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Food Conversion Efficiency (food + conversion_efficiency)
Selected AbstractsThe relationships between stocking density and welfare in farmed rainbow troutJOURNAL OF FISH BIOLOGY, Issue 3 2002T. Ellis There is increasing public, governmental and commercial interest in the welfare of intensively farmed fish and stocking density has been highlighted as an area of particular concern. Here we draw scientific attention and debate to this emerging research field by reviewing the evidence for effects of density on rainbow trout. Although no explicit reference to ,welfare' has been made, there are 43 studies which have examined the effects of density on production and physiological parameters of rainbow trout. Increasing stocking density does not appear to cause prolonged crowding stress in rainbow trout. However, commonly reported effects of increasing density are reductions in food conversion efficiency, nutritional condition and growth, and an increase in fin erosion. Such changes are indicative of a reduced welfare status,although the magnitude of the effects has tended to be dependent upon study-specific conditions. Systematic observations on large scale commercial farms are therefore required, rather than extrapolation of these mainly small-scale experimental findings. There is dispute as to the cause of the observed effects of increasing density, with water quality deterioration and/or an increase in aggressive behaviour being variously proposed. Both causes can theoretically generate the observed effects of increasing density, and the relative contribution of the two causes may depend upon the specific conditions. However, documentation of the relationship between density and the effects of aggressive behaviour at relevant commercial densities is lacking. Consequently only inferential evidence exists that aggressive behaviour generates the observed effects of increasing density, whereas there is direct experimental evidence that water quality degradation is responsible. Nevertheless, there are contradictory recommendations in the literature for key water quality parameters to ensure adequate welfare status. The potential for welfare to be detrimentally affected by non-aggressive behavioural interactions (abrasion, collision, obstruction) and low densities (due to excessive aggressive behaviour and a poor feeding response) have been largely overlooked. Legislation directly limiting stocking density is likely to be unworkable, and a more practical option might be to prescribe acceptable levels of water quality, health, nutritional condition and behavioural indicators. [source] Effects of reduced salinities on growth, food conversion efficiency and osmoregulatory status in the spotted wolffishJOURNAL OF FISH BIOLOGY, Issue 2 2001A. Foss No significant differences in mean mass between groups were found at any time in spotted wolffish Anarhichas minor, mean (±S.D.) initial mass 76 (±21) g, reared at salinities of 12, 17, 25 and 34, for 12 weeks at 8° C. Salinity did not have a significant effect on daily feeding rates, total food consumption, food conversion efficiency and protein efficiency ratio. Growth trajectories varied between groups, but no overall difference in growth was found. Plasma osmolality and plasma chloride levels decreased with salinity in a 48 h abrupt exposure trial, and in the growth experiment the low salinity groups (12 and 17,) exhibited significantly lower values compared with 25 and 34,. The decrease was moderate and concentrations were well within the range described for other marine species. The results indicate that the spotted wolffish is a strong osmoregulator which could be reared at various salinity levels. [source] Effects of CO2 and light on tree phytochemistry and insect performanceOIKOS, Issue 2 2000Jep Agrell Direct and interactive effects of CO2 and light on tree phytochemistry and insect fitness parameters were examined through experimental manipulations of plant growth conditions and performance of insect bioassays. Three species of deciduous trees (quaking aspen, Populus tremuloides; paper birch, Betula papyrifera; sugar maple, Acer saccharum) were grown under ambient (387±8 ,L/L) and elevated (696±2 ,L/L) levels of atmospheric CO2, with low and high light availability (375 and 855 ,mol×m,2×s,1 at solar noon). Effects on the population and individual performance of a generalist phytophagous insect, the white-marked tussock moth (Orgyia leucostigma) were evaluated. Caterpillars were reared on experimental trees for the duration of the larval stage, and complementary short-term (fourth instar) feeding trials were conducted with insects fed detached leaves. Phytochemical analyses demonstrated strong effects of both CO2 and light on all foliar nutritional variables (water, starch and nitrogen). For all species, enriched CO2 decreased water content and increased starch content, especially under high light conditions. High CO2 availability reduced levels of foliar nitrogen, but effects were species specific and most pronounced for high light aspen and birch. Analyses of secondary plant compounds revealed that levels of phenolic glycosides (salicortin and tremulacin) in aspen and condensed tannins in birch and maple were positively influenced by levels of both CO2 and light. In contrast, levels of condensed tannins in aspen were primarily affected by light, whereas levels of ellagitannins and gallotannins in maple responded to light and CO2, respectively. The long-term bioassays showed strong treatment effects on survival, development time, and pupal mass. In general, CO2 effects were pronounced in high light and decreased along the gradient aspen birch maple. For larvae reared on high light aspen, enriched CO2 resulted in 62% fewer survivors, with increased development time, and reduced pupal mass. For maple-fed insects, elevated CO2 levels had negative effects on survival and pupal mass in low light. For birch, the only negative CO2 effects were observed in high light, where female larvae showed prolonged development. Fourth instar feeding trials demonstrated that low food conversion efficiency reduced insect performance. Elevated levels of CO2 significantly reduced total consumption, especially by insects on high light aspen and low light maple. This research demonstrates that effects of CO2 on phytochemistry and insect performance can be strongly light-dependent, and that plant responses to these two environmental variables differ among species. Overall, increased CO2 availability appeared to increase the defensive capacity of early-successional species primarily under high light conditions, and of late-successional species under low light conditions. Due to the interactive effects of tree species, light, CO2, and herbivory, community composition of forests may change in the future. [source] Effect of salinity on survival, growth, oxygen consumption and ammonia-N excretion of juvenile whiteleg shrimp, Litopenaeus vannameiAQUACULTURE RESEARCH, Issue 12 2009Peidong Zhang Abstract In this study, we tested the lower salinity tolerance of juvenile shrimps (Litopenaeus vannamei) at a relatively low temperature (20 °C). In the first of two laboratory experiments, we first abruptly transferred shrimps (6.91 ± 0.05 g wet weight, mean ± SE) from the rearing salinity (35 000 mg L,1) to salinities of 5000, 15 000, 25 000, 35 000 (control) and 40 000 mg L,1 at 20 °C. The survival of L. vannamei juvenile was not affected by salinities from 15 000 to 40 000 mg L,1 during the 96-h exposure periods. Shrimps exposed to 5000 mg L,1 were significantly affected by salinity, with a survival of 12.5% after 96 h. The 24-, 48- and 96-h lethal salinity for 50% (LS50) were 7020, 8510 and 9540 mg L,1 respectively. In the second experiment, shrimps (5.47 ± 0.09 g wet weight, mean ± SE) were acclimatized to the different salinity levels (5000, 15 000, 25 000, 35 000 and 40 000 mg L,1) and then maintained for 30 days at 20 °C. Results showed that the survival was significantly lower at 5000 mg L,1 than at other salinity levels, but the final wet weight under 5000 mg L,1 treatment was significantly higher than those under other treatments (P<0.05). Feed intake (FI) of shrimp under 5000 mg L,1 was significantly lower than those of shrimp under 150 00,40 000 mg L,1; food conversion efficiency (FCE), however, showed a contrasting change (P<0.05). Furthermore, salinity significantly influenced the oxygen consumption rates, ammonia-N excretion rates and the O/N ratio of test shrimps (P<0.05). The results obtained in our work provide evidence that L. vannamei juveniles have limited capacity to tolerate salinities <10 000 mg L,1 at a relatively low temperature (20 °C). Results also show that L. vannamei juvenile can recover from the abrupt salinity change between 15 000 and 40 000 mg L,1 within 24 h. [source] Integrating molecular genetic technology with traditional approaches for genetic improvement in aquaculture speciesAQUACULTURE RESEARCH, Issue 1 2000G P. Davis Genetic improvement of aquaculture species offers a substantial opportunity for increased production efficiency, health, product quality and, ultimately, profitability in aquacultural enterprises. Technolo-gies exist that can be implemented immediately to improve multiple traits that have economic value, while simultaneously accounting for inbreeding effects. Genetic improvement techniques for delivering genetic gain include formal definition of the breeding objective, estimation of genetic parameters that describe populations and their differences, evaluation of additive and non-additive genetic merit of individuals or families and defining the structure of a breeding programme in terms of mating plans. Novel genetic technologies involving the use of DNA-based tools are also under development for a range of aquaculture species. These gene marker technologies can be used for identification and monitoring of lines, families and individuals, monitoring and control of inbreeding, diagnosis of simply inherited traits and genetic improvement through selection for favourable genes and gene combinations. The identification of quantitative trait loci (QTL), and direct or linked markers for them, will facilitate marker-assisted selection in aquaculture species, enabling improvement in economically important traits, particularly those that are difficult to breed for, such as food conversion efficiency and disease resistance. [source] | ||||||||||