Dissolved oxygen and dietary phosphorus modulate utilization and effluent partitioning of phosphorus in rainbow trout (Oncorhynchus mykiss) aquaculture

Phosphorus (P) is the limiting nutrient in freshwater primary production, and excessive levels cause premature eutrophication. P levels in aquaculture effluents are now tightly regulated. Increasing our understanding of waste P partitioning into soluble, particulate, and settleable fractions is important in the management of effluent P. When water supply is limited, dissolved oxygen concentration (DO) decreases below the optimum levels. Therefore, we studied effects of DO (6 and 10mg/L) and dietary P (0.7 and 1.0% P) on rainbow trout growth, P utilization, and effluent P partitioning. Biomass increased by 40% after 3 weeks. DO at 10mg/L significantly increased fish growth and feed efficiency, and increased the amount of P in the soluble fraction of the effluent. Soluble effluent P was greater in fish fed 1.0% P. DO increases fish growth and modulates P partitioning in aquaculture effluent.     

Numerical simulation of propane detonation in medium and large scale geometries

A modelling strategy has been developed for consequence analysis of medium and large scale gaseous detonation. The model is based on the solution of Euler equations with one-step chemistry. The Van Leer flux limited method which is a total variation diminishing scheme is used for shock capturing. Preliminary calculations were firstly conducted for small domains with fine grids which resolve the wave, relatively coarse grids which have less than 10 grids across the wave and coarse grids in which the minimum grid size is larger than the wave thickness to ensure that the reaction scheme has been properly tuned to capture the correct detonation pressure, temperature and velocity in the resolutions used in the different cases. The model was firstly tested against a medium scale detonation test in a shock tube with U-bends. Reasonably good agreement is achieved on detonation pressure and mean shock wave velocities at different measuring segments of the tube. Following the validation, the detonation of a hypothetical planar propane-air cloud is simulated. The predictions uncovered some interesting features of such large scale detonation phenomena which are of significance in the safety context, especially for accidental investigations. The findings from the present analysis are in line with the forensic evidence on damages in some historic accidents and challenges previous analysis of a major accident in which forensic evidence suggested localised detonation but was considered as the consequence of fire storms by the investigation team.     

Estimation of Efficiency of Processing Soil Samples for Pesticide Residues Analysis

The efficiency of four sample processing methods was tested with eight different types of soils representing the major proportion of cultivated soils. The principle of sampling constant was applied for characterizing the efficiency of the procedures and testing the well-mixed status of the prepared soil. The test material was 14C-labeled atrazine that enabled keeping the random error of analyses ≤ about 1%. Adding water to the soil proved to be the most efficient and generally applicable procedure resulting in about 6% relative sample processing uncertainty for 20 g test portions. The expected error is inversely proportional to the mass of test portion. Smashing and manual mixing of soil resulted in about four times higher uncertainty than mixing with water. Grinding of soil is applicable for dry soils only, but the test procedure applied was not suitable for estimating a typical uncertainty of processing dry soil samples. Adding dry ice did not improve the efficiency of sample processing.     

Effluent profile of commercially used low-phosphorus fish feeds

Excess phosphorus (P) in aquaculture feeds contributes to the eutrophication of natural waters. While commercially available low-P (LP) fish feeds have been developed, there is uncertainty about their potential to reduce effluent P while maintaining fish growth relative to regular P (RP) feeds. We therefore simulated commercial aquaculture conditions and fed for 55 days rainbow trout (approximately 190 kg/raceway, n = 3 raceways/diet) RP (1.4% total P) and LP (1.0%) feeds then determined effluent P levels, fish growth, and feed costs. Excretions of fecal-P and soluble-P, but not particulate-P, in effluents were greater in RP than in LP ponds. Fish growth, bone-P and plasma-P were similar between diets, demonstrating that LP feeds can lower effluent P levels without compromising growth. Costs were 0.97 dollars/kg fish production for LP feeds, and 0.74 dollars/kg for RP. Because feed is the largest variable cost in commercial aquaculture, the use of LP feeds can significantly increase production costs.     

Osmotic and chloride regulation in the hemolymph of the tiger prawn Penaeus monodon during molting in various salinities

The effect of molting on osmotic and chloride concentrations in the blood of the prawn Penaeus monodon Fabricius (20±3 g) at various salinities was investigated. Prawns were obtained from ponds in Iloilo, Philippines, in 1984. They were stocked in salinities of 8, 20, 32 and 44, and their hemolymph was sampled during molt (Time 0), and then 0.125, 0.25, 0.5, 1, 2, 4, 6, 10 and 14 d after molting. Prawns during and immediately after molt tended to conform to the environmental osmolality. Subsequent postmolt (0.5 d) stages displayed more divergence from external salinity. The isosmotic point was higher (940±30 mOsm kg^-1) during molt than during intermolt (663±8 mOsm/kg^-1), suggesting different osmotic requirements in early molt. Hyperregulation of hemolymph chloride below 20 S, as well as isoionic point (301±6 mM), were independent of molting stage. At 20 S and above, newly molted (0 to 0.25 d post-molt) individuals tended to conform to the external chloride concentration while intermolt (0.5 d) post-molt individuals did not. Contribution of hemolymph chloride to hemolymph osmolality was greater during intermolt than during ecdysis, suggesting an important role for other negatively charged ions during molt. When molt occurred in 20 S (the test salinity most similar to the isoionic salinity), there was little or no change in hemolymph osmolality or chloride concentration from 0 to 14 d postmolt. At 8, 32 and 44 S, the change from molt to intermolt values in hemolymph osmotic and chloride concentrations was hyperbolic. Non-linear least-squares regression showed that prawns generally achieved intermolt values within 1 d after molting. Prawns at intermolt regulated hemolymph osmolality (620 to 820 mOsm kg^-1) and chloride concentration (300 to 450 mM) at a much narrower range than during molt (520 to 1 170 mOsm kg^-1 and 250 to 520 mM, respectively). Hemolymph osmolality was a more sensitive indicator of physiological response than hemolymph chloride concentration. Distribution and culture of P. monodon might be limited in low salinities by its ability to maintain a hemolymph osmolality 500 mOsm kg^-1 during molt and 600 mOsm kg^-1 in intermolt, and in high salinities by its capacity to reduce the hemolymph osmolality from values at molt to those in intermolt. Osmotic and chloride concentrations in the blood of P. monodon clearly varied with both molt stage and salinity of the medium. Dependence on external factors, however, gradually declined in older molt stages, suggesting a reduction in integument permeability and greater development of ion absorption/secretion mechanisms as the exoskeleton hardened.SEAFDEC Contribution No. 197     

Physiological responses to fluctuation in temperature of salinity in invertebrates. Adaptations ofAlpheus viridari (Decapoda,Crustacea),Terebellides parva (Polychaeta) andGolfinigia cylindrata (Sipunculida) to the mangrove habitat

The snapping shrimpAlpheus viridari (Armstrong, 1949), the polychaeteTerebellides parva Solis-Weiss, Fauchald and Blankensteyn 1990, and the sipunculanGolfingia cylindrata (Keferstein, 1865) are commonly found in the same mangrove habitat, where they experience frequent, acute fluctuations in temperature and salinity. Ecological studies indicate a temporal variation, including occasional absence, in the distribution of bothG. cylindrata andT. parva; this fed us to examine the physiological adaptations of the three species (collected at Western Bay, Twin Cays, Belize in 1985, 1986 and 1988). Each was subjected to acute, repeated exposure to either control (35 S) and decreased (25 S) salinity or to control and increased (45 S) salinity. Ability to regulate water and ion content (g H₂O or mol g^-1 solute free dry wt) was examinedA. viridari behaved as a hyperosmotic conformer at decreased salinity but as an osmoconformer at increased salinity. Regardless of direction of salinity change,A. viridari regulated water content through change in Na⁺, K⁺, and Cl^– contents. In contrast,G. cylindrata behaved as an osmoconformer and did not demonstrate ability to regulate water content.T. parva behaved as an osmoconformer, showed incomplete regulation of water content via change in Na⁺, K⁺, and Cl^– contents but had limited survival following exposure to 45 S. Each species was also exposed to change in temperature. Species were subjected to acute, repeated exposure either to control (28°C) and decreased (21°C) temperature or to control and inereased (35°C) temperatureA. viridari regulated water and ion content under both experimental conditions. In contrast,T. parva did not regulate water and ion content under either experimental temperature.G. cylindrata did not regulate water and ion content during exposure to decreased temperature and did not survive exposure to increased temperature. ForA. viridari, weight specific oxygen uptake rates (mg O₂ g^-1 ash-free dry wt) were determined. Exposure to decreased salinity or to increased temperature resulted in a small sustained elevation in O₂ uptake. It is concluded that, unlikeA. viridari, T. parva andG. cylindrata are only marginally adapted to withstand the salinity and temperature stresses, respectively, of the mangrove habitat. The inability ofT. parva andG. cylindrata to fully adapt to extremes in the mangrove habitat could well explain the temporal variation seen in the distribution of these two species.Contribution number 380. Caribbean Coral Reef Ecosystems, National Museum of Natural History, Smithsonian Institution     

Use of vitrified MSWI bottom ashes for concrete production

Bottom ashes from a north Italian municipal solid waste incinerator (MSWI) were vitrified at 1450 degrees C without adding any vitrifying agent, then ground and sieved to different granulometry (ranging from 50 microm to 20mm), and used as filler, sand, or aggregate for concrete. Samples were characterized via slump tests (UNI 9418), alkali-silica reactivity (UNI 8520/22 and ASTM C 298), and compression strength tests (UNI 6132, 6132/72, 6686/72), and compared to reference samples obtained without vitrified bottom ashes (VBA). Our results show that vitrified bottom ashes are unsuitable as a sand substitute; however, concrete containing up to 20 wt.% of VBA filler used as a substitute for cement and up to 75 vol.% of VBA as a substitute for natural aggregate retains the same mechanical properties as reference samples. Alkali-silica or other detrimental reactions were not observed in VBA-containing concrete samples after a period of two years. The results of this work demonstrate that vitrified bottom ashes from MSWI can be used instead of natural aggregates in mortar and concrete production.     

Effect of salinity on hemolymph calcium concentration during the molt cycle of the prawn Penaeus monodon

Prawns (Penaeus monodon) were obtained from ponds in Iloilo, Philippines, in 1984 and 1985 and maintained in salinities from 8 to 44. Total hemolymph calcium was largely affected by molt stage and less so by salinity. A sharp, transient increase in hemolymph calcium occurred 3 to 6 h postmolt, followed by an equally rapid decrease from 6 h postmolt to intermolt. This biphasis response was limited to prawns in 8, 20 and 32S; in 44S, hemolymph calcium remained the same throughout the sampling period. Peak concentrations of total calcium were greater in low (8 and 20S) than in high salinities. Salinity had no effect on the duration of molt cycle nor on time of occurrence of molt. Almost half of molting incidents occurred between 18.01 and 0.00 hrs, and one-third between 0.01 and 06.00 hrs.     

Natural and anthropogenic influences on the diversity structure of reef fish communities in the Tuamotu Archipelago (French Polynesia)

Despite the rapid rate of human-induced species losses, the relative influence of natural and anthropogenic factors on the functional diversity of species assemblages remains unknown for most ecosystems. A model was previously developed to predict the diversity structure of coral reef fish assemblages in 10 atolls of low human pressure and contrasting morphology of the Tuamotu Archipelago (French Polynesia). This existing model predicted smoothed histograms (spectra) of species richness according to size classes, diet classes and life-history classes of fish assemblages using a combination of environmental characteristics at different spatial scales. The present study applied the model to Tikehau, another atoll of the same archipelago where commercial fishing is practiced and where the same sampling strategy was reproduced. Significant differences appeared between predicted and observed species richness in several size, diet and life-history classes of fish assemblages in Tikehau. Two parameters which were not accounted for in the initial model, i.e. fishing pressure and atoll position within the archipelago, explained together 63% of variance in model residuals, >60% being explained by fishing pressure only. The respective effects of fishing and atoll position on the diversity of coral reef fish assemblages are discussed, with the potential of such modelling approach to assess the relative importance of factors affecting functional diversity within communities.