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1.
In this study, we have tested the effect of seaweed stocking density in an experimental seaweed biofilter using the economically important red seaweed Hydropuntia cornea integrated with the cultivation of the pink shrimp Farfantepenaeus brasiliensis. Nutrient removal efficiency was evaluated in relation to seaweed stocking density (2.5, 4, 6 and 8 g fw L?1). Total ammonia nitrogen (TAN) was the main nitrogen source excreted by F. brasiliensis, with concentrations ranging from 41.6 to 65 μM of NH4+‐N. H. cornea specific growth rates ranged from 0.8 ± 0.2 to 1.4 ± 0.5% day?1 with lowest growth rates at higher seaweed stocking density (8 g fw L?1). Nutrient removal was positively correlated with the cultivation densities in the system. TAN removal efficiency increased from 61 to 88.5% with increasing seaweed stocking density. Changes in the chemical composition of the seaweed were analysed and correlated with nutrient enrichment from shrimp effluent. The red seaweed H. cornea can be cultured and used to remove nutrients from shrimp effluents in an integrated multi‐trophic aquaculture system applied to a closed recirculation system. Recirculation through seaweed biofilters in land‐based intensive aquaculture farms can also be a tool to increase recirculation practices and establish full recirculation aquaculture systems (RAS) with all their known associated benefits.  相似文献   

2.
Empirical data on ammonia excretion rates were compiled from several published and unpublished growth studies on post-smolt Atlantic salmon, Salmo salar L. Fish in all studies were fed to satiation with commercially produced high-energy diets (ME = 18–19 MJ kg-1) with a protein content of 40–45%. About 35 ± 3% (mean SE) of the nitrogen supplied to fish was excreted as total ammonia (TAN = NH3-N + NH4+-N). The results of a linear regression analysis of N intake to N excretion demonstrated, however, that TAN excretion rates could be divided into two components: TANexcretion [g N kg fish-1 day-1] = 0.036 + 0.26 Nintake [g N kg fish-1 day-1]. The intercept of the regression equation indicates that the endogenous TAN excretion rates in post-smolts could be estimated as 36 mg TAN kg fish-1 day-1, and about 26% of the nitrogen supplied to the fish was excreted postprandially. This postprandial TAN excretion was lower than that from other salmonid species fed low-energy diets. The daily maximum TAN excretion rate was about 43% higher than daily mean values, which agree with several studies. The ammonia quotient (A.Q.) measured was independent of the nitrogen supplied, and was calculated as 0.112. The outputs from the present model were compared to those from other ammonia excretion models.  相似文献   

3.
Stressful husbandry conditions are likely to affect growth and amino acid metabolism in fish. In this study, chronic ammonia exposure was used to test the effects of a stressor on growth and amino acid metabolism of Senegalese sole juveniles. The fish were exposed for 52 days to 11.6 mg L−1 [low‐TAN (L‐TAN)] or 23.2 mg L−1 [high‐TAN (H‐TAN)] of total ammonia nitrogen (TAN), or to 0 mg L−1 (Control). Growth in L‐TAN groups was slightly but significantly different from the Control groups [relative growth rate (RGR=0.35±0.13 and 0.52±0.23% day−1 respectively)]. In H‐TAN groups, growth was severely affected (RGR=0.01±0.13% day−1). Stress parameters (plasma cortisol and glucose) showed slight or no significant differences between treatments. Plasma free amino acid (FAA) concentrations were affected after H‐TAN treatment. Increases in glutamine and aspartate concentrations in H‐TAN fish suggest alterations in amino acid metabolism related to nitrogen excretion processes. Some of the changes in FAA concentrations also suggest mobilization to energy supply and synthesis of metabolites related to stress response. Therefore, Senegalese sole seem to adapt to the L‐TAN concentration tested, but the H‐TAN concentration reduced growth and affected amino acid metabolism.  相似文献   

4.
A comprehensive acute toxicity trial was conducted using a static water system to study the toxic effect of ammonia on haematology and enzyme profiles of Cirrhinus mrigala H. The LC50 of total ammonia‐nitrogen (TAN) was 11.8 mg L?1 TAN (1.029 mg L?1 NH3‐N). The sub‐lethal test revealed that with increasing concentration of TAN, the total erythrocyte counts were reduced in lower concentrations (1–4 mg L?1 TAN) followed by higher levels in fish exposed to higher concentrations (8–16 mg L?1 TAN). In contrast, the total leucocyte counts were opposite. With increasing concentration of TAN, haemoglobin and serum protein content were reduced, whereas the blood glucose level increased. As the concentration of ammonia increased, there was a reduction in acetylecholinesterase activity in the brain and liver; alkaline phosphatase activity in the serum, brain and gill; and acid phosphatase (ACP) activity in the gill. The activity of lactate dehydrogenase in the gill, liver, kidney and brain increased with increased concentration of ammonia. In addition, activities of ACP in the serum and brain, alanine aminotransferase in the serum, brain and gill, and aspartate aminotransferase in the serum, brain and gill were increased.  相似文献   

5.
The study investigated the growth performance of abalone from juvenile to marketable size in a commercial-scale recirculating aquaculture system. The rearing system consisted of 12 raceways (4.0 × 0.8 × 0.6 m) with a protein skimmer and a submerged biofilter for juveniles and 10 raceways (6.6 × 1.3 × 0.6 m) with a protein skimmer and a trickling biofilter for on-growing. Sea mustard (Undaria pinnatifida) and kelp (Laminaria japonica) were fed to the abalone. The total weight of abalone in the recirculating aquaculture system at the juvenile stage increased from 22.0 kg (average shell length 24.5 mm) to 75.5 kg (average shell length 42.5 mm) after 180 days. Feed conversion ratios increased slightly from 13.7 for the first 90 days to 16.3 thereafter. The shell growth rate of juvenile abalone between 24.5 mm and 34.8 mm was 3.4 mm month−1, while for juveniles between 34.8 mm and 42.5 mm it was 2.6 mm month−1. The total weight of abalone in the recirculating aquaculture system for the on-growing stage increased from 100.0 kg (average shell length 44.0 mm) to 433.3 kg (average shell length 72.7 mm) after 570 days. The feed conversion ratios for the first 173 days, the next 320 days, and the last 570 days were 19.6, 22.1, and 24.8, respectively. The growth rate of the average shell length during the on-growing period was 1.5 mm month−1. Total ammonia nitrogen (TAN) concentrations were stabilized below 0.12 mg l−1 in the juvenile recirculating system and 0.14 mg l−1 in the on-growing recirculating system after conditioning of the biofilters.  相似文献   

6.
The tolerance of Litopenaeus vannamei larvae to increasing concentrations of total ammonia nitrogen (TAN) using a short‐term static renewal method at 26°C, 34 g L?1 salinity and pH 8.5 was assessed. The median lethal concentration (24 h LC50) for TAN in zoea (1‐2‐3), mysis (1‐2‐3) and postlarvae 1 were, respectively, 4.2‐9.9‐16.0; 19.0‐17.3‐17.5 and 13.2 mg L?1TAN (0.6‐1.5‐2.4; 2.8‐2.5‐2.6 and 1.9 mg L?1 NH3‐N). The LC50 values obtained in this study suggest that zoeal and post‐larval stages are more sensitive to 24 h ammonia exposure than the mysis stage of L. vannamei larvae. On the basis of the ammonia toxicity level (24 h LC50) at zoea 1, we recommend that this level does not exceed 0.42 mg L?1 TAN – equivalent to 0.06 mg L?1 NH3‐N – to reduce ammonia toxicity during the rearing of L. vannamei larvae.  相似文献   

7.
This study determined the digestibility of nitrogen and phosphorus, and the excretion rate of different‐sized groups of milkfish fed a commercial diet, a SEAFDEC formulated diet or lab‐lab (natural food‐based diet). Fish (31.2–263.0 g) were stocked in 12 units of 300‐L fibreglass tanks filled with aerated seawater. The postprandial total ammonia‐nitrogen (TAN) and phosphate (PO4‐P) excretion of fish were estimated from changes in TAN and PO4‐P concentrations in water for 24 h. Digestibility was determined from the nitrogen, phosphorus and Cr2O3 content of the diets, and pooled faeces after the fish had been fed diets marked with chromic oxide. TAN excretion rate (mg TAN kg?1 fish day?1) was significantly lowest (P < 0.05) in medium to very big fish fed the lab‐lab diet (60.8–124.4) and highest in small and medium fish fed the SEAFDEC diet (333.3–331.6) and small fish fed the commercial diet (280.1). Regardless of size, fish fed lab‐lab excreted (mg PO4‐P kg?1 fish day?1) significantly lower PO4‐P (36.2) but did not differ with fish fed the commercial diet (64.8). Excretion rates decreased exponentially as fish weight increased but positively increased with feed ration. Excretion pattern of milkfish revealed two peaks: the first peak occurred 6 h after feeding and the second peak at 18 h for TAN and 21 h for PO4‐P, coinciding with the start of the daylight hours. TAN and PO4‐P excretion accounted for 20.5–34.6% of total N consumed and 18.7–42.6% of P consumed respectively. Approximately 27.9–42.5% of N consumed and 47.2–58.5% of P consumed were lost as faeces. Total nutrient losses were lower using the lab‐lab diet (0.31 g N and 0.14 g P kg?1 fish) compared with the formulated diets (0.47–0.48 g N and 0.17–0.19 g P kg?1 fish); the losses decreased per kg of fish as fish size increased. Results suggest that the diet and size of fish influence wastage of N and P to the environment with greater losses in small fish and when artificial diets are used. Such measurements will provide valuable information for the preparation of N and P budgets for milkfish in grow‐out systems.  相似文献   

8.
The pink shrimp Farfantepenaeus brasiliensis is native in southern Brazil and is potentially suited for aquaculture. Under intensive culture, the accumulation of nitrogenous compounds results from excretion by the shrimp and from the processes of feed decomposition and nitrification. The objective of this study was to evaluate ammonia, nitrite, and nitrate toxicity effects on oxygen consumption of juvenile pink shrimp. Shrimps (initial weight 0.7 ± 0.15 g) were exposed over a period of 30 days to 50%, 100%, and 200% of the safe levels of total ammonia (TAN = 0.88 mg/L), nitrite (NO2? = 10.59 mg/L), and nitrate (NO3? = 91.20 mg/L) for the species. The specimens were individually collected and placed in respirometry chambers, where the oxygen consumption was measured over a period of two hours. Throughout the experiment there was no significant difference (p > 0.05) among treatments in terms of survival and growth. The pink shrimp juveniles exposed to nitrogen concentrations of 200% of the nitrite and nitrate safe level showed the highest oxygen consumption (p < 0.05).  相似文献   

9.
White spot disease is caused by a highly virulent pathogen, the white spot syndrome virus (WSSV). The disease is usually triggered by changes in environmental parameters causing severe losses to the shrimp industry. This study was undertaken to quantify the relative WSSV load in shrimp exposed to ammonia, using a TaqMan‐based real‐time PCR, and their subsequent susceptibility to WSSV. Shrimp were exposed to different levels of total ammonia nitrogen (TAN) (8.1, 3.8 and 1.1 mg L?1) for 10 days and challenged with WSSV by feeding WSSV‐positive shrimp. WSSV was detected simultaneously in haemolymph, gills and pereopods at four hours post‐infection. The TaqMan real‐time PCR assay showed a highly dynamic detection limit that spanned over 6 log10 concentrations of DNA and high reproducibility (standard deviation 0.33–1.42) and small correlation of variability (CV) (1.89–3.85%). Shrimp exposed to ammonia had significantly higher (P < 0.01) WSSV load compared to the positive control, which was not exposed to ammonia. Shrimp exposed to 8.1 mg L?1 of TAN had the highest (P < 0.01) WSSV load in all three organs in comparison with those exposed to 3.8 and 1.1 mg L?1 of TAN. However, haemolymph had significantly higher (P < 0.01) viral load compared to the gills and pereopods. Results showed that shrimp exposed to ammonia levels as low as 1.1 mg L?1 (TAN) had increased susceptibility to WSSV.  相似文献   

10.
The effects of alternate starvation and refeeding on food consumption and compensatory growth of hatchery‐bred abalone, Haliotis asinina (Linnaeus), were determined. Two groups of abalone juveniles (mean shell length = 29 mm, body weight = 5 g) were alternately starved and refed a macro‐alga, Gracilariopsis bailinae at equal duration (5/5 or 10/10) over 140 days. A control group (FR) was fed the seaweed ad libitum throughout a 200‐day experimental period. Starved and refed abalone showed slower growth rates (DGR, 63 and 70 mg/day in the 5/5 and 10/10 groups respectively), as a result of reduced food intake (DFI 15% and 16% day?1 respectively), after repeated starvation and refeeding cycles. Percentage weight gains (5/5 = 196%, 10/10 = 177%) were significantly lower than that of the control (397%). When refed continuously over 60 days, the starved groups exhibited increased DFI and fed at the rate of 24% and 25% day?1, which were not significantly different from that of the control at 26% day?1. At the end of the experiment, no significant differences were observed among three treatments in terms of shell length (range: 46–48 mm), body weight (range 25–28 g), % weight gain (392–465%) and per cent survival (range 87–98%). The results indicated that H. asinina had a complete compensatory growth following a return to full rations after a series of intermittent starvation and refeeding cycles.  相似文献   

11.
Three terrestrial leaf meals, Carica papaya, Leucaena leucocephala, Moringa oliefera and a freshwater aquatic fern, Azolla pinnata were evaluated as potential ingredients for farmed abalone diet. All diets were formulated to contain 27% crude protein, 13% of which was contributed by the various leaf meals. Fresh seaweed Gracilariopsis bailinae served as the control feed. Juvenile Haliotis asinina (mean body weight=13.4±1.6 g, mean shell length= 38.8±1.4 mm) were fed the diets at 2–3% of the body weight day–1. Seaweed was given at 30% of body weight day–1. After 120 days of feeding, abalone fed M. oliefera, A. pinnata‐based diets, and fresh G. bailinae had significantly higher (P<0.01) specific growth rates (SGR%) than abalone fed the L. leucocephala‐based diet. Abalone fed the M. oliefera‐based diet had a better growth rate in terms of shell length (P<0.05) compared with those fed the L. leucocephala‐based diet but not with those in other treatments. Furthermore, protein productive value (PPV) of H. asinina was significantly higher when fed the M. oliefera‐based diet compared with all other treatments (P<0.002). Survival was generally high (80–100%) with no significant differences among treatments. Abalone fed the M. oliefera‐based diet showed significantly higher carcass protein (70% dry weight) and lipid (5%) than the other treatments. Moringa oliefera leaf meal and freshwater aquatic fern (A. pinnata) are promising alternative feed ingredients for practical diet for farmed abalone as these are locally available year‐round in the Philippines.  相似文献   

12.
This study investigated the ability of the brown sea cucumber, Stichopus (Australostichopus) mollis, to grow on diets made from aquaculture waste. Weight‐standardized rates (ingestion, assimilation, respiration, ammonia excretion, and fecal excretion) of small (juvenile), medium (mature), and large (mature) sea cucumbers were measured and energy budgets constructed to quantify their growth rates when offered three different diets at 14, 16, and 18 C. Three types of diet were offered: uneaten abalone food (diet A) and two types of abalone feces, one where abalone were fed 50% Macrocystis pyrifera and 50% Undaria pinnatifida macroalgae (diet B) and the other where abalone were fed 25% M. pyrifera, 25% U. pinnatifida, and 50% Adam & Amos Abalone Food, where the latter is an industry standard diet (diet C). The organic contents of the diets were much higher than natural sediments and varied such that diet A (76.40%) > diet B (54.50%) > diet C (37.00%). Diet had a significant effect on S. mollis ingestion rates, assimilation efficiencies, and consequently energy budgets and growth rates. Greater quantities of organic matter (OM) from diet A and diet B were ingested and assimilated by the sea cucumbers compared with the OM in diet C. The energy budgets indicated that after taking routine metabolism into account, all sizes of sea cucumbers had energy to allocate to growth when offered diet A and diet B, but only juveniles had energy to allocate to growth when offered diet C. Fecal excretion rates when offered diet A and diet C at 14 C were greater than those at 18 C, but neither was significantly different from that at 16 C. Ammonia excretion rates increased nonlinearly with temperature for small and medium sea cucumbers but not for large sea cucumbers. Weight‐standardized respiration rates increased with temperature and unexpectedly with animal size, which may have been because of the narrow weight range of test animals biasing the results. These results suggest that industry standard type abalone waste lacks sufficient energy to meet the metabolic requirements of mature sea cucumbers but that growing juveniles on these wastes appears to be feasible and warrants further investigation.  相似文献   

13.
Ongoing research in recirculation aquaculture focuses on evaluating and improving the purification potential of different types of filters. Algal Turf Scrubber (ATS) are special as they combine sedimentation and biofiltration. An ATS was subjected to high nutrient loads of catfish effluent to examine the effect of total suspended solids (TSS), sludge accumulation and nutrient loading rate on total ammonia nitrogen (TAN), nitrite and nitrate removal. Nutrient removal rates were not affected at TSS concentration of up to 0.08 g L?1 (P > 0.05). TAN removal rate was higher (0.656 ± 0.088 g m?² day?1 TAN) in young biofilm than (0.302 ± 0.098 g m?² day?1 TAN) in mature biofilm at loading rates of 3.81 and 3.76 g m?² day?1 TAN (P < 0.05), respectively, which were considered close to maximum loading. TAN removal increased with TAN loading, which increased with hydraulic loading rate. There was no significant difference in removal rate for both nitrite and nitrate between young and mature biofilms (P > 0.05). The ATS ably removed nitrogen at high rates from catfish effluent at high loading rates. ATS‐based nitrogen removal exhibits high potential for use with high feed loads in intensive aquaculture.  相似文献   

14.
Argyrosomus regius (3.0 ± 0.9 g) were exposed to different concentrations of ammonia in a series of acute toxicity tests by the static renewal method at three temperature levels (18, 22 and 26°C) at a pH of 8.2. Low temperature clearly increased the tolerance of the fish to total ammonia nitrogen (TAN) and unionized ammonia (NH3) (P < 0.05). While the 96‐h LC50 values of TAN were 19.79, 10.39 and 5.06 mg L?1, the 96‐h LC50 of NH3 were 1.00, 0.70 and 0.44 mg L?1 at 18, 22 and 26°C respectively. The safe levels of NH3 for A. regius was estimated to be 0.10, 0.07 and 0.04 mg L?1 at 18, 22 and 26°C respectively (P < 0.05). This study clearly indicates that A. regius is more sensitive to ammonia than other marine fish species cultured on the Mediterranean and Eastern Atlantic coasts.  相似文献   

15.
Ammonia toxicity and morphological changes in gills of juvenile Japanese flounder Paralichthys olivaceus (5.76 ± 0.12 g) were investigated when fish were separately exposed to normal dissolved oxygen (DO) at 6.5 ± 0.5 mg L?1 and supersaturated oxygen at 16.0 ± 2.0 mg L?1 at different ammonia concentrations. Under normal oxygen, ammonia concentrations were tested from 0.04 (control) to 93.3 mg L?1 total ammonia nitrogen (TAN), whereas under oxygen supersaturation, ammonia concentrations ranged from 0.04 (control) to 226.7 mg L?1 TAN in the trial. After exposure to ammonia for 96 h, the ammonia LC50 for fish was 62.48 mg L?1 TAN (0.50 mg L?1 NH3–N) at normal oxygen and 160.71 mg L?1 TAN (0.65 mg L?1 NH3–N) at oxygen supersaturation. Light microscopic observations confirmed that gill damage in normal oxygen was more profound than in oxygen supersaturation when fish were exposed to the same level of TAN (93.3 mg L?1). Furthermore, electron microscopic scanning also showed more crimple, retraction and fibrosis on the secondary lamella surface in fish exposed to normal oxygen than those in fish exposed to supersaturated oxygen at the same TAN (93.3 mg L?1). This study suggests that supersaturated oxygen can increase ammonia tolerance in Japanese flounder through reducing gill damage by ammonia, which partially explains the merit of using pure oxygen injection in intensive fish farming.  相似文献   

16.
The effects of nitrite concentration on larval development of Amazon river prawn, Macrobrachium amazonicum, were studied in laboratory. In Experiment 1, larvae were reared in 600‐mL glass beakers filled with 300‐mL water with nitrite concentration of 0, 0.2, 0.4, 0.8 and 1.6 mg/L NO2‐N. In Experiment 2, total ammonia nitrogen (TAN, NH3‐N + NH4‐N) excretion were analyzed in zoea (Z) I, III, VII and IX exposed to 0, 0.4, 0.8 and 1.6 mg/L NO2‐N. In both experiments each treatment was conducted in five replicates. The experiments were carried out in test solutions at 10 salinity, constant temperature 30 C and 12:12 h daylight : darkness regime. Survival, productivity, weight gain and larval stage index decreased linearly with increasing ambient nitrite concentration. However, there was no significant difference among larvae reared at concentration ranging from 0 to 0.8 mg/L NO2‐N by ANOVA in all variables. Individual ammonia‐N and mass‐specific ammonia‐N excretion increased in ZI and ZIX, was almost constant in ZIII and decreased in ZVII from 0 to 1.6 mg/L NO2‐N. The relationship between individual TAN and body mass suggested that 1.6 mg/L NO2‐N stress the larvae. Despite of the effects of nitrite on larvae follow a dose‐dependent response and shows large variability among individuals, levels below 0.8 mg/L may be used as a general reference in commercial hatcheries, which should be applied carefully.  相似文献   

17.
The effects of total ammonia (TAN; NH4++ NH3) on the reproductive performance, survival, growth and moulting of wild Penaeus paulensis (Pérez-Farfante) broodstock were studied to determine optimal rearing conditions. Based on previously established ‘safe levels’ for P. paulensis adults (3.4 and 4.2 mg L?1 TAN), two 46-day trials were performed. In the first trial, six females and four males were stocked in 700-L tanks under three treatments (0.37, 2.53 and 6.86 mg L?1 TAN) with at least two replicates per treatment. In trial 2, ammonia levels of 0.68, 1.55 and 2.62 mg L?1 TAN were assigned to three 6000-L tanks, each stocked with 36 females and 24 males. Ammonia only influenced the survival of females and the growth of males exposed to 6.86 mg L?1 TAN (0.21 mg L?1 NH3). No further effects of ammonia on moulting and reproductive performance were detected. The present results demonstrate that up to 2.62 mg L?1 TAN, coupled with 0.07 mg L?1 NH3 and 1.50 mg L?1 NO2, will not impair reproductive performance of P. paulensis. It is suggested that water quality for the maturation of P. paulensis may be maintained through lower daily water exchange rates instead of the usual high levels (150-300%) employed on penaeid shrimp maturation systems.  相似文献   

18.
Yucca schidigera is a plant native to southwestern USA and Mexico. Its extract has been used in the livestock industry to control ammonia accumulation in animal holding facilities, and to reduce ammonia concentration in animal excreta. This study investigated the potential and effectiveness of Y. schidigera extract (YUPE) for ammonia reduction in seawater. A dose–response experiment was conducted to determine the effect of different concentrations of YUPE at 0, 18, 36, 72 and 108 mg L−1 on total ammonia nitrogen (TAN) at 1, 3 and 9 mg L−1. At a higher YUPE dosage rate, higher TAN reduction was observed, and TAN reduction was highest during the first 12 h, and decreased thereafter. A stepwise multiple linear regression that included the initial TAN, YUPE concentration and time was developed, which accurately predicted empirical TAN concentrations. Applications of this model for ammonia management strategies were formulated for hypothetical tiger prawn (Penaeus monodon) rearing conditions. YUPE's efficacy for ammonia reduction, natural origin and safety make YUPE a potentially suitable compound for water quality management in mariculture.  相似文献   

19.
A 117‐day feeding trial was conducted in ponds with juvenile Australian red claw crayfish (Cherax quadricarinatus) to evaluate the effects on growth, survival, body composition, and processing traits when fed diets containing three different protein levels (22%, 32%, and 42%), and the effects of feeding these diets on pond water quality. Juvenile crayfish (mean weight of 4.6±2.2 g) were randomly stocked into nine 0.02‐ha ponds at a rate of 500 per pond (25 000 ha?1), and each diet was fed to three ponds. There were two feedings per day, each consisting of one‐half of the total daily ration. At harvest, there were no significant differences (P>0.05) in the individual weight, percentage weight gain, or specific growth rate among treatments, which averaged 75.3 g, 1535%, and 2.38% day?1 respectively. Red claw fed the 42% crude protein diet had significantly higher (P<0.05) feed conversion ratio (7.34) compared with crayfish fed diets containing 22% (5.18) or 32% (5.13) crude protein, and had significantly lower percentage survival (46.1%) compared with red claw fed diets with 22% (61.1%) or 32% (58.2%) protein. Total yield was significantly lower (P<0.05) in red claw fed the 42% protein diet (640 kg ha?1) compared with red claw fed diets containing 22% (920 kg ha?1) or 32% (904 kg ha?1) protein. Mean total ammonia nitrogen (TAN) levels were significantly higher (P<0.05) in ponds with red claw fed the 42% protein diet (0.55 mg L?1) compared with ponds with red claw fed diets containing 22% (0.32 mg L?1) or 32% (0.38 mg L?1) protein. Mean total nitrite concentrations in ponds with red claw fed the 42% protein diet was significantly higher (0.05 mg L?1) compared with red claw fed diets containing 22% (0.01 mg L?1) or 32% (0.02 mg L?1) protein. These results indicate that a practical diet containing 22% (as fed basis) protein may be adequate for pond production of red claw when stocked at the density used in this study, and that a diet containing 42% protein adversely affected levels of TAN and nitrite, possibly reducing overall survival of red claw. Use of a diet with 22% protein may allow red claw producers to reduce diet costs and thereby increase profits.  相似文献   

20.
Haliotis tuberculata coccinea has been identified as a target species for European aquaculture development, in order to fulfil the rising demand for abalone. The effects of different stocking densities on the growth performance, feed utilization and survival of two different initial size groups (30 and 40 mm) of abalones, during the final grow‐out to cocktail/market size (45–60 mm), were determined over a 6‐month period. Trials were performed in abalone cages installed in a commercial open‐sea cages fish farm. Animals were fed the red algae Gracilaria cornea and the green one Ulva rigida, both obtained from a land‐based integrated multi‐trophic aquaculture system. Survival rates were very high (94–98%) regardless the density employed. Sustained high linear growth was recorded both in shell and weight. However, a 17–19% reduction in weight gain was obtained by doubling the initial stocking density, suggesting a higher competition for space or food. Nevertheless, the high growth performance (70–94   μm day?1; 250–372% weight gain) and survival attained, even at high densities, denoted the suitability of the offshore mariculture system as well as the biofilter produced macroalgae for grow‐out culture of H. tuberculata coccinea that overall could reach cocktail/commercial size in only 18–22 months.  相似文献   

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