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1.
Assessing the responses of lysozyme activity and antioxidant defences to hypoxia is important to understand the adaptation and tolerance strategies of fish under hypoxia. This study investigated the effects of different dissolved oxygen (DO) levels on Carassius auratus, a natural triploid fish, from Qihe River. The content of malondialdehyde (MDA) and the activities of lysozyme and antioxidant enzymes were measured in the kidney and spleen after hypoxic exposure. At the DO concentrations of 1 and 2 mg L?1, the activities of antioxidant enzymes and lysozyme significantly decreased and the content of MDA significantly increased (P < 0.01). This result suggests that hypoxia decreased antioxidant enzyme and lysozyme activities and caused MDA accumulation in a concentration‐dependent manner. The DO level of 4 mg L?1 increased the activities of superoxide dismutase and catalase in the kidney and the activities of glutathione peroxidase and catalase in the spleen (P < 0.05). This result implies that slight hypoxic stress can enhance antioxidant defences to alleviate the damage of oxidative stress. The reduced activities of antioxidant enzymes and the accumulation of MDA at the DO level of ≤2 mg L?1 implied the decrease in antioxidative ability and the occurrence of oxidative stress. The decrement in lysozyme activity indicated that the antibacterial ability was weakened to some degree. Therefore, hypoxic stress at DO levels ≤2 mg L?1 should be removed by aeration to avoid the oxidative damage resulting from the reduced antioxidative ability and prevent the outbreak of diseases caused by weakened antibacterial effects.  相似文献   

2.
A 9‐week feeding experiment was conducted to determine the effect of dietary biotin levels on growth performance and non‐specific immune response of large yellow croaker. Fish (6.16 ± 0.09 g) were fed twice daily to apparent satiation with diets containing 0.00 (as the basal diet), 0.01, 0.05, 0.25, 1.24 and 6.22 mg biotin kg?1 diet. Results showed that fish fed the basal diet had the lowest survival rate, and fish fed 0.05 mg kg?1 dietary biotin achieved significantly higher final weight and weight gain. Dietary biotin levels had no significant influence on carcass crude lipid, moisture and ash content, but significantly influenced the carcass crude protein. Liver biotin concentration significantly increased with the supplementation of biotin, but no tissue saturation was found within the supplementation scope of biotin. Broken‐line regression analysis of weight gain showed that juvenile large yellow croaker requires a minimum dietary biotin of 0.039 mg kg?1 for maximal growth. The analyses of serum parameters showed that the moderate‐ (0.05 mg kg?1) and high‐dose (6.22 mg kg?1) dietary biotin significantly improved both lysozyme and alternative complement pathway activities, indicating dietary biotin within a certain range could improve the non‐specific immune response of large yellow croaker.  相似文献   

3.
Ichthyobodo necator is a single‐celled biflagellate parasite, which in high density can cause significant mortality in young fish. Copper sulphate (CuSO4), potassium permanganate (KMnO4) and peracetic acid (PAA) were evaluated for effectiveness against ichthyobodosis. Treatments were: untreated control, 2.1 mg L?1CuSO4, 3.0 mg L?1 KMnO4, 1.5 mg L?1 PAA and 3.0 mg L?1 PAA, and were applied to flow‐through tanks on three consecutive days. The study was designed to simulate the flow‐through systems utilized in the commercial rearing of juvenile channel catfish (Ictalurus punctatus). Mortality was monitored daily to compare survival rate among treatments. Parasite intensity was assessed pre chemical exposure and 20–24 h after the third application to determine effectiveness of the treatment. An assessment was also done 7 days post application to investigate possible reoccurrence. Copper sulphate, KMnO4 and PAA (3.0 mg L?1) significantly reduced the infestation rate of I. necator. Copper sulphate significantly improved the survival of I. necator infested channel catfish after three flow‐through applications compared with the untreated control. The 3.0 mg L?1 PAA resulted in significantly lower survival than the untreated control, the 1.5 mg L?1 PAA and the KMnO4 were not statistically different from the untreated control.  相似文献   

4.
A 12‐week feeding trial was conducted to evaluate the effects of dietary vitamin C on growth performance, antioxidant status and innate immune responses in juvenile yellow catfish, Pelteobagrus fulvidraco. Six isonitrogenous and isolipidic diets (44% crude protein and 7% lipid) were formulated to contain six graded dietary vitamin C (ascorbate‐2‐poly‐ phosphate, ROVIMIX® STAY‐C® 35) levels ranging from 1.9 to 316.0 mg kg?1 diet. The results of present study indicated that fish fed the lowest vitamin C diet had lower weight gain (WG) and specific growth rate (SGR) than those fed the diets supplemented vitamin C. WG and SGR did significantly increase with dietary vitamin C levels increasing from 1.9 to 156.5 mg kg?1. However, no significant increase was observed with further dietary vitamin C levels increasing from 156.5 to 316 mg kg?1. Survival, protein efficiency ratio and feed efficiency were not significantly affected by the dietary vitamin C levels. The activities of serum superoxide dismutase, catalase and glutathione peroxidase significantly increased when dietary vitamin C levels increased from 1.9 to 156.5 mg kg?1, fish fed the lowest vitamin C diet had higher serum malondialdehyde content than those fed the diets supplemented with vitamin C. Fish fed the diet containing 156.5 mg kg?1 vitamin C had the highest lysozyme, total complement activity, phagocytosis index and respiratory burst of head kidney among all treatments. The challenge test with Aeromonas hydrophila indicated that lower cumulative survival was observed in fish fed the lowest vitamin C diet. Analysis by broken‐line regression of SGR and lysozyme activity indicated that the dietary vitamin C requirement of juvenile yellow catfish was estimated to be 114.5 and 102.5 mg kg?1 diet, respectively.  相似文献   

5.
Egg disinfection is considered the most important routine work in hatcheries to avoid fungal and/or bacterial infection of fish eggs. The aim of this study was to determine the effectiveness of three disinfectants: formalin, iodine and sodium chloride on the hatching success of yellow perch eggs. The disinfectants were tested in triplicate at different concentrations for 15 and 30 min bath treatments. Two experiments were conducted; formalin at five concentrations (25, 50, 100, 150 and 200 mg L?1) and 25 mg L?1 iodine were tested in the first experiment. The second experiment involved formalin at three concentrations (250, 500 and 1000 mg L?1), iodine at three concentrations (50, 100 and 250 mg L?1) and sodium chloride at three concentrations (500, 1000 and 3000 mg L?1) were used. Iodine and sodium chloride‐treated eggs hatched earlier than formalin‐treated eggs. The highest mean percentage of eyed stage, hatching rate and survival to first feeding fry was observed at 200 mg L?1 formalin for 30 min, 50 mg L?1 iodine for 15 min and 500 mg L?1 sodium chloride for 30 min. High concentrations of formalin (1000 mg L?1), iodine (250 mg L?1) and sodium chloride (1000 and 3000 mg L?1) showed toxicity to yellow perch eggs, resulting in low hatching rate and survival to first feeding fry. We recommended formalin at a concentration of 150–200 mg L?1 for 30 min as an effective, easily available and low‐cost disinfectant for routine use to improve yellow perch hatchability.  相似文献   

6.
Ammonia is a metabolite of aquatic organisms which might reach deleterious levels in intensive fish farms. The aim of the present study was to determine median lethal concentrations (96‐h LC50) of total ammonia nitrogen (TA‐N) on marbled spinefoot rabbitfish (Siganus rivulatus) and chronic effects of TA‐N on survival, growth and behaviour of juvenile rabbitfish over a 50 day period. In the first experiment, fish were exposed to 0, 2, 4, 6, 8, 10, 12, 14, 16, 18 and 20 mg L?1 TA‐N for 96 h and survival evaluated. In the second experiment, 12 fish were stocked per 50‐L tank and treated with one of 0, 2, 4, 6, 8, 10 and 12 mg L?1 TA‐N with three replicate tanks per treatment. Survival and growth were determined and histopathological alterations of gills due to chronic ammonia exposure were studied by light and electron microscopy. The 96‐h LC50 values were 16–18 mg L?1 TA‐N. In the chronic exposure experiment, fish reared in water with 0 mg L?1 TA‐N had 100% survival and had 50% weight increase in 50 days. Fish at 2 and 4 mg L?1 TA‐N all died whilst fish in 6, 8, 10 and 12 mg L?1 TA‐N survived and grew albeit less than in treatment 0 mg L?1. Gills from ammonia treated fish displayed severe histological and ultrastructural alterations including hyperplasia, hypertrophy and fusion of secondary lamellae, aneurysms and presence of pleomorphic altered cells. Chronic exposure to ammonia is deleterious to marbled spinefoot rabbitfish and low concentrations of ammonia appear to kill the fish in <50 days whilst fish can survive for more than 50 days at concentrations between 6 and 12 mg L?1 TA‐N.  相似文献   

7.
An 8‐week study was conducted to determine folic acid requirement and its effect on antioxidant capacity and immunity in juvenile Chinese mitten crab Eriocheir sinensis (Milne‐Edwards, 1853), followed by a challenge assay with the pathogen Aeromonas hydrophila for 2 weeks. Folic acid was added to a basal diet at seven levels (0, 0.5, 1.0, 2.0, 4.0, 8.0, 16.0 mg folic acid kg?1 diet), and a diet free of folic acid and vitamin B12 was also included as a control. Crabs were fed twice daily in 32 tanks with 7.76–8.17 mg oxygen L?1, 25.0–31.0 °C and 7.5–8.3 pH. Growth and feed efficiency were significantly greater in crabs fed ≥2.0 mg folic acid kg?1, but not significantly different between crabs fed diets >2.0 mg folic acid. The superoxide dismutase activity and glutathione S‐transferase activity were highest in crabs fed ≥2.0 mg folic acid kg?1, followed by those fed 0.5 and 1.0 mg folic acid kg?1, and the control diet. The malondialdehyde content was highest in crabs fed the control diet, followed by those fed 0 mg folic acid kg?1, and the lowest value occurred in those fed ≥0.5 mg folic acid kg?1. Phenoloxidase activity and total haemocytes were significantly higher in crabs fed ≥2.0 mg folic acid kg?1 than other diets. Crabs fed 2.0 mg folic acid kg?1 had the highest lysozyme, acid phosphatase and alkaline phosphatase activities but the lowest cumulative mortality. The optimum dietary folic acid requirement by E. sinensis was estimated at 2.29–2.90 mg kg?1 diet.  相似文献   

8.
Responses to anaesthesia with essential oil (EO) of Aloysia triphylla (135 and 180 mg L?1) and tricaine methanesulfonate (MS222) (150 and 300 mg L?1) were assessed in silver catfish. Exposure to the anaesthetics elicited a stress response in the species. In the case of MS222, it was displayed as a release of cortisol into bloodstream, elevation in hematocrit and plasma ion loss. The EO presented cortisol‐blocking properties, but increased haematocrit and disturbances of hydromineral balance were observed. Liver antioxidant/oxidant status of EO and MS222‐anaesthetized silver catfish was also estimated. The synthetic anaesthetic induced lipoperoxidation, notwithstanding increased catalase contents, whereas the naturally occurring product was capable of preventing the formation of lipid peroxides, possibly due to combined actions of catalase and glutathione‐S‐transferase. Anaesthetic efficacy was also tested via induction and recovery times. Overall, the promising results obtained for the physiological parameters of the EO‐treated fish counterbalanced the slight prolonged induction time observed for 180 mg L?1. As for 135 mg L?1, both induction and recovery times were lengthy; despite that, the EO was able to promote oxidative protection and mitigate stress. None of the MS222 concentrations prompted such responses concomitantly.  相似文献   

9.
Piaractus mesopotamicus juveniles (total length 12 ± 0.5 mm) were exposed to different concentrations of ammonia‐N (un‐ionized plus ionized ammonia as nitrogen), using the static renewal method at different temperature levels (15, 20 and 25°C) at pH 7. The 24, 48, 72, 96 h LC50 values of ammonia‐N in P. mesopotamicus juveniles were 5.32, 4.19, 3.79 and 2.85 mg L?1 at 15°C; 4.81, 3.97, 3.25 and 2.50 mg L?1 at 20°C; and 4.16, 3.79, 2.58 and 1.97 mg L?1 at 25°C respectively. The 24, 48, 72, 96 h LC50 values of NH3‐N (un‐ionized ammonia as nitrogen) were 0.018, 0.014, 0.013, 0.009 mg L?1 at 15°C temperature; 0.023, 0.019, 0.016 and 0.012 mg L?1 at 20°C; 0.029, 0.026, 0.018 and 0.014 mg L?1 at 25°C. The temperature increase from 15 to 25°C caused an increase of ammonia‐N susceptibility by 21.80%, 9.55%, 31.92% and 30.87%, after 24, 48, 72 and 96 h exposure respectively. Furthermore, we found that exposure of fish to ammonia‐N caused an elevation in total haemoglobin and blood glucose with an increase of 2 mg L?1 concentration. Ammonia levels tolerated, especially in different temperatures levels, have important implications for the management of aquaculture.  相似文献   

10.
A 75‐day experiment was conducted with juvenile gibel carp (Carassius auratus gibelio) (4.80 ± 0.01 g) to evaluate effects of dietary chitosan on fish growth performance, haematology, intestine morphology and immune response. Six isonitrogenous (crude protein: 383 g kg?1), isolipid (97.5 g kg?1) and isocaloric (gross energy: 16.7 kJ g?1) diets were formulated to contain 0, 1800, 4000, 7500, 10 000, 20 000 mg kg?1 chitosan, respectively. The results showed that the growth was depressed when the fish fed with 10 000 mg kg?1 chitosan. Serum cholesterol, triglyceride and low‐density lipoprotein decreased in 10 000 and 20 000 mg kg?1 chitosan. On day 75, blood leucocyte phagocytic activity respiratory burst and alternative pathway of complement haemolytic activity were enhanced in 4000 mg kg?1 chitosan. The number of goblet cell, intraepithelial lymphocyte of mid‐intestine and microvilli height of distal intestine increased at 4000 mg kg?1 dietary chitosan. Dietary chitosan modulated intestine microbiota, depressed pathogen bacteria Aeromonas veronii‐like and improved Cellulomonas hominis‐like, Bacillus oceanisediminis‐like and two uncultured bacterium‐like species on day 75. Dietary 7500 and 10 000 mg kg?1 chitosan enhanced the protection against Aeromonas hydrophila infection. In conclusion, oral administration of dietary 7500 mg kg?1 chitosan for 75 days is recommended for the survival of gibel carp.  相似文献   

11.
A study was conducted to investigate effects and interactions of magnesium (Mg) and vitamin E (VE) on growth performance, body composition, hepatic antioxidant capacity and serum biochemistry parameters of juvenile Japanese seabass Lateolabrax japonicus under oxidative stress condition. Fish (initial average body weight of 6.10 ± 0.20 g) were fed 9 oxidized oil diets supplemented with 3 grade levels of Mg (0, 520 and 1570 mg kg?1 diet) and VE (0, 60 and 200 mg kg?1 diet) for 8 weeks in freshwater. The results showed that diets supplemented 520 mg kg?1 Mg and/or 60 mg kg?1 VE had highest growth and muscle lipid content. There were highest total superoxide dismutase, catalase, glutathione peroxidase activities and lowest malondialdehyde content in liver of fish fed diets supplemented 520 mg kg?1 Mg and/or 60 mg kg?1 VE. Contrary to Mg concentrations, Ca concentrations and Ca/Mg ratio in whole body were inversely related to dietary Mg levels. However, combined deficiency or excess of dietary Mg and VE led to the decrease of hepatic antioxidant capacity, body lipid deposition and growth of Japanese seabass under oxidative stress condition.  相似文献   

12.
A 12‐week feeding trial was conducted to estimate the dietary copper requirement of fingerling Channa punctatus. Six casein?gelatin‐based test diets (450 g kg?1 crude protein; 18.81 kJ g?1 gross energy) with graded levels of copper as copper sulphate (3.7, 4.7, 5.7, 6.7, 7.7 and 8.7 mg copper equivalent kg?1 diet) were formulated and fed to triplicate groups of fish (7.25 ± 0.81 cm; 5.21 ± 0.27 g) near to satiation. Fish fed diet with 6.7 mg kg?1 copper had highest absolute weight gain (AWG; 51.63 g fish?1), protein efficiency ratio (PER; 1.42 g fish?1), protein gain (PG; 8.34 g fish?1), haemoglobin (Hb; 9.68 g dL?1), haematocrit (Hct; 31.18%) and RBCs (3.24 × 106 × mm?3). Feed conversion ratio (FCR) was found to be best (1.57) at above level of dietary copper. Whole body copper concentration was found to increase with the increasing levels of dietary copper. Hepatic thiobarbituric acid‐reactive substances concentration was found to decrease with increasing dietary concentrations of copper up to 6.7 mg kg?1 beyond which a reverse trend in this parameter was noted. Broken‐line regression analysis of AWG, FCR and PG concentrations against varying levels of dietary copper yielded the requirement in the range of 6.66–6.78 mg kg?1. Data generated during this study would be useful in formulating copper‐balanced commercial feeds for the intensive culture of this fish.  相似文献   

13.
The efficacy of anaesthetic tricaine methanesulfonate (MS‐222) was evaluated in four freshwater aquarium fish species, Zebrafish (Danio rerio), Guppy (Poecilia reticulata), Discu (Symphysodon discus) and Green swordtail (Xiphophorus helleri). The correct dose of anaesthetic should induce the plane 4 of anaesthesia in less than 180 s, recovery in less than 300 s and must survive when exposed during 30 min to anaesthetic. Fishes were exposed to six concentrations of anaesthetic (75, 100, 125, 150, 200 and 250 mg L?1) and the time of fish reaching plane 4 of anaesthesia, post exposure recovery, and the percentage of survival when fish were subject to 30 min in the anaesthetic were recorded. The optimal doses varied according to the species: D. rerio – 75, 100 and 125 mg L?1, P. reticulata – 125, 150 and 200 mg L?1, S. discus – 75 and 100 mg L?1 and X. helleri – 125 and 150 mg L?1. The induction time generally decreased significantly with increasing concentration of MS‐222 for all of the species evaluated. The recovery time had a tendency to increase with the increase of the MS‐222 concentration for D. rerio, P. reticulata and S. discus. On the other hand, X. helleri recovery time decreased with the increase of MS‐222 concentration. MS‐222 proved to be effective in anaesthesia for all the freshwater ornamental species studied. The main results clearly show that the optimal dose to anesthetize is fish species dependent and it is completely wrong to extrapolate optimal anaesthetic concentrations between different species.  相似文献   

14.
The nitrite toxicity was estimated in juveniles of L. vannamei. The 24, 48, 72 and 96 h LC50 of nitrite‐N on juveniles were 8.1, 7.9, 6.8 and 5.7 mg L?1 at 0.6 g L?1; 14.4, 9.6 8.3 and 7.0 mg L?1 at 1.0 g L?1; 19.4, 15.4, 13.4 and 12.4 mg L?1 at 2.0 g L?1 of salinity respectively. The tolerance of juveniles to nitrite decreased at 96 h of exposure by 18.6% and 54.0%, when salinity declined from 1.0 to 0.6 g L?1 and from 2.0 to 0.6 g L?1 respectively. The safe concentrations at salinities of 0.6, 1.0 and 2.0 g L?1 were 0.28, 0.35 and 0.62 mg L?1 nitrite‐N respectively. The relationship between LC50 (mg L?1), salinity (S) (g L?1) and exposure time (T) (h) was LC50 = 8.4688 + 5.6764S – 0.0762T for salinities from 0.6 to 2.0 g L?1 and for exposure times from 24 to 96 h; the relationship between survival (%) and nitrite‐N concentration (C) for salinity of 0.6–2.0 g L?1, nitrite‐N concentrations of 0–40 mg L?1 and exposure times from 0 to 96 h was as follows: survival (%) = 0.8442 + 0.1909S – 0.0038T – 0.0277C + 0.0008ST + 0.0001CT–0.0029SC, and the tentative equation for predicting the 96‐h LC50 to salinities from 0.6 to 35 g L?1 in L. vannamei juveniles (3.9–4.4 g) was 96‐h LC50 = 0.2127 S2 + 1.558S + 5.9868. For nitrite toxicity, it is shown that a small change in salinity of waters from 2.0 to 0.6 g L?1 is more critical for L. vannamei than when wider differences in salinity occur in brackish and marine waters (15–35 g L?1).  相似文献   

15.
Two experiments were conducted to quantify the dietary thiamin (experiment I) and pyridoxine (experiment II) requirements of fingerling Cirrhinus mrigala for 16 weeks. In experiment I, dietary thiamin requirement was determined by feeding seven casein–gelatin‐based diets (400 g kg?1 CP; 18.69 kJ g?1 GE) with graded levels of thiamin (0, 0.5, 1, 2, 4, 8 and 16 mg kg?1 diet) to triplicate groups of fish (6.15 ± 0.37 cm; 1.89 ± 0.12 g). Fish fed diet with 2 mg kg?1 thiamin had highest specific growth rate (SGR), protein retention (PR), RNA/DNA ratio, haemoglobin (Hb), haematocrit (Hct), RBCs and best feed conversion ratio (FCR). However, highest liver thiamin concentration was recorded in fish fed 4 mg thiamin kg?1 diet. Broken‐line analysis of SGR, PR and liver thiamin concentrations exhibited the thiamin requirement in the range of 1.79–3.34 mg kg?1 diet (0.096–0.179 μg thiamin kJ?1 gross energy). In experiment II, six casein–gelatin‐based diets (400 g kg?1 CP; 18.69 kJ g?1 GE) containing graded levels of pyridoxine (0, 2, 4, 6, 8 and 10 mg kg?1 diet) were fed to triplicate groups of fish (6.35 ± 0.37 cm; 1.97 ± 0.12 g). Fish fed diet containing 6 mg kg?1 pyridoxine showed best SGR, FCR, PR, RNA/DNA ratio, Hb, Hct and RBCs, whereas maximum liver pyridoxine concentration was recorded in fish fed 8 mg kg?1 dietary pyridoxine. Broken‐line analysis of SGR, PR and liver pyridoxine concentrations reflected the pyridoxine requirement from 5.63 to 8.61 mg kg?1 diet. Data generated during this study would be useful in formulating thiamin‐ and pyridoxine‐balanced feeds for the intensive culture of this fish.  相似文献   

16.
A 9‐week feeding trial was conducted to determine the optimal dietary vitamin C requirement and its effects on serum enzymes activities and bacterial resistance in the juvenile yellow drum Nibea albiflora (initial weight 33.2 ± 0.10 g). Six practical diets were formulated containing vitamin C 2.1, 45.3, 89.6, 132.4, 178.6 and 547.1 mg kg?1 diet supplied as l ‐ascorbyl‐2‐monophosphate. The fish fed 547.1 mg kg?1 diet showed a significantly higher survival than that fed 2.1 mg kg?1 diet. The weight gains and specific growth rate of the fish fed 2.1 mg kg?1 diet were significantly lower than those of the fish fed 89.6–547.1 mg kg?1 diets. The liver vitamin C concentration firstly increased with increasing dietary vitamin C supply from 2.1 to 178.6 mg kg?1 diet and then stabilized. The serum superoxide dismutase activities of the fish fed 547.1 mg kg?1 diet were significantly lower than those of the fish fed 2.1–89.6 mg kg?1 diet. The fish fed 2.1 mg kg?1 diet had a significantly higher alkaline phosphatase activity than those in the other groups except the 45.3 mg kg?1 group. Fish that received diets containing vitamin C at 547.1 mg kg?1 had significantly higher nitro blue tetrazolium and lysozyme activity, and fish that received diets containing vitamin C at 45.3–547.1 mg kg?1 exhibited resistance against Vibrio alginolyticus infection. The dietary vitamin C requirement of the juvenile yellow drum was established based on broken‐line model of weight gain to be 142.2 mg l ‐ascorbyl‐2‐monophosphate kg?1 diet.  相似文献   

17.
Marbled rabbitfish, Siganus rivulatus, is an economically valuable herbivorous fish and a potential candidate for warmwater aquaculture. This study was carried out to: (1) assess the effect of various oxygen concentrations on survival and behaviour of S. rivulatus fingerlings and (2) investigate the response of S. rivulatus to hypoxia and determine its critical oxygen tension (Pcrit). In the first experiment, groups of rabbitfish (15 fish per group) were maintained for 1 h in waters of various oxygen concentrations. They were then transferred to well‐aerated tanks and observed for 72 h. Survival was recorded, fish behaviour at low oxygen concentrations observed, and LC50 after 1‐h hypoxia and 72‐h recovery evaluated. In the second experiment, a series of stop‐flow respirometry experiments were performed during which dissolved oxygen was allowed to drop to 0.5 mg L?1 and respiration rate recorded at various oxygen concentrations. In the first experiment, all fish survived for 1 h at oxygen concentration of 1.44 mg L?1 and greater, but started dying at oxygen concentrations below 0.65 mg L?1 (16% survival). The LC50 of S. rivulatus fingerlings was 0.6 mg L?1. Results of the second experiment showed that S. rivulatus is an oxyregulator until Pcrit (1.7 mg L?1 O2) is reached, becoming an oxyconformer below this concentration. Findings allow for a better understanding of environmental oxygen tolerances and minimum acceptable oxygen concentration in rabbitfish aquaculture.  相似文献   

18.
Effect of different carbon sources on nursery performance of Pacific white shrimp (Litopenaeus vannamei) cultivated in biofloc system was investigated. Shrimp postlarvae (98.47 ± 8.6 mg) were fed for 32 days in tanks with water volume of 130 L and density of 1 individual L?1. One control treatment and four biofloc treatments (BFT1, BFT2, BFT3 and BFT4) with adding different carbon sources including molasses, starch, wheat flour and mixture of them, respectively, were considered at equal weight ratios. According to the results, salinity, dissolved oxygen and pH were not significantly different among the biofloc treatments (P > 0.05). Maximum pH (8.27) and maximum dissolved oxygen (6.35 mg L?1) were recorded in the control. Maximum (0.43 mg L?1) and minimum (0.09 mg L?1) ammonia were recorded in the control and BFT2, respectively (P < 0.05). Using simple carbohydrates (molasses and starch) lowered the ammonia concentration significantly. The highest increase in body weight (1640.43 ± 231.28 mg), growth rate, specific growth rate (8.97 ± 0.42% per day) and biomass (190.29 ± 26.83 mg) were found in BFT1 and the highest survival (90 ± 0.77%) was found in BFT4. The highest feed conversion (1.52 ± 0.23) and the lowest feed efficiency (66.81 ± 7.95) were observed in the control (P < 0.05). The proximate composition analysis revealed an increase in lipid and ash in biofloc treatments. Results indicated that using biofloc technology with zero‐water exchange system and adding carbon sources could help to recycle waste and improve the water quality. Moreover, the type of carbonaceous organic matter as a substrate for heterotrophic bacteria would be effective in degradation and metabolization of ammonia and nitrite.  相似文献   

19.
An 11‐week feeding trial was conducted to evaluate the effect of dietary methionine on the growth, antioxidant status, innate immune response and disease resistance to Aeromonas hydrophila of juvenile yellow catfish. Six isonitrogenous and isolipidic practical diets were formulated to contain different graded methionine levels ranging from 6.1 to 16.4 g kg?1 of dry weight. The results indicated that growth performance and feed utilization were significantly influenced by the dietary methionine levels; fish fed the diet containing 6.1 g kg?1 methionine level had lower specific growth rate, percentage weight gain (PWG), feed efficiency and protein efficiency ratio than those fed the other diets (P < 0.05). Fish fed the diet containing 16.4 g kg?1 methionine level had lowest protein contents in whole body and muscle among all treatments. Triacylglycerols, cholesterol, aspartate aminotransferase, alanine aminotransferase and haemoglobin (Hb) in plasma or whole blood were significantly affected by dietary methionine levels. Fish fed the diet containing 6.1 g kg?1 methionine level had higher superoxide dismutase, glutathione peroxidase activities and malondialdehyde values than those fed other diets. Fish fed diets containing 9.7 and 11.8 g kg?1 methionine levels had higher lysozyme activity, total immune globulin, phagocytic activity and respiratory burst than those fed other diets. The lowest survival after A. hydrophila challenge was observed in fish fed a diet containing 6.1 g kg?1 methionine. Quadratic regression analysis of PWG against dietary methionine levels indicated that the optimal dietary methionine requirement for the maximum growth of juvenile yellow catfish was estimated to be 11.5 g kg?1 of the diet in the presence of 4.0 g kg?1 cystine (corresponding to 23.5 g kg?1 of dietary protein on a dry weight basis).  相似文献   

20.
This experiment was conducted to study the effects of different forms and levels of manganese (Mn) on the growth performance, antioxidant activities, tissue Mn content and cytosolic manganese superoxide dismutase (cMnSOD) gene expression of Litopenaeus vannamei. Treatments consisted of 0, 10, 20, 30, 40 and 60 mg Mn kg?1 from manganese sulphate (Mn‐S) and manganese methionine (Mn‐Met), providing the actual dietary value of 5.17, 15.62, 25.55, 34.22, 44.48 and 67.90 mg Mn kg?1 Mn‐S, and 5.17, 15.71, 25.36, 35.86, 45.16 and 65.06 mg Mn kg?1 Mn‐Met, respectively. Each diet was fed to triplicate groups of L. vannamei (initial body weight: 1.925 ± 0.002 g) in a recirculated fresh water rearing system for 8 weeks. Weight gain rate (WGR) increased in prawns provided with from 25.55 to 44.48 mg Mn kg?1 Mn‐S and 15.71 to 45.16 mg Mn kg?1 Mn‐Met and then declined above these levels. The lowest protein efficiency ratio (PER) and the highest feed conversion rate (FCR) were observed in prawns fed the control diet (P < 0.05) and showed no significant differences among other treatments (P > 0.05). Survival rate (SR) was not affected by the dietary treatments (P > 0.05). Total SOD and Mn‐SOD activities were higher in the hepatopancreas of prawns fed with Mn‐supplemented diets from 15.71 to 44.48 mg Mn kg?1 (P < 0.05). On the contrary, malondialdehyde (MDA) content was lower in the hepatopancreas of prawns fed the basal diet (P < 0.05). Mn concentrations in the hepatopancreas and muscles increased with increasing levels of dietary Mn supplementation. Moreover, Mn accumulation was lower in the muscle than in the hepatopancreas of the prawns. The mRNA expression of cMnSOD gene in the hepatopancreas of prawns was upregulated with increasing dietary Mn levels of Mn‐S from 25.55 to 44.48 mg Mn kg?1, Mn‐Met from 15.71 to 45.16 mg Mn kg?1 and then plateaued above these levels. Broken‐line regression analysis of WGR indicated that the optimal dietary Mn requirements for juvenile L. vannamei were 32.26 mg Mn kg?1 Mn‐S and 23.90 mg Mn kg?1 Mn‐Met, respectively.  相似文献   

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