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1.
In the present study, the influence of high stocking density and food deprivation on red porgy (Pagrus pagrus L.) energy metabolism was investigated after 14 and 21?days assessing plasmatic, hepatic, and muscular parameters. Specimens were submitted to four different experimental conditions: (1) fed fish under low stocking density (4?kg?m?3, LSD-F); (2) food-deprived fish under low stocking density (LSD-FD); (3) fed fish under high stocking density (50?kg?m?3, HSD-F); and (4) food-deprived fish under high stocking density (HSD-FD). At plasmatic level, cortisol concentration enhanced in fish maintained under HSD condition, with higher effect in fed fish, whereas FD condition decreased values of lactate, protein, and triglycerides. In liver, significant increases in triglyceride levels, together with a decrease in glycogen values, were observed in FD specimens. Furthermore, a weak effect of density in fed fish was observed, with decreasing hepatic glycogen. In white muscle, aminoacid and triglyceride values diminished in FD group, while increased in specimens submitted to HSD condition. Our results suggested an enhancement in P. pagrus gluconeogenic and glycogenolytic potential when submitted to HSD and FD conditions to cope reallocation of metabolic energy due to these different stress situations.  相似文献   

2.
Fish gills are the vital multifunctional organ in direct contact with external environment. Therefore, activation of the cytoprotective mechanisms to maintain branchial cell viability is important for fish upon stresses. Salinity is one of the major factors strongly affecting cellular and organismal functions. Reduction of ambient salinity may occur in coral reef and leads to osmotic stress for reef-associated stenohaline fish. However, the physiological responses to salinity stress in reef-associated fish were not examined substantially. With this regard, the physiological parameters and the responses of protein quality control (PQC) and osmoregulatory mechanisms in gills of seawater (SW; 33–35 ‰)- and brackish water (BW; 20 ‰)-acclimated blue-green damselfish (Chromis viridis) were explored. The results showed that the examined physiological parameters were maintained within certain physiological ranges in C. viridis acclimated to different salinities. In PQC mechanism, expression of heat-shock protein (HSP) 90, 70, and 60 elevated in response to BW acclimation while the levels of ubiquitin-conjugated proteins were similar between the two groups. Thus, it was presumed that upregulation of HSPs was sufficient to prevent the accumulation of aggregated proteins for maintaining the protein quality and viability of gill cells when C. viridis were acclimated to BW. Moreover, gill Na+/K+-ATPase expression and protein amounts of basolaterally located Na+/K+/2Cl? cotransporter were higher in SW fish than in BW fish. Taken together, this study showed that the cytoprotective and osmoregulatory mechanisms of blue-green damselfish were functionally activated and modulated to withstand the challenge of reduction in salinity for maintaining physiological homeostasis.  相似文献   

3.
Impact of osmoregulation on plasma sex steroid levels and gonadal histo‐architecture was monitored to elucidate the effects of deviation from habitat salinity on gonadal recrudescence in an active reproductive season of an euryhaline fish Etroplus suratensis (pearlspot). Fish were maintained in three different salinities of 0 ppt Fresh Water (FW), 15 ppt Brackish Water (BW) and 30 ppt Sea Water (SW) for a period of 60 days. Plasma osmolality values were found to be significantly highest in SW‐acclimated fish accompanied by highest levels of plasma K? and Cl¯ ions. The progress of gonadal recrudescence was higher in BW followed by FW and SW as evident from the cellular features of gonads and increased level of plasma sex steroids, such as, in case of female and 11‐keto Testosterone and Testosterone in case of males. Plasma cortisol levels were comparatively higher in fish of both sexes in SW group. Significantly high levels of cortisol in SW suggest its role in hypo‐osmoregulation and associated stress. This study clearly reveals that salinity changes during the active reproductive phase can suppress the steroid‐mediated gonad recrudescence maximally under hypo‐osmoregulation in an euryhaline fish.  相似文献   

4.
Effects of daily feeding frequency, water temperature, and stocking density on the growth of tiger puffer, Takifugu rubripes, fry were examined to develop effective techniques to produce tiger puffer in a closed recirculation system. Fish of 4, 14, and 180 g in initial body weight were fed commercial pellet diets once to five times a day to apparent satiation each by hand for 8 or 12 wk at 20 C. Daily feeding frequency did not affect the growth of 14‐ and 180‐g‐size fish. However, the daily feed consumption and weight gain of the 4‐g‐size fish fed three and five times daily were significantly higher than those of fish fed once daily (P < 0.05). Fish of 4 and 50 g in initial body weight were reared with the pellet diet at 15–30 C for 8 wk. The weight gain of fish increased with increasing water temperature up to 25 C and decreased drastically at 30 C for both sizes. Similar trends were observed for feed efficiency, although 4‐g fish had highest efficiency at 20 C. Effects of stocking density on growth were examined with fish of 8, 13, and 100 g in initial body weight. Fish were reared with the pellet diet for 8 or 16 wk at 20 C. Fish were placed in floating net cages in the culture tank, and the stocking density was determined based on the total weight of fish and volume of the net cage. Fish of 8 g in body weight grew up to 35–36 g during the 8‐wk rearing period independent of the stocking density of 8, 15, and 31 kg/m3 at the end of rearing. Final biomass per cage reached 32, 60, and 115 kg/m3 for 13‐g‐size fish, and 10, 18, and 35 kg/m3 for 100‐g‐size fish, and the growth of the fish tended to decrease with increasing stocking density for both sizes.  相似文献   

5.
Effects of salinity on the growth, survival, superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX) and sodium‐potassium adenosine triphosphatase (Na+K+‐ATPase) activities of juvenile golden pompano Trachinotus ovatus were studied under a laboratory condition. Experimental fish were reared at the salinities of 10‰, 18‰, 26‰ and 34‰ for 30 days. Growth and survival of juvenile golden pompano were significantly affected by the rearing salinity. Fish reared at 34‰ achieved the highest specific growth rate, while the highest survival was obtained when fish were cultured at the salinity of 26‰. The highest GPX activity was obtained when fish were cultured at 26‰, and the lowest GPX activity was observed when fish reared at 34‰ salinity. The SOD activities of fish reared at 18‰ and 34‰ were significantly higher than those reared at 10‰ and 26‰. The lowest of Na+K+‐ATPase activity was obtained in fish reared at 34‰, while the highest Na+K+‐ATPase activity was obtained when fish reared at 18‰. Results from present study indicate that juvenile golden pompano can be reared above 18‰ without sacrificing fish survival, and the best growth can be achieved when fish is reared at the salinity of 34‰. The salinity of 10‰ may be too low for juvenile golden pompano as the growth, survival and SOD activity were reduced.  相似文献   

6.
A physiological study was performed to explore the effects in Sphoeroides annulatus (Jenyns 1842) juveniles of exposure to different salinities 10, 17, 23, 29, 35 and 41‰ on oxygen consumption rate (OCR), ammonium excretion rate (AER), the oxygen‐nitrogen atomic ratio (O:N), osmoregulation and Na+/K+‐ATPase expression. The OCR values ranged from 27.9 to 30.9 mg O2 h?1 kg?1, displaying a Type 1 response pattern Kinne (1977). AER ranged from 0.60 to 0.69 mg h?1 kg?1, and O:N values were from 53.12 to 59.26, indicating that the puffers use proteins and lipids as an energy‐substrate. Osmoregulation in S. annulatus was hyposmotic in salinities of 23, 29, 35 and 41‰ and hyperosmotic in a salinity of 10‰. The isosmotic point of the bullseye puffer was 356 mmol kg?1 (10.5‰). The enzyme expression analysis indicates that the fish acclimated to 41‰ had the highest Na+/K+‐ATPase expression level, whereas, the lowest expression level was found close to the isosmotic point. Na+/K+‐ATPase expression in the gills was found to have a U‐shaped relationship with environmental salinity. We conclude that the bullseye puffer is strongly euryhaline and can be cultivated in a wide range of environments that has important economic implications.  相似文献   

7.
The present study was conducted to elucidate the osmoregulatory ability of the fish pearl spot (Etroplus suratensis) to know the scope of this species for aquaculture under various salinities. Juvenile pearl spot were divided into three groups and acclimated to freshwater (FW), brackish water (BW) or seawater (SW) for 15 days. The fish exhibited effective salinity tolerance under osmotic challenges. Although the plasma osmolality and Na+, K+ and Cl? levels increased with the increasing salinities, the parameters remained within the physiological range. The muscle water contents were constant among FW-, BW- and SW-acclimated fish. Two Na+/K+-ATPase α-isoforms (NKA α) were expressed in gills during acclimation in FW, BW and SW. Abundance of one isoform was up-regulated in response to seawater acclimation, suggesting its role in ion secretion similar to NKA α1b, while expression of another isoform was simultaneously up-regulated in response to both FW and SW acclimation, suggesting the presence of isoforms switching phenomenon during acclimation to different salinities. Nevertheless, NKA enzyme activities in the gills of the SW and FW individuals were higher (p < 0.05) than in BW counterparts. Immunohistochemistry revealed that Na+/K+-ATPase immunoreactive (NKA-IR) cells were mainly distributed in the interlamellar region of the gill filaments in FW groups and in the apical portion of the filaments in BW and SW groups. The number of NKA-IR cells in the gills of the FW-acclimated fish was almost similar to that of SW individuals, which exceeded that of the BW individuals. The NKA-IR cells of BW and SW were bigger in size than their FW counterparts. Besides, the relative abundance of branchial Na+/K+/2Cl? co-transporter showed stronger evidence in favor of involvement of this protein in hypo-osmoregulation, requiring ion secretion by the chloride cells. To the best of our knowledge, this is the first study reporting the wide salinity tolerance of E. suratensis involving differential activation of ion transporters and thereby suggesting its potential as candidate for fish farming under different external salinities.  相似文献   

8.
We evaluated the performance of whiteleg shrimp Penaeus vannamei (Boone, 1931) in response to different stocking densities and acclimation periods. Shrimp postlarvae were acclimated from seawater (30 g L?1) to low‐salinity well water (<1.0 g L?1) at a constant hourly reduction rate of 40, 60, 80 and 100 h. After acclimation to low‐salinity well water, postlarvae from each acclimation time treatment were stocked in three replicate tanks at densities of 50, 100, 150 or 200 shrimps m?2 for 12 weeks of growth. Salinity averaged <1.0 g L?1 for each growth study. The different treatments resulted in significant differences in both the final body weight and the survival rate (SR). Shrimp acclimated for 100 h showed substantially improved survival (83%) relative to shrimp acclimated for shorter periods. Shrimp yields for all cultured periods ranged from 0.32 kg m?2 in tanks stocked at 50 m?2 to 1.14 kg m?2 in tanks stocked at 200 m?2. We conclude that whiteleg shrimp can be successfully grown in low‐salinity well water, and that the growth, production output and SRs are significantly higher when shrimp are acclimated for longer periods.  相似文献   

9.
A study was performed to examine the effects of salinity on water quality, fish performance, carcass composition and haemato‐biochemical parameters in juvenile meagre, Argyrosomus regius. Fish (5.0 g) were stocked in fibreglass tanks at four salinity levels: 8‰, 16‰, 24‰ and 32‰, and fed a pelleted diet (47/17 protein/lipid) for 56 days. Results indicated that the growth, feed utilization, carcass composition and haemato‐biochemical parameters of meagre gradually improved with the increase in salinity up to 24‰ and then significantly (p ≤ .05) decreased at 32‰. The survival per cent showed a significant decrease when A. regius exposed to 8‰ salinity. An improvement with 32%, 47% and 34.1% of FCR, protein productive value and energy utilization was detected at 24‰ compared with 8‰ salinity respectively. The highest content of protein and the lowest of lipids were recorded in fish carcass at 24‰ compared with the opposite trend at 8‰ salinity. The 24‰ salinity treatment exhibited the highest value of haemoglobin (4.9 g/dl) and the lowest ratio (0.73) of albumin/globulin. The serum total protein, albumin and globulin were significantly higher at 24‰ and 32‰ salinity than those at 8‰ and 16‰ salinity groups. These findings indicate that 24‰ salinity level might be the best for meagre.  相似文献   

10.
This study was conducted to investigate the effect of stocking density (125 or 200 fish m?3) on the growth performance of three strains of the Nile tilapia, Oreochromis niloticus: the non‐improved strain (NS), the genetically improved farmed tilapia (GIFT) and the Freshwater Aquaculture Center selected tilapia known as the FaST selected line (SL). Each strain and density combination was triplicated in 0.42 m3 fibreglass tanks within a re‐circulating water system. Water temperature was maintained at 29.0±1.0°C. Large Nile tilapia having a mean body weight of 100–110 g were stocked in each tank and hand‐fed four times daily with commercial tilapia pellets (35% protein) for 104 days. Results showed that at the two stocking densities, the GIFT and SL strains showed a significantly higher (P<0.05) mean weight (MWT), daily growth rate (DGR), specific growth rate (SGR), feed conversion ratio (FCR) and gross yield (GY) than the NS. In all three strains, growth performance was negatively affected by stocking density. The lower density (125 fish m?3) treatments had significantly higher MWT, DGR and SGR than the higher density one (200 fish m?3). However, higher FCR and GY were observed at the higher density. Survival rates were high in all treatments and were not affected by strain or density. In general, the SL strain had better growth parameters than the GIFT strain. The findings of this study demonstrated the superior growth performance of the improved strains at both densities compared with the NS. The higher density (200 fish m?3) could be more profitable for the tilapia farms in Kuwait than the lower density of (125 fish m?3) in terms of reduced land cost and facilities, demand on the limited low‐salinity underground water and manpower.  相似文献   

11.
Scale loss is a common occurrence in both wild fish and those in aquaculture production systems, and regeneration of scales has been described in several freshwater species. Relatively little information exists about this process in marine fish, and in the present study, the chronology of scale regeneration was characterized in juvenile sea bass Dicentrarchus labrax, maintained in full seawater (SW; 36 ‰, 11.2 mM Ca2+) or brackish water (BW; 3.5 ‰, 1.1 mM Ca2+). Despite the significant differences in plasma osmolality, plasma calcium (Ca) and phosphorus (P) were similar between SW and BW. Removal of scales (2.25 cm2) did not modify plasma osmolality but a significant reduction in plasma Ca occurred in sea bass in BW during early phases of scale regeneration. Scale Ca and P contents changed during regeneration in SW and BW fish, and in fully regenerated scales, their concentration was comparable to ontogenic scales which had a Ca/P ratio around 1.0. Regenerating scales were first visible at 3 days after removal, and by 6 days, the descaled area was covered with new scales in both SW and BW fish. From this stage onwards, while scale area and mass rose gradually, a rapid accretion of calcium crystals was observed over the basal plate, especially in SW, and Ca and P content per scale increased at a very high rate, decreasing only at the later stages, and between 21 and 30 days the newly formed scales had already ontogenic-like morphometric features. Scale tartrate-resistant acid phosphatase (TRAP) or alkaline phosphatase (ALP) activity was initially similar in SW and BW. However, during regeneration, TRAP was significantly higher in scales of sea bass in SW compared to those in BW where ALP predominated; these differences persisted at 30 days.  相似文献   

12.
To investigate the effects of family, stocking density, and their interaction on mortality, growth rate, and size dispersal in the sea urchin Strongylocentrotus intermedius, 1,440 juveniles from six full‐sib families were exposed to three stocking densities, that is, low stocking density (LD), middle stocking density (MD), and high stocking density (HD), and reared for 10 months in sea‐based suspended cages. The results demonstrated significant family effects on cumulative mortality rate (CMR); specific growth rate for test diameter (SGR for TD); specific growth rate for body weight (SGR for BW); coefficient of variation for body weight at the 10th month (CV for BW10); and significant stocking density effects on SGR for TD, SGR for BW, and CV for BW10. Statistically significant family by stocking density interaction was only found in SGR for TD. A certain degree of family‐ranking inversions occurred in SGR for TD. The present study provides evidence for the existence of family by stocking density interaction on the growth rate of test diameter in the family selection for S. intermedius. More attention should be paid to this interaction effect to select correct parents in S. intermedius.  相似文献   

13.
We examined the effects of cyclic fasting in red porgy (Pagrus pagrus) fed different dietary carnitine levels. Juvenile fish (23.58 ± 3.49 g) were divided into eight groups – four groups were fed every day to apparent satiation, while the other four were fasted for 7 days every 2 weeks. In each feeding regime, two replicates were fed an l ‐carnitine non‐supplemented diet (46 mg kg?1) and the other two groups were fed an l ‐carnitine supplemented diet (630 mg kg?1). Fish fed 630 mg l ‐carnitine accumulated two times more l ‐carnitine in muscle than fish fed 46 mg l ‐carnitine. Cyclic fasting reduced the growth performance and lipid content in the liver. Carnitine supplementation did not affect performance and body composition, but decreased the n‐6 PUFA content. Moreover, the combined effects of fasting and carnitine supplementation were observed on reducing the n‐3 fatty acid content. Areas of steatosis were found in the livers of red porgy, but the results revealed that supplementation of l ‐carnitine in cyclic fasted fish contributed towards a lower degree of vacuolization than in fish fed to apparent satiation. Regardless of the feeding regime applied, the spleen of fish fed the l ‐carnitine‐supplemented diet was haemorrhagic and hyper activation of melanomacrophage cells was observed.  相似文献   

14.
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   

15.
Two feeding trials were conducted to determine the minimum dietary protein level producing maximum growth, and the optimum protein to energy ratio in diets for red porgy (Pagrus pagrus) fingerlings, respectively. In the first trial, six isoenergetic diets were formulated with protein levels ranging from 400 to 650 g kg?1 in increments of 50 g kg?1, and fed for 11 weeks to 2.8 g average initial weight fish. Weight gain, specific growth rate and feed efficiency were significantly higher with diets containing higher protein levels, when compared with dietary levels below 500 g kg?1. The highest protein efficiency ratios were obtained in fish fed 500 g kg?1 dietary protein. The minimum dietary protein level producing maximum fish growth was found to be 500 g kg?1. In the second trial, 15 g average initial weight fish were fed for 12 weeks, six diets containing three different lipid levels (100, 150 and 200 g kg?1) combined with two protein levels (450 and 500 g kg?1). Weight gain values increased when dietary lipids increased from 100 to 150 g kg?1, with a further decrease for 200 g kg?1 lipids in diets; the lowest fish growth being supported by 200 g kg?1 dietary lipids. Fish growth was significantly higher when dietary protein increased from 450 to 500 g kg?1. There was no evidence of a protein‐sparing effect of dietary lipids. Liver protein and lipid contents were low when compared with other fish species. All diet assayed produced high liver glycogen accumulation. The recommended protein and lipid levels in diets for red porgy fingerlings were 500 and 150 g kg?1, respectively.  相似文献   

16.
Two experiments were conducted to evaluate the initial stocking density in larvae of Bay snook, Petenia splendida, and Mexican mojarra, Cichlasoma urophthalmus, using a recirculation system. Five initial stocking densities (0.5, 1, 5, 10, and 20 larvae/L) were evaluated by triplicate for 45 d. Weight and total length (TL) were measured every 15 d, and fish production was calculated for each density. The larvae stocked at the lowest densities (0.5 and 1 larvae/L) presented the highest growth for both species: C. urophthalmus (0.78 g and 45‐mm TL, and 0.76 g and 45‐mm TL, respectively) and P. splendida (0.80 g and 52‐mm TL, and 0.79 g and 49‐mm TL, respectively). However, lowest fish production was recorded (35 and 69 fish per tank, respectively, for C. urophthalmus and 34 and 70 fish per tank, respectively, for P. splendida) compared with those at densities of 5, 10, and 20 larvae/L (336, 584, and 604 fish per tank, respectively, for C. urophthalmus and 341, 679, and 912 fish per tank, respectively, for P. splendida). The polynomial model for biomass production related to the stocking density shows that the optimum stocking densities for C. urophthalmus and P. splendida are 12 and 14 larvae/L, respectively.  相似文献   

17.
To address the preference of mud crab farmers for larger size Scylla serrata juveniles (5.0–10 g body weight or BW; 3.0–5.0 cm internal carapace width or ICW), a study was conducted to compare the growth and survival of crab juveniles (2.0–5.0 g BW; 1.0–3.0 cm ICW) produced a month after stocking of megalopae in net cages when reared further in net cages installed in earthen ponds or when stocked directly in earthen ponds. In a 3 × 2 factorial experiment, three stocking densities (1, 3 and 5 ind m−2), two types of rearing units (net cages or earthen pond) were used. Megalopae were grown to juvenile stage for 30 days in net cages set inside a 4000 m2 brackishwater pond and fed brown mussel (Modiolus metcalfei). Crab juveniles were then transferred to either net cages (mesh size of 1.0 mm) or earthen ponds at three stocking densities. After 1 month, no interaction between stocking density and rearing unit was detected so data were pooled for each stocking density and rearing unit. There were no significant differences in the growth or survival rate of crab juveniles across stocking density treatments. Regardless of stocking density, survival in net cages was higher (77.11±6.62%) than in ponds (40.41±3.59%). Growth, however, was significantly higher for crab juveniles reared in earthen ponds. The range of mean BW of 10.5–16.0 g and an ICW of 3.78–4.33 cm obtained are within the size range preferred by mud crab operators for stocking grow‐out ponds.  相似文献   

18.
The sutchi catfish, Pangasius sutchi (Fowler 1937) was grown at 10 stocking densities in cages suspended in a river‐fed channel during the summer of 2000. Catfish fingerlings (mean length 9.1–9.7 cm and mean weight 5.9–6.7 g) were stocked at densities of 60, 70, 80, 90, 100, 110, 120, 130, 140 and 150 fish m?3. After 150 days, growth and yield parameters were studied and a simple economic analysis was carried out to calculate profitability. The mean gross yield ranged from 15.6±0.27 to 34.5±0.44 kg m?3 and the net yield ranged from 15.2±0.22 to 33.5±0.36 kg m?3 and showed significant variations (P<0.05). The mean weights of fish at harvest were inversely related to stocking density. Both gross and net yields were significantly different and were directly influenced by stocking density but the specific growth rate, survival rate and feed conversion rate were unaffected. Higher stocking density resulted in higher yield per unit of production cost and lower cost per unit of yield. The net revenue increased positively with increasing stocking density. A density of 150 fish m?3 produced the best production and farm economics among the densities tested in this experiment.  相似文献   

19.
This research was conducted to investigate the effect of stocking density on the growth performance and yield of Oreochromis niloticus in cage culture in Lake Kuriftu. The treatments had stocking densities of 50 (50F), 100 (100F), 150 (150F), and 200 (200F) fish per m?3. All treatments were in duplicate. Juveniles with an average weight of 45. 76±0.25 g were stocked in the treatments. The fish were fed a composite mixture of mill sweeping, cotton seed, and Bora food complex at 2% of their body weight twice per day using feeding trays for 150 days in powdered form. The growth performance of O. niloticus was density dependent. The final mean weight of O. niloticus ranged 147.76±0.28–219.71±1.42 g and the mean daily weight gain was 0.69±0.01–1.15±0.02 g day?1. Fish held in cages with lower density were heavier than the ones held at higher densities, and showed higher weight gain and daily weight gain. The most effective stocking density, in terms of growth parameters, was 50 fish m?3. The gross yield (4.5–20.55 kg cage?1) showed a significant difference with increasing stocking density (P<0.05). Moreover, the apparent food conversion ratio (2.48–7.22) was significantly affected by stocking density (P<0.05). However, survival rate was not affected by stocking density (P>0.05). It can be concluded that the most effective stocking densities were at 50 fish m?3 cage for larger size fish demand in a short period and 200 fish m?3 for higher gross production with supplementary feed.  相似文献   

20.
Two consecutive experiments were conducted to study the effects of stocking density on growth, food utilization, production and farming profitability of Nile tilapia (Oreochromis niloticus) fingerlings (initial mean weight: 16.2 ± 0.2 g) fed Azolla, as a main component in diet. In experiment 1, fish were hand‐fed twice daily with three isonitrogenous (28.5% crude protein) and isocaloric (14.5 kJ g−1) diets A30, A35 and A40 containing 30%, 35% and 40%Azolla, respectively, for 90 days. Diets were formulated by mixing Azolla with locally available by‐products. No significant differences were found in growth parameters and production (P>0.05). Total investment cost was significantly higher with A30 (P<0.05), but same profitability values were obtained with all diets (P>0.05). In experiment 2, three stocking densities, 1, 3 and 5 m−2, were assigned to three treatments T1, T2 and T3 respectively. Fish were hand‐fed twice daily with diet A40. The final mean weight (89.53–115.12 g), the mean weight gain (0.81–1.10 g day−1), the specific growth rate (1.90–2.20% day−1) and the apparent food conversion ratio (1.29–1.58) were affected by stocking density, with significant difference (P<0.05) at 5 m−2, compared with the other densities. Stocking density did not affect survival rate (P>0.05). Yield and annual production increased with increasing stocking density, ranging from 7.10 ± 0.90 to 25.01 ± 1.84 kg are−1 and 28.79 ± 3.66 to 101.42 ± 7.48 kg are−1 year−1, respectively, with significant differences between all densities (P<0.05). Higher stocking density resulted in higher gross return and lower cost of fish production, with significant variations (P<0.05). The net return increased with increasing stocking density (P<0.05). However, both densities of 3 and 5 m−2 produced the same profitability values. On the basis of growth values and economic return, it was concluded that Nile tilapia could be raised at a density of 3 fish m−2 with A40 to improve production and generate profit for nutritional security and poverty alleviation in rural areas.  相似文献   

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