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1.
This study investigated the effects of nursing duration on the subsequent performance of rohu (R) Labeo rohita and mrigal (M) Cirrhina mrigala in polyculture with monosex male Nile tilapia (T) Oreochromis niloticus at four levels of pond fertilization. Nile tilapia, rohu and mrigal were stocked at a ratio of 4:1:1 in a 90‐day trial based on 40 20‐m2 pens fixed in four 400‐m2 earthen ponds. Growth of carp fingerlings during prolonged nursing (5 or 12 months) was stunted compared with fish nursed over a conventional duration of 3 months (3) but showed superior growth subsequently. Mean daily weight gain of stunted rohu (12) ranged from 2.2 to 2.8 g per fish day?1 compared with 1.1–1.6 g per fish day?1 for younger fish (3). The comparable ranges for mrigal were 1.9–2.8 and 1.4–2.1 g per fish day?1. Growth of Nile tilapia was inversely related to duration of carp nursing at the four levels of fertilization. Nile tilapia showed more response to increasing levels of fertilizer input (Y=?1.421+1.716X, where Y is the daily weight gain of Nile tilapia and X is the fertilizer level, r2=0.98, P<0.01, n=12). At a high level of fertilization (3.0 kg N:1.5 kg P ha?1 day?1), performance of stunted fingerlings (5 and 12) of both rohu and mrigal was similar (range 2.3–2.8 g per fish day?1, P>0.05), but younger mrigal (M3) grew faster than rohu (2.1 g per fish day?1 and 1.6 g per fish day?1 respectively). Older rohu (12) appeared to perform particularly well, and Nile tilapia poorly at the lowest level of fertilization (1.5 N:0.75 kg P ha?1 day?1), suggesting the impact of age of seed on competition within polycultures. The net fish yield (NFY) of tilapia was not affected significantly (P>0.05) by differential stocking age of carps; therefore, combined NFY of the three experimental fish species was not affected by the age of carp, as tilapia was the dominant species in polyculture. The highest combined NFY of all species in the most intensively fertilized pond (3.0 N:1.5 P kg ha?1 day?1) was calculated at 4.06±0.08 g·m?2 day?1, which was significantly higher (P<0.001) than the yield (1.82±0.12 g·m?2 day?1) from the pond with the lowest fertilization. At the highest fertilizer level, tilapia, rohu and mrigal contributed 72%, 14% and 14%, respectively, to the NFY, whereas the ratio was 60%, 20% and 20% at the lowest fertilization level. The study indicated that yields from tilapia in polyculture with the two carp species in more eutrophic water can be optimized if advanced nursing of carps is practised. Moreover, higher inputs of inorganic fertilizer and advanced nursing of carp are economically attractive under Bangladeshi conditions. Advanced nursing of rohu also improves its performance in more extensive systems when tilapia densities are high.  相似文献   

2.
Coral reef fish are collected from the wild and exhibited in aquaria worldwide. Some of the fish spawn in captivity; however, the eggs are usually neglected. In this study, we collected the eggs spawned naturally in the exhibit tanks, hatched and cultured them indoor in 2000‐L fibreglass tanks (initial density = 18 000 egg tank?1). We applied an inorganic fertilization method commonly used in freshwater fish culture in raising these coral reef fish larvae. We maintained inorganic phosphorus concentration at 100 μg P L?1 and inorganic nitrogen at 700 μg N L?1 daily in the fertilized group (n = 4), while the control tanks (n = 4) were fed with rotifers (10 ind mL?1). Chlorophyll a at particle sizes of both 0.45–20 μm and >20 μm, as well as NH3‐N, NO3‐N, and PO4‐P concentrations were significantly higher in the fertilized group than the control. Zooplankton in the size groups of 10–50 μm (mainly flagellates) and 50–100 μm (mainly ciliates) were abundant (about 10~60 ind mL?1) during 3–7 days in fertilized tanks. The average larval fish survival rate at 21 day after hatch in fertilized group was consistently higher than the control in two trials. The experiments demonstrated that the inorganic fertilization approach can be successfully adapted for coral reef fish culture in an aquarium to achieve sustainable exhibits.  相似文献   

3.
Growout production of the camouflage grouper, Epinephelus polyphekadion (Bleeker), in a 10-m3-capacity fibreglass tank culture system was evaluated, using hatchery-produced fingerlings (56-59 g initial weight) at stocking densities of five, 15 and 45 fish m?3. During the first 9 months of a 12-month growout period, the fish were fed twice a day with a moist pellet feed containing 40.9% protein. From month 10 onwards until harvest, the fish were fed moist pellets in the morning and trash fish in the evening at a 1:1 ratio. The final weight of fish at harvest was up to 900 g, with mean weights of 544.6 ± 170.72 g at five fish m?3, 540.2 ± 150.82 g at 15 fish m-?3 and 513.3 ± 134.52 g at 45 fish m?3. The results showed no significant differences (P > 0.05) in growth rate and fish size between the different stocking densities tested. The average daily growth rate ranged from 0.62 to 3.38 g fish?1 day?1, with mean weights of 1.49 ± 0.74 g fish?1 day?1 at five fish m?3 through 0.53 to 2.38 g fish?1 day?1, 1.32 ± 0.57 g fish?1 day?1 at 15 fish m?3 to 0.48-3.32 g fish?1 day?1 and 1.31 g fish?1 day?1 at 45 fish m?3 stocking density. Although up to 100% survival was observed at the lowest stocking density, the survival rate significantly decreased (P < 0.05) with increasing stocking density. The food conversion ratio (FCR) significantly decreased (P <0.05) with increasing stocking densities, showing efficient feed utilization with increasing stocking densities of E. polyphekadion. The FCR averaged 2.1 at a stocking density of 45 fish m?3. The yield in terms of kg fish produced m?3 of water used in the culture system significantly increased (P < 0.001) from five to 45 fish m?3. The yield averaged 17.3 ±0.53 kg m?3 at a stocking density of 45 fish m?3. The present results show that the present tank culture system could sustain more biomass in terms of increasing fish stocking densities. The growth performance of E. polyphekadion observed during this investigation has been reviewed with other grouper species.  相似文献   

4.
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   

5.
The effects of pond fertilization and feeding rate on growth, economic returns and water quality were investigated to develop a low‐cost cage‐cum‐pond integrated system for production of Oreochromis niloticus (L.). Hand‐sexed male fingerlings averaging 19±0.39 and 32±0.69 g were stocked in cages and open ponds at 150 fish cage?1 and 2 fish m?2 respectively. Fish were cultured for 114 days in five triplicate treatments. Cages were installed into ponds and caged fish were fed a 24% protein diet at 3% (T1) and 6% (T2) body weight day?1 (BWD) without pond fertilization, and 6% BWD with pond fertilization (T3). The open water in the fourth treatment (T4) was not stocked but contained caged fish, which were fed 6% BWD for the first 57 days followed by 3% BWD for the remaining period. Ponds in the control (T5) had no cages and were neither fertilized nor open‐pond fish fed. Feeding rate and pond fertilization significantly (P<0.05) affected fish growth, profitability and water quality among treatments. Fish growth, feed utilization, fish yield, water quality and profits were significantly (P<0.05) better in T3 than the other treatments. It was concluded that fish production and economic returns were optimized at 6% BWD in fertilized ponds.  相似文献   

6.
A field study was carried out to assess the use of the bottom‐feeding grey mullet (Mugil cephalus) within benthic enclosures as a means to reduce the benthic impacts of a net cage fish farm in the Gulf of Aqaba, Red Sea. Five experimental 1‐m3 net‐cage enclosures were stocked with 12 grey mullets each (fish weights 50, 70 or 144 g). The enclosures had no bottom and the mullets had access to the enclosed organically enriched sediments and to particulate matter (PM) falling from the overlying cages. Sediment traps were used to quantify and qualify the PM falling from the fish farm to the sea floor. Simultaneously, a feeding trial was performed with mullets (50 and 70 g) in experimental tanks. In order to estimate the potential growth rate and to quantify energy and protein requirements, the fish were fed a formulated diet with known composition. After approximately 70 days at sea, mullets in the enclosures had used up all the available food in the sediment and gained up to 0.78 g day?1 fish?1. Applying the values for energy and protein requirements for maintenance and growth derived from the experimental trial, estimates indicated that the grey mullets effectively removed 4.2 g organic carbon, 0.70 g nitrogen and 7.5 mg phosphorus kg?1 mullet m?2 day?1 from the organically enriched sediment. Thus deployment of grey mullets may be an efficient means to improve the quality of sediments below intensive net‐cage fish farms.  相似文献   

7.
The study was conducted to determine the optimum stocking density for rearing tilapia. Oreochromis spilurus (Günther), fingerlings in tanks during winter using warm (21-26°C) underground sea water (37%o). Seawater-acclimated fingerlings with mean weight of 2 g were stocked in eighteen 400-1 fibreglass tanks at 750 and 1000 fish m?3. Fish were fed at the rates of 2.5, 3.0 and 3.5% day?1 of the fish biomass. After 83 days, the mean individual daily weight gain was significantly higher (P < 0.028) at stocking of 750 fish m?3 than at 1000 fish m?3. Feed conversion ratio was significantly higher at stocking of 1000 fish m?3 than at 750 fish m?3 and at feeding rate of 3.5% day1 than at 2.5% day?1. However, because no significant differences were observed on survival rates between the two stocking densities and among feeding rates, it is recommended that the stocking density of 1000 fish m?3 and a feeding rate of 2.5% day?1 be used for optimum production of tilapia fingerlings in tanks during winter using warm underground sea water.  相似文献   

8.
The study was carried out to quantify the periphyton biomass developed on glass substrates over time, to investigate the effects of periphyton quantity and fish size on the ingestion rate by fish, and to determine the feed conversion ratio (FCR) of periphyton by tilapia Oreochromis niloticus. Periphyton was grown in two fertilised 1000‐l tanks on glass slides and monitored as dry matter (g), ash‐free dry matter (g) and chlorophyll a concentrations (mg) per unit surface area (m2) over a six week period. Ingestion rate was determined for two sizes of tilapia (7 and 24 g) which were provided with four different periphyton densities. Determination of FCR was made after feeding three individual fish ad libitum with periphyton for two weeks. Periphyton ash‐free dry matter increased sharply during the first half of the trial with a peak being recorded at week 3 (75.5 g m?2). Productivity was 2.4 g ash‐free dry matter m?2 d?1 during the first three weeks. Mean chlorophyll a concentration showed a cyclic pattern throughout the study with the lowest value being measured during the last week. Ingestion rates were 0.90 and 0.18 mg dry matter g fish body weight?1 h?1 for small and medium fish respectively. Ingestion rate among small fish increased significantly (P < 0.05) with periphyton density, but not for medium size fish. Although periphyton ash content was high (55% dry matter), fish growth was sustained. Fish harvested 70% of total periphyton dry matter that was offered to them. The FCR for periphyton was 2.81 on a dry matter basis and 1.34 on an ash‐free dry matter basis.  相似文献   

9.
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   

10.
A major constraint in successful larviculture of groupers has been the small gape of the larvae and hence the requirement for small prey at first feeding. In this study, we examined how maintaining a phosphate concentration of 100 μg P L?1 and an inorganic nitrogen (N) level of 700 μg N L?1 via weekly fertilization with inorganic fertilizers affected phytoplankton, zooplankton and giant grouper larval survival in relation to a control group that was provided with rotifers immediately after larvae hatched. Unicellular algae, zooplankton within the size ranges of 10–50 μm and 50–100 μm and survival of giant grouper larvae were all significantly higher in the fertilized treatment compared with the control. Stomach analysis revealed that ciliates and flagellates were actively consumed by larval fish in the fertilized group, whereas few rotifers were consumed in the control. We conclude that the inorganic fertilization method provides high densities of suitable‐sized prey for larval groupers at the onset of exogenous feeding before they are able to consume larger, commercially available rotifers and copepods.  相似文献   

11.
A high rate algal pond (HRAP) system was used to treat effluent from a recirculating sea water aquaculture system in southern France. Dicentrarchus labrax L. were farmed at a high density, with effluents containing an average of 10 mg L?1 dissolved inorganic nitrogen (DIN) and 1.3 mg L?1 reactive phosphorus (RP). On a yearly basis, the algal pond removed 59% of the dissolved nitrogen and 56% of the phosphorus input, which was converted into 3.3 kg DW m?2 algae. Green macroalgae were dominant throughout the year and the algal biomass mirrored the seasonal changes in daily irradiance and temperature. This first year study supports the possibility of treating marine aquaculture wastes using HPAPs, although conditions will have to be found to mitigate the strong influence of climate on the algal community during winter. During the more temperate season, only 150 m2 of treatment ponds would be necessary to remove the nutrients produced by 1 ton of fish. Treated water was characterized by a high pH, elevated levels of dissolved oxygen (midday value) and low concentrations of nutrients and suspended solids. The absence of toxic phytoplankton meant that the water could be recycled through the farm tanks.  相似文献   

12.
Abstract. Brown trout. Salmo trutta L., estimates were obtained for the Owendoher, a tributary of the River Dodder. Data were collected at live stations on 21 occasions from May 1981 to May 1983. Total population densities ranged from 0·07 to 1·29 fish/m2 Mean annual densities varied from 0·20 to 0·77 fish/m2. Trout in this stream are typically slow-growing fish reaching a maximum length of 7·68, 13·05 and 17·54cm at the end of their first, second and third years respectively. Growth improved in a downstream direction with the highest rates recorded in stretches overlying limestone. There was some evidence of density-dependent growth in the upper reaches Daily instantaneous growth rates were highest for all age groups during the months May to August but became depressed during the winter. There was considerable variation in the total monthly biomass figures with values ranging from 1·32 to 33·46 g/m2. Mean annual values ranged from 3·96 to 13·48 g/m2. Annual production (somatic) varied from 3·77 to 14·38 g/m2. in 1981–1982 and from 6·12 to 12·70 g/m2. in 1982–1983. The mean annual production figure for this stream was 11·24 g/m2. Production was contributed mainly by 1+ and 2+ trout at all stations. Egg production. accounting for 3–4% of the total estimate, was contributed mainly by resident 1+ and 2+ fish. It ranged from 0·33 to 0·45 g/m2 in 1981–1982 and from 0·14 to 0·53 g/m2 in the following year. Ratios of annual production to mean biomass (P/B?) were highest for 0+ trout hut decreased with increasing age. The mean P/B? ratios for all age classes varied from 0·95 to 1·17. The mean value for the Owendoher stream was 1·1. The effects on production of changes in age structure, population density and habitat alterations are discussed.  相似文献   

13.
A series of outdoor, continuous-flow seawater cultures (50 l; 0.23 m2) were used to investigate the effects of culture density (kg/m2), nutrient loading (total nitrogen input/day) with both NH4+N and NO3?N, and turnover rate (flow rateculture volume) on the growth and yield of Gracilaria tikvahiae. Although specific growth rates as high as 60% per day were recorded for Gracilaria at low densities (0.4 kg wet wt/m2) in summer conditions, maximum year-round yields were obtained at densities of 2.0–3.0 kg wet wt/m2. Above a minimal daily nitrogen loading the yield of Gracilaria was independent of (1) nutrient concentration, (2) nitrogen loading, or (3) whether nitrogen was in the form of NH4+N or NO3?N, but was (4) highly dependent upon flow rate. The time weighted mean annual production during 1976–1977 was 34.8 g dry wt/m2·day or 127 t/ha·yr based on 12-months continuous operation at near optimal densities and flow rates in the non-nutrient limited culture system.  相似文献   

14.
Cultivation of Gracilaria (Rhodophyta) in shrimp pond effluents in Brazil   总被引：3，自引：0，他引：3  
Shrimp aquaculture produces a large amount of waste, including nitrogen and phosphorus. To investigate the utilization of those elements as sources of nutrients for the growth of the red seaweed, Gracilaria sp. J. Agardh, an experiment in shrimp pond effluents was carried out over a period of 5 months. The biomass varied significantly (P < 0.01), reaching a maximum of 2540 g m?2 and a minimum of 380 g m?2. The mean was 1418 ± 708 g m?2. The higher biomass values occurred during the first 15 days and sometimes exceeded the initial inoculum by 190%. According to the results, production of 23.93 t ha?1 year?1 (dry weight) can be expected. anova showed significant differences in RGR (relative growth rate) values (P < 0.05). RGR varied from 8.8% per day to 1.8% per day. The fluctuation of nutrients was mainly influenced by pond fertilization frequency, with NH4 being the most abundant nutrient. Correlations between RGR and environmental parameters during the study period were not significant (P > 0.05). We conclude that Gracilaria sp. can be cultivated in shrimp ponds effluents. However, despite this relative success, it is necessary to perform some adjustments regarding the utilized cultivation technique.  相似文献   

15.
Slow growth and losses to bird predation and infectious diseases in winter can compromise the profitability of silver perch farming. To evaluate over‐wintering silver perch (Bidyanus bidyanus) in a recirculating aquaculture system (RAS), fingerlings (38 g) were stocked in either cages in a pond at ambient temperatures (10–21 °C) or tanks in the RAS at elevated temperatures (19–25 °C) and cultured for 125 days. Mean survival (96%), final weight (146 g), specific growth rate (1.07% day?1) and production rate (28.1 kg m?3) of fish in the RAS were significantly higher than for fish over‐wintered in cages (77%, 73 g, 0.53% day?1, 11.1 kg m?3). Fish from both treatments were then reared in cages for a further 129 days. Final mean weight of fish originally over‐wintered in the RAS was 426 g, while fish over‐wintered in cages were only 273 g. To determine optimal stocking densities, fingerlings (11.8 g) were stocked at 500, 1000 or 1500 fish m?3 in tanks in the RAS and cultured for 124 days. Survival was not affected, but growth was significantly slower and feed conversion ratio higher at 1500 fish m?3 compared with 500 or 1000 fish m?3. Results demonstrate that over‐wintering silver perch in an RAS can produce large fingerlings for grow‐out in early spring. This strategy could eliminate bird predation, reduce losses to diseases and shorten the overall culture period.  相似文献   

16.
An experiment was conducted in rice field plots each of 30 m2 to determine the appropriate combination of feeding and fertilization regimes for the giant freshwater prawn Macrobrachium rosenbergii (De Man, 1879) cultured along with rice in rice fields. There were four treatments: rice culture only with regular fertilization (A, control); rice–prawn integrated culture with regular fertilization (B); rice–prawn integrated culture with basal fertilization and commercial feed (C) and rice–prawn integrated culture with regular fertilization and commercial feed (D). Juvenile prawns of 1.5‐g size were stocked on the third day after rice transplantation at a density of 2 prawns m?2 and fed twice daily at 5% reducing to 2% of body weight during the experiment. The rice yield in treatment D (0.42 kg m?2) was significantly higher than that in other treatments (0.34, 0.36, 0.34 kg m?2 in treatments A, B, C respectively). Prawns grew significantly faster (P<0.05) in treatments C and D (23.8±0.9 and 22.0±1.7 g prawn?1 respectively) than in treatment B (14.7±1.6 g prawn?1). Prawn production in treatment C (347±13 kg ha?1 crop?1) was significantly (P<0.05) higher than that (234±30 kg ha?1 crop?1) in treatment B, while in treatment D (296±53 kg ha?1 crop?1) it was not significantly different from that in treatments B and C (P>0.05). Treatment C gave the highest economic returns among all treatments, followed by treatments D and B, indicating that the combination of basal fertilization and commercial feed is the most appropriate nutrient input regime for the rice–prawn integrated culture system.  相似文献   

17.
Abstract. Nearly 2000 marked coarse fish of four species were introduced into a stretch in the middle reaches of the River Derwent. Derbyshire, England in an attempt to estimate the fish population size from catch returns. It was estimated that 800 dace, 1975 roach, 1481 chub and 366 bream were present in the reach and the density of the fish population (0·35 fish m?2) was low. The validity of employing anglers as samplers in a mark-recapture exercise to estimate fish population size in large fisheries is discussed. Angler catch data were collected from angling clubs holding competitions on the Hoveringham Fishery on the lower reaches of the River Derwent over the period 1973/1974 to 1983/1984 to assess the impact of achange in management strategy on the fishery in 1979. Catch rates improved gradually until 1979/1980 when a dramatic increase occurred. This elevated catch rate, in excess of 400 g man-h?1, was maintained and, in recent years, further enhanced (>500 g man-h?1). The improvement was the result of a strong year-class of chub entering the catchable cohort and dominating anglers' catches and not the change in management policy.  相似文献   

18.
Abstract. A brown trout, Salmo trutta fario L., population in homeothermous stream conditions was investigated in terms of age, length-weight relationship, annual and seasonal growth, changes in seasonal condition and specific growth rates, as management variables. The growth of this species in the stream studied was very good, with the most rapid growth in the first year of its life (15·9cm) when the juvenile trout emerged early (April) from the stream bed. The greatest specific growth rate in length was between birth and the first year of life (182·6%). There was an agreement between the condition factor (K) and the growth rate. The values of K, for the juvenile trout, increased continuously because these mainly resulted from their growth through the year. The growth of the two sexes was similar except for the period from October to February when the growth of males was higher than that of females. Also the growth for both sexes was well described by the Von Bertalanffy growth model. No effect was found on the growth rate of tagged and untagged fish. The density and biomass were low, ranging between 0·008 and 0·035 fish.m?2 and 1·25 and 5·63 g.m2 respectively.  相似文献   

19.
为了解三沙湾大黄鱼（）网箱养殖衍生有机物（AOM）的沉降特征,采用原位实验方法,收集区域内使用颗粒饲料和冰鲜饵料两种典型饲喂方式下距离网箱200 m范围内AOM样品,分析其沉降量、营养物质[颗粒有机物（POM）、颗粒有机碳（POC）、颗粒态氮（PN）、总磷（TP）]沉降通量和扩散特点。研究结果表明,饲喂颗粒饲料状态下AOM沉降量显著高于投喂冰鲜饵料,两者均值分别为（563.66±119.18）g/（m2·d）和（266.07±139.15）g/（m2·d）。POM、POC、PN和TP沉降通量在两种饲喂方式下的差异与之相似,饲喂颗粒饲料时各参数均值分别为（27.25±2.43）g/（m2·d）、（6.03±0.58）g/（m2·d）、（0.66±0.06）g/（m2·d）和（0.39±0.04）g/（m2·d）;饲喂冰鲜饵料时各参数均值分别为（13.04±1.62）g/（m2·d）,（3.57±0.45）g/（m2·d）、（0.51±0.06）g/（m2·d）和（0.22±0.04）g/（m2·d）。沿近底层海流主导流向距离养殖网箱100 m的空间范围内,AOM沉降量和营养物质沉降通量均呈现自网箱处递减的变化特征,下降程度在饲喂冰鲜饵料时尤为显著。AOM中POC、PN和TP含量在饲喂冰鲜饵料时较高,在距离养殖网箱50 m范围内呈现递减趋势。综上,在三沙湾大黄鱼网箱养殖过程中,投喂颗粒饲料引发的环境污染程度高于冰鲜饵料,两种情形下的AOM沉降影响主要限于距离养殖网箱50~100 m的空间范围。三沙湾内饲喂颗粒饲料引发较高营养物质沉降通量源于较大的AOM沉降量,此现象说明养殖过程中可能存在颗粒饲料过度投喂、饵料利用效率较低等问题,围绕此类问题的针对性研究对于减缓区域内养殖活动的环境影响具有重要意义。  相似文献   

20.
A 28‐week feeding trial was conducted in concrete tanks with Nile tilapia, Oreochromis niloticus (L.) with an average initial weight and length of 61.9±6.03 (g fish?1) and 17.6±0.45 (cm fish?1), respectively, to examine the effect of two protein levels and three feeding levels (% body weight (BW) day?1) on growth performance, production traits and body composition. Twelve 4‐m3 concrete tanks (2 × 2 × 1.25 m, long, width and height) were each stocked with 100 fish and fed diets containing either 25% or 30% crude protein at rates of 1%, 2% and 3% BW daily (2 × 3 factorial experiment). The results revealed that there was no significant increase in growth rate with increasing dietary protein levels, whereas there was significant increase in growth rate with increasing feeding levels (P≤0.05). The same trend was also observed for mean BW (g), mean body length (cm), production rate (kg m?3), specific growth rate (SGR % day?1), feed conversion ratio (FCR), condition factor (K) and survival rate (%). The best final mean BW (g), final mean body length (cm), SGR (% day?1), FCR, K, production rate (kg m?3) and survival rate (%) were recorded in groups of fish fed with 25% dietary protein at the 2% feeding level. Whole fish fat and energy contents were not significantly influenced (P>0.05) by protein levels and feeding levels. Protein and ash contents were significantly (P≤0.05) influenced by feeding level, but not by dietary protein level. Economic evaluation indicated that dietary protein 25% (diet A) at the 2% BW day?1 feeding level was the most cost‐effective and affordable feed strategy for farmers. We conclude that a 25% protein diet fed at 2% BW day?1 is recommended for adult Nile tilapia reared in concrete tanks.  相似文献   

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