Ecuadorian Penaeus vannamei were cultured in dirt ponds (each of approximately 163 m2) at four different stocking densities, i.e. 5 shrimp m−2, 10 shrimp m−2, 15 shrimp m−2 and 20 shrimp m−2. Experiments were carried out over three different periods during the year. Each experiment lasted for 11–14 weeks. No commercial feed was given to the shrimp. The only input to the ponds was about 30 kg of cattle manure per pond per week. Chemical composition of the cattle manure was analyzed. Water quality parameters such as temperature, pH, DO and turbidity were recorded twice daily for each experiment; nutrients (nitrite, nitrate, ammonium and phosphate), water ATP, sediment ATP, H2S and chlorophyll were measured twice weekly for each experiment. Shrimp were sampled either weekly or bi-weekly for body weight measurements.
The results showed a negative correlation between stocking density and growth. Weekly growth ranged from 0·44 to 1·58 g week−1. Survival was over 50% in all treatments and averaged at 70·8%. Under these stocking densities, shrimp production ranged from 4·4 to 18·8 kg ha−1 day−1. The stocking density of 15 shrimps m−2 provides better production than the other stocking densities.
Water quality data did not relate to any shrimp growth. Water nutrient levels in pond discharge water were less than or equal to the nutrients in the incoming water in spite of the weekly addition of cattle manure and did not increase with the addition of cattle manure. No coliform bacteria were detected in any pond water samples through the study period. This indicates digestion of cattle manure in marine shrimp ponds would not pollute the environment with high concentrations of dissolved nutrients.
Thus, a marine shrimp pond can be considered a dissolved nutrient marine treatment plant converting unwanted cattle manure (1841 kg cattle manure ha−1 week−1 in this study) into a valuable commodity — shrimp. 相似文献
Maedi-visna, a chronic viral disease of adult sheep characterized by progressive dyspnoea or neurological manifestations, was first recognized and described clinically in Canada in 1970. Seroepidemiological study was conducted in sheep and goats in various areas of Quebec. Sera of 10% of the animals of selected flocks were collected and specific antibodies against maedi-visna virus were tested by a modified direct complement fixation test. Results show seropositive rate of 67.6% for Sherbrooke sheep; of 40.5, 41.1 and 47.1% for Quebec, Saint-Hyacinthe and Nicolet sheep respectively and only 29.2 and 20.0% positive sera in l'Assomption and Rimouski animals. Prevalence rate of positive goats varied according to geographic areas (0 to 36.8%). Statistical analysis of various factors, e.g. age, breed, mode of raising, origin and size of flock showed no relation between these factors and the geographic areas. But, some clinical problems in the sheep flocks such as cough, rapid breathing, mortality and abortion were associated with high infection rate (greater than or equal to 50%) to maedi-visna virus. In goats, no correlation was demonstrated between these clinical signs and serological results. Our results suggest that it is important to consider this disease in an adequate program of preventive medicine in Quebec. 相似文献
Various types of trap-tubs were tested both under controlled conditions in standardised trial series and in the field. New trap-tubs were poorly accepted by the animals, whereas weathered tubs were readily accepted within a very short period of time. The trapping mechanisms of tubs used in Lower Saxony and improved tubs in Hesse were both found to be suitable. The trapping method proved to be highly selective since long-tailed mice (Apodemus spp.) can easily escape by jumping onto the edge of the tub. Voles (Microtus agrestis, Clethrionomys glareolus) explored the inside of the tub and worked its exits with decreasing intensity during the time of captivity. They died of hypothermia within a few hours. Elimination of the trapped rodents by their natural enemies was not observed. The trials showed that trap-tubs are suitable for selective reduction of the density of field voles and red-backed voles in forests. The results also contribute to assessing the humaneness of the control method. 相似文献