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1.
Sea bass (Dicentrarchus labrax) (135 ± 4 g) were reared under tank-based recirculating aquaculture system for a 63-day period at four densities: 10, 40, 70, 100 kg m?3. Fish performance, stress indicators (plasma cortisol, proteonemia plus other blood parameters—Na+, K+, glucose, pH, total CO2?) and water quality were monitored. At the end of the 63-day period, resistance to infection was also studied by a nodavirus challenge. A 25-day test was performed on fish from two extreme densities (10 and 100 kg m3) and one intermediate density (40 kg m3).With regards to the different density treatments, there was no significant difference between the daily feed intake (DFI) and the specific growth rate (SGR) up to a density of 70 kg m?3. No significant difference was found between treatments concerning the feed conversion ratio (FCR) and the mortality rate. No density effect was observed on the fish stress level (plasma cortisol) or on sensitivity to the nodavirus challenge. Under these experimental rearing conditions, the density above 70 kg m?3 has an impact on growth performance (DFI and SGR) indicators and also some blood parameters (CO2) at the highest density tested (100 kg m?3).This study suggests that a density up to 70 kg m?3 has no influence on sea bass performance and welfare. At 100 kg m?3, average specific growth rate was decreased by 14% without welfare deterioration according to the welfare indicators monitored.  相似文献   

2.
This paper presents the field testing of a new technology to harvest marine copepods (Calanus sp.) by bubble-induced upwelling. Two large-scale bubble rafts, a 21 m2 and a flexible 75 m2 bubble raft with tow-parallel and tow-perpendicular sparger elements, respectively, were tested in the sea with high Calanus densities in the upper 25 m. Bubble-driven upwelling velocities (Vup) measured with different air flows (Q) and source depths (z0), gave Vup ～ Q0.27 with stratified water, and were in agreement with other results for stratified conditions. Bubble trawls significantly enhanced Calanus concentrations in the upper water column: up to 1416%, with the best results for the transverse sparger raft, which also was tested with weak stratification. Bubble trawl performance also was affected by the stratification, with the highest enhancement for the lowest stratification. Catch species analysis showed reduced bycatch. Thus, this new harvesting technology showed a potential to develop an economically robust, environmentally benign, and sustainable fishery on a renewable resource at lower trophic levels in the food web, within the context of ecosystem-based management.  相似文献   

3.
Leakage of water soluble nutrients from larval microparticulated feeds is probably extensive and needs to be further investigated. Leaching rates of 14C-labelled serine, pepsin hydrolysed, protein enriched 14C-algae extract and intact protein enriched 14C-algae extract were measured from three microparticulated feeds for marine fish larvae (heat coagulated, protein bond feed; agglomerated feed; protein encapsulated feed). The effects of particle size (< 0.3 mm, 0.3–0.6 mm; 0.6–1.0 mm) and immersion time (1–60 min) in salt water were also tested. Leaching increased by decreasing molecular weight of leaching component (P < 10− 5), by the feeds in order encapsulated, heat coagulated and agglomerated feeds (P < 10− 5), by longer immersion time (P < 10− 5), and by decreasing feed particle size (P < 10− 5). Due to low protein content of the algae extract, the leaching rates of intact and hydrolysed algae extract did not represent absolute estimates for protein and hydrolysed protein leaching. A new estimate for leakage of hydrolysed protein was calculated based on molecular weight distribution of the hydrolysed algae extract analysed by cutoff centrifugation of the extract. Assuming that molecules < 300–600 or < 9–18 kD would leak, leakage of hydrolysed protein from the smallest feed particles after 5 min immersion would be 80–98%, 43–54% and 4–6% of the agglomerated, heat coagulated and protein encapsulated feeds, respectively. The feeds were also tested for preference in cod larvae of two different sizes (5.6 ± 2.5 mg and 15.8 ± 7.2 mg). The preference was highest for the heat coagulated feed in the first experiment (feed intake 0.32 ± 0.06 mg dry feed larvae− 1) and the agglomerated in the second (2.04 ± 0.32 mg dry feed larvae− 1), while the protein encapsulated feed was preferred at lower rates in both experiments (0.11–0.14 mg dry feed larvae− 1).  相似文献   

4.
In vivo digestibility determination in shrimp is a challenge because these animals are coprophagous, benthic and slow feeders and the small amount of feces that they produce is difficult to collect. The objective of this study was to evaluate an efficient tank design for the purpose of studying shrimp digestibility. Different tank designs were evaluated considering drain system (dual-drain and single-drain), water inlet flow rate (8, 12, and 16 L min−1) and bottom drain diameter (6, 13, 19, 25 and 50 mm) and their effects on tank hydraulics, water velocity and solids flushing. A circular and slightly conical 500 L tank was adapted with a clarifier for the two dual-drain designs (Cornell-type and central-type) and settling columns for the two single-drain designs (Guelph-F and Guelph-L). Results showed that: (1) water rotational velocity profile was more homogeneous in tanks with larger bottom drain outlets, and water velocity increased with water inlet flow rate from almost zero up to 14.5 ± 0.7 cm s−1; (2) solids flushing, measured as the percentage of feed pellets retained at both the bottom drain and in the settling devices, was positively correlated with the surface loading rate (L min−1 flow per m2) and was more effective at the Guelph-L design fitted with a 150 mm diameter settling column. In this system 100% of the solids were removed at the inflow rate of 16 L min−1. It can be concluded that among the systems evaluated, the Guelph-L at an inflow-rate of 12 L min−1 was most efficient for both solids removal and water velocity profile and thus seemed more suitable for shrimp digestibility studies in high performance conditions. Technologies involving hydrodynamic must be intensively applied to solids removal for aquatic species production as well as research purposes like digestibility, which is highlighted in this study.  相似文献   

5.
A study was undertaken to measure the water flow (Qw) delivered by a vacuum airlift designed for recirculating aquaculture systems (RAS) in fresh (<1‰ of salinity) and sea water (35‰ of salinity). The vacuum airlift consists of two concentric tubes connected at their top to a depression chamber. The water rises in the inner tube as a result of air being injected in its lower section and flows back through the external downcomer tube. The vacuum airlift was adjusted at three different lengths: 2, 4 or 6 m and water discharge could be lifted from 0 to 30 cm. Air flow rate (Qg) varied from 0 to 80 L min−1. Different types of air injectors were tested, delivering different bubble sizes (0.1–5 mm) depending on porosity and functioning at low or high injection pressure. Results show an increase in water flow when pipe length and air flow were increased and lift height reduced. Water flow also depended on the type of water and ranged from 0 to 35 m3 h−1 (0–580 L min−1) for fresh water and only from 0 to 20 m3 h−1 (0–330 L min−1) for sea water (for a 6 m high vacuum airlift). This difference was attributed to the smaller bubble diameter and higher gas holdup (ɛg) observed in sea water (0–20%) compared to fresh water (0–10%). When bubbles were present in the downcomer tube, they created a resistance to flow (counter-current airlift) that slowed down liquid velocity and thus water flow. Increasing the vacuum made it possible to use low air injection pressures and high injection depths. Vacuum also increased bubble size and airflow (20 L min−1 at atmospheric pressure to 60 L min−1 at 0.3 barA) and thus water flow rates. With RAS, the presence of fish feed in water rapidly increased water flow delivered by the airlift because of changes of water quality and gas holdup. When working with low head RAS (under 0.3 m), vacuum airlift could save up to 50% of the energy required for centrifugal pumps. An empirical predictive model was developed and calibrated. Simulation shows a good correlation between predicted values and measurements (R2 = 0.96).  相似文献   

6.
A survey was conducted to determine the geometry, operating parameters, and other key features of large circular or octagonal culture tanks used to produce Atlantic salmon smolt and post-smolt at six major Norwegian Atlantic salmon production companies. A total of 55 large tanks were reported at seven land-based hatchery locations, i.e., averaging 7.9 (range of 4–12) large tanks per land-based site. In addition, one 21,000 m3 floating fiberglass tank in sea was reported. Culture volume ranged from 500 to 1300 m3 for each land-based tank. Most tanks were circular, but one site used octagonal tanks. Land-based tank diameters ranged from 14.5 to 20 m diameter, whereas the floating tank was 40 m diameter. Maximum tank depths ranged from 3.5 to 4.5 m at land-based facilities, which produced diameter-to-average-depth ratios of 3.6:1 to 5.5:1 m:m. The floating tank was much deeper at 20 m, with a diameter-to-average-depth ratio of only 2.4:1 m:m. All land-based tanks had floors sloping at 4.0–6.5% toward the tank center and various pipe configurations that penetrated the culture tank water volume at tank center. These pipes and sloping floors were used to reduce labor when removing dead fish and harvesting fish.Maximum flow ranged from 3 to 19 m3/min per land-based tank, with 400 m3/min at the floating tank, but tank flow was adjustable at most facilities. Land-based tanks were flushed at a mean hydraulic retention time (HRT) of 35–170 min. Maximum feed load on each land-based tank ranged from 525 to 850 kg/day, but the floating tank reached 3700 kg/day. Almost half of the large tanks reported in this survey were installed or renovated since 2013, including the three tank systems with the highest flow rate per tank (greater than 17.6 m3/min). These more recent tanks were operated at more rapid tank HRT’s, i.e., from 34.8 to 52.5 min, than the 67–170 min HRT typical of the large tanks built before 2013. In addition, flow per unit of feed load in land-based tanks that began operating before 2010 were lower (19–30 m3 flow/kg feed) than in tanks that began operating later (33–40 m3 flow/kg feed). In comparison, the floating tank operates at a maximum daily tank flow to feed load of 160 m3 flow/kg feed, which is the least intensive of all tanks surveyed. Survey results suggest that the recently built tanks have been designed to operate at a reduced metabolic loading per unit of flow, a tendency that would improve water quality throughout the culture tank, all else equal. This trend is possible due to the ever increasing application of water recirculating systems.  相似文献   

7.
Irrigated rice fields have enormous potential for expanding the aquaculture production in rice producing countries. Two field experiments were carried out at the Bangladesh Agricultural University, Mymensingh, to optimize the productivity of integrated rice–fish systems using Nile tilapia, Oreochromis niloticus (L.), and common carp, Cyprinus carpio L. Both experiments were laid out in a randomized complete block design with three replicates per treatment and regular rice monoculture as control. In the first trial, carp and tilapia were tested in single culture and in mixed culture with supplementary feeding at 2× maintenance level. The highest fish yield was obtained in the carp/tilapia mixed culture (586 ± 125 kg ha− 1), followed by tilapia alone (540 ± 65 kg ha− 1), and carp alone (257 ± 95 kg ha− 1). Carp had significantly lower yield than the other two fish groups (p < 0.05) due to high mortality and inefficient feed utilization. As the carp/tilapia combination performed the best in the first experiment, it was tested with different inputs in the second trial, i.e. regular urea fertilization and two different feeding levels. The feeding levels were: continuous feeding at 2× maintenance level (feed level I) and a declining feeding schedule from 4× to 2× maintenance level (feed level II). The highest fish yield was obtained in feed level II (935 ± 29 kg ha− 1), followed by feed level I (776 ± 22 kg ha− 1), and the non-fed group (515 ± 85 kg ha− 1). Yield differences between the treatments were significant at p < 0.05. Rice yields showed controversial effects between the rice–fish treatments and were dependent on the inputs provided. The highest rice production (4.2 t ha− 1) was obtained from rice–fish plots with regular urea fertilization. Various significant effects of fish on water quality parameters were observed. Fish decreased the dissolved oxygen (DO) and pH value compared to rice only, especially when supplementary feed was provided. Moreover, fish stimulated the growth of phytoplankton and increased chlorophyll-a concentration. In conclusion, carp/tilapia mixed culture with supplementary feeding was found to be optimal for maximizing the output from rice–fish culture.  相似文献   

8.
《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   

9.
《Aquacultural Engineering》2010,42(3):166-175
Fish oxygen requirement is a fundamental variable of aquaculture system design and management, as it is the basis for determining water flow rates for sustaining stock. A study on oxygen consumption of California halibut (Paralichthys californicus) between 3.2 and 165.6 g was conducted in small raceways (2.41 m long, 0.28 m wide, and 0.22 m high; operational water depth between 0.05 and 0.10 m with a quiescent zone 19 cm long in the effluent section) working as open respirometers in a recirculating system under farm-like conditions. The fish were fed commercial dry pelleted feeds at a ratio of ∼0.70–3.00% of body weight (BW) and stocked at densities between 94% and 316% percent coverage area (PCA). Oxygen consumption rates were determined by mass balance calculations. The mean and maximum oxygen consumption rates (g O2/kg fish/day) for juvenile California halibut under the conditions tested can be expressed by Mday = 15.077W−0.2452 and Mday = 17.266W−0.2033, respectively, where W is fish weight in grams. The determination of oxygen consumption by California halibut in farm-like conditions provides valuable information on the oxygen requirement of these fish in an aquacultural setting. This information can be used for designing and sizing a rearing facility for the intensive culture of California halibut.  相似文献   

10.
Disease costs the Norwegian aquaculture industry approximately NOK 1 billion ($ 150 000 000) every year, and NOK 250 000 000 ($36 000 000) is spent on vaccines each year by the industry. Many of the disease outbreaks take place during the first months of transfer to the sea sites. Thus, the aim of this project was to monitor physiological stress parameters as plasma cortisol, glucose and lactate in salmon smolts before and after regular well boat transports. The loading process was observed to be a more severe stressor than the transport itself. Only minor plasma cortisol increases were observed during unloading. In four out of five transports, plasma cortisol had returned to resting level at arrival. However in one, which showed an unusually high mortality rate during the first month after transfer to the sea, the plasma cortisol level remained high during unloading. The study showed that well boat transports seemed to have an important recovery function. Without this ability to recover between the stressors, as on- and unloading, the ability for salmon smolts to handle multiple stressors was reduced. Further, the present study seems to strengthen the fact that some of the increased mortality experienced at sea sites in Norway may be explained by handling and transport prior to deliverance of smolts. Care should be taken during commercial boat transports. Planning of well boat routes, and avoidance of high seas could contribute to minimise mortality experienced after transports.  相似文献   

11.
《Aquacultural Engineering》2007,36(2):198-211
  相似文献   

12.
Selective breeding of European sea bass (Dicentrarchus labrax) receives a growing interest, as the estimated heritability of growth is medium to high. In this study, we compared the offspring of four groups of sea bass sires, mated with the same wild dams: wild (W), first generation of domestication (D), first generation of mass selection for length (M), first generation of PROSPER-like selection for length (P). The comparison was done both in replicated tanks (separate rearing) and in mixed tanks (mixed rearing) where sire origins were recovered by genotyping of eight microsatellite markers. Weight, length and growth rate were measured from day 238 post-fertilization (69 g mean weight) to day 611 post-fertilization (390 g mean weight). Both in mixed and separate tanks, both selected groups (P, M) were larger than unselected groups (W, D). No difference was seen at any time between W and D, nor between M and P. The selection response estimate on weight was larger in mixed tanks when compared to separate tanks (+ 42% in mixed tanks, + 23% in separate tanks at day 611), yielding realized heritability estimates of 0.60 and 0.34, respectively, and confirming the excellent potential of the species for growth improvement through selective breeding. Both selection response and the amplification effect between mixed and separate tanks decreased as rearing density increased. Our hypothesis is that selection response is magnified by competition in mixed tanks, while sub-optimal rearing conditions lower the observed selection response, more in separate tanks (where selected thus larger fish are at a higher density than unselected ones) than in mixed tanks (where all fish experience the same density effects).  相似文献   

13.
《Fisheries Research》2007,84(3):345-357
Movements of the edible crab Cancer pagurus were investigated from mark-recaptures in the Skagerrak and Kattegat. Crabs were released in 1968–1973 and in 2003 from six main areas along the Swedish west coast, and from one offshore bank in the Kattegat. Recaptures were reported for up to 7 years after the release. Sex-specific differences in migration were found: females migrated significantly longer distances than males, and higher proportions of males stayed within the area of release (60 and 48% of males versus 28 and 19% of females) were recaptured within 1 km of the release site: initial and recent mark-recapture studies, respectively. The movement direction varied with sampling location, however females tended to move in a net southerly direction. The range of mean rates of movement within the first month were 325–345 m d−1 for females and 202–299 m d−1 for males. Over longer time periods mean rates of movement were significantly lower. There was no significant impact of size class on the distance migrated. Short-term (2 months) movements of nine male edible crabs were studied with acoustic transmitters and active tracking. The movement pattern varied among individuals: some stayed in the same area for weeks whereas some made regular movements every day during the tracking period. The difference in migration pattern of females and males, and the largely southward migration of females is consistent with the hypothesis that the migration is related to reproduction. By moving to the south to release their larvae, females may compensate for larval dispersion in the northbound current along the Swedish west coast. The observed migration pattern indicates advisable management options in Sweden for this commercially fished species: protection of areas with high proportion of egg-bearing females from fishing, especially in the Kattegat. Significantly, local management only on a small spatial scale is not recommended as the resource is seasonally shared, if not the effect on the crab population is monitored.  相似文献   

14.
Fish oxygen requirement is a fundamental variable of aquaculture system design and management, as it is the basis for determining water flow rates for sustaining stock. A study on oxygen consumption of California halibut (Paralichthys californicus) between 3.2 and 165.6 g was conducted in small raceways (2.41 m long, 0.28 m wide, and 0.22 m high; operational water depth between 0.05 and 0.10 m with a quiescent zone 19 cm long in the effluent section) working as open respirometers in a recirculating system under farm-like conditions. The fish were fed commercial dry pelleted feeds at a ratio of ～0.70–3.00% of body weight (BW) and stocked at densities between 94% and 316% percent coverage area (PCA). Oxygen consumption rates were determined by mass balance calculations. The mean and maximum oxygen consumption rates (g O2/kg fish/day) for juvenile California halibut under the conditions tested can be expressed by Mday = 15.077W?0.2452 and Mday = 17.266W?0.2033, respectively, where W is fish weight in grams. The determination of oxygen consumption by California halibut in farm-like conditions provides valuable information on the oxygen requirement of these fish in an aquacultural setting. This information can be used for designing and sizing a rearing facility for the intensive culture of California halibut.  相似文献   

15.
Drag measurements are conducted to determine if inhalant and exhalant of fluid during mussel feeding has a detectable influence on the drag of a mussel-encrusted rope such as is commonly used in suspended aquaculture. The experiment is conducted using an artificial mussel crop rope constructed using the shells of Perna canaliculus, with 100 mussels (mean shell length 83.4 mm, S.D. 8.7 mm) attached over a length of 0.90 m. Fluid pumping from mussel feeding is simulated using inhalant and exhalant jets pumping at a rate of 7 L h?1 per mussel. The mussel rope is towed at speeds between 0.05 and 0.4 m s?1. No significant difference is found between drag with and without the mussels pumping indicating that assessments of the drag on or from mussel long-lines may safely neglect the effect of mussel feeding. We suggest using twice the mussel shell size to define mussel rope diameter which gives a drag coefficient of CD ～1.0. A value of CD ～1.3 is obtained if the projected area of the mussel rope is used. Particle tracking velocimetry (PTV) is also used on a similar but shorter crop rope (0.3 m length) in a recirculating flume which reveals that mussel pumping induces only small changes to mean velocity and turbulence distributions downstream of the rope. The wake of the crop rope is highly turbulent and dominated by shear instabilities formed in the free shear layer, similar to bluff body wakes. The sharp edges of the mussel shells provide many points for flow separation to occur. At typical ambient velocities, turbulent kinetic energy produced by the exhalant jets is small in comparison to that from flow around the crop rope.  相似文献   

16.
《Fisheries Research》2007,84(2-3):246-252
We used a chemical marking experiment to validate the daily periodicity of otolith increment deposition in juvenile sablefish, Anoplopoma fimbria. The sagittal otoliths of 26 live juvenile sablefish were marked twice by immersion in saltwater baths containing elevated levels of strontium chloride (SrCl2) during June–August of their first year of life (age 0). The number of otolith increments detected between strontium bands from three readings (median 15–20) was compared to the number of days between marking events (15–17 days). Median discrepancies between otolith increment counts and days between strontium bands were small (mean 1.1, S.E. 0.81, n = 20) and suggest that otolith increment counts from age 0 juvenile sablefish may provide a useful proxy for daily age. However, median discrepancies in June (mean 4.7, S.E. 0.65, n = 9 otoliths) were significantly (*P ≤ 0.05) higher than those in July (mean −1.8, S.E. 0.40, n = 6) and August (mean −1.8, S.E. 0.66, n = 5). Increment banding patterns were more difficult to identify in otoliths marked in June (mean sablefish size 84.9 mm FL) because of changes in the structure of the sagittae associated with the formation of accessory primordia.  相似文献   

17.
Short-term hooking mortality was evaluated for three sparid species [Diplodus vulgaris (Geoffroy Saint-Hilaire), Sparus aurata L. and Spondyliosoma cantharus (L.)] in the Algarve, south Portugal. Fishes were caught from the shore during October 2009 at a fish farm reservoir (Ria Formosa), using three different hook sizes. The relationships between hooking mortality and seven independent variables were analyzed using logistic regression models. In all, 384 fishes representing the three target species were caught during the angling sessions. The most caught species was S. cantharus (n = 181; 100% undersized), followed by S. aurata (n = 137; 89% undersized) and D. vulgaris (n = 66; 97% undersized). Mortalities ranged between 0% for D. vulgaris and 12% for S. aurata (S. cantharus, 3%). For S. aurata, anatomical hooking location was the main predictor of mortality, with 63% of the fishes that died being deeply hooked. Our results support the current mandatory practices of releasing undersized fish for the studied species, given the low post-release mortality rates observed.  相似文献   

18.
A three-dimensional (3D) simulation of a commercial-size mixed-cell raceway (MCR) was performed using computational fluid dynamics (CFD). Hydrodynamics of the MCR were fully characterized and validated against experimental data. A simulation of path and residence time of aquaculture-like particles was also conducted to understand solids removal mechanisms and potential efficiencies within a mixed-cell. A structured 3D grid model of one mixed-cell was constructed using 250,000 hexahedral elements, and simulations were conducted using the Realizable k–ɛ turbulence model. From the results of the CFD simulations, average cell rotational velocities, radial velocity profiles, and velocity contour and vector plots were generated at three different water depths. As observed in experimental trials conducted by the authors, predicted velocity contours and vector plots revealed the development of a strong rotational flow in each mixed-cell with lower velocity zones at the center and corners of the cells. Also, a linear trend of increasing rotational velocities from the cell's center to its circumferential perimeter was described. Good fluid-flow pattern agreement was observed between the experimental and predicted vector and contour plots. Average rotational velocities at the bottom (95 cm depth), middle (50 cm depth), and top (20 cm depth) planes of the mixed-cell (1-m water depth) were 17.2, 14.9, and 13.7 cm/s, respectively. Comparison of these velocities with the observed values revealed an overall agreement of nearly 96%. Similarly, when the average velocities at radial distances of the MCR were compared at the three depths, the correlation between the experimental and predicted data was on the range of 89–95%.Simulations of aquaculture-like particles trajectories revealed that roughly 100% of particles larger than 500 μm settled and were removed in less than 15 min through the mixed-cell’ central drain. Also, 100% of the 100-μm particles were removed within one mixed-cell hydraulic retention time (HRT) cycle, with approximately half being removed by the bottom-center drain and half being removed via the upper-side drains. Only 50% of the 10-μm particles was removed; and this mainly occurred through the upper-side drains of the mixed-cell after 17 HRT cycles. Smaller particles appeared to stay in the tank for an indefinite period of time.  相似文献   

19.
Basic data describing the physical characteristics of fish fecal waste are important in the design of effective solid waste management in aquaculture, especially in land-based facilities such as recirculating aquacultural systems (RAS).This study describes the physical properties of feces from rainbow trout fed eight different commercially available and widely used diets in Germany. Additional data from an earlier but unpublished study pertaining to feces derived from two rather extreme all-vegetarian diets are also presented for consideration of the settling properties. The diets were tested on duplicate groups of 50 rainbow trout in a flow-through aquaculture system. The effects of the diets on the physical properties of fecal particles such as particle size distribution (PSD), modeled settling velocity and rheological character were examined and the effects of each diet on fish health, growth and feed utilization were determined. Specific growth rate (SGR) and feed conversion ratio (FCR) for the different diets ranged from 0.98% d−1 ± 0.012% d−1 to 1.39% d−1 ± 0.012% d−1 and 0.97 ± 0.017 to 1.61 ± 0.017 (mean ± S.E.), respectively. The density of presoaked feces was significantly lower than that of intestinal feces and ranged from 1.01013 ± 0.00692 g cm−3 to 1.04547 ± 0.00692 g cm−3 (mean ± S.E.). Stability data were in the range from 390.12 ± 29.4 Pa to 1214.79 ± 29.0 Pa for elastic modulus and from 62.12 ± 6.1 Pa s to 232.68 ± 6.0 Pa s for dynamic viscosity. Based on the stability and PSD data theoretical efficiencies for removal of fecal waste using a drum filter showed remarkable variation, ranging from 82.5 to 95.9% (60 μm gauze). Based on the same data, theoretical removal by a sedimentation basin with routinely using overflow rates of 0.057 cm s−1 to 0.394 cm s−1 ranged from 62.8 to 93.8%. Both fecal density and PSD have an exponential impact on settling performance. Increasing fecal density improves the removal efficiency of a sedimentation basin by about 20%, however sedimentation was seen to be a less robust and efficient removal technique than drum filtration. Sedimentation systems also experience additional problems with respect to leaching. Turbulence that was mimicked in this study reflects to an optimal fish farm, which means disintegrating effects are mainly caused by fish motion. If disintegrating units e.g. pumps are used, which are known to promote further particle breakdown the effects would be amplified.The results demonstrate the central importance of density of suspended solids in defining removal efficiencies and suggest that manipulation of fecal density might offer a new and effective means of managing and optimizing waste output from aquaculture operations. This study describes the basic properties of fecal wastes generated by commercial diets and can be used as a basis for further research.  相似文献   

20.
An ornithological survey was conducted along the eastern coastline of New Brunswick, Canada, where oysters are cultivated in suspension using PVC bags and wire-mesh cages. Thirteen bird species and a variety of unidentified shorebirds were observed roosting on the floating oyster gear. The double-crested cormorant (Phalacrocorax auritus) was the most common species observed (47.6% of all counts), closely followed by herring gulls (Larus argentatus) and common terns (Sterna hirundo) at 18.7% and 13.0%, respectively. Birds were densely aggregated where few cages or bags had been deployed. A gear-type effect was also detected: birds were more abundant on floating cages (mean = 47.9/100 m2 of exposed area, S.E. = 5.8) than on floating bags (mean = 32.8/100 m2, S.E. = 1.9). The survey was followed by two experiments designed to test the effects of gear modifications on bird abundance and diversity. For bags, results indicated that shallow immersion (～6 cm below surface) and floater instability were effective deterrents to P. auritus, reducing its abundance by a 37-fold factor. For wire-mesh cages, a dented triangular structure mounted on top of floaters was a harassing physical barrier to roosting behaviour, consequently reducing bird abundances to null (or near null) values.  相似文献   

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