The Effects of Fertilization and Water Management on Growth and Production of Nile Tilapia in Deep Ponds During the Dry Season

Fertilization guidelines developed for shallow ponds (1 m) with controlled depths were tested in deeper (2.5 m) ponds to determine effectiveness of these guidelines for culture of Nile tilapia Oreochromis niloticus . Twelve ponds of 2.5-m depth were used in four treatments: (A) weekly fertilization with water addition; (B) weekly fertilization without water addition; (C) one early fertilization without water addition; and (D) fertilization frequency dependent on nutrient concentrations, without water addition. Sex-reversed Nile tilapia were stocked at 2 fish/m 2 with an initial weight of 15 g, and harvested after 234 d. Depth of water declined from 2.4 m to 1.6 m over the experiment in ponds without water addition. Fish growth rate was significantly higher in treatments A and B (0.86 g/d), than in other treatments, as was yield (3,830 kg/ha). Treatment C was lowest in growth (0.086 g/d) and yield (168 kg/ha), with treatment D intermediate. Fish growth rates and yields were strongly correlated to manure input ( R 2 = 0.89 and 0.94, respectively), and residuals were not correlated to any physical or chemical variables. Growth and yield in these deep ponds were somewhat lower than those in previous experiments for shallow ponds with regular water inputs. However, stagnant ponds did not accumulate nutrients and metabolites at rates higher than ponds with controlled water depths.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73615/1/j.1749-7345.1998.tb00664.x.pd

Techniques for assessment of stratification and effects of mechanical mixing in tropical fish ponds

Density stratification isolates near-surface from bottom pond waters and prevents exchange of dissolved oxygen (DO) and nutrient elements, potentially restricting photosynthesis and production. Destratification strategies have become important for cost-effective intensification of pond aquaculture. Evaluation of methods and devices has emphasized effects on production, with little detailed description of effects on physicochemical components of pond ecosystems.This paper describes short-term effects of mechanical mixing on temporal and spatial distribution of temperature and DO in tropical freshwater fish ponds. Intensely stratified ponds of 1.5 m depth were monitored at eight depths for temperature and two depths for DO every 30 min with a modest-cost automated system of commercially available hardware. Results are presented as time-series plots, isotherm diagrams of temperature distribution with time and depth, and a stability index of energy required to mix a pond to uniform temperature.Required mixing energy is minuscule compared with electrical energy consumption of the lowest-powered mixing devices discussed in literature. Strategy for application of mechanical energy to water is critical for efficiency. A relatively subtle difference between two mixing regimes (daytime mixing for one 2-h period or two 1-h periods) produced potentially important differences in temperature and DO distribution.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28820/1/0000654.pd

Zastosowanie modelowania komputerowego do planowania zabiegów chirurgii szczękowej

The article describes application of reverse engineering techniques for modeling the appearance and the planning of correction of mandibular prognathism and FEM numerical analysis process components designed to perform anastomoses condylar fracture.W artykule przedstawiono zastosowanie technik inżynierii odwrotnej dla modelowania wyglądu i planowania zabiegu korekcji progenii. Przeprowadzono proces analizy numerycznej MES elementów przeznaczonych do wykonania zespoleń wyrostka kłykciowego