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排序方式: 共有482条查询结果,搜索用时 15 毫秒
371.
Red porgies, Pagrus pagrus L., were fasted for 7, 14 or 28 days, and were then allowed to feed on pellets released from demand feeders. Biological responses during fasting and refeeding were examined. The factors considered were growth, organosomatic indices and proximate body composition (protein, fat, ash and moisture). Fasted red porgies lost weight and had higher relative weights of eviscerated body than control fish. Refeeding was accompanied by hyperphagy, which resulted in similar total food demand being shown by all groups. Fish which had been deprived of food displayed compensatory growth and the final weights of these fish at the end of the experiment were similar to controls. There were no significant changes caused by fasting in the relative proportion of body chemical components. Calculations based upon changes in protein and lipid content suggest that more protein than lipid is metabolized during the first phase (14 days) of a fast. 相似文献
372.
Pablo Arechavala‐Lopez Pablo Sanchez‐Jerez Just Bayle‐Sempere Damián Fernandez‐Jover Laura Martinez‐Rubio José Angel Lopez‐Jimenez Francisco Javier Martinez‐Lopez 《Aquaculture Research》2011,42(7):996-1010
Coastal aquaculture installations concentrate large numbers of wild fish species of both ecological and economic importance, including schools of bogue, Boops boops (L.), in high abundance and biomass. The aggregated species consume large quantities of the easily available pellets lost from cages. As a consequence, the physical condition of farm‐associated wild fish is increased and their physiology is altered. These changes may influence local fisheries as many of these aggregating species are targeted by fishers. We assess whether local fishers catch wild fish that have previously aggregated at fish farms by comparing the body condition, trophic indexes, diet overlap and the fatty acid (FA) composition of B. boops obtained from local fish markets and around fish farms. Bogue captured by trammel‐nets and around fish farms facilities presented a similar biological condition, as well as high quantities of pellets in the gut, and their FA profile was affected by vegetal‐derived FAs. In contrast, bogue captured by trawlers were not influenced by fish farms, as they consumed natural trophic resources. We conclude that artisanal fishers exploit these aggregated fish populations once they have dispersed away from farms, and benefit from a ‘biomass export’ from fish farms at a local scale. 相似文献
373.
Lindsay G Ross L. Lynne Falconer Antonio Campos Mendoza Carlos A Martinez Palacios 《Aquaculture Research》2011,42(6):797-807
The tilapia fishery in a large Mexican reservoir has declined in recent years, promoting efforts to enhance stock quality in conjunction with feasibility studies for cage aquaculture. Spatial models to optimize cage location have been developed, incorporating aspects of topography, climate, hydrography, water quality and quantity, land use, infrastructure and socioeconomics. Three cage sizes were modelled, 5, 10 and 15 m diameter, for both high‐ and low‐water levels. When full the, reservoir has a total area of 312 km2 but a reduction in water level of 13 m was recorded between wet and dry seasons, significantly reducing the surface area available for cages to 265 km2. The results indicate a significant difference in the availability of sites between seasons. For the small, medium and large cages at high water level, the areas classified as highly suitable or suitable were 151, 184 and 146 km2, respectively, while at low‐water level these areas reduced to 113, 88 and 62 km2. Modelling this change in water level and the subsequent loss of available sites provide qualitative and quantitative guidelines for the development of aquaculture sites, their seasonal management and future monitoring, outcomes that can only be achieved using Geographical Information Systems and associated technologies. 相似文献
374.
Edgar Sanchez‐Zazueta Juan M. Hernández Francisco Javier Martinez‐Cordero 《Aquaculture Research》2013,44(4):574-587
This article analyses the optimal selection of stocking density and date in semi‐intensive culture of shrimp Litopenaeus vannamei (Boone, 1931). The empirical evaluation of productive and economic scenarios derived from the specific choice of these management variables is often unfeasible for decision makers. To overcome this limitation, the bioeconomic modelling is widely applicable in aquaculture systems. In the present study, profit maximization for a semi‐intensive shrimp farm is obtained through the development of a bioeconomic model to analyse the combination of stocking density (range: 6–30 postlarvae (PL) m?2) and date (from March 1st to June 1st) as decision variables for a shrimp farm located in Sinaloa, Mexico. The results show that pond water temperatures prevailing during culture cycle when the stocking date is June 1st (temperature in 19‐weeks culture period: 30.76 ± 0.87°C) and the stocking density is 20–24 PL m?2 produce a maximized Present Value Profit (PVπ) of USThis article analyses the optimal selection of stocking density and date in semi‐intensive culture of shrimp Litopenaeus vannamei (Boone, 1931). The empirical evaluation of productive and economic scenarios derived from the specific choice of these management variables is often unfeasible for decision makers. To overcome this limitation, the bioeconomic modelling is widely applicable in aquaculture systems. In the present study, profit maximization for a semi‐intensive shrimp farm is obtained through the development of a bioeconomic model to analyse the combination of stocking density (range: 6–30 postlarvae (PL) m?2) and date (from March 1st to June 1st) as decision variables for a shrimp farm located in Sinaloa, Mexico. The results show that pond water temperatures prevailing during culture cycle when the stocking date is June 1st (temperature in 19‐weeks culture period: 30.76 ± 0.87°C) and the stocking density is 20–24 PL m?2 produce a maximized Present Value Profit (PVπ) of US$?ha 10 350 and PVπ US$?ha 2526 for weekly mortality rates at low (2.1%) and medium (5.8%) levels respectively. The marginal change in the cost of feed (±1%) has the greatest effect on PVπ (?0.58% and 0.59% respectively). The discussion focuses on the combined effect of mortality rate, stocking density and especially, on the stocking date decision, for a given production planning framework, taking into account that the stocking date is the main management decision variable to cope with viral diseases outbreaks. 相似文献
375.
J. Antonio Martinez J. Carlos Seijo 《Aquaculture Economics & Management (Blackwell Science)》2013,17(3-4):129-145
Abstract Reducing water exchange in shrimp aquaculture to minimize discharge of pollutants is a search for sustainability. In desert regions, like most of northwest Mexico, low water exchange must be complemented with artificial aeration to compensate for low levels of oxygen in warm and highly saline water. The economic yield of a low‐water‐exchange production system is compared against yield from a typical water‐exchange‐without‐aeration system for Penaeus vannamei culture. The difference between two systems is centered on pumping and aeration rates for a 100 ha semi‐intensive farm in northwest Mexico. A bioeconomic model was built to compare the systems. Risk analysis is adopted to account for uncertainty of seed price, shrimp growth rate, survival rate, and shrimp prices. The typical system was slightly more profitable than the low‐water‐exchange, aerated system. The latter used less electricity than the former in all of the three mortality‐rate scenarios. However, the difference in profitability is so small that for practical purposes both production systems provide similar economic yield. For a typical system, the probability of reaching a positive net present value (NPV) is high, therefore under the assumed risks, a 100 ha semi‐intensive shrimp farm in northwest Mexico is a good investment choice. 相似文献
376.
377.
MB Vieira I Bianchi EM Madeira VFB Roll CA Oliveira P Viau I Pivato NC Severo FAB Del Pino A Schneider MN Corrêa 《Reproduction in domestic animals》2010,45(6):1110-1113
This study aimed to evaluate the effect of the exogenous recombinant bovine somatotropin (rbST) on plasma concentrations of insulin‐like growth factor I (IGF‐I), insulin and semen quality of bulls. Twenty bulls (Aberdeen Angus and Brangus) were divided by breed into two groups. Placebo group was injected with NaCl 0.9% (s.c.) and treatment group with rbST (s.c., 500 mg) at days 0 and 14 of the experiment. Immediately after semen collection, blood samples were taken on days 0, 14, 28, 42 and 56 of the experiment. Semen was also collected on day 70 of the experiment. Evaluation of sperm motility was performed at pre‐freezing and post‐thawing stage, whereas assessment of sperm membrane integrity was performed after freezing and thawing. Analysis of data revealed that the effect of treatment and treatment‐by‐collection day on plasma concentrations of IGF‐I and insulin was not significant. However, mean plasma concentrations of IGF‐I and insulin were affected (p < 0.0001) by days of blood sampling. Effect of treatment and treatment‐by‐collection day on motility of spermatozoa was similar (p > 0.05) at pre‐freezing and post‐thawing stage. Intactness of plasmalemma and tail membrane of spermatozoa at post‐thawing stage was higher (p < 0.05) in rbST‐treated group than in control. In conclusion, rbST did not affect plasma concentrations of IGF‐I and insulin, however, it did improve post‐thaw sperm membrane integrity. 相似文献
378.
379.
Sulfate adsorption by variable charge soils: Effect of low-molecular-weight organic acids 总被引:1,自引:0,他引:1
C. E. Martinez A. W. Kleinschmidt M. A. Tabatabai 《Biology and Fertility of Soils》1998,26(3):157-163
Sulfate (SO4
2–) movement and transport in soils has received considerable attention in recent years. In most soils, SO4
2– coexists with a variety of natural organic compounds, especially organic acids. Studies were conducted to assess the effect
of low-molecular-weight organic acids (eight aliphatic and five aromatic acids) on SO4
2– adsorption by variable charge soils from Chile and Costa Rica. The effects of type of organic acid, pH, type of soil, and
organic acid concentration were investigated. In one experiment, a 1.0 g soil sample was equilibrated with 25 ml 0, 0.5, 1.0,
2.0, 4.0, or 6.0 mM K2SO4 in 1 mM NaCl in the presence or absence of 5 mM citric acid. In the second set of experiments, the adsorption of 2 mM SO4
2– in soils at pH 4 or pH 5 in the presence or absence of one of 13 organic acids at a concentration of 2 mM or 5 mM was studied. Results showed that citric acid significantly decreased SO4
2– adsorption by the two soils. Sulfate adsorption decreased with increasing pH of the equilibrium solution. Aliphatic acids,
with the exception of cis-aconitic acid, decreased the amount of SO4
2– adsorbed by the two soils, with oxalic, tartaric, and citric acid showing the greatest effect. The differences in pH values
of the equilibrium solutions in the presence and absence of organic acids were significantly, but negatively, correlated with
the amount of SO4
2– adsorbed, suggesting chemisorption of SO4
2– and the release of hydroxide ions. The ionization fraction values of the organic acids at the equilibrium pH were correlated
with the amounts of SO4
2– adsorbed, suggesting that the protonation of surface hydroxyl groups of the mineral phase increased as the strength of the
ionization of the acid increased, thus creating more positively charged surfaces.
Received: 12 February 1997 相似文献
380.