), and/or insufficient denitrification reactions taking place (excessive NO2-N production).  相似文献   

19.
The effects of fingerlings immersion in low‐dose benzocaine (15 and 30 mg L−1, silver carp and rohu) and quinaldine (100 μL L−1 silver crap and 250 μL L−1 rohu) for 1, 3 and 6 h on stress responses and survival of rohu, Labeo rohita and silver carp, Hypophthalmichthys molitrix fingerlings were evaluated in a transport simulation experiment. Both quinaldine and benzocaine showed low mortalities (0–2%). The total mortality in control (with no anaesthesia) was 30% for rohu and 14% for silver carp. Quinaldine and benzocaine‐treated fingerlings had significantly higher plasma chloride levels than the control in both species. Benzocaine, quinaldine, as well as the control, had an initial elevation of plasma cortisol levels. Benzocaine lost its effectiveness after 3 h exposure while quinaldine persisted throughout the 6 h experimental period. Both sedatives reduced bacterial build‐up compared with the control. No post‐exposure mortality was observed for any of the transport methods assessed 48 h after the treatment. This study suggests that the use of low‐dose benzocaine or quinaldine during transport has positive effect on the survival and health of rohu and silver carp fingerlings.  相似文献   

20.
Amoebic gill disease (AGD) of Atlantic salmon is treated commercially by bathing affected fish in freshwater. Recently, the efficacy of freshwater bathing has been questioned, and the aim of this study was to examine the potential for improving bathing efficacy using additives to the freshwater bath. AGD‐affected Atlantic salmon were bathed in 350 L tanks containing oxygenated freshwater to which chlorine dioxide (0–50 mg L?1), chloramine‐T (0–50 mg L?1) or hydrogen peroxide (0–100 μL L?1) was added. Before and following a 3‐h exposure to the freshwater and chemical additive, the gills were removed from a sub‐sample of fish and the number of live amoebae on the gills were counted and smears made for confirmation of the presence of Neoparamoeba pemaquidensis, the causative agent of AGD. Following a further 3‐h exposure, a sub‐sample of fish was bled from the caudal vein and the gills were removed for histological examination. Chlorine dioxide and chloramine‐T at 25–50 and 10–50 mg L?1, respectively, reduced the number of amoebae on the gills by approximately 50% compared with pre‐exposure numbers. The results from hydrogen peroxide treatment were equivocal and the toxicity of hydrogen peroxide was high. The toxicity of chlorine dioxide varied with freshwater hardness and/or suspended solid load, whereas chloramine‐T toxicity was low, with mortalities attributable only to elevated temperatures at the highest concentration tested. In conclusion, chlorine dioxide and chloramine‐T show promise as potential freshwater additives for the improved removal of N. pemaquidensis and possibly, other amoebae from the gills of commercially farmed Atlantic salmon.  相似文献   

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