Acute Toxicity of Ammonia and Nitrite to Sea Bream,Sparus aurata (Linnaeus, 1758), in Relation to Salinity

Sea bream, Sparus aurata, is one of the most important fish species that is commonly cultured in the Mediterranean and the eastern coasts of the Atlantic Ocean. The life cycle of sea bream in its natural habitat passes through hyposaline and hypersaline lagoons. It is important to determine the tolerance of the fish to nitrogenous compounds for aquaculture at maximum stocking densities. In the present study, a series of acute experiments were performed to evaluate the effect of salinity on ammonia and nitrite toxicity to sea bream. The fish were exposed to different ammonia and nitrite concentrations according to the static renewal methodology at three different salinities (10, 20, and 30 ppt) and at a temperature of 20 C and a pH of 8.2. The toxic effect of total ammonia nitrogen (TAN) and nitrite nitrogen (NO₂‐N) decreased with increasing salinity levels (P < 0.001). Acute toxicity (96‐h lethal concentration 50 [LC₅₀]) values of TAN were determined to be 5.93, 11.72, and 19.38 mg/L at 10, 20, and 30 ppt salinity, respectively. The 96‐h LC₅₀ values of NO₂‐N were determined to be 370.80, 619.47, and 806.33 mg/L at 10, 20, and 30 ppt salinity, respectively. Results indicate that sea bream is less tolerant to ammonia but more tolerant to nitrite compared with some other fish species.     

Acute Toxicity of Ammonia and Nitrite to Painted River Prawn,Macrobrachium carcinus,Larvae

This study evaluated the toxicity of ammonia and nitrite to different larval stages of Macrobrachium carcinus. Three replicated groups of larvae in the zoea stages II, V, and VIII (hence named Z₂, Z_5, and Z₈, respectively) were exposed separately to five ammonia (5, 10, 20, 40, and 80 mg total ammonia nitrogen [TAN]/L) and six nitrite concentrations (5, 10, 20, 40, 80, and 160 mg NO₂‐N/L), plus a control treatment with no addition of ammonia and nitrite, at a salinity of 20 g/L. The ammonia LC₅₀ values at 96 h for Z₂, Z₅, and Z₈ were 8.34, 13.84, and 15.03 mg TAN/L (0.50, 0.71, and 0.92 mg NH₃‐N/L), respectively, and the nitrite LC₅₀ values at 96 h for Z₂, Z₅, and Z₈ were 3.28, 9.73, and 34.00 mg NO₂‐N/L, respectively. The estimated LC₅₀ values for NO₂‐N were lower than those for TAN in most of the stages evaluated. This observation suggests that M. carcinus larvae are more tolerant to ammonia, except at Z₈, in which larvae had a higher tolerance to nitrite. Based on the lethal concentrations at 96 h, it may be concluded that the tolerance of M. carcinus to ammonia and nitrite increases with larval development. Safe levels were estimated to be 0.834 mg TAN/L (0.05 mg NH₃‐N/L) and 0.328 mg NO₂‐N/L; therefore, efforts should be made to maintain lower concentrations of these compounds throughout the larval rearing of M. carcinus.     

Nitrite Toxicity and Methemoglobin Changes in Southern Flounder,Paralichthys lethostigma,in Brackish Water

This study was performed to estimate the nitrite toxicity to southern flounder, Paralichthys lethostigma, in brackish water (7.5 ppt of salinity). For a LC₅₀ test, 20 fingerlings (5.7 ± 0.4 cm) in each aquarium (15 L) were exposed to the concentrations of 0, 1, 5, 10, 15, 30, 60, 120, and 240 mg NO₂^?‐N/L in duplication for 10 d. Median lethal concentration at 96 h (96‐h LC₅₀) was calculated as 81.6 mg NO₂^?‐N/L. For a verification test, young flounder (164.2 ± 9.1 g) were exposed to a simulated culture condition in recirculating systems (1000 L). Sodium nitrite was not added to control system, whereas it was added to Treatment system 1 (TS 1) and Treatment system 2 (TS 2) to maintain nitrite concentrations of 20 and 30 mg NO₂^?‐N/L, respectively. The plasma nitrite concentrations of the young flounder in TS 1 and TS 2 were 4.5 and 6.6 mg NO₂^?‐N/L, respectively, after 2 wk. At this time, the methemoglobin percentages in TS 1 and TS 2 reached 85.8 and 89.7%, and survival rates were 37.5 and 25.0%, respectively. The results of these tests indicate that southern flounder do not concentrate nitrite in blood from the environment, but they seem to be more sensitive to nitrite compared with other species that do not concentrate nitrite.     

Acute and Sublethal Effects of Ammonia on Striped Bass and Hybrid Striped Bass

Bioassays in static water (mean ± SD; temperature, 20–22 C; pH, 8.2–8.4; alkalinity, 205 ± 10 mg/L CaCO₃; total hardness, 220 ± 10 mg/L CaCO₃) were used to determine median lethal concentrations (LC₅₀) of un-ionized ammonia (NH₃-N) for striped bass Moronc saxatilis and hybrid striped bass M. saxatilis × M. chrysops. The 96 h LC₅₀ for striped bass was 1.01 ± 0.24 mg/L NH₃-N₃ and was significantly higher than the LC₅₀ for hybrid striped bass (0.64 ± 0.05 mg/L NH₃-N). The effects of sublethal ammonia were evaluated after fish were exposed for 96 h to 0.0, 0.25, or 0.5 mg/L NH₃-N or to additional exposure to oxygen depleted water (about 2.0 mg O₂/L). Plasma ammonia of striped hass did not change as sublethal ammonia increased, but exposure to oxygen depletion caused a decrease in plasma ammonia. In contrast, plasma ammonia of hybrid striped bass increased as environmental ammonia increased, and increased further after exposure to oxygen depletion. Plasma cortisol levels of striped bass were significantly higher and more variable than cortisol levels of hybrid striped bass; additional exposure to oxygen depletion increased this variability, but these responses may be due to the stress of handling and confinement. Mean differences also existed between species for hemoglobin and hematocrit, while differences in variability occurred for osmolality and oxygen depletion rates. Striped bass tolerated ammonia better than hybrid striped bass but were more susceptible than hybrid striped bass to the additional stress of oxygen depletion. Most changes in physiological characteristics were relatively independent of environmental ammonia, but they were affected by oxygen depletion challenge.     

Acute tolerance of juvenile Florida pompano, Trachinotus carolinus L., to ammonia and nitrite at various salinities

The acute tolerance of juvenile Florida pompano Trachinotus carolinus L. (mean weight±SE=8.1±0.5 g) to environmental unionized ammonia‐nitrogen (NH₃‐N) and nitrite‐nitrogen (NO₂‐N) at various salinities was determined via a series of static exposure trials. Median‐lethal concentrations (LC₅₀ values) of NH₃‐N and NO₂‐N at 24, 48, and 96 h of exposure were calculated at salinities of 6.3, 12.5 and 25.0 g L^?1 at 28 °C (pH=8.23–8.36). Tolerance of pompano to acute NH₃‐N exposure was not affected by salinity, with 24, 48 and 96 h LC₅₀ values ranging from 1.05 to 1.12, 1.00 to 1.08 and 0.95 to 1.01 mg NH₃‐N L^?1 respectively. Regarding NO₂‐N, tolerance of pompano to this environmental toxicant was compromised at reduced salinities. Median‐lethal concentrations of NO₂‐N to pompano at 24, 48 and 96 h of exposure ranged from 67.4 to 220.1, 56.9 to 140.7 and 16.7 to 34.2 mg NO₂‐N L^?1 respectively. The results of this study indicate that juvenile Florida pompano are relatively sensitive to acute NH₃‐N and NO₂‐N exposure, and in the case of the latter, especially at lower salinities.     

Oxidative stress and antioxidant responses in juvenile Brazilian flounder <Emphasis Type="Italic">Paralichthys orbignyanus</Emphasis> exposed to sublethal levels of nitrite

This study evaluated the effects of short-term exposure to sublethal levels of nitrite on oxidative stress parameters and histology of juvenile Brazilian flounder Paralichthys orbignyanus. An assessment of fish recovery was also performed. Fish were exposed to 0.08 (control), 5.72, 10.43, and 15.27 NO₂-N mg L^?1 for 10 days followed by the same recovery time. Gill, liver, and muscle samples were collected after 1, 5, and 10 days of exposure and after recovery for the measurement of antioxidant capacity against peroxyl radicals (ACAP), glutathione-S-transferase (GST) activity, content of non-protein (NPSH) and protein thiols (PSH), and lipid peroxidation levels by thiobarbituric acid-reactive substances (TBARS) content. Nitrite exposure induced alterations which compromised the overall antioxidant system (reduced ACAP and GST activity) and enhanced oxidative damage in lipids and proteins. Increases in GST activity and NPSH and PSH contents were also demonstrated. The recovery period allowed for resumption of basal levels for all (treatment 5.72 NO₂-N mg L^?1) or some of the evaluated parameters (other treatments). In conclusion, exposure to nitrite concentrations from 5.72 to 15.27 NO₂-N mg L^?1 induced oxidative stress and antioxidant responses in juvenile Brazilian flounder. The 10-day recovery period was sufficient for a complete resumption of basal physiological condition of fish exposed to concentrations of up to 5.72 NO₂-N mg L^?1.     

The Effect of Ammonia,Nitrite, and Nitrate on the Oxygen Consumption of Juvenile Pink Shrimp Farfantepenaeus brasiliensis (Latreille, 1817) (Crustacea: Decapoda)

The pink shrimp Farfantepenaeus brasiliensis is native in southern Brazil and is potentially suited for aquaculture. Under intensive culture, the accumulation of nitrogenous compounds results from excretion by the shrimp and from the processes of feed decomposition and nitrification. The objective of this study was to evaluate ammonia, nitrite, and nitrate toxicity effects on oxygen consumption of juvenile pink shrimp. Shrimps (initial weight 0.7 ± 0.15 g) were exposed over a period of 30 days to 50%, 100%, and 200% of the safe levels of total ammonia (TAN = 0.88 mg/L), nitrite (NO₂^? = 10.59 mg/L), and nitrate (NO₃^? = 91.20 mg/L) for the species. The specimens were individually collected and placed in respirometry chambers, where the oxygen consumption was measured over a period of two hours. Throughout the experiment there was no significant difference (p > 0.05) among treatments in terms of survival and growth. The pink shrimp juveniles exposed to nitrogen concentrations of 200% of the nitrite and nitrate safe level showed the highest oxygen consumption (p < 0.05).     

Mortality,hematology, and histopathology of common snook Centropomus undecimalis (Perciformes: Centropomidae) exposed to acute toxicity of ammonia

This study aimed to evaluate the tolerance of common snook Centropomus undecimalis larvae and juveniles exposed to acute concentrations of un-ionized ammonia for 96 h at 35g L^?1 salinity, after 24 h starvation. For that, 10 larvae (20.85 ± 1.46 mm) of 47 days post hatch (DPH) per experimental unit (1.5 L) were exposed to 0.00 ± 0.00, 0.65 ± 0.04, 1.29 ± 0.09, 2.59 ± 0.18, 3.88 ± 0.27, 5.17 ± 0.34, and 6.47 ± 0.43 mg L^?1 NH₃, in triplicates, at 26.72 ± 0.08°C, dissolved oxygen at 5.72 ± 0.10 mg L^?1 and pH 8.45 ± 0.06. During this period, no mortalities were observed. Another trial was performed with five juveniles (20.35 ± 6.10 g, 13.90 ± 1.75 cm) per experimental unit (60 L) exposed to 0.00 ± 0.00, 2.26 ± 0.07, 2.68 ± 0.11, 3.20 ± 0.13, 3.68 ± 0.17, and 4.27 ± 0.16 mg L^?1 NH₃, in triplicates, at 21.90 ± 0.76°C, dissolved oxygen at 6.27 ± 0.21 mg L^?1 and pH at 8.38 ± 0.04. Fish mortality increased as ammonia concentrations increased at each day, and LC₅₀ 96 h was 3.52 mg L^?1 NH₃. Larvae were less sensitive than juveniles, demonstrating that the environmental toxicity of ammonia to common snook is influenced by age. Sublethal exposition to ammonia caused histological damages in gills of common snook juveniles and variation on glucose levels, hematocrit, and red blood cells number, showing negative effects on fish homeostasis. Moreover, compared to other species, the common snook has great resistance to ammonia.     

A wide difference in susceptibility to nitrite between Eurasian perch (Perca fluviatilis L.) and largemouth bass (Micropterus salmoides Lac.)

Influence of nitrite on two fish species, Eurasian perch (Perca fluviatilis L.) and largemouth bass (Micropterus salmoides Lacépède), was assessed in two acute toxicity tests. In the first one, lethal concentrations (48hLC50) of nitrite were estimated at 11 mg l^?1 NO₂ ^? for perch and 882 mg l^?1 NO₂ ^? for bass. In the second test, fishes were exposed for 48 h to concentrations representing ¼ and ½ value of 48hLC50 for each species. This test showed that the higher nitrite concentration in the water the higher methaemoglobin content in the blood, and nitrite levels in the blood plasma were observed in both species. On the other hand, leucocyte count showed opposite trend. Activity of NADH-methaemoglobin reductase was markedly lower in largemouth bass compared to Eurasian perch and was stimulated by nitrite exposure in neither of the species.     

Secondary Stress Responses in Juvenile Brazilian Flounder,Paralichthys orbignyanus,throughout and after Exposure to Sublethal Levels of Ammonia and Nitrite

This study investigated the secondary stress responses of Paralichthys orbignyanus exposed to ammonia and nitrite and after recovery. Fish were exposed to 0.12, 0.28, and 0.57 mg NH₃‐N/L, or 5.72, 10.43, and 15.27 mg NO₂‐N/L for 10 d followed by the same time length for recovery. Ammonia‐ and nitrite‐free water was used as a control treatment. Blood samples were collected after 1, 5, and 10 d of exposure and after recovery. Fish exposed to ammonia presented lower and higher glucose levels after 10 d of exposure and recovery, respectively. Ammonia induced initial and transient ionic disturbances and metabolic alkalosis. Nitrite exposure caused hyperglycemia, increased plasma K⁺ levels, and respiratory alkalosis, whereas metabolic acidosis was observed after recovery. Increased proportion of monocytes and/or granulocytes and reduced number of lymphocytes were demonstrated in fish exposed to 0.28 mg NH₃‐N/L (Day 1) and 10.43 mg NO₂‐N/L (Day 5) and after recovery in the 0.28 and 0.57 mg NH₃‐N/L treatments. Exposure to ammonia decreased the proportion of granulocytes on Day 5. In conclusion, exposure to concentrations at 0.12 mg NH₃‐N/L and 5.72 mg NO₂‐N/L provoked physiological disorders in Brazilian flounder. Nonetheless, fish exposed to 5.72 mg NO₂‐N/L following a 10‐d recovery period showed complete resumption of homeostasis.     

The acute toxicity and sublethal effects of nitrite on growth and feed utilization of European eel, Anguilla anguilla (L.)

Eels cultured in recirculation systems are regularly confronted with high concentrations of nitrite, a well-known toxicant for fish. In this study, the acute toxicity of nitrite to European eel, Anguilla anguilla (L.), was assessed by determination of a 96-h LC₅₀. The 96-h LC₅₀ measured for eels was 143.7 ± 2.3 gm^-3 NO₂-N (mean SD), which is high compared with the LC₅₀ for other fish species. The sublethal effects of nitrite on growth and feed utilization were evaluated in a feeding trial lasting 77 days, divided into an acclimation period and two experimental periods. Eels of 24 g on average were divided over 20 aquaria, connected to five separate recirculation systems. In each system, the desired nitrite concentration level was maintained by water suppletion and continuous addition of NaNO₂. Fish were continuously exposed to levels of 0, 1, 5, 10 or 20 g m^-3 NO₂-N. Half of the experimental groups were fed ad libitum to study effects on feed intake, while the other half were fed a restricted ration to study effects on feed utilization. At the start and end of each experimental period, nitrite in the blood plasma, haemoglobin and methaemoglobin were measured. Fish weight and body composition were used to calculate specific growth rate and conversion efficiencies. In the range of concentrations studied, no significant effect of nitrite on maximum growth rate or feed utilization could be demonstrated. At the start of the experiment, low concentrations of nitrite were detected in the blood plasma, which suggests an ability of the eel to adapt to environmental nitrite. Nitrite, in the range normally encountered in intensive eel farms (max. 15 g m^-3 NO₂-N), can therefore be considered a factor of little significance.     

Effects of acute and chronic toxicity of unionized ammonia on mud crab, Scylla serrata (Forsskål, 1755) larvae

While the effects of ammonia on fish and prawn larvae are well documented, little is known of its effect on mud crab (Scylla serrata) (Forsskål, 1755) larvae. Two experiments were conducted in 5 L hemispherical plastic bowls, containing 3 L of ultra‐filtered and settled seawater and various larval stages of mud crab to (1) determine the acute median lethal concentration (LC₅₀) of unionized ammonia and (2) to determine the chronic effects of unionized ammonia on survival and percentage moulting to zoea and megalop stages. The larval stages that exhibited the highest tolerance to ammonia over 24 h were zoea 1 (LC₅₀ of 4.05 mg L^?1 of unionized ammonia) and zoea 5 (LC₅₀ of 6.64 mg L^?1 of unionized ammonia). The megalop stage had the lowest total ammonia LC₅₀ at both 24 and 48 h, making it the larval stage most susceptible to total ammonia. Exposure to 6.54 mg L^?1 of unionized ammonia resulted in 100% death of all larvae within 24 h. The tolerance of S. serrata larvae to total ammonia did not appear to increase with ontogenetic development. The results indicate that the concentrations at which total ammonia produces an acute or chronic response in mud crab larvae are far higher than those experienced in current larval production systems (0–0.5 mg L^?1 of total ammonia) used as industry standards in Australia.     

Ammonia‐, Sodium Chloride‐, and Calcium Sulfate‐induced Changes in the Stress Responses of Jundiá, Rhamdia quelen,Juveniles

Salt (NaCl) and gypsum (CaSO₄) are used as water additives to mitigate fish stress and improve specimen survival. High stocking densities and the transportation of fish can increase aqueous ammonia, which can, in turn, alter fish cortisol secretion. The objectives of this study were to assess the effects of salt, gypsum, and aqueous ammonia on some stress‐induced physiological responses of jundiá, Rhamdia quelen, juveniles induced by captivity and handling, and to determine the lethal ammonia concentration for this species. Jundiá juveniles were subjected to the following five treatments: water only, water + ammonia (0.4 mg/L), water + NH₃ + NaCl (6 g/L), water + NH₃ + gypsum (150 mg/L), and water + NH₃ + NaCl + gypsum. Blood samples were taken after intervals of 1, 5, 24, and 96 h, and the concentrations of cortisol, glucose, chloride, ammonia, and hematocrit were determined. The NH₃ LC₅₀ value after 96 h of exposure (LC_50?96h) was measured to be 1.9 mg/L NH₃. Either salt or gypsum reduced both cortisol and glucose levels during most of the experimental period, but the combination of both reduced these levels even further. The combined use of NaCl and CaSO₄ demonstrates a synergic effect on mitigating stress responses induced by handling and aqueous ammonia in jundiá juveniles.     

Acute toxicity of ammonia to the early stage-larvae and juveniles of Eriocheir sinensis H. Milne-Edwards, 1853 (Decapoda: Grapsidae) reared in the laboratory

Static-renewal bioassays were performed to evaluate the acute toxicity of ammonia to Eriocheir sinensis (H. Milne-Edwards) at three growing stages, namely zoea-I, zoea-II, and juvenile (0.06 g wet weight per crab). The 24 h LC₅₀ values were 13.3, 20.2, and 109.3 mg (NH₃+ NH₄⁺) 1^?1 (0.47, 0.71, and 3.10 mg NH₃ I^?1), the 48 h LC₅₀ values being 6.8, 10.3, and 60.9 mg (NH₃⁺ NH₄⁺) 1^?1 (0.24, 0.36, and 1.73 mg NH₃1^?1), while the 72 h LC₅₀ values were 5.7, 7.6, and 45.3 mg (NH₃+ NH₄⁺) 1^?1 (0.20, 0.27, and 1.29 mg NH₃ 1^?1) for zoea-I, zoea-II, and juveniles, respectively. The 96 h LC₅₀ value for juveniles was 31.6 mg (NH₃+ NH₄⁺) 1^?1(0.90 mg NH₃1^?1). It was evident that the tolerance to ammonia increased during the same exposure time as the larvae developed to juveniles and decreased with prolonged exposure time. Compared with larvae, juveniles were more sensitive to the fluctuation of ambient ammonia concentrations in the certain range within which partial kills took place. The ‘safe level’ of ammonia based on the 96 h LC₅₀ value and an application factor of 0.1 was 3.16 mg (NH₃+NH₄⁺)1^?1 (0.09 mg NH₃ 1^?1) for juveniles and those for zoea-I and zoea-II were 0.57 and 0.76 mg (NH₃+ NH₄⁺) 1^?1 (0.02 and 0.03 mg NH₃ 1^?1) based on 72 h LC₅₀ values.     

海水观赏鱼居室养殖循环系统中三态氮的变化规律及硝化细菌对水质的影响

于 2005年 3月 5日 ~5月 3日连续监测了海水观赏鱼居室养殖循环系统的水质，研究该系统中三态氮的变化规律以及添加硝化细菌后对水质的影响。结果表明：1)试验初期氨氮的质量分数迅速上升， 在 1周内达到高峰(峰值2．56mg/L)，并在1．50mg/L的范围内维持 1周左右，此后迅速下降至0．01mg/L 左右，并一直维持在该水平直至试验结束。亚硝态氮的质量分数在氨氮的质量分数迅速回落时(约试验开始后 2周)呈现出直线上升的趋势，并在 3~3．5mg/L左右的水平上维持 2~3周时间(峰值为3．65 mg/L)，此后迅速下降至0．01mg/L以下，并一直维持在低水平直至试验结束。而硝酸盐的质量分数在整个试验期间基本保持稳定上升的趋势，至本试验末期，NO₃ ^- -N的质量分数达到 15mg/L左右。2)系统的生物滤器需要 4~5周左右时间才能基本成熟，即氨氮和亚硝酸氮均降至 ＜0．01mg/L，到达安全的质量分数，适合海水观赏鱼健康生长。3)添加硝化细菌的试验组，氨氮和 NO₃ ^- -N的质量分数变化与对照组基本相似，而 NO₂ ^- -N的质量分数变化与对照组明显不同。试验组从高质量分数水平迅速下降的时间比对照组提前了约 1周。     

Acute toxicity of ammonia in Meagre (Argyrosomus regius Asso, 1801) at different temperatures

Argyrosomus regius (3.0 ± 0.9 g) were exposed to different concentrations of ammonia in a series of acute toxicity tests by the static renewal method at three temperature levels (18, 22 and 26°C) at a pH of 8.2. Low temperature clearly increased the tolerance of the fish to total ammonia nitrogen (TAN) and unionized ammonia (NH₃) (P < 0.05). While the 96‐h LC₅₀ values of TAN were 19.79, 10.39 and 5.06 mg L^?1, the 96‐h LC₅₀ of NH₃ were 1.00, 0.70 and 0.44 mg L^?1 at 18, 22 and 26°C respectively. The safe levels of NH₃ for A. regius was estimated to be 0.10, 0.07 and 0.04 mg L^?1 at 18, 22 and 26°C respectively (P < 0.05). This study clearly indicates that A. regius is more sensitive to ammonia than other marine fish species cultured on the Mediterranean and Eastern Atlantic coasts.     

Effect of Combined Non‐ionized Ammonia and Dissolved Oxygen Levels on the Survival of Juvenile Dourado,Salminus brasiliensis (Cuvier)

The aim of this study was to assess the mean lethal concentration (LC₅₀) of dissolved oxygen in high ammonia concentration and also the LC₅₀ of ammonia under hypoxic conditions for juveniles of dourado, Salminus brasiliensis. In the first experiment, the non‐ionized ammonia (NH₃) concentrations were: 0.026, 0.447, 0.612, 0.909, and 1.334 mg/L, and the dissolved oxygen concentration was maintained at approximately 1.65 mg/L. In the second experiment, the dissolved oxygen concentrations were: 1.64, 1.99, 3.33, 5.10, and 7.77 mg/L, and the non‐ionized ammonia concentration was kept at approximately 0.927 mg/L. The mean lethal concentrations of non‐ionized ammonia varied from 0.584 to 0.577 mg/L, indicating that LC₅₀ values were almost unaffected by exposure time. The estimated LC₅₀ of dissolved oxygen varied from 4.02 to 5.02 mg/L, indicating a slight increase in the mean lethal concentrations as the exposure time increased. Results from this study indicate that interaction between these two parameters increases mortality and also suggest that dourado is susceptible to the combination of high ammonia with low dissolved oxygen concentrations.     

Daily patterns of ammonia nitrogen output of Siberian sturgeon Acipenser baeri (Brandt) of different body weights

The daily pattern of ammonia nitrogen outputs of five weight groups of Siberian sturgeon, Acipenser baeri (Brandt), was studied. Regardless of weight, there was a delay of 3 h between the start of feeding and the increase in ammonia output. For sturgeon reared at 17°C with continuous feeding, the total ammonia output levels (NH₄-N + NH₃-N) decreased from 530 mg kg^?1 per day for fish weighing 40 g, to 239 mg kg^?1 per day for fish weighing 1700 g. The study showed that continuous feeding is suitable in sturgeon farms in terms of ammonia loadings.     

草鱼养殖水体中参与氮转化途径的异养菌分析

为分析草鱼池塘中参与氮代谢的异养细菌比例及其代谢途径,从杭州郊区取得4个草鱼池塘的水样,每个水样通过涂布随即挑选100株菌株进行定性显色试验,并据此选取11株异养菌进行16S rRNA序列分析。结果表明,4个草鱼养殖池塘中NH4+-N和NO2--N的平均水平分别为5.597 mg/L和0.135 mg/L。池塘中可培养的异养菌平均为3.26×105cfu/mL,其中的89.75%参与了氮的不同代谢途径,其中31.25%的氨化菌和33.50%NO3--N(NO2--N)还原菌参与了NH4+-N的生成,32.45%的氨氧化菌参与了NH4+-N的降低;NO2--N生成途径主要包括蛋白质直接转化(11.26%)、氨氧化(4.25%)和硝酸盐氮还原(10.75%),而NO2--N降低主要通过15.50%的亚硝酸氧化菌、8.75%的NO2--N还原菌和10.75%的反硝化菌实现。结果提示,草鱼养殖水体中存在大量的异养硝化菌参与不同的氮代谢途径,且产生氨氮的异养菌比例远高于去除氨氮的菌,这是草鱼养殖水体中氨氮含量易偏高的原因。同时,11株不同功能的异养菌16SrRNA鉴定结果为寡养食单胞菌(Stenotrophomonas)6株、假单胞菌(Pseudomonas)3株、克雷伯氏菌(Klebsiella)和肠杆菌(Enterobacter)各1株,而且细菌对氮源的利用具有菌株特异性。     

Lethal doses of ammonia on the late-stage larvae of Chinese mitten-handed crab, Eriocheir sinensis (H. Milne-Edwards), (Decapoda: Grapsidae) reared in the laboratory

Four successive life stages (zoea-III, zoea-IV, zoea-V and megalopa) of the Chinese mitten-handed crab, Eriocheir sinensis (H. Milne-Edwards), were exposed to ammonia in a series of short-term bioassays with the static-renewal method at 22°C, pH 8.0 and 25%o salinity. The greatest sensitivity was observed in the zoea-III stage. The 24-h LC₅₀ values for zoea-III, zoea-IV, zoea-V and megalopa were 32.8, 73.1, 84.0 and 90.1 mg L^?1 for NH₃+ NH₄⁺, and 1.11, 2.36, 2.77 and 3.18 mg L^?1 for NH₃, respectively. The 72-h LC₅₀ values for zoea-III, zoea-IV and zoea-V were 11.9, 23.6 and 38.2 mg L^?1 for NH₃+ NH₄⁺, and 0.40, 0.76 and 1.26 mg L^?1 for NH₃, respectively. The 96-h LC₅₀ values for megalopa were 37.3 mg L^?1 for NH₃+ NH₄⁺ and 1.31 mg L^?1 for NH₃. It was found that ammonia tolerance increased with larval development from zoea-III to megalopa, especially from zoea-III to zoea-IV and from zoea-IV to zoea-V. A comparison of safe levels of ammonia among the different life stages indicated that all stages were significantly different with respect to safe levels of ammonia (P < 0.05) except zoea-V and megalopa, which had the highest safe levels. In general, both the larvae and juveniles of E. sinensis are less resistant to ammonia than those of other crustacean species studied so far.