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1.
Four different fertilization frequencies, namely twice per week, once per week, twice a month and once a month, were used in ponds to assess their effects on nutrient release, pond productivity and fish biomass. All ponds received the same total fertilizer inputs during the experimental period of 60 days (cow dung 208.3 kg ha?1 week?1, TSP 9.8 kg ha?1 week?1, urea 6.0 kg ha?1 week?1). Studies have revealed that the highest values of fish biomass, specific growth rate (SGR), net primary productivity (NPP), plankton population and nutrients were observed in the ponds that were fertilized twice a month. A strong and significant correlation of fertilization frequency was observed with dissolved oxygen, biochemical oxygen demand (BOD), alkalinity, nutrient release, NPP, plankton density (no. L?1), fish biomass and SGR. The linear relationship between NPP and fish biomass/SGR for all the ponds was strong (r2= 0.88). Sediment chemistry revealed that O‐PO4, NO3‐N, organic carbon and electrical conductivity (EC) increased significantly (P<0.05) with a decrease in the frequency of fertilization, while alkalinity and calcium were high in ponds that were fertilized twice a month.  相似文献   

2.
Techniques for head starting or nursing postlarvae (PL) has received considerable attention with regards to nursery protocols, yet there is little data pertaining to the effects of nursery period on the final growout of shrimp to marketable size. This study was performed to investigate the influence of nursery duration on survival and growth of Litopenaeus vannamei during subsequent pond culture. For this research, a single population of high health PL were received from a commercial hatchery and held in a tank for acclimation, quantification, and distribution to nursery tanks or ponds. Treatments included direct stocking of 10-d-old postlarvae (PL10) into production ponds as well as the nursing of PL in a covered greenhouse nursery system for an additional 10 or 20 d. After nursing, the PL were harvested, quantified, and transferred to growout ponds. All ponds were stocked at a density of 35 PL/m2 and maintained under standardized conditions. Shrimp were fed with a 35% protein shrimp feed, twice daily during the 112-d growth trial. Ponds were aerated as needed using a maximum of 19 hp/ha to maintain adequate dissolved oxygen (DO > 3.0). No statistical differences (P >0.05) were found in survival, yield, or growth between treatments. At harvest, survivals during growout were generally higher in ponds with nursed shrimp (77% for PL20 and 79% for PL30) than in ponds receiving PL10 shrimp (67%). Yields were similar between treatments, ranging from 3,525 for direct stocked shrimp to 3,747 kg/ha for those that were nursed for 10 d. Although growth rates of PL under pond conditions will be faster than that of a nursery system, results suggest that a nursery period of at least 10 d helps improve survival during pond production and promotes better size uniformity. Shrimp nursed for 20 d showed little improvement in survival over shrimp nursed for 10 d but did result in a more uniform size of shrimp at harvest.  相似文献   

3.
The dissolved oxygen (DO) concentration that induces the onset of anaerobic metabolism in hard clams was found to be 1.11 mg O2 L?1, at which time, the concentration of succinate in the body fluid was 4.4 μmol mL?1. When the DO concentration was <1.11 mg O2 L?1, the burial depth was significantly reduced, and succinate significantly accumulated in the body fluid. After 24 h of anoxic exposure, succinate had accumulated in the gills and equal amounts of succinate and alanine had accumulated in the foot. This indicates that carbohydrates in the gills and amino acids in the foot contribute to anaerobic energy production. The accumulation rates of succinate and propionate in the body fluid were the highest compared with those in other tissues, while no accumulation of alanine in the body fluid was found. The recovery rates of succinate in the body fluid and alanine in the foot were the highest compared with those in other tissues. The results of this study suggest that the DO concentration in the bottom water of clam ponds should be maintained at ≥1.11 mg O2 L?1, and the anoxia‐tolerant ability of hard clams can be assessed by the contents of carbohydrates.  相似文献   

4.
Transport of post‐larvae shrimp used in aquaculture is an important element of successful cultivation because of the potential for stress during stocking procedures. To find optimum transport conditions, several bioassays were performed in the laboratory to evaluate survival of whiteleg shrimp Litopenaeus vannamei 5–30‐day‐old postlarvae under conditions similar to those encountered during transport from the hatchery to nursery and shrimp ponds. Postlarvae were exposed for 4 h to different temperatures and pH levels ammonia concentrations. Survival was significantly reduced after a 4 h exposure to pH 9 and was inversely related to temperature with or without 7 mg L?1 of ammonia. The 15‐ and 20‐day‐old postlarvae had higher survival rates than other ages. The lowest survival occurred in alkali conditions (pH 9), with 7 mg L?1ammonia at 30 and 32°C. To assure optimal survival of postlarvae during transfer from the hatchery to the nursery and shrimp ponds, we recommend temperatures below 28°C, pH no higher than 8, no ammonia and post‐larval age at least 15 days.  相似文献   

5.
Silver catfish, Rhamdia quelen (Quoy & Gaimard, 1824), is an endemic species from Latin America that is raised in cultivation ponds, and consequently may be exposed to low oxygen levels. Therefore, the objective of this study was to verify the lethal concentration (CL50?96 h) of dissolved oxygen levels for silver catfish juveniles. In addition, the effects of different dissolved oxygen levels (1.96±0.08, 3.10±0.10, 4.14±0.09, 5.20±0.07 and 6.16±0.03 mg L?1) on growth and metabolic parameters (glycogen, glucose, protein, lactate levels and catalase activity) were also investigated. CL50?96 h was 0.52 mg L?1 (CI 0.42–0.61 mg L?1) or 6.7% oxygen saturation. After exposure of silver catfish to hypoxia for 30 days, there were no changes in biochemical parameters indicating the use of an anaerobic pathway by the fish. However, the dissolved oxygen levels influenced silver catfish juvenile behaviour, survival and growth, and under the experimental conditions 5.2 mg L?1 (or 65.6% oxygen saturation) is the minimum oxygen level recommended for the growth of this species.  相似文献   

6.
The main aim of this study was to examine the effects of a polyculture system on the control of the external parasites of western white shrimp, Litopenaeus vannamei. To this end, the western white shrimp postlarvae (PLs) were stocked in nine earthen ponds (600 m2) at a density of 20 PLs m?2 and reared for 4 months. After 40 days of shrimp stocking, Mullets, Mugil cephalus, were stocked at various densities including: control (0 fish/100 m2 pond), treatment 1 (T1: 2 fish/100 m2 pond) and treatment 2 (T2: 4 fish/100 m2 pond). Over the course of the experiment, the external parasites of shrimps were investigated by the preparation of a wet mount from the gill tissue. Based on the obtained results, totally two genera of protozoan parasites, i.e. Zoothamnium sp. and Epistylis sp., were identified over the course of the experiment. In all experimental groups, the incidence and abundance of Zoothamnium sp. was significantly higher than Epistylis sp. (P < 0.05). Also, mean incidence per cent and mean abundance of Zoothamnium sp. and Epistylis sp. were significantly lower in the polyculture treatments (T1 and T2) compared to the monoculture group (control) (P < 0.05). Throughout this experiment, the total organic matter (TOM %) content of the bottom sediments and biological oxygen demand (BOD5 mg L?1) of water samples in the polyculture ponds were significantly lower than the monoculture group (P < 0.05). In contrast, the polyculture ponds had a higher concentration of water dissolved oxygen (O2 mg L?1) compared to the monoculture (P < 0.05). In conclusion, our results show that mullet as a secondary farmed species can reduce indirectly the parasitic pollution of western white shrimp probably through reducing the total organic matters in water and sediments and improving the water quality parameters.  相似文献   

7.
Galaxias maculatus is an osmeriform native fish of the Southern Hemisphere, in which the crystalline larvae is considered as a luxury delicacy, for this reason, it has been commercially exploited in Chile, Argentina and New Zealand. However, the fisheries have been rapidly decreasing due to the overexploitation and the predation of introduced species. Because of these events, there is a need to determine a carrying capacity for an intensive fish culture. In order to optimize stocking densities for fish culture, this paper proposes objectives to determine oxygen consumption (OC) rates, dissolved oxygen concentrations that produce signs of hypoxia and the average time elapsed between food intake and peak OC in G. maculatus. In the oxygen experiments under routine metabolism conditions, we found that G. maculatus adults and whitebait showed signs of asphyxia at dissolved oxygen concentrations between 1.3 and 2.2 mg L?1 and that adults tolerated dissolved oxygen levels as low as 1.3 mg L?1. The results showed that G. maculatus individuals with an average weight of 0.04 g consumed 0.048 mg O2 h?1, whereas individuals with an average weight of 1.4 g consumed 0.345 mg O2 h?1. Galaxias maculatus increased the OC rate by 31%, from 0.39 to 0.51 mg O2 h?1 g?1, occurring 14 min after food intake. The carrying capacities for industrial cultures of G. maculatus, were estimated using an allometric equation (OC=0.2363 ×W 0.612 ), a water flow rate of 1 m3 h?1 and an input oxygen concentration of 10 mg L?1 at 12 °C. The density culture of whitebait (4 g) can be allowed to reach 8–11 kg m?3; therefore, these stocking densities reduce the risk of hypoxia and mortality, ensuring the appropriate growth and feed conversion rates.  相似文献   

8.
Pond fertilization studies usually are restricted by availability of ponds forcing researchers to limit treatments to maintain adequate replicates for statistical analysis. Data from a wide range of fertilizer rates applied over a single season in un‐replicated ponds were treated using regression analysis to establish the optimum phosphorus application rate for bluegill (Lepomis macrochirus) ponds. The response to phosphorus fertilization conformed to a saturation model (R2=0.92). Bluegill production increased with greater fertilization rate up to 3 kg P2O5 ha?1, but production was similar (501–558 kg ha?1) at rates of 3–7 kg P2O5 ha?1. The observation that 3 kg P2O5 ha?1 per application was adequate phosphorus fertilization for bluegill ponds with sufficient nitrogen agrees closely with the usual recommendation of 4 kg P2O5 ha?1 per application. Results of this research also revealed that nutrient assessment in bluegill ponds can be based on total nitrogen and total phosphorus analyses, and Secchi disk visibility may be used as an index of plankton abundance.  相似文献   

9.
The valine requirement of juvenile tiger shrimp, Penaeus monodon Fabricius, was determined. Shrimp postlarvae, PL20, with a mean weight of 14 mg, were randomly distributed in 36 oval 40-L capacity fibreglass tanks at 10 shrimp per tank in a flow-through seawater system and reared for 8 weeks. Postlarvae were fed amino acid test diets containing 400 g kg?1 protein with casein and gelatine as intact sources of protein. Crystalline L-amino acids were supplemented to simulate the amino acid profile of the shrimp muscle except valine. Valine was added in graded levels to obtain 7, 10, 13, 16, 19 and 22 g kg?1 of the diet or 18, 25, 33, 40, 48 and 55 g kg?1 of dietary protein. At termination of the feeding experiment, growth and survival were determined and nutritional deficiency signs noted. The relationship between weight gain and dietary valine level was analysed by the broken-line regression method to derive the valine requirement. The dietary valine requirement of Penaeus monodon postlarvae was found to be 13.5 g kg?1 of the diet or 34 g kg?1 of dietary protein. This value was lower than the level found in the shrimp tissue.  相似文献   

10.
Effects of temperature on food consumption, growth and oxygen consumption were estimated for the freshwater prawn Macrobrachium rosenbergii postlarvae at 23 °C, 28 °C and 33 °C in the laboratory. The results showed that the animal's initial body weight had a close linear relationship with food consumption and growth. Food consumption increased directly with temperature. Consumption rates (C; mg day?1 ind?1 ) of the 28 °C and 33 °C groups were much higher than that of the 23 °C group (P < 0.001), and the 33 °C group's consumption rate was higher than that of the 28 °C group (P < 0.05). The relationship of food consumption with temperature and initial body weight (W; mg) could be described as: C = 0.0679W + 0.185t? 3.17. Growth increased significantly with increased temperature. The relationship among specific growth rate, temperature and initial body weight was as follows: SGR = ?0.110W + 0.213t + 0.176. However, temperature showed no effect on growth efficiency. Oxygen consumption increased significantly with temperature (P < 0.01). The weight‐specific oxygen consumption rates (mg O2 g?1 h?1) at 23 °C, 28 °C and 33 °C were 0.83, 1.16 and 1.49 mg O2 g?1 h?1 for 61.92 mg M. rosenbergii.  相似文献   

11.
The effect of dietary protein and energy content on the activity of digestive enzymes (total proteinases, trypsin, chymotrypsin α‐amylase and lipase), and growth and survival of Litopenaeus setiferus postlarvae was investigated under controlled conditions. There was a clear relationship between the diet fed to the postlarvae, growth and survival. Highest weight gain (2110 ± 96.7%) was obtained with a 400 g kg?1 protein and low energy diet (13.9 kJ g?1) (P < 0.05). The optimal protein to energy ratio (P/E) estimated was 28.8 mg of protein kJ?1. Good survival was obtained with low energy diets containing between 200 and 400 g kg?1 protein and with high energy diets containing 300–500 g kg?1 protein. Higher values for total proteinases, trypsin and α‐amylase were obtained with the low energy, 400 g kg?1 protein diet. Chymotryptic activity was considerably lower than that of other proteinases and lipase activity was too low to be reliably measured with the turbidimetric method employed. Total proteinase activity was significantly lower than in experimentally grown postlarvae. The α‐amylase activity was at least two orders of magnitude higher in wild postlarvae than in animals fed with the best experimental diet. Protein requirement was related to total energy content of the diet: best growth and digestive enzyme activity coincide with the low energy, 400 g kg?1 protein diet. These results suggest that dietary carbohydrates cannot spare protein because growth rates obtained with diets containing 200–300 g kg?1 protein (337 and 226 g kg?1 dextrin content, respectively) were significantly lowered.  相似文献   

12.
Three channel catfish (Ictalurus punctatus) ponds were treated at two-week intervals with sodium nitrate at 2 mg NO3 ?-N/L per application and three ponds served as controls. Average concentration of nitrite-nitrogen measured midway between application dates never exceeded 1.2 mg/L in treated ponds, but on most sampling dates, nitrate concentrations were greater than those in control ponds (P < 0.1). Disappearance of nitrate-nitrogen from waters of treated ponds resulted primarily from nitrate reduction to free nitrogen gas. Soluble reactive and total phosphorus concentrations tended to be higher (P < 0.1) in treated ponds than in control ponds. There were no differences (P > 0.1) in pH and concentrations of total alkalinity, total ammonia nitrogen, and dissolved oxygen between treated and control ponds. The higher chlorophyll a concentration (P < 0.1) suggested that greater availability of nutrients in treated ponds resulted in more phytoplankton growth than in control ponds. Because of greater phytoplankton biomass, turbidity was higher and Secchi disk visibility less in treated ponds as compared to control ponds (P < 0.1). There were no obvious differences in phytoplankton community composition with respect to treatment—blue-green algae dominated the phytoplankton community in both treated and control ponds. Redox potential in sediment during crops was higher in ponds treated with sodium nitrate than in control ponds, indicating less anaerobic conditions. However, catfish survival, production, and feed conversion ratio did not differ (P > 0.1) between treatment and control.  相似文献   

13.
Microbial biomass estimates (based on ATP concentrations) were highly correlated with water and sediment respiration rates in freshwater prawn ponds. Water column biomass-specific respiration rates (x ± 1 SD, 572.4 ± 410.6 μl O2 μg ATP?1 day?1) were higher than sediment rates (11.5 ± 8.1 μl O2 μg ATP?1 day?1). Phytoplankton cells dominated the seston, with nutrient-saturated, light-limited growth in the range 75–80%μmax. Doubling times of phytoplankton ranged from 0.4–19 days. Measurement of benthic ATP biomass is recommended as a diagnostic water quality parameter for commercial freshwater prawn culture.  相似文献   

14.
The effect of graded levels of dietary taurine on growth, enzyme activities and pretrypsinogen (Ptry) mRNA expression in the tongue sole postlarvae was evaluated in this study. Four microdiets supplemented with 0 (T0), 5 (T0.5), 10 (T1.0) or 20 (T2.0) g kg?1 taurine were prepared. These diets were fed to the postlarvae with an average initial body dry weight of 3.32 ± 0.06 mg for 28 days. Survival and growth performance of the tongue sole postlarvae were significantly (P < 0.05) influenced by dietary taurine. Survival rate of fish fed with 20 g kg?1 dietary taurine was significantly lower than other treatments. The growth of fish initially increased with increasing dietary taurine level and then decreased. Postlarvae fed with 10 g kg?1 dietary taurine showed the best growth performance. Trypsin activities showed a significant increase with increasing dietary taurine level and then reached a plateau, while amylase activities and alkaline phosphatase activities increased in the start with increasing dietary taurine and then decreased. Ptry mRNA expression was stimulated by dietary taurine. Excessive dietary taurine (20 g kg?1) had adverse effects on survival, growth, digestive enzyme activities of the experimental fish. The suggested dietary taurine supplementation in microbound diets was 10 g kg?1 for the tongue sole postlarvae.  相似文献   

15.
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   

16.
Growth, net production, and survival rates of milkfish cultured with Gracilariopsis bailinae at two stocking density combinations (T1– 30 fingerlings 100‐m?2 pond+1‐kg G. bailinae 4‐m?2 net cage, T2– 30 fingerlings 100‐m?2 pond+2‐kg G. bailinae 4‐m?2 net cage) in brackish water earthen ponds over four culture periods were determined. The control (T3) was stocked at 30 fingerlings 100‐m?2 pond. Specific growth and production rates of G. bailinae were also calculated. There were no significant differences in mean growth, survival, and net production rates of milkfish between the three treatments. Irrespective of stocking singly or in combination with G. bailinae, significantly higher mean growth and mean production rates for milkfish were obtained during the third culture period of year 1 than those obtained from the other culture periods. Survival rates were not significantly different among the four culture periods. There were no significant differences in mean specific growth and mean net production rates between the two stocking densities of G. bailinae. Significantly higher mean specific growth and mean net production rates of red seaweed were also obtained during the third culture period of year 1 than those obtained from other culture periods. The production of milkfish and red seaweed was higher during the dry season. Growth rates of milkfish was positively correlated with temperature and salinity, while net production rates were positively correlated with temperature and total rainfall, but was inversely correlated with dissolved oxygen. G. bailinae growth and net production rates were positively correlated with water temperature and salinity. Results show that milkfish can be polycultured with G. bailinae grown in net cages in brackish water ponds at stocking density combination of 30 fingerlings 100‐m?2 pond+1‐kg G. bailinae 4‐m?2 net cage.  相似文献   

17.
We evaluated the performance of whiteleg shrimp Penaeus vannamei (Boone, 1931) in response to different stocking densities and acclimation periods. Shrimp postlarvae were acclimated from seawater (30 g L?1) to low‐salinity well water (<1.0 g L?1) at a constant hourly reduction rate of 40, 60, 80 and 100 h. After acclimation to low‐salinity well water, postlarvae from each acclimation time treatment were stocked in three replicate tanks at densities of 50, 100, 150 or 200 shrimps m?2 for 12 weeks of growth. Salinity averaged <1.0 g L?1 for each growth study. The different treatments resulted in significant differences in both the final body weight and the survival rate (SR). Shrimp acclimated for 100 h showed substantially improved survival (83%) relative to shrimp acclimated for shorter periods. Shrimp yields for all cultured periods ranged from 0.32 kg m?2 in tanks stocked at 50 m?2 to 1.14 kg m?2 in tanks stocked at 200 m?2. We conclude that whiteleg shrimp can be successfully grown in low‐salinity well water, and that the growth, production output and SRs are significantly higher when shrimp are acclimated for longer periods.  相似文献   

18.
Experiments on the intensive cultivation of Pacific white shrimp, Penueus vunnumei, in ponds in South Carolina were begun in 1985 at the Waddell Mariculture Center. A preliminary study involved two 0.1 ha ponds stocked at an average of 43 postlarvae/m2, with management practices based on those used in Taiwan for intensive pond culture of Penueus monodon. Harvest yields averaged 6,757 kg/ha for one crop, demonstrating the technical feasibility of such intensive culture of P. vannumei. In 1986, 2.5 ha of ponds at the Waddell Center (six ponds totaling 2.0 ha at 40 postlarvae/m2 and two totaling 0.5 ha at 60/m2) yielded a total of 13,606 kg (5,442 ke/hn). These results were obtained even though aeration and water exchange rates were substanthlly reduced and South Carolina experienced its worst heat wave and drought. This served as a pilot-sde, proof-ofconcept test. Tank studies in 1985 and 1986 showed little effect of stocking density on shrimp growth rate at densities of 20–100 animals/m2. This was confirmed in ponds in 1987 when no differences in growth rates were observed at densities of 20–100 postlarvae/m2. Harvest biomass increased directly with stocking density in all trials, reaching a maximum of 12,680 kg/ha/crop at 100 shrimp/m2 in 1987. Initial attempts to intensify production in the nascent South Carolina shrimp farming industry occurred in 1986, when approximately 32 ha of private ponds were stocked at densities of 10–32 postlarvae/m2. Farm harvests increased with stocking density, with maximum yield of 3,656 kg/ ha/crop. This trend toward intensification in the private sector is continuing, and in 1987 maximum harvests from private ponds were 5,050 kg/ha from a 0.3 ha pond and 4,625 kg/ha from a 1.5 ha pond. Prospects for further implementation of intensive culture in the private sector appear excellent, with yields of ≥ 10,000 kg/ha/crop expected from private farms within the next few years.  相似文献   

19.
Four experiments were conducted in order to determine the optimum dosageof Azotobacter chroococcum vis-a-vis organic fertilizer(cow-dung) required for optimum pond productivity. Hydrobiological parameters ofpond water, Azotobacter survival (viable counts), netprimary productivity (NPP) and fish growth were monitored. Studies have revealedthat irrespective of the treatments, dissolved oxygen (DO) levels weresignificantly (P < 0.05) lowered on inoculating the ponds withAzotobacter. Alkalinity, O-PO4,NO3-N, turbidity, NPP, plankton population and fish growth weresignificantly (P < 0.05) enhanced in ponds inoculated withAzotobacter @ 100.0 ml pond–1w–2 in combination with cow-dung @ 10000 kgha–1 y–1. At higher or lower dosages offertilizers, the values in most of these parameters remained low. On the otherhand, total kjeldahl nitrogen and NH4-N increased continuously. Ingeneral, viable bacterial counts decreased with increase in pH, however, therate of nitrogen fixation was not affected. Multivariate analysis of the data revealed a significantpositive correlation of nutrients (Total kjeldahl Nitrogen, NO3-N andO-PO4), with NPP and plankton populations. NH4-N, however,showed a significant negative correlation with DO, NPP and plankton populations.Highest fish biomass and SGR also coincided with the highest NPP and planktonpopulations, revealing that a dose of 100.0 ml pond–1w–2 (for 25 m3 ponds) ofAzotobacter along with 10000 kg ha–1y–1 of cow-dung appears to be optimum for obtainingoptimum pond productivity and fish yield. Nutrients in the sediment(NO3-N and O-PO4) also followed similar trend. On theother hand, organic carbon increased continuously with each increase in thedosage of fertilizers. A decline in fish biomass and pond productivity at higherfertilizer dosages has been attributed to low DO, high NH4-N and BOD.  相似文献   

20.

The effects of fish size and nitrite level on metabolic rate and growth were investigated in the obligate air-breathing snakehead Channa striata, which is an important aquaculture species in Vietnam. Channa striata displayed respiratory size dependence, whereby the standard metabolic rate (SMR) and routine metabolic rate (RMR) decreased progressively in an exponential manner as fish size increased from 50 to 200 g. A mildly elevated nitrite level of 5% of the LC50 96 h (12 mg NO2?/L or safe concentration) induced significant increases in Channa striata SMR and RMR, which were almost double that of the control at the same size. At mild elevation, nitrite caused no significant effect on fish growth and survival during 3 months of rearing. However, both growth and survival rates of fish reared at severely elevated nitrite levels were significantly lower than those of the control; in particular, survival rates were under 50%. While changes in size reduced SMR and RMR, the percentage of air oxygen partitioning remained unchanged. Channa striata upregulation of SMR and RMR and air-breathing regulation were not significantly proven in this study. In summary, maintaining water environments at levels lower than 12 mg NO2?/L with ample oxygenation will not affect the growth and survival rate of snakeheads.

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