Effect of partial harvesting strategies on Artemia biomass production in Vietnamese salt works

The effect of partial harvest strategies on the production of Artemia biomass was evaluated for 12 weeks under Vietnamese salt farm conditions. The initial stocking density was 100 nauplii L^?1. After 3 weeks of inoculation, Artemia adults were partially harvested at intervals of 1, 3, 6 and 9 days starting with an initial quantity of 30 kg ha^?1 day^?1 at first harvest, and then the quantity of harvestable biomass was adjusted according to the standing stock present in the culture pond, combined with the time needed to harvest these quantities and with the weight of biomass harvested in each pond. The results showed that in most cases, the total densities were not significantly different among harvesting frequencies (P>0.05). However, a relatively higher Artemia adult density and its standing stock were better maintained in the 3‐day than in the 1‐day interval, and were significantly higher compared with the other two harvesting frequencies. The total biomass yields were the highest (1587 kg ha^?1) in the 3‐day harvesting interval, followed by 1‐, 6‐ and 9‐day harvesting interludes, corresponding to 1323, 1091 and 975 kg ha^?1 respectively. However, no statistical difference was observed between the 1‐ and the 3‐day interval as well as between the 6‐ and the 9‐day harvest schemes (P>0.05). The results of this study suggest that partial harvest of Artemia biomass performed every 3 days appears to be an appropriate strategy to enhance biomass productivity.     

Hatching and nutritional quality of Artemia cysts progressively deteriorates as a function of increased exposure to hydration/dehydration cycles

Nauplii hatching from Artemia cysts are crucial in larviculture nutrition. Artemia cysts may be exposed to repeated hydration/dehydration (H/D) cycles pre-harvesting or during processing and storage. To observe the effect of these cycles on cyst quality, Artemia franciscana cysts were exposed to a comprehensive set of various H/D treatments, differing in the number of cycles (1, 2, or 3) and the duration of the freshwater hydration period (2 or 4 h). Cyst quality was assessed using the criteria of immediate relevance for aquaculture use, such as hatching percentage directly after H/D treatment and after ?18 °C storage up to 1 month, longevity of axenically hatched starved nauplii, cyst and naupliar energy content, and (for the most extreme H/D treatment) cyst and naupliar fatty acid and vitamin C content. Repeated H/D cycles resulted in significantly (P < 0.05) decreased cyst hatching, reduced starved naupliar longevity and individual energy content, loss in vitamin C and fatty acid content, and moreover a close correlation between these parameters as a function of progressive H/D treatments. This is of immediate relevance for aquaculture nutrition, as commercial Artemia cysts may have gone through an unknown sequence of H/D cycles in nature or in the processing line, which affects the nutritional quality of the nauplii used in larviculture operations.     

Generating information for aquaculture development: The art and science of economic policy modelling

Abstract

The rapid growth of aquaculture and concerns about economic and ecological ‘sustainability’ have focused attention on industry externalities. Developing institutions which ‘sustain’ aquaculture will require skills in the ‘art and science’ of public policy modelling. Analysis of existing approaches demonstrates that no single modelling paradigm is ‘best’ for all aquaculture policy situations. Modelling approaches other than cost‐benefit including multiobjective analysis may be more appropriate if the objective of the modeller is to improve the effectiveness of the policy process itself. A review of the relatively small but growing literature on aquaculture policy models reveals a wide range of issues and approaches. In general, economic models have focused on the single objective of maximizing efficiency; in contrast, models used in actual aquacultural policy and planning focus on controlling environmental pollution. The findings suggest that economic models have not yet played a significant role in aquacultural policy development. This raises concerns that myopic views of ‘sustainability’ will result in institutions which do not promote socially efficient aquacultural industry growth.     

Growth response of potato tuber eyes to irradiation with X-rays and fast neutrons

Only slight reductions were observed in sprouting and growth from irradiated tuber eyes of ‘Katahdin” and B5141-6 potatoes at irradiation doses below 4500 rads X-rays or 1200 rads fast neutrons. Survival was reduced about 50% by 1400 rads fast neutrons and 97% by 5500 rads X-rays. Visible mutants and pollen steriles were rare at all doses used. A small number of subclones of irradiated ‘Katahdin’ having greater than normal pollen abortion were selected in an effort to locate irradiationinduced chromosome mutations.     

DOHUBLE-PHASE PARATHYROID SCINTIGRAPHY IN DOGS USING TECHNETIUM-99M-SESTAMIBI

The purpose of this study was to evaluate the utility of double-phase parathyroid scintigraphy using 99mTc-sestamibi for detecting and localizing hyperfunctioning parathyroid glands in hypercalcemic dogs. Fifteen hypercalcemic dogs that underwent parathyroid scintigraphy were included in this study: 3 dogs with hypercalcemia of malignancy, and 12 dogs with hyperfunctioning parathyroid tissue (parathyroid adenoma or parathyroid hyperplasia). The presence of parathyroid adenoma or parathyroid hyperplasia was documented by histopathologic examination. In 3 dogs with hypercalcemia of malignancy, parathyroid scintigraphy was negative for hyperfunctioning parathyroid tissue and the scans were classified as true negative. Parathyroid scintigraphy correctly identified the presence and location of hyperfunctioning parathyroid tissue in only 1 of 6 dogs with a parathyroid adenoma. False positive and false negative results occurred in dogs with parathyroid adenomas. Parathyroid scintigraphy failed to detect hyperfunctioning parathyroid tissue in 5 of 6 dogs with parathyroid hyperplasia and were classified as false negative. False positive results were obtained in the remaining dog with parathyroid hyperplasia. Sensitivity of parathyroid scintigraphy for detecting and localizing hyperfunctioning parathyroid tissue was 11%, specificity was 50%, and overall accuracy was 27%. Positive and negative predictive value were 25% and 27%, respectively. Sensitivity for detection of parathyroid adenomas was 25%, and sensitivity for detection of hyperplastic glands was 0 %. Results of this study indicate that double-phase parathyroid scintigraphy does not appear to have acceptable accuracy in detecting hyperfunctioning parathyroid glands in dogs. Due to the poor sensitivity and specificity of the technique in dogs, parathyroid scintigraphy is not recommended for definitive identification of abnormal parathyroid glands as the cause of hypercalcemia in dogs.     

Diurnal and Seasonal Light Transmission to Cowpea in Sorghum–Cowpea Intercrops in Mali

Tall cereal–short legume intercropping is ubiquitous in the semiarid tropics of West Africa, yet little is known regarding the dynamics of light interception in these systems. A field study was conducted in Cinzana, Mali, to characterize light transmission to cowpea in sorghum [Sorghum bicolor (L.) Moench]–cowpea [Vigna unguiculata (L.) Walp] intercropping systems. Different sorghum–cowpea planting configurations were used to examine photosynthetically active radiation (PAR) incident on the cowpea. The 4‐m tall sorghum cultivar CSM 219E intercepted > 60 % of incoming PAR from 2 m height to harvest (50 days). Consequently, total seasonal PAR received by intercropped cowpea was 60–66 % that of the unshaded monocrop. Thirty‐minute averages of PAR transmitted around solar noon had poor agreement (R²=0.53) with fractional daily light interception and overestimated seasonal PAR received by cowpea by 17 % in the north–south row orientation used. Thirty‐minute averages at 1100 h (R²=0.93) and 1430 h (R²=0.91) had the closest correlation to diurnal average PAR incident on cowpea. This study indicates that tall guineense sorghum captures significant amounts of light at low leaf area index (LAI) (< 2.0). Row orientation, time of measurement, plant height and LAI should be considered in calculating light interception in these intercropping systems.