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1.
A simple and inexpensive device is described which maintains cultures of marine microalgae at predetermined cell densities by the automatic control of harvesting and replenishment of the culture volume with fresh medium. Cultures were maintained at a range of cell densities in 80-litre internally illuminated vessels and the daily cell production yield was evaluated.Maximum yields of 0·8–1·0×1012 cells day?1 of Isochrysis aff. galbana Green and 0·8–1·2×1011 cells day?1 of Tetraselmis suecica (Kylin) Butch. were obtained at culture densities of 15–17×103 cells μlitre?1 and 19–21×102 cells μlitre?1, respectively. Turbidostat cultures of Skeletonema costatum (Grev.) Cleve could not consistently be maintained above 5–7×103 cells μlitre?1.  相似文献   

2.
The efficiency of ammonium and nitrite oxidation was studied in two trickling filters filled with different plastic media (A, Hydropak®-Folia, Uhde Dortmund, 200 m2 active surface area per m3 volume; B, Bio-Net material, Norddeutsche Seekabelwerke, 260 m2 m?3). Both filters were operated simultaneously under comparable conditions (hydraulic load: of A = 40·2 m3 m?3 day?1; of B = 43·4 m3 m?3 day?1). Ammonium removal efficiency depended on pH value and on initial total ammonium concentration (range investigated: pH = 5·6–7·0; total ammonium concentration = 0·15?1·8 mg litre?1; nitrite concentration = 0·08?1·85 mg litre?1). Ammonium removal efficiency was reduced to almost zero at pH values below 5·6. Medium A was less efficient than medium B at higher pH levels (removal efficiency was above 50% at all times at pH values higher than 6·2, compared to 6·8 in medium A). With increasing initial ammonium concentration the removal efficiency decreased drastically in both filters (always below 60% at concentrations higher than 1·0 mg litre?1). In general, nitrite oxidation efficiency followed a similar trend in both filters indicating a better performance of substrate B. Reasons for these differences are discussed.  相似文献   

3.
Experiments over three years, in a pond of approximately 1500 m2, to intensify production at high stocking densities with controlled feeding resulted in a substantial increase in yield (weight gain per hectare and year: 2·6 tonne for C3–4, 9·1 tonne for C2–3, 15·4 tonne for C1–2). At the same time water requirement could be reduced to 4 m3 kg?1 fish produced. However, the stocking densities achieved resulted in a continuously increasing eutrophication effect which expressed itself in mass development of phytoplankton. This led to considerable diurnal fluctuations in oxygen concentration (0·5–20·0 mg O2 litre?1) and total ammonia (0–11·0 mg NH3NH4+ litre?1; maximum of 1·5 mg NH3 litre?1). The high stocking density contributed indirectly to the diurnal fluctuations (fertilization through faeces and lost feeds). However, its contribution to the overall oxygen depletion amounted to less than 25% at night. The amplitude of the fluctuation was mainly determined by the photosynthetic and respiratory activity of the phytoplankton and by microbiological degradation processes. With increasing water temperature during summer, increasing feeding rate, continuous fish biomass increment, and decreasing light period per day and danger of total fish stock mortality was greatest in August. Only at maximum photosynthetic activity during daylight was the total ammonia production in the pond adequately counteracted and sufficient oxygen produced. Even heavy aeration could not always successfully provide for oxygen during night. In order to avoid a breakdown of the system, algae and nutrients had to be diluted from time to time by excessive water replacement. Despite the temporary overloading of the pond system, losses in numbers had been kept below 6·5% (normally: 10–20%).Pellets were offered via self-feeding devices. Food uptake was continuously recorded. No diurnal feeding rhythmic could be observed, but feeding activity was entirely dependent on oxygen levels in pond water. Feed conversion efficiencies reached values between 1·96 and 2·48.  相似文献   

4.
A 1000 litre recirculation system of eight cylindrical rearing tanks has been tested in three 40-day periods to determine its capacity for rearing larval turbot (Scophthalmus maximus L.).The larvae were fed on rotifers and Artemia nauplii, as well as mixed marine algae. Continuous artificial light of 1500–2000 lux was applied at the surface. The applied algae served a dual function; keeping rotifers and Artemia at a high nutritional level as well as effectively removing the released ammonia. The combination of upwelling water and light at the surface maximized the contact surface between larvae, food items and algae.With this system, using a stocking density of 16 larvae litre?1 in the rearing tanks, a survival total of 40% at Day 40 was achieved, giving a production of 6·4 larvae litre?1 or 3000 larvae metre?2 of the surface of the rearing tanks.  相似文献   

5.
Poultry manure added to concrete ponds lined with 5 cm of soil increased fish growth only when applied up to a rate equivalent to 470 kg ha?1 week?1. When manure was supplied at 940 kg ha?1 week?1 fish growth was significantly (P < 0.05) reduced. Parameters which may explain the lower fish growth were electrical conductivity, pH, alkalinity, phosphorus and chlorophyll a production. Dissolved oxygen values fluctuated from 3 to 25 mg l?1 at 04.30 h and 6 and 25 mg l?1 at 14.00 h, and were considered not limiting to fish growth. The results of this study may help explain observed low fish growth in manure-loaded ponds in monoculture in the tropics.  相似文献   

6.
Effects of different feeding rates (0–20% live body weight) on food intake, growth and conversion efficiency of Heteropneustes fossilis were studied using the oligochaete worm Tubifex tubifex as food. An amount of worm substance equivalent to 12.73% live body weight/fish day?1 represents the maximum amount which a 4.015 ± 0.340-g H. fossilis can consume under laboratory conditions. Geometrically derived feeding rations of 12, 40 and 130 mg/g live fish day?1 represent the maintenance, optimum and maximum levels for H. fossilis. The SDA (specific dynamic action) increased from 14 mg/g day?1 at optimum to 70 mg/g day?1 at maximum feeding rate.  相似文献   

7.
Data obtained during the culture of tropical prawns Penaeus sp. and European lobsters Homarus gammarus (L.) in 20 laboratory recirculation systems over a number of years were used to obtain gross estimates of (a) the rates and diurnal patterns of ammonia excretion, (b) food utilization and wastage, and (c) nitrification rates in biological filters. Ammonia excretion in Penaeus monodon decreased with increase in animal size from 0·93 to 0·30 mg N g?1 day?1 at 1·6 and 27 g live weight, respectively. Large lobsters (300 g) excreted 0·3 mg N g?1 day?1. Peak excretion times were approximately 3, 9 and 15 h after a single morning feed for prawns and after 6 and 12 h for lobsters. Uneaten food solids amounted to 11% (lobsters) and 32% (prawns) of the daily ration and, for 4 g animals, only 69% (lobsters) and 45% (prawns) of the food nitrogen in the daily ration was converted into crustacean flesh. Nitrification rates ranged from 0·03 to 0·43 g N oxidized per m2 of filter media surface per day. Some evidence for periodicity in nitrifying activity was also found and is discussed in relation to the published literature.  相似文献   

8.
Growth rate, soluble protein content, osmotic stress and digestive enzyme activity were studied in early Litopenaeus schmitti postlarvae under different feeding regimens, by partially or completely replacing Artemia nauplii with Moina micrura. Growth was significantly higher in the postlarvae fed with a mixture of M. micrura, Artemia nauplii and algae (0.030 mg dry weight (dw) larva?1 day?1, 17.4 ± 2.1% day?1), together with the postlarvae fed on Artemia nauplii and algae (0.027 mg dw larva?1 day?1, 18.3 ± 1.9% day?1). Complete replacement of Artemia nauplii by M. micrura produced the lowest growth rate (0.018 mg dw larva?1 day?1, 14.3 ± 1.6% day?1) and induced the highest protease and α‐amylase activities and lower soluble protein contents. No significant difference among the treatments could be detected in postlarval resistance to osmotic stress. Based on the growth results, soluble protein content, enzymatic activity and osmotic stress resistance, we determined that the partial replacement of Artemia nauplii by M. micrura did not affect the growth, the soluble protein content and the nutritional state in the postlarvae of L. schmitti. To our knowledge, this is the first reported use of M.micrura as feed for early postlarvae of L. schmitti.  相似文献   

9.
To investigate the illuminance requirements for the culture of red algae in finfish effluent, both Chondrus crispus and Palmaria palmata were assessed simultaneously at three irradiances. Apical tips, 3.5 cm length, were stocked at 2 g L?1 in 1-L glass flasks with enriched seawater in two 24-day experiments, at 10 and 14 °C, respectively. Palmaria grew up to 70 % better and up took more nutrients than Chondrus under five of the six experimental conditions, except at 14 °C and low irradiance (daily photon dose of 3.4 mol photon m?2 day?1). Specific growth rate of both species at high irradiance, 13.1 and 17.2 mol photon m?2 day?1, at each trial, 10 and 14 °C, respectively, was 40 and 20 % better than at medium irradiance, but nutrient uptake was similar at both medium and high irradiance. Chondrus growth rate was higher during Experiment 2 (14 °C and 17.2 mol photon m?2 day?1) than during Experiment 1 (10 °C and 13.1 mol photon m?2 day?1), while Palmaria growth rate was similar in both trials, but always significantly higher than Chondrus. In the range 10–14 °C, Palmaria is the best candidate for integration with Atlantic halibut juveniles (Hippoglossus hippoglossus).  相似文献   

10.
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   

11.
To develop a feeding strategy for the Australian freshwater fish silver perch (Bidyanus bidyanus Mitchell), a series of eight experiments was done in 1 m3 cages in an aerated, earthen pond to determine the effects of feeding rate (% body weight) and feeding frequency (no. of feeds day?1) on the growth and feed conversion ratio (FCR) of fingerlings and larger fish under ambient water temperatures over the range 13.8–30.6°C. Fish were fed extruded pellets of a silver perch diet containing 34% digestible protein and 14 MJ kg?1 digestible energy. Commercial silver perch farmers were consulted about feeding practices for large fish (>500 g) and at water temperatures below 12°C, and winter feeding practices for other warmwater species were used to complete the strategy. In the feeding experiments, growth and FCR increased with increasing feeding rates to a level above which only FCR increased. Optimal feeding rates and frequencies were those which resulted in maximal growth, while minimizing effort (feeding frequency) and FCR. The highest feeding frequency required for maximal growth, including that of small fingerlings was twice (2 ×) daily, and the optimal feeding rates varied with water temperature and size of fish. The optimal daily regimes were: small fingerlings (initial mean weight, 2.0 g) 7.5% 2 × at a mean temperature of 23.3°C; fingerlings (14.9–27.7 g) 7.5% 2 × at 27.1°C, 5.0% 2 × at 23.7°C and 2.0% 1 × at 16.8°C; and large silver perch (162.5–510.6 g) 0.5% 1 × daily or 1.0% on alternate days at 15.6°C, 1.0% 1 × at 17.3°C, 3.0% 2 × at 24.1°C and 2.0% 2 × at 27.9°C. It is suggested that regimes of 0.5% 1 × daily for fingerlings (<50 g) and 0.5% 1 × on alternate days for larger fish are used at temperatures of 9–12°C, and 0.5% 3 days week?1 and 0.5% 1 day week?1 for fingerlings and larger fish, respectively, at 6–9°C. Feed inputs should not exceed 150 kg ha?1 day?1 in ponds less than 0.3 ha and 100 kg ha?1 day?1 in larger ponds. Our research has established a feeding strategy for silver perch based on restricted rations.  相似文献   

12.
The individual food intake of each fish in each of four groups of Atlantic halibut, Hippoglossus hippoglossus (L.) (mean weight: 422 g) was monitored by direct observation over a period of 21 days. Gross feed conversion efficiency (= growth·feed intake?1), net feed conversion efficiency and maintenance ration were estimated by regression analysis. Specific growth rates were found to be linearly related to weight-specific consumption at a temperature of 8–9°C: growth = 1.922· feed intake ? 0.242. Maintenance ration was 0.126% of body weight day?1. The gross feed conversion efficiency increased asymptotically with increasing feed intakes and growth rates, and was found to approach 1.9 at high growth rates (0.5 on a dry weight basis). One feeding per day seemed to be sufficient for maximum food intake and growth rate.  相似文献   

13.
Four fixed-film biological filters (rotating biological contactor, biodrum, trickling filter, and a submerged anaerobic filter) were tested for the removal of ammonia using a simulated warmwater fish and invertebrate culture water supply. Filter design may be determined based on the results of ammonia removal efficiency over a wide range of hydraulic loads. The rotating biological contactor (RBC) provided the best ammonia removal (over 90%) up to about 0·06 m3 m?2 day?1 (1·2 gpd ft?2). The biodrum removed over 80% of the ammonia to a hydraulic load of 0·05 m3 m?2 day?1 (0·9 gpd ft?2). The trickling filter removed 50% of the ammonia at a hydraulic loading of 0·012 m3 m?2 day?1 (0·3 gpd ft?2).  相似文献   

14.
Enteromorpha linza and E. intestinalis thrive in aquatic systems rich in inorganic fixed nitrogen. At 15°C and ca. 1800 μW cm?2 these algae showed a Vmax for nitrate uptake of 129 μmol h? g?1 dry weight ( = ca. 22 μmol h?1 g?1 wet weight) and a Ks of 17 μM. At 20 μM rates averaged 70 ± 21 μmol h?1 g?1. They dropped to 19% of this value at 5°C, and at 0°C nitrate uptake ceased. In the first hour of darkness, nitrate uptake decreased to 35% and in the second hour to 10% of the rate in light. Enteromorpha spp. scavenged nitrate from the medium at concentrations < 0.5 μM, and no nitrate leaked out of the tissue into nitrate-free water. Information from this study may be useful in designing nutrient feeding strategies in aquaculture systems.  相似文献   

15.
The effect of recombinant bovine placenta) lactogen (rbPL) treatment upon growth of juvenile chinook salmon, Oncorhynchus tshawytscha (Walbaum) (14.0 ± 0.31 g wet wt), was examined over a period of 6 weeks. Experimental animals were either injected (5 μg rbPL g?1 week?1), implanted with a cholesterol pellet containing 0.4 mg rbPL (approximately 4 μg g?1 week?1), or orally and rectally intubated with 7.5 μg rbPL g?1 week?1. Control animals were injected with bovine serum albumen (BSA), 5 μg g?1 week?1, implanted with a placebo or orally intubated (7.5 μg BSA g?1 week?1). Significant (P < 0.05) growth acceleration was recorded for rbPL-injected and pellet-implanted groups from week 2 onwards when compared against all other groups. Oral or rectal intubation of rbPL (7.5 μg rbPL g?1 week?1), however, was without effect. Condition factor decreased in all groups, but was significantly lower in rbPL-injected and pellet-implanted fish at trial end when compared against controls. No differences were recorded between groups for per cent body moisture or relative gut length. Hepatosomatic index was significantly (P < 0.05) higher in rbPL-injected and rbPL-implanted chinook salmon versus other fish.  相似文献   

16.
Five diets were compared for their efficiency at maturing the gonads of the blue mussel, Mytilus edulis. The diets consisted of a 1:1:1 mixture of Isochrysis galbana (T-Iso), Pavlova lutheri, and Chaetoceros calcitrans given at concentrations of 2.4 × 1011 cells day?1 for the positive control treatment (PF) and 3.0 × 1010 cells day?1 (=1/8) for the negative control treatment (NF). The other three treatments, MB10+, MyStock+, and Frippak+, consisted of the NF diet supplemented with one of the micro-encapsulated diets MB10 (mixture of dried algae), MyStock (formulated diet), and FRiPPAK® Fresh #1 CAR (larval shrimp diet) at a level of 0.2% of the live weight (LW). Treatments PF, MB10+, and MyStock+ led to high percentages of spawning animals (80, 78, and 85%, respectively) and large numbers of eggs (on average 3.0 × 106 eggs female?1). Females given the NF and Frippak+ treatments produced only half the number of eggs per female, and only 17 and 6%, respectively, of the animals spawned. A high hatching rate was observed for all treatments, 71% for the pure algae diets PF and NF and more than 80% for the micro-encapsulated diets. The larvae resulting from the NF treatment were smaller, with 41% of D-larvae measuring less than 90 μm, whereas with the other treatments only 5–11% belonged to that size category. The four most important fatty acids found in mussel eggs were 16:0, 16:1(n?7), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA); these represented at least 50% of the fatty acids in all treatments. The high DHA content of MB10 and MyStock was not reflected in the fatty acid composition of the eggs whereas the high concentration of linoleic acid in MyStock was. To our knowledge, this is the first time that mussels are successfully conditioned with formulated feeds.  相似文献   

17.
Selected (G8) and wild‐type (W) genotypes of black tiger shrimp (Penaeus monodon) juveniles (initial weight G8 = 9.14 ± 0.36 g per animal and W = 8.44 ± 0.10 g per animal) were fed either of two diet types in a clear‐water tank trial to examine the effects of diet type and genetics on growth and feed utilization parameters. Animals were fed twice daily at one of the five ration levels from starvation to apparent satiety. All uneaten feed was accounted for and moults removed. Starved animals were measured after 3 weeks; those fed were measured at both three and 6 weeks. Diet type varied by protein content, raw material choice and the presence [high‐specification diet (HSD)] or absence [low‐specification diet (LSD)] of bioactive substances. At the end of the study, faecal samples were also collected to determine the digestible protein and energy content of each diet by each genotype. Whole animal protein and energy content were also assessed from samples from the initial populations and those from each tank. Growth after 6 weeks of those animals fed to satiety showed that the G8 animals fed the HSD diet had grown at a rate of 2.56 g week?1, significantly faster than any other treatment. Those G8 animals fed the LSD diet (1.81 g week?1) had grown significantly faster than the W animals fed the HSD diet (1.25 g week?1), while those W animals fed the LSD diet (0.61 g week?1) grew the slowest. Using the data from the varying ration levels, we were able to define that the growth gains of the G8 animals were achieved not only by a greater appetite, but also through lower maintenance energy costs (29 versus 57 kJ kg?0.8 day?1) and a more efficient energy conversion (19.5% versus 11.6% when fed the HSD diet). Use of a low‐specification diet with the G8 and W shrimps limited their growth and impaired their potential as demonstrated by a curvilinear response of growth to intake. By comparison, those shrimp fed the HSD diet had a relatively linear growth response to intake.  相似文献   

18.
A 2 × 3 factorial study was conducted to investigate the effects of dietary protein levels (DPLs) and feeding rates (FRs) on the growth and health status of juvenile genetically improved farmed tilapia (GIFT), Oreochromis niloticus. Triplicate tanks of fish (initial weight 15.87 ± 0.11 g) were fed diets containing 25 or 35% protein at rates of 3, 5, or 7% body weight per day (BW day?1) for 8 weeks. At the end of the feeding trial, the results showed that fish growth (final mean weight 34.61–81.07 g) and condition factor (3.39–4.45 g cm?3) increased with the DPLs and FRs. Feed efficiency (FE, 0.48–0.88) increased as DPLs increased but decreased as FRs increased; the opposite trend was observed for feed cost (FC, 3.24–5.82 CHN Yuan kg?1) and hepatosomatic index (0.98–2.33%). Apparent protein retention efficiency (APRE, 23.92–38.78%) was reduced by high FR. A 35% protein diet resulted in higher (P < 0.05) FE and APRE, and lower (P < 0.05) FC at 5% BW day?1 than those at 7% BW day?1. As FRs increased, lipid contents of the hepatopancreas, viscera, muscle, and eviscerated body increased, while moisture contents of hepatopancreas and viscera decreased. All serum biochemical parameters, including glutamic-oxalacetic transaminase and glutamic-pyruvic transaminase activity and levels of creatinine, glucose, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, total cholesterol, triglyceride, and total protein were unaffected by DPL or FR (P > 0.05), except urea nitrogen levels, which were affected by DPLs (P < 0.05). Moreover, the size of hepatocytes and the area ratio of hepatocyte vacuoles were enlarged (P < 0.05), whereas the area ratios of the nucleus and cytoplasm were reduced (P < 0.05) with increasing FRs. These results suggested that the optimal feeding strategy for juvenile GIFT is 35% protein diet at 5% BW day?1.  相似文献   

19.
We isolated the rotifers Brachionus ibericus and Proales similis from the sediment of shrimp tanks and studied their individual demographic characters and competition between them at two food levels (0.25?×?106, 1.00?×?106 cells ml?1 of Nannochloropsis oculata at 25 °C) and salinities ranging from 10 to 30‰. Our hypothesis was that growth rates would be higher with increasing food levels and salinities. Observations were taken twice a day for life table studies and daily once for population growth experiments. Using survivorship and fecundity data, we derived various life history variables. Although the average life span (7.6?±?0.4 days) and gross reproductive rate (33.8?±?2.9 neonate female?1 day?1) of B. ibericus were higher than those of P. similis (average life span 5.4?±?0.6 days and gross reproductive rate 13.0?±?0.6 neonate female?1 day?1), the population growth experiments showed that P. similis had higher r values (0.32?±?0.005 day?1) than B. ibericus (0.23?±?0.002 day?1) at 1.0?×?106 cells ml?1 of N. oculata. The rotifer P. similis was more adversely affected due to the presence of B. ibericus than vice versa. The data are important for developing techniques for a large-scale culture of these rotifers as food in aquaculture.  相似文献   

20.
Microbound feeds have been well accepted by shrimps and farmers in many penaeid shrimp hatcheries. The present study focused on an adequate level of replacement of Artemia nauplii and microalgae by a microbound diet for rearing Litopenaeus setiferus (Burkenroad) larvae. A microbound diet (MBD) consisting of fishmeal, squid meal, shrimp meal, yeast meal and soybean meal was used. The first experiment was designed to obtain the optimum level of MBD to complete the live feeding schedule, from Protozoea (PZIII) to Mysis (MIII). The experimental levels of the microbound diet tested were 2, 4, 6 and 8 mg MBD L?1 day?1. The next step was to determine the Artemia nauplii replacement level from PZI to MIII by MBD. These experiments were carried out either in the presence (Experiment 2) or in the absence of algae (Experiment 3). Four replacement levels were tested: 0% (4 mg MBD L?1 day?1: 1 Artemia nauplii mL?1), 40% (5.5 mg MBD L?1 day?1: 0.6 Artemia nauplii), 60% (6.5 mg MBD L?1 day?1: 0.4 Artemia nauplii) and 100% (8 mg MBD L?1 day?1: 0 Artemia nauplii). In all experiments growth, survival, development, quality index (QI) and performance index (PI), were used to determine the optimum concentration of microbound diet. Results showed that 6 mg MBD L?1 day?1 can be recommended as a complement to live food for L. setiferus larvae from PZIII to MIII. In the presence of algae, maximum growth and survival may be obtained in 40–60% (5.5–6.5 mg MBD L?1 day?1) of Artemia nauplii replacement levels. In the absence of algae, the Artemia nauplii replacement resulted in slower development, less salinity resistance, lower growth and lower survival than was obtained in larvae fed with algae.  相似文献   

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