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1.
The objective of this study was to compare fish performance and welfare at different stocking densities in a recirculating system (RS) and a flow through system (FTS) under field conditions. During the 77 days experiment, the fish survival rate was high (99.3%) and stocking density increased from 57 to 98–108 kg m?3. No significant differences in growth were observed between RS and FTS until day 56. Later, growth decreased in the FTS, while it remained similar to the farm reference at 50 kg m?3 in the RS. Final weight was 17% higher in RS than in FTS. The maximum carrying capacity of the RS was near 100 kg m?3, limited by NO2 increase up to safe level at the end of the experiment, the maximum carrying capacity of the FTS was near 85 kg m?3, probably limited by CO2 concentration (17.8 ± 5.7 mg l?1). In the RS, the relative length index of pectoral and dorsal fins was lower than in the FTS, which may be attributed to the tank hydrodynamics. In both systems, an improvement of the pectoral and dorsal profile was observed at the end of the experiment, attributed to a swimming activity reduction that may have decreased contact between individuals. In the RS, high caudal fin deterioration (50% versus 20% in FTS) was observed irrespective of stocking density, that could be linked to the highest water velocity modifying the fish swimming activity. The results confirm that when water quality is maintained in safe level ranges, high densities can be used in trout RS without fish performance and pectoral or dorsal fin deterioration, but with a major caudal impairment.  相似文献   

2.
An on-station trial was conducted to evaluate the effect of stocking density of freshwater prawn and addition of different levels of tilapia on production in carbon/nitrogen (C/N) controlled periphyton based system. The experiment had a 2 × 3 factorial design, in which two levels of prawn stocking density (2 and 3 juveniles m? 2) were investigated in 40 m2 earthen ponds with three levels of tilapia density (0, 0.5 and 1 juveniles m? 2). A locally formulated and prepared feed containing 30% crude protein with C/N ratio close to 10 was applied considering the body weight of prawn only. Additionally, tapioca starch was applied to the water column in all ponds to increase C/N ratio from 10 (as in feed) to 20. Increasing stocking density of tilapia decreased the chlorophyll a concentration in water and total nitrogen in sediment, and increased the bottom dissolved oxygen. The concentrations of inorganic nitrogenous species (NH3–N, NO2–N and NO3–N) were low due to maintaining a high C/N ratio (20) in all treatment ponds. Increasing prawn density decreased periphyton biomass (dry matter, ash free dry matter, chlorophyll a) by 3–6% whereas tilapia produced a much stronger effect. Increasing stocking density of freshwater prawn increased the total heterotrophic bacterial (THB) load of water and sediment whereas tilapia addition decreased the THB load of periphyton. Both increasing densities of prawn and tilapia increased the value of FCR. Increasing prawn density increased gross and net prawn production (independent of tilapia density). Adding 0.5 tilapia m? 2 on average reduced prawn production by 12–13%, and tilapia addition at 1 individual m? 2 produced a further 5% reduction (independent of prawn density). The net yield of tilapia was similar between 0.5 and 1 tilapia m? 2 treatments and increased by 8.5% with increasing stocking density of prawn. The combined net yield increased significantly with increasing stocking density of prawn and tilapia addition. The significantly highest benefit cost ratio (BCR) was observed in 0.5 tilapia m? 2 treatment but freshwater prawn density had no effect on it. Therefore, both stocking densities (2 and 3 juveniles m? 2) of prawn with the addition of 0.5 tilapia m? 2 resulted in higher fish production, good environmental condition and economic return and hence, polyculture of prawn and tilapia in C/N controlled periphyton based system is a promising options for ecological and sustainable aquaculture.  相似文献   

3.
A model is presented for the prediction of mercury (Hg) concentrations in the edible tissues of farmed southern bluefin tuna, Thunnus maccoyii (SBT) during commercial culture. The predictive model was developed using the initial Hg concentration of wild-caught SBT (mg kg? 1), Hg concentration of feed (mg kg? 1), SBT feeding rate (kg kg? 1 day? 1), SBT tissue growth rate (kg day? 1) and least squares minimisation estimation of Hg uptake efficiency, η. Model development and validation was based on experimental data collected from commercially cultured SBT which are farmed in in-sea pontoons (sea-pontoons). Model predictions indicate that over a typical farming season SBT from each of three commercially operated sea-pontoons experienced a 0.1 mg kg? 1, 0.14 mg kg? 1 and > 0.2 mg kg? 1 reduction in the Hg concentration of muscular tissues respectively. This is the first study to attempt to estimate Hg uptake efficiency in a tuna species. Estimation of Hg uptake efficiency and development of a working model for prediction of Hg concentration in SBT under varying culture diets, represent the first steps towards taking the guesswork out of managing Hg residues in cultured tuna.  相似文献   

4.
《Aquacultural Engineering》2011,44(3):114-119
A dynamic stock model was used for quantification of shrimp production and analysis of alternative management schemes of stocking density, pond size, starting time of aeration, and duration of cultivation for intensive commercial production of the shrimp Litopenaeus vannamei. Databases from Mexican farms were used to calibrate the model. Multiple linear regression models were employed to establish relationships between parameters of the stock model and the management variables. Water quality variables (dissolved oxygen, temperature, and salinity) were complementarily analyzed. The final weight of shrimp was directly related to duration of cultivation and dissolved oxygen, and inversely related to stocking density, pond size, and salinity. There were inverse relationships between the growth coefficient and temperature and dissolved oxygen and between mortality rate and temperature. Dissolved oxygen was significantly related to starting time of aeration. Simple linear regression and an equivalence test indicated that biomass at harvest (after 13 weeks in winter, and 20 weeks in summer) was adequately predicted by using the stock model and the multiple regression models. The highest production (winter, 6900 kg ha−1; summer, 12,600 kg ha−1) were predicted using 60 postlarvae m−2, small ponds (2 ha), and starting aeration at the first week of cultivation; while the lowest yields (winter, 2600 kg ha−1; summer, 6000 kg ha−1) were obtained using 40 postlarvae m−2, large ponds (8 ha), and delaying the start of aeration until the fifth week of cultivation. The lowest production was 38% (winter) and 48% (summer) of the highest yield. Using small ponds could be particularly important during winter cycles to increase production, while stocking density and starting time of aeration contributed less. In contrast, pond size played a minor role during summer cycles and stocking density was the most sensitive variable.  相似文献   

5.
Rainbow trout (100 g initial weight) were subjected to the combined effect of two culture densities (15 and 40 kg m−3, D15 and D40, respectively) and two dietary energy levels (22 and 27 MJ kg−1 E22 and E27, respectively) during a 75-days experimental period. At the end of the experiment, the growth rate as well as the metabolic and oxidative status of liver and muscle of fish were studied.The results showed that combination of culture density and dietaryenergy level negatively affected growth, cholesterol and LDL plasma levels and oxidative stress in muscle. Higher culture density negatively affected the values of total protein, triglycerides, and HDL in plasma, values of hepatic and muscular metabolic activities pyruvate kinase (PK), citrate synthase (CS), and hydroxiacil-CoA dehydrogenase (HOAD); glutamate pyruvate transaminase (GPT) and glutamate oxaloacetate transaminase (GOT) activities in plasma, liver, and muscle; glucose 6P dehydrogenase (G6PDH) activity in muscle; and oxidative stress in liver.High energy intake, adversely affected the hepatic activity of G6PDH, HOAD, GPT and oxidative stress in muscle.Consequently our results indicate that a combination of high culture density and a high level of dietary energy (27 MJ kg−1 in diet) exert a negative impact on the physiology and consequently on the welfare of the farmed fish.  相似文献   

6.
《Fisheries Research》2007,85(3):285-290
Avoidance reactions of young-of-the-year fish assemblages were investigated in the offshore zone of three reservoirs in the Czech Republic during late summer. Pikeperch (Stizostedion lucioperca) strongly dominated in the Lipno Reservoir in 2003, bream (Abramis brama) and bleak (Alburnus alburnus) were the most abundant species in the Slapy Reservoir in 2004 and roach (Rutilus rutilus) and bleak dominated in the Želivka Reservoir in 2004 and 2005. Densities of fry ranged between 1.09 ind./100 m3 in the Lipno Reservoir and 2.95 ind./100 m3 in the Slapy Reservoir. In each reservoir, three trawl nets of different widths (dimensions 1.5 m × 3 m, 3 m × 3 m, 6 m × 3 m) were used in the pelagic area at night. For each trawl the estimated fish density was determined as the catch per 100 m3 of water and was compared between all three trawls. The fish length–frequency distribution was also compared between all the trawls. Day catches were much lower compared with those taken at night. Adult fish showed very clear avoidance of fry trawls. At night, no important differences in estimated fry density, obtained by these trawls, were observed in any locality for any fish species, nor in the length distribution of important species between trawls. According to these results, the avoidance reactions of fry in the late summer (August, September), at night, are unimportant. At this time of year, nighttime pelagic trawling appears to be an effective method for quantitative fry sampling. We recommend the 3 m × 3 m trawl for quantitative night sampling of the fry community as a good compromise between assured efficiency and relatively easy handling.  相似文献   

7.
In intensive recirculating aquaculture systems (RAS) ortho-phosphate (ortho-P) is one of the main accumulating substances, but effects of chronically elevated concentrations on fish health and production performance are still unknown. Therefore 120 juvenile turbot (Psetta maxima) were exposed to ortho-P concentrations of 3 mg/L (control – C), 26 mg/L (low – LP), 52 mg/L (medium – MP) and 82 mg/L (high – HP) for 56 days and fed until satiation with a commercial diet. Health status and feed conversion ratio (FCR) were not significantly affected by treatment (p > 0.05). Specific growth rates (SGR) and daily feed intake (DFI) of C were not considered significantly different from LP, MP and HP treatments, however LP showed significant higher DFI and SGR than HP (p < 0.05). Using non-linear regression between SGR and ortho-P concentrations, 27 mg/L ortho-P was found as the optimum for turbot growth. Although not reflected in blood plasma P levels (p > 0.05) a potential aqueous P uptake might result in metabolic benefits leading to the observed growth enhancement in the LP treatment.In a second experiment 114 juvenile turbot were exposed to ortho-P concentrations of 2 mg/L (C2) and 25 mg/L (LP2) for 63 days and fed until satiation with a low P diet (4.6 g digestible-P/kg diet). Overall production performance was low due to low voluntary feed intake. Whereas the FCR was unaffected by treatment (p > 0.05), significantly higher feed intake and biomass gain were observed for LP2 compared to C2 (p < 0.05). LP2 treatment showed a trend for higher protein retention efficiency and lower whole body lipid content (p < 0.1). The dry matter, ash, Phosphorus, Calcium and protein content in whole body did not significantly vary between treatments (p > 0.05).In conclusion the accumulation of ortho-P in RAS does not negatively affect health of turbot. Elevated ortho-P seems to have slight positive effects on production performance of juvenile turbot. Further research to quantify dietary P requirements for turbot in general, as well as for turbot raised under elevated ortho-P conditions in RAS is strongly required.  相似文献   

8.
The aim of this study was to evaluate the effect of two methodologies of carbohydrate fertilization on the volume and characteristics of effluent from intensive biofloc shrimp cultivation. Six fiberglass circular tanks (50 m2 each) were divided into two treatments. In the treatment called continuous (CONT), the tanks received daily molasses fertilization throughout the entire rearing period. In the treatment named initial (INI), molasses was used only in the early weeks of cultivation. Juvenile Litopenaeus vannamei (0.87 ± 0.10 g) were stocked at a density of 180 animals m−2 and cultured during 12 weeks until they reached an average weight of 12 g. The tanks were operated with no water exchange and the total suspended solids concentration were kept between 300 and 400 mg L−1 using settling chambers. The sludge produced and the wastewater at harvest were quantified and their characteristics were determined. The production of TSS in the CONT treatment was higher (0.25 kg of solids per kg of applied feed) than in the INI treatment (0.16 kg kg−1) (P < 0.05). The analysis of the sludge revealed a high amount of volatile solids in both treatments, between 636 and 702 g kg−1. However, due to the elevated sludge nitrogen content, the carbon to nitrogen (C:N) ratio was low, with values of 6.4 ± 1.4 and 7.5 ± 1.6 for INI and CONT respectively. The BOD:TSS ratio was also low in both treatments, but the INI showed lower values (10.3 ± 0.6%) than the CONT (14.9 ± 0.0%) (P < 0.05). Both fertilization strategies were able to modify the characteristics of sludge produced during cultivation. Moreover, the high nitrogen and sulfate content of the sludge in both treatments indicated that it may be difficult to use an anaerobic digestion process to treat sludge. In the INI treatment tanks, the sludge is partially stabilized, while in the CONT there was a greater need for stabilization.  相似文献   

9.
Inclusion of kalbasu, Labeo calbasu as a candidate species in the Indian major carps based polyculture system was evaluated through a six-month grow-out trial in earthen ponds of 0.08 ha each. Species performance was assessed through provision of varied inputs viz., fertilizers (T-1), fertilizers + supplementary feed (T-2) and fertilizers + supplementary feed + periphytic substrate (T-3) as the three treatments, which were evaluated in replicates. Catla (35%), rohu (35%), mrigal (15%) and kalbasu (15%) were stocked at combined density of 7500 fingerlings/ha. While ponds were fertilized with cowdung, urea and single super phosphate, mixture of groundnut oilcake and rice bran at 1:1 (w/w) was provided as supplementary feed. The periphytic substrate, comprised stripe bamboo mat, was provided at 10% of the pond surface area. Provision of each additional input caused significantly higher increase in overall mean survival, growth, SGR and net biomass yield of carps. Among the carp species, while only rohu and kalbasu showed significantly higher weight gain (234.4 g and 170.3 g, respectively) in T-3, no such increase was noticed either in catla or mrigal. The net production in T-3 (1516.1 ± 24.3 kg ha− 1 6 months− 1) was 13.0 and 73.2% higher than those of T-2 (1341.7 ± 15.5 kg ha− 1 6 months− 1) and T-1 (875.2 ± 15.6 kg ha− 1 6 months− 1), respectively. The study revealed the relative advantage of using periphytic substrates in carp polyculture systems with kalbasu as a component species.  相似文献   

10.
《Fisheries Research》2007,87(2-3):99-104
A bow-mounted surface pushnet and an obliquely towed plankton net were compared to evaluate gear efficiency and effectiveness in collecting larval fishes under daytime and nighttime conditions. The diadromous species targeted were striped bass Morone saxatilis, white perch, Morone americana, and river herring Alosa sp. We sampled the lower Roanoke River, North Carolina, from March through June of 2002 and 2003. Striped bass, white perch and river herring represented over 90% of the larvae collected during the study period. Mean larval densities (number/100 m3) were 63.4 for striped bass, 26.4 for river herring, and 17.7 for white perch. Striped bass larval densities were significantly higher in the surface pushnet for both years (P ≤ 0.05). In 2002, white perch mean larval density was significantly higher at night in the surface pushnet samples, but in 2003 there were no differences between day and night samples. River herring mean densities were significantly higher in the surface pushnets for both years, but showed no clear patterns between day and night samples. Larger larvae were consistently collected in the surface pushnets for all species. Overall, the surface pushnet was easier to operate. The pushnet was mounted on the bow of a small jon boat and required less specialized gear and fewer personnel than oblique sampling. The method also allows for sampling in shallow water or vegetated habitats. Because larvae were significantly larger in the surface samples, using surface pushnets may not allow for detection of the smaller-sized larvae therefore underestimating the abundance of smaller fish. Depending on the question being asked, we recommend that sampling programs should use both gear types to reduce any gear biases.  相似文献   

11.
A new physico-chemical process for ammonia removal from fresh-water recirculated aquaculture systems (RASs) is introduced. The method is based on separating NH4+ from RAS water through an ion-exchange resin, which is subsequently regenerated by simultaneous chemical desorption and indirect electrochemical ammonia oxidation. Approach advantages include (1) only slight temperature dependence and no dependence on bacterial predators and chemical toxins; (2) no startup period is required and the system can be switched on and off at will; and (3) the fish are grown in much lower bacterial concentration, making the potential for both disease and off-flavor, lower. A small pilot scale RAS was operated for 51 d for proving the concept. The system was stocked by 105 tilapia fish (initial weight 35.8 g). The fish, which were maintained at high TAN (total ammonia nitrogen) concentrations (10–23 mgN L−1) and fish density of up to 20 kg m−3, grew at a rate identical to their established growth potential. NH3(aq) concentrations in the fish tank were maintained lower than the assumed toxicity threshold (0.1 mgN L−1) by operating the pond water at low pH (6.5–6.7). The low pH resulted in efficient CO2 air stripping, and low resultant CO2(aq) concentrations (<7 mg L−1). Due to efficient solids removal, no nitrification was observed in the fish tank and measured nitrite and nitrate concentrations were very low. The system was operated successfully, first at 10% and then at 5% daily makeup water exchange rate. The normalized operational costs, calculated based on data derived from the pilot operation, amounted to 28.7 $ cent per kg fish feed. The volume of the proposed process was calculated to be ∼13 times smaller than that of a typical RAS biofilter. The results show the process to be highly feasible from both the operational and economical standpoints.  相似文献   

12.
《Aquaculture Research》2017,48(4):1759-1766
A shrimp protein hydrolysate (SPH) containing 894.2 g kg−1 crude protein (CP) and 54.3 g kg−1 total lipids was tested as a partial replacement for fish meal (FM) in diets of juvenile cobia. The effects of increasing dietary levels of SPH on the survival, weight gain (WG), specific growth rate (SGR), feed conversion ratio (FCR), nitrogen retention efficiency (NRE) and daily feed intake (DFI) of cobia with initial body weight of 11.9 g were evaluated. Four isoproteic (from 431.1 to 439.7 g kg−1) and isoenergetic (20 825–21 347 MJ kg−1) diets were formulated to contain 0 (Control), 120, 240 or 360 g kg−1 of dietary CP derived from SPH. Survival, WG, SGR, FCR, NRE and DFI ranged from 90 to 100%, 40.2–56.5 g, 4.7–6.1% day−1, 1.04–1.54, 26.3–44.0% and 4.7–6.0% fish−1 day−1 respectively. Survival and DFI were not affected by the dietary treatments. On the other hand, fish fed the control diet and the one containing 120 g kg−1 SPH had higher WG, SGR and FCR. Nitrogen retention efficiency was significantly higher for fish fed diets 0 and 120. It is concluded that up to 120 g kg−1 of SPH in cobia diets can be used with no significant effects on feed utilization and fish performance.  相似文献   

13.
A 56-day study was conducted in which shrimp (Litopenaeus vannamei) were stocked at 300 m−3 into 16, 500-L tanks. Four treatments were created: chemoautotrophic (CA), heterotrophic sucrose (HS), heterotrophic molasses (HM), and heterotrophic glycerol (HG). The heterotrophic treatments were managed such that the C:N ratio of inputs (feed and carbohydrate source) was 22:1. The chemoautotrophic treatment received no added carbohydrate, only shrimp feed. Each treatment was assigned randomly to four replicate tanks. Nitrate-N was significantly greater in the CA treatment, accumulating to a peak mean concentration of 162 mg NO3-N L−1 and nitrate was typically below detection (<0.01 mg NO3-N L−1) in the heterotrophic treatments. 5-Day biochemical oxygen demand (BOD5) was significantly greater in the heterotrophic treatments compared to the chemoautotrophic treatment. Total suspended solids concentration was significantly lower in the CA treatment compared to any other. Shrimp growth rate was significantly greater in the CA and HS treatments versus the HM treatment and there was no significant difference in growth rate between the HG treatment and any other treatment. These results indicate that differences in management and carbohydrate source can lead to substantial disparity in system function and shrimp production.  相似文献   

14.
A jet fish pump with a throat of ø60 mm was designed to study its performance in the transport of different fish species and the physiological changes in fish thereafter. Experiments were conducted to investigate the fish transport rate and energy required to transport each ton of fish when transporting Carassius auratus, commonly known as the Chinese goldfish, Megalobrama amblycephala, or Wuchang bream, and Ctenopharyngodon idella, the grass carp. Fish were examined for external injuries as well as for several important enzymes and hormones which are indicators of tissue injury and stress. The results showed that the transport rate for all three species of fish rose dramatically with an increase in the primary stream rate. In this experiment, the transport rates of C. auratus, M. amblycephala and C. idella reached 2357 ± 37.2 kg ∙ h−1, 2888 ± 41.6 kg ∙ h−1, and 2060 ± 40.2 kg ∙ h−1, respectively. However, both injury rate and energy required to transport each ton of fish increased no matter whether the primary stream rate was too low or too high. Considering both transport rate and injury rate, the mean primary stream rate of 80 m3 ∙ h−1 was determined to be the optimal operating condition in this experiment. Fish were stressed and most likely some of their organs were damaged. However, most physiological indexes almost fully recovered after several hours.  相似文献   

15.
Some benthic cephalopods are considered potential candidates to diversify marine aquaculture, as they show fast growth and high market price. Most research on cephalopod culture is currently focusing on the development of specific enrichments and compound feeds, while little research has been conducted in order to test new rearing systems for cephalopods. The rigid characteristic of the floating cages commonly used for the ongrowing of Octopus vulgaris has restricted their use to calm water conditions (estuaries and harbors). Such sites are scarce and highly demanded, especially by the tourism industry; therefore the development of O. vulgaris grow out at these locations competes with touristic interests. The present study was set to compare the biological performance of O. vulgaris reared in a benthic cage (2 m2) as opposed to the traditional floating cage (2.5 m2), during two ongrowing trials. Initial rearing density was 10 kg m−3 and octopuses (892 ± 125 g) were fed on bogue Boops boops, discarded from fish farms, for 60–67 days. High growth (1.8–1.9% day−1) and high survival (91–97%) were observed, regardless of the rearing system, and led to best biomass increment (178–212%) and food conversion rates (2.3–2.6) ever recorded for O. vulgaris under industrial rearing conditions. These results underline the adequacy of the benthic cage for the ongrowing of this species, and also the potential of aquaculture discarded fishes, particularly bogue, as a single diet for this species. High growth rates obtained and the high lipid content of bogue (44% dry weight) suggest efficient lipid utilization in this species. Proximate composition and fatty acid profile in octopus muscle was not affected by the rearing system. High dietary lipid content was not reflected in muscle proximate composition, which showed high protein (87% dw) and low lipid content (5% dw) by the end of the experimental period. Farmed octopus showed high levels of n-3 HUFA (42%), which should enhance its value for the consumers.  相似文献   

16.
The main aim of the study was to decide the effect of specific water consumption (L/kg/min) and feed load per water flow (g/m3) on the water quality parameters pH, CO2, total ammonia nitrogen (TAN) and suspended solids (SS) in two large semi-closed containment systems (S-CCS). The reported production parameters (range) in the two S-CCS were specific water consumption (q): 0.04–0.47 L/kg/min and feed load per water flow: 9.0–64 g/m3. The study period was split in two sub-periods; January–May (4.4–7.5 °C), and June–September (7.5–13.2 °C) before a regression model was used to determine the relationship between production intensity (q, feed load) and water quality (pH, CO2). With the acceptable level of CO2 defined as ≤10 mg/L, the model predicted a minimum specific water consumption (L/kg/min) between 0.07 (winter) and 0.2 (summer). The predicted maximum feed load per water flow (g/m3) was between 35 (summer) and 45 g/m3 (winter). These calculated limits for production intensity were close to the values earlier reported for smolt or post-smolt production in large, onshore tanks.  相似文献   

17.
Although the use of artificial substrates can favor shrimp culture, some studies indicate that their presence in growth tanks does not improve water quality or the performance of the animals. One objective of this study was to evaluate whether the presence of artificial substrates modifies the microbial activity and the water quality of the culture of Litopenaeus vannamei with bioflocs. The substrate effects on the shrimp performance and the relationship between these effects and the stocking density/biomass of shrimp were also evaluated. The experiment consisted of four treatments: D238: 238 shrimp m−3; D238 + S: 238 shrimp m−3 + substrates; D473: 473 shrimp m−3; D473 + S: 473 shrimp m−3 + substrates. Twelve experimental units of 850 L were stocked with juvenile L. vannamei (2.6 g) that were grown for 34 days. The substrates did not appear to affect water quality since the concentrations of orthophosphate, ammonia and nitrite were not significantly different in tanks with or without substrates. The periphyton biomass was low and the biological activity on the substrates was not significant, indicating that the water quality variables were mainly controlled by the microbial community associated with the suspended bioflocs. The shrimp grown in the presence of the substrate exhibited greater weight gain (D238 + S = 1.40 ± 0.05 and D473 + S = 1.20 ± 0.04 g week−1) than those grown without substrates (D238 = 0.73 ± 0.04 and D473 = 0.44 ± 0.13 g week−1). The final biomass was 314% greater in the tanks with substrates. The shrimp survival was significantly higher in the tanks with substrates (93.9 ± 2.4%) than in the tanks without substrates (42.5 ± 35.9%). The results indicate that the substrates served to increase the surface area of the tank and to reduce the relative stocking density, which appears to reduce the stress levels of shrimp, indicated by higher shrimp performance. In tanks with higher biomass, where the negative effects of intensification were most severe, the presence of the substrates had a positive effect on the production indices.  相似文献   

18.
The sharptail mola, Masturus lanceolatus, is one of the largest teleost fishes in the world, and can be found in warm temperate and tropical regions worldwide. The increase of sharptail mola catch in the eastern Taiwan in recent years stimulated a concern that increasing exploitation of this species might lead to a decline of the stock. However, biological information of this species is very limited. Hence, this study provides the first information on age and growth of this species in the waters off eastern Taiwan based on 265 specimens (105 females and 160 males) collected from January 2003 to November 2006 at the Nanfanao and Hualien fish markets, eastern Taiwan. The relationships between whole weight (W) and standard length were expressed as: W = 9.98 × 10?4 SL2.45 (n = 105, p < 0.01) for females, and W = 3.33 × 10?4 SL2.68 (n = 160, p < 0.01) for males. Based on the MIR analysis, growth band pairs (including translucent and opaque bands) in vertebrae formed once a year and were counted up to 23 and 16 for females and males, respectively. Three growth functions, the von Bertalanffy (VBGF), Robertson, and Gompertz, were used to model the observed length at age data. The VBGF had the best fit and predicted an asymptotic length (L∞) = 262.5 cm SL, growth coefficient (k) = 0.046 yr?1, age at zero length (t0) = ?3.350 yr (n = 80, p < 0.01) for females, and L∞ = 231.0 cm SL, k = 0.059 yr?1, t0 = ?1.852 yr (n = 135, p < 0.01) for males. The longevities were estimated to be 105 and 82 yr based on the VBGF for females and males, respectively.  相似文献   

19.
Denitrification reactors have proven their functionality in commercial recirculation aquaculture systems (RAS). Nevertheless, clogging occurs due to the low hydraulic loads necessary to accomplish anoxic conditions for a successful denitrification process in RAS, which hampers the adjustment of stable working conditions within fixed bed denitrification reactors. Reactors working on the basis of activated sludge demand careful hydraulic control and/or complex configurations for sludge retention.To develop a low-maintenance denitrification reactor, an enclosed moving bed filter, driven by recirculation of the inherent, oxygen poor gas was designed. A Self cleaning Inherent gas Denitrification reactor (SID-reactor) of 0.65 m3, which offered a moving bed volume of 0.39 m3 was connected with a RAS of semi-industrial scale for pike perch (Sander lucioperca) production. This species indicates suboptimal environmental conditions (as e.g. NO3-N concentrations above approximately 68 mg l−1) by prompt reduction of the feed intake. In different experimental series, the SID-reactor was operated with denatured ethanol, methanol, acetic acid or glycerin as carbon sources and changing operational modes.Clogging was prevented by a 40 second inherent gas recirculation twice an hour, which provided continuous, maintenance free operation with marginal energy demand. With inlet (RAS) and outlet NO3-N concentrations in the range of 49 mg l−1 and 12 mg l−1, mean denitrification rates of 199 g to 235 g NO3-N per m3 moving bed volume and day were determined for all tested carbon sources. Negative effects on the feed intake of the reared pike perch were detected with all carbon sources except methanol. Changing the mode of operation to continuous circulation of the filter bed at inlet NO3-N concentrations of 26 mg l−1, the denitrification performance reached 451 g NO3-N per m3 moving bed volume and day. The SID-reactor allowed for the reduction of freshwater exchange in the pike perch RAS from 600 l to 70 l (−88%) and the sodium bicarbonate buffer from 182 g to 31 g (−83%) per kg of administered food. The easy and reliable operation of the SID-reactor could help to establish controlled denitrification as a routine purification step in RAS.  相似文献   

20.
Settling rates of faecal material from three size categories of cultured gilthead sea bream, Sparus aurata, and sea bass, Dicentrarchus labrax, were determined. Faecal material was collected from underneath commercial cages and subsequently transferred to a settling column. Particle settling velocity was determined using particle tracking software. Image analysis software was used to determine dimensions of selected faecal particles from which particle volume was then estimated. Faecal particles (all fish sizes) had a mean settling velocity of 0.48 cm/s (range 0.05–3.94 cm/s, n = 1021) for sea bream and 0.70 cm/s (range 0.10–6.27 cm/s, n = 1042) for sea bass. The faecal material largely consisted of very small particles and mean particle size was 0.71 mm (n = 151) and 1.12 mm (n = 150) for S. aurata and D. labrax, respectively. More than 50% of the total particle volume had a settling velocity less than 2.0 cm/s in all S. aurata size categories. In D. labrax, more than 75% of the total particle volume had settling velocities greater than 2.0 cm/s. The particle tracking DEPOMOD model was highly sensitive to different representations of these data. The predicted seabed flux of waste faecal material (g/m2/year) for D. labrax using the mean settling velocity at 0 m and 50 m from the cage was 3196 g/m2/year and 248 g/m2/year, respectively. However, when using particle settling velocity and volume distribution data, the predicted flux was over three times greater at 0 m but five times less at 50 m. For S. aurata, the predicted flux using the mean settling velocity was 3018 g/m2/year and 464 g/m2/year at 0 and 50 m, respectively. However, where distribution data were used, the values were over twice as high at 0 m and but were halved at 50 m. These results indicate that use of a single mean settling velocity value in this type of modelling does not accurately predict the extent of benthic flux. In addition, species-specific faecal settling rates should be used when modelling polyculture operations.  相似文献   

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