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1.
The aim of the present study was to evaluate the effect of acute stress and cortisol injection on oocyte final maturation process in female Nile tilapia (Oreochromis niloticus). Handling followed by a prophylactic treatment (0.3?mL?L?1 H2O2, 5?g?L?1 NaCl solution during 30?min) and an environmental change (transfer from a 2?m3 fibreglass square tank to 50?L aquaria) were used as acute stressors and compared to a single cortisol injection (0.5 or 5?mg?kg?1 body weight). For both acute stress and cortisol injection (0.5?mg?kg?1 body weight), serum cortisol level was significantly increased from 2.3 to 134.1?ng?mL?1 1?h post-stress/injection and returned to a resting basal value 24?h after the stress/injection. In fish injected with 5?mg?kg?1 body weight cortisol, mean serum cortisol level reached a peak up to 2500?ng?mL?1 1?h after injection. 63?% of the females (mean body weight: 242?±?4?g) submitted to the acute stress ovulated within 72?h after the stress. In the same way, cortisol injection (5?mg?kg?1 body weight) at the 10th day of the maturation cycle led to a twofold reduction of the time before ovulation compared to vehicle injected control fish. Relative and total fecundity were significantly decreased in females submitted to an acute stress or cortisol injected at 5?mg?kg?1 body weight, but not fertilization or hatching rates. In conclusion, acute stress and cortisol induction exert both positive and negative effects on the final reproductive process in O. niloticus, and cortisol is the endocrine mediator causing these changes.  相似文献   

2.
In order to evaluate impacts of benthic shellfish culture on sediments in the Daguhe Estuary, surface sediments are sampled in February, May, August and November 2009 and the water content and nitrogen content of sediment, accumulation flux of nitrogen are studied. About 40 % of the mudflat in the estuary is used for bottom sowing culture for Manila clam Ruditapes philippinarum. The seeding density is 1.1–1.5 kg m?2 in the estuary if the mean weight of juvenile clam is 0.3–0.5 g. Moreover, the stock density of cultivated clam that can be harvested (with mean weight 8 g) is 450–1,600 individual m?2, and the annual yield of this species of clam is about 3.4 kg m?2. There is significant spatial difference of water content of sediment from February to November, during which the water content in the uncultured mudflat, the cultured mudflat and the river way is 32.07, 43.95 and 37.69 %, respectively. There is no significant spatial difference of TN (total nitrogen) content of sediment, and the TN content in the cultured mudflat, the uncultured mudflat and the river way is 0.26, 0.22 and 0.29 mg g?1, respectively. Moreover, the IN (inorganic nitrogen) content of sediment in the cultured mudflat, the uncultured mudflat and the river way is 0.09, 0.08 and 0.14 mg g?1, which implies that there is no significant spatial difference of IN content. Furthermore, there is no significant spatial difference of EN (exchangeable nitrogen) content of sediment from February to November, during which the EN content in the uncultured mudflat or the river way is about 0.04 μg g?1 and it is 0.03 μg g?1 in the cultured mudflat. Thus, the benthic shellfish culture may increase the water content and there is no significant effect of benthic shellfish culture on nitrogen content. The accumulation flux of TN in the cultured mudflat, the uncultured mudflat and the river way is 0.94, 1.13 and 1.40 mg cm?2 year?1. The accumulation flux of IN in the cultured mudflat, the uncultured mudflat and the river way is 0.31, 0.39 and 0.66 mg cm?2 year?1. Moreover, the accumulation flux of EN in the uncultured mudflat and the river way is nearly equal, which is 0.21 and 0.20 μg cm?2 year?1, respectively. The accumulation flux of EN in the cultured mudflat is 0.10 μg cm?2 year?1. Thus, the benthic shellfish culture in the estuary does not enhance the accumulation of TN or IN. Nevertheless, it may reduce the accumulation of EN. Furthermore, it is cautious to evaluate the effect of benthic shellfish culture on sediments by the nitrogen content only. The accumulation flux of nitrogen may be one better index to evaluate the impact.  相似文献   

3.
This experiment was conducted to study the effects of Bacillus preparations on immunity and antioxidant activities in grass carp. A total of 315 grass carp, with similar initial weight (average weight of fish 45?g), were randomly divided into three groups with three replicates. The control group was fed the basal diet without Bacillus; treatment group 1 was added Bacillus preparation no. 1 with 1?×?108?cfu/m3 per 7?days in culture water and also fed the basal diet; treatment group 2 was fed the basal diet mixed with 0.5?% Bacillus preparation no. 2, and the culture water was added 1?×?108?cfu/m3 Bacillus preparation no. 1 per 7?days. After 4?weeks of culture, 12 grass carp from each replicate were taken randomly for the determination of immune response and oxidization resistance indices. The results showed that compared with control, the level of globulin and IgM of treatment group 2 was significantly increased (P?<?0.05), which was also significantly higher (P?<?0.05) than that of group 1. For the non-specific immunity index, compared with control, the lysozyme activity and complement (C3) content of treatment group 1 significantly increased (P?<?0.05), and the level of myeloperoxidase and C3 of treatment group 2 was significantly higher (P?<?0.05) than that of control, which was also significantly higher (P?<?0.05) than that of group 1. In the serum, compared with the control, the level of total antioxidant activity (T-AOC), antisuperoxide anion free radical (ASAFR) and glutathione (GSH) of two treatment groups was significantly increased (P?<?0.05); GSH content of treatment group 2 was significantly (P?<?0.05) higher than that of treatment group 1 and control. There was no significant difference between T-AOC and ASAFR among the two treatment groups; no significant effect was found on glutathione peroxidase (GSH-Px) and maleic dialdehyde (MDA) among the three groups. In the liver, T-AOC, SOD, ASAFR, GSH-Px and GSH from two treatment groups were significantly higher (P?<?0.05) than those of control; T-AOC, SOD and catalase from treatment group 2 were significantly higher (P?<?0.05) than those of treatment group 1; and MDA of two treatment groups was significantly decreased (P?<?0.05) as compared with the control. The results indicate that Bacillus preparations added into water can increase serum immunoglobulin levels and most of non-specific immune parameters content and enhance the antioxidant ability of grass carp, while adding Bacillus preparation into the water and feed is much better.  相似文献   

4.

The shellfishery of the smooth Venus clam Chionista fluctifraga is not regulated in Mexico. Therefore, information on the ecology of this species and the effects of the fishery on its populations is necessary to inform management. We present results from a comparative analysis of the density, biomass, and size structure of smooth Venus clam populations in an area not subjected to harvest (UH) and two areas under harvest (H1 and H2) in Bahía de San Jorge (Gulf of California). The UH population had a density of 20.8?±?1.4 ind m?2 and a biomass of 392?±?39.7 g m?2 on average; the size range was 3.1–55.5 mm (average 28?±?15.2 mm), and the predominant size class was 40–50 mm. The H1 and H2 populations had, respectively, densities of 14.5?±?9.5 and 7?±?6.8 ind m?2 and biomass of 123.4?±?20.4 and 123.6?±?22.6 g m?2; the size ranges were 2.1–49 and 4.3–48.7 mm (averages 24.5?±?14.3 and 30.1?±?13.2 mm), and the predominant size classes were 0–10 mm and 40–50 mm. Clams in the three populations show an aggregated distribution and live in medium-fine sands (no significant differences in grain size among sites) with oligotrophic water. Although the densities observed in the harvested sites are relatively high, negative effects of the shellfishery are detected. For example, all clam sizes are being harvested, and clams are no longer found in the uppermost zone in harvested sites, with potential impacts on other species. This poses various threats that, together, may decrease the stability of the intertidal ecosystem and affect productivity.

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5.
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   

6.
This study compared the spawning performance of four crosses between the salt‐tolerant tilapia Oreochromis spilurus and the fast‐growing genetically improved farmed tilapia (GIFT) strain of the Nile tilapia Oreochromis niloticus: (1) O. spilurus♀×O. spilurus♂ (SS); (2) Nile ♀× Nile ♂ (NN); (3) Nile ♀×O. spilurus♂ (NS) and (4) O. spilurus♀× Nile ♂ (SN). In each cross, males and females having mean weights of 157 and 115 g, respectively were stocked in 0.43 m3 tanks at a male to female ratio of 1:3. Seeds (unhatched eggs, yolk‐sac fry and free swimming fry) were harvested biweekly for 127 days. Viable spawns resulted from all crosses. The NN cross produced the highest total seeds tank?1 (2890), seeds (kg female)?1 day?1 (48.3), seeds m?2 day?1 (23.3) and seeds female?1 day?1 (7.9), followed by the SS and SN crosses. The NS cross had the lowest fecundity. Lower spawning parameters in the NS and SN crosses may be attributed to the lower social compatibility between the males and females compared with that of the pure parents. The survival and growth of the offspring from the four crosses will be compared in seawater (37–40 g L?1) to assess whether hybrid vigor was produced.  相似文献   

7.
The objective of this study was to assess the effects of stocking density on growth performance, serum biochemical parameters, and muscle texture properties of genetically improved farmed tilapia (Oreochromis niloticus, GIFT). Juvenile GIFT with an average initial weight of 12.54?±?0.45 g (mean?±?SD) were randomly stocked in 16 tanks (80 L) in a recirculation aquaculture system at four densities of 10 (D1), 20 (D2), 30 (D3), and 40 (D4) fish per tank for 56 days, with quadruplicate for each density. There were no significant differences in water temperature among the four treatments (P?>?0.05). D4 had the significantly lowest dissolved oxygen content (5.52 vs 5.69–6.09 mg L?1) (P?>?0.05) and pH (6.63 vs 6.87–7.20) (P?<?0.05). NO2-N and NH4-N concentrations significantly increased with increasing stocking density (P?<?0.05). Weight gain (WG) and specific growth rates (SGR) decreased with increasing stocking density. The lowest WG (617.20 vs 660.45–747.06%), SGR (3.52 vs 3.62–3.81% day?1), and highest feed conversion ratio (1.68 vs 1.53–1.58) were observed in D4. Fish at D4 had significantly lower condition factor (3.11 vs 3.29–3.37%) and survival rate (91.25 vs 97.50%) than those from D1 and D2 (P?<?0.05). With increasing stocking density, serum total cholesterol, triglyceride, and total protein concentrations decreased (P <?0.05) and aspartate aminotransferase and alanine aminotransferase activities increased (P <?0.05). D4 fish had higher moisture content (78.80 vs 76.97%) and lower crude protein content (18.14 vs 19.39%) in muscle than D1 fish (P?<?0.05). Compared to D1 and D2, D3 and D4 had lower muscle hardness (1271.54–1294.07 vs 1465.12–1485.65 g), springiness (0.62–0.65 vs 0.70–0.72), gumminess (857.33–885.32 vs 1058.82–1079.28 g), and chewiness (533.04–577.09 vs 757.53–775.69 g) (P <?0.05). High stocking density resulted in growth inhibition, declines in flesh quality, and disturbance to several serum biochemical parameters.  相似文献   

8.
Provisioning and regulatory ecosystem services of Pacific geoduck clam (Panopea generosa) culture were simulated for an intertidal shellfish farm in Eld Inlet, South Puget Sound, Washington, USA. An individual geoduck clam growth model was developed, based on a well-established framework for modeling bivalve growth and environmental effects (AquaShell?). Geoduck growth performance was then validated and calibrated for the commercial farm. The individual model was incorporated into the Farm Aquaculture Resource Management (FARM) model to simulate the production cycle, economic performance, and environmental effects of intertidal geoduck culture. Both the individual and farm-scale models were implemented using object-oriented programming. The FARM model was then used to evaluate the test farm with respect to its role in reducing eutrophication symptoms, by applying the Assessment of Estuarine Trophic Status (ASSETS) model. Farm production of 17.3 t of clams per 5-year culture cycle is well reproduced by the model (14.4 t). At the current culture density of 21 ind m?2, geoduck farming at the Eld Inlet farm (area: 2684 m2) provides an annual ecosystem service corresponding to 45 Population-Equivalents (PEQ, i.e. loading from humans or equivalent loading from agriculture or industry) in top-down control of eutrophication symptoms. This represents a potential nutrient-credit trading value of over USD 1850 per year, which would add 1.48% to the annual profit (USD 124,900) from the clam sales (i.e. the provisioning service). A scaling exercise applied to the whole of Puget Sound estimated that cultured geoducks provide a significant ecosystem service, of the order of 11,462 PEQ per year (about USD 470,600) in removing primary symptoms of eutrophication, at the level of the whole water body. The modeling tools applied in this study can be used to address both the positive and negative externalities/impacts of shellfish aquaculture practices in the ecosystem and thus the trade-offs of the activity.  相似文献   

9.
The color of Undaria pinnatifida after boiling is an important factor determining its marketable value. Our previous study showed that decreased nutrients and elevated irradiance resulted in increases of lightness and yellowness (i.e., discoloration) of this alga. However, little is known about the optimal levels of nutrients and irradiance required to decrease these color values and the combined effects of these factors and boiling. We conducted two culture experiments to test the effects of nutrients (non-enriched and 1.25, 5, and 25% PESI enriched treatments), irradiance (0, 10, 30, and 180 µmol m?2 s?1), and boiling on lightness L*, redness a*, and yellowness b* of this alga. L* and b* did not differ between non-enriched and 1.25–5% PESI treatments, but were lower in the 25% PESI treatment. L* and b* were lowest at 0–10 µmol m?2 s?1, although negative growth occurred at 0 µmol m?2 s?1. Decreased irradiance had a positive or little effect on a* before boiling, but had a negative effect after boiling. These results suggest that around 25% PESI and 10 µmol m?2 s?1 were the optimal levels to decrease the three color values of this species after boiling.  相似文献   

10.
Stocking density, representing a potential source of long‐term stress, is widely recognized as a critical factor in aquaculture husbandry. Atlantic salmon were reared at low‐density (LSD, ~9.80–18.41 kg m?3, initial to final density), medium‐density (MSD, ~19.62–36.96 kg m?3) and high‐density (HSD, ~28.79–53.54 kg m?3) stocking levels for 66 days to investigate the stress‐induced changes in fish growth and welfare. At the end of the trial, the salmon in HSD group showed significant lower final weight and higher ration level than those in MSD and LSD groups (P < 0.05). The salmon farmed in LSD group had higher special growth rate (SGR) and lower feed conversion ratio (FCR) (P < 0.05). However, stocking density could not affect the mortality, condition factor and coefficient of variation of salmon. The pectoral fin index of salmon in LSD group was significantly higher than that in HSD group (P < 0.05). Fifteen haematological and serum parameters were detected to assess the stress and welfare levels of salmon. The salmon farmed in HSD group had higher glucose (GLU) level and lower Cl?, haemoglobin (HGB) and red blood cell (RBC) concentrations (P < 0.05). Contrast to the pattern of superoxide dismutase (SOD) activity, the cortisol, maleic dialdehyde (MDA) and alkaline phosphatase (ALP) levels of HSD group were higher than those in other two groups (P < 0.05). All these findings will provide a reference for selecting suitable stocking density in Atlantic salmon farming industry.  相似文献   

11.
This study was conducted to compare the effects of shrimp and rabbitfish in mono‐ and polyculture stocked at high biomass on production and environmental conditions in a mesocosm system. Shrimp (14 g) and/or rabbitfish (19 g) were stocked in four treatments with different density but with the same total biomass (236 g m?2), including shrimp monoculture (SM) (17 shrimp m?2), shrimp–fish polyculture (SF) (11 shrimp and 4 rabbitfish m?2), fish–shrimp polyculture (FS) (6 shrimp and 8 rabbitfish m?2) and fish monoculture (FM) (12 rabbitfish m?2). After 10 weeks of experiment, shrimp survival and biomass were low in the treatments where shrimp were dominant (SM, SF), while rabbitfish survival and biomass were high in all the treatments. Shrimp mortality was assumed to be related to an excess of the system carrying capacity (CC). Results suggested that CC is linked to shrimp biomass/density rather than the system eutrophication level. The ecosystem became heterotrophic as daily feed supply was beyond 7 g m?2 per day. This threshold corresponded to the environmental CC of the semi‐intensive shrimp culture system. Under these conditions, the combination of high fish biomass and low shrimp biomass appeared as the most valuable in terms of system performances.  相似文献   

12.
To determine the optimal salinity, stocking density, and algal density for hatchery culture of the Iwagaki oyster Crassostrea nippona larvae, three experiments with salinities of 14, 18, 22, 26, 30, and 34 practical salinity unit (PSU); stocking densities of 0.5, 1, 2, 4, 8, and 12 larvae ml?1; and algal densities of 10, 20, 40, and 100?×?103 cells ml?1 were designed, which included the developmental stages from newly hatched D-larvae to pediveligers. Results showed that larval growth of C. nippona was the fastest at a salinity of 26 PSU, and when salinity was adjusted to a level that was lower or higher than this salinity, survival and growth rate of larvae declined (P <?0.05), resulting both in a decreased mean shell length and a high mortality. Larval growth decreased significantly with increasing stocking density. Larvae reared at 4 larvae ml?1 had the smallest shell length (198.9 μm) and lowest survival rate (7.9%), whereas larvae reared at 0.5 larvae ml?1 had the largest shell length (245 μm) and highest survival rate (66.3%) on day 13. And the shell length of larvae reared at 0.5 and 1 larvae ml?1 was significantly (P?<?0.05) larger than the values in other treatments, except those reared at 2 larvae ml?1 (P?>?0.05). When feeding the single-algal diet of Isochrysis galbana (clone T-ISO), the shell length of larvae increased markedly as the algal density was increased. Larvae reared at the highest algal density (100?×?103 cells ml?1) had the largest mean shell length; however, under the conditions of our experiment, there was no significant difference (P?>?0.05) in growth and survival rates between the treatments at algal densities of 40?×?103 and 100?×?103 cells ml?1. For a large-scale culture, based on the results of this study, a salinity of 26 PSU, stocking density of 0.5–1 larvae ml?1, and algal density of 40?×?103 cells ml?1 are recommended for an early development of C. nippona.  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.
Sperm quality parameters in rainbow trout (Oncorhynchus mykiss) were investigated during normal season spawning (November–January) and out-season spawning (July–August) treated with artificial photoperiod manipulation. Normal spawning males (n?=?15) were kept in an open concrete pond under natural condition. Out-season spawning males (n?=?15) were treated with artificial LED light (50 lm/m2) in a closed concrete pond. In these two experimental groups, five fish were used in each of three spawning periods. The mean weight and body length of males (2?+ years, n?=?30) were 1213.43?±?39.43 g and 45.08?±?0.62 cm, respectively. Sperms were collected from July to August 2016 in the out-season spawning or photoperiod-manipulated group (PG) (water temperature 14.21?±?0.31 °C) and from December 2016 to January 2017, in the normal season spawning group (NG) (water temperature 8.81?±?1.03 °C). Volume of sperm, osmolality of seminal plasma, density of sperm, percentage of motile spermatozoa (MOT), curvilinear velocity (VCL), and duration of motility were measured for each male. Seminal plasma osmolality, density of sperm, and the motility of duration were 358.47?±?37.24 and 308.87?±?44.09, 4.37?±?2.10 and 9.8?±?1.56, and 8.8?±?2.42 and 24.6?±?6.76 in PG and NG, respectively. Fertilization rate was 37.79?±?9.37% and 94.51?±?1.33% in PG and NG, respectively. Sperm quality parameters showed significant differences in most of the cases (p?<?0.05) and fertilization rate at eyed egg stage (150–160 degree-days) was significantly higher in normal season spawning group than the photoperiod-manipulated group (p?<?0.05). Though the rate of fertilization was low in out-season, it was able to get enough gametes in summer using only artificial light having no changes in other parameters.  相似文献   

15.
Quantitative and qualitative analyses of bacterial flora associated with pond water, gills, and intestine of polycultured healthy common carp (Cyprinus carpio) and African catfish (Clarias gariepinus) were carried out and identified to species level where possible. Total viable bacterial counts in the pond water ranged from 9.2?±?5.5?×?103 to 6.6?±?5.1?×?104 colony-forming units (cfu)/mL; in the gill filaments of carp and catfish, 3.3?±?3.8?×?106 to 7.9?±?5.6?×?106 and 1.1?±?4.6?×?105 to 2.3?±?5.2?×?106 cfu/g, respectively; and in the intestine of carp and catfish, 1.4?±?2.9?×?1010 to 1.7?±?6.0?×?1011 and 2.7?±?3.4?×?1010 to 1.0?±?4.5?×?1011 cfu/g, respectively. Gram-negative rod-shaped bacteria dominated the populations: 90% in carp, 89% in catfish, 80% in water, and 86% in the total populations. Altogether, 14 bacterial species of 10 genera were identified in total populations. Pond water bacteria had a reflection on the bacterial composition of the gills and intestine of carp and catfish. Aeromonas hydrophila, Shewanella putrefaciens, Vibrio cholerae, Staphylococcus sp., and Vibrio vulnificus appeared as the common bacteria in the populations, where the first three were highly significantly abundant (P?<?0.0001). Moreover, A. hydrophila was the most significantly dominant bacteria (32%; P?<?0.005) among the total populations. Pantoea sp. and Pasteurella pneumotropica were present only in carp and catfish, respectively, but Corynebacterium urealyticum and Micrococcus sp. were present only in pond water.  相似文献   

16.
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   

17.
  • 1. Despite a heightened global concern for native mussels, fundamental research on mussel ecology in large rivers is lacking. These gaps in knowledge about where mussels occur, and why, are limiting habitat restoration activities.
  • 2. Large‐scale systematic surveys for native mussels in three reaches of the Upper Mississippi River documented mussel communities composed of 16–23 species and ranging from 2.9–4.5 live mussels m?2 that were actively recruiting new cohorts into their populations (87–100% of the species were found as juveniles ?5 years old). Estimates of mean tissue biomass and production in these reaches ranged from 2.1–3.1 g C m?2 and 0.4–0.6 g C m?2 year?1, respectively.
  • 3. Mussels filtered a significant amount of water (range, 0.05–0.07 m3 m?2 d?1) over a 480 km reach of the Upper Mississippi River – amounting to a filtration rate of 53.1 million m3 day?1. The filtration rate of mussels as a percentage of river discharge ranged from 0.5–1.4% at high flows (5% exceedance), from 1.5–4.4% at moderate flows (50% exceedance) and from 4.4–12.2% during low flows (95% exceedance).
  • 4. Collectively, these data suggest that native mussels play an integral role in this ecosystem by sequestering suspended materials that can be used by other benthic organisms. Published in 2011 by John Wiley and Sons, Ltd.
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18.
Redox potential represents the intensity of anaerobic condition in the pond sediment, which may affect the dominant microbial transformations of substances, the toxins production, mineral solubility, as well as the water quality in the sediment–water interface inhabited by the shrimp. This study evaluates the effect of sediment redox potential in conjunction with stocking density on shrimp production performance, immune response and resistance against white spot syndrome virus (WSSV) infection. A completely randomized two factors experimental design was applied with three different sediment redox potential, i.e. ?65, ?108 and ?06 mV, and two shrimp densities, i.e. low (60 shrimp m?2) and high (120 shrimp m?2). Shrimp juveniles with an initial mean body weight of 5.32 ± 0.22 g were maintained in semi‐outdoor fibre tanks (270 L in capacity) for 35 days of experimental periods. At the bottom of each tank, 5‐cm deep soil substrate with different redox potential was added according to the treatments. The survival and biomass production were significantly reduced at ?206 mV sediment redox potential, regardless of stocking density. Highly negative sediment redox potential (?206 mV) and higher stocking density significantly reduced total haemocyte counts and phenoloxydase activity, and shrimp resistance to WSSV infection. We recommend to maintain the redox potential of pond sediment at a level of more than ?206 mV.  相似文献   

19.
The effects of replacing fish meal (FM) with corn gluten meal (CGM) on growth and physiological performance were evaluated in common carp (Cyprinus carpio). Six experimental diets were formulated by substituting 0 (control), 20, 40, 60, 80, and 100% CGM protein for FM protein. The concentrations of dietary protein in the experimental diets were 27.8–29% and the P:E ratios were 14.7–15.46 mg/kJ. Eighteen fish with an initial weight of 13.5?±?0.1 g were allocated to each of 18 circular tanks (450 L) to give triplicate groups for each dietary treatment. The fish were fed to satiation for 8 weeks. At the end of the feeding trial, growth indices, body proximate composition, and hematological and biochemical parameters were measured. Blood samples were taken from six fish in each tank. Final weight and total length were significantly higher in fish fed 100% CGM (27.8?±?1.2 g and 11.9?±?0.3 cm) than for those fed the control (22.7?±?1.4 g and 10.9?±?0.5 cm) or 20% CGM (22.3?±?1.2 g and 11?±?0.4 cm) diets. No effect of FM replacement by CGM was observed for condition factor or hepatosomatic index (P?>?0.05). The highest value of protein productive value (14.31?±?0.65) was observed in fish fed 20% CGM (P?<?0.05). There were no significant differences in percentage body moisture and fat, but percentages of protein and ash were significantly different among experimental groups; the highest values of protein (15.6?±?0.24%) and ash (3.01?±?0.26%) were recorded in fish fed 40% CGM. For hematological parameters, the highest number of white blood cells (4.1?±?0.1?×?103 mm?3) was observed in fish fed 100% CGM (P?<?0.05). In addition, the highest hematocrit (42.1?±?0.7%) and triglyceride (294.11?±?23.82 mg dl?1) were seen in fish fed the diet containing 40% CGM, while 80% CGM gave the highest cholesterol level (204.44?±?9.0 mg dl?1; P?<?0.05). Replacement of FM with CGM had no negative effects on growth and physiological parameters of common carp fingerlings in this short (8 weeks) trial, suggesting that it may be feasible to replace FM with CGM in diets formulated for juvenile common carp.  相似文献   

20.
Common snook (Centropomus undecimalis) is one of the most important marine species under commercial exploitation in the Gulf of Mexico; for this reason, interest in developing its culture is a priority. However, larviculture remains as the main bottleneck for massive production. In this sense, our objective was to determine the changes of digestive enzymes activities using biochemical and electrophoretic techniques during 36?days of Common snook larviculture fed with live preys (microalgae, rotifers, and Artemia). During larviculture, all digestive enzymatic activities were detected with low values since yolk absorption, 2?days after hatching (dah) onwards. However, the maximum values for alkaline protease (6,500?U?mg?protein?1), trypsin (0.053?mU?×?10?3?mg?protein?1), and Leucine aminopeptidase (1.4?×?10?3?mU?mg?protein?1) were detected at 12 dah; for chymotrypsin at 25 dah (3.8?×?10?3?mU?mg?protein?1), for carboxypeptidase A (280?mU?mg?protein?1) and lipase at 36 dah (480?U?mg?protein?1), for ??-amylase at 7 dah (1.5?U?mg?protein?1), for acid phosphatases at 34 dah (5.5?U?mg?protein?1), and finally for alkaline phosphatase at 25 dah (70?U?mg?protein?1). The alkaline protease zymogram showed two active bands, the first (26.3?kDa) at 25 dah onwards, and the second (51.6?kDa) at 36 dah. The acid protease zymogram showed two bands (RF?=?0.32 and 0.51, respectively) at 34 dah. The digestive enzymatic ontogeny of C. undecimalis is very similar to other strictly marine carnivorous fish, and we suggest that weaning process should be started at 34 dah.  相似文献   

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