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251.
V. L. L. de Almeida N. S. Hahn A. E. A. de M. Vazzoler 《Ecology of Freshwater Fish》1997,6(3):123-133
Abstract— Between March 1992 and February 1993 five piscivorous fish species, Acestrorhynchus lacustris (Reinhardt, 1874), Hoplias malabaricus (Bloch, 1794), Rhaphiodon vulpinus Agassiz, 1829, Salminus maxillosus , Valenciennes, 1840 and Plagioscion squamosissimus (Heckel, 1840), of the high Paranà River floodplain showed a wide total prey spectrum though only three to four taxa were dominant in their diet. Shrimp, Macrobrachium amazonicum , were also common to the majority of species. Seasonal and spatial variations occurred throughout the study period probably due the availability of prey species. The main resources shared by the predators were also the most abundant in the area, with consumption markedly focused on prey about 5.0 cm long. Detrended correspondence analysis was effective in discriminating two groups of predators species that exploited distinct microhabitats. The predators with the least scores consumed small characids that inhabit mid-water or the littoral region, whereas those with the largest scores consumed prey associated to the bottom. 相似文献
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随机抽取艾维茵鸡苗各500羽,分成试验组和对照组,试验组按每100kg饮水添加益生素300g,饲养条件和管理一致,饲养38d。试验组料肉比为1.88∶1,对照组料肉比为1.96∶1。试验组的纯利润为2416.8元,比对照组多收益274.2元。 相似文献
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O. DOMÍNGUEZ-DOMÍNGUEZ S. NANDINI & S. S. S. SARMA 《Fisheries Management and Ecology》2002,9(5):285-291
Abstract To improve survival of cultured juvenile fishes, it is important to understand prey preferences and predation behaviour of fish larvae. In this study, the feeding behaviour and prey preference of Allotoca dugesi (Bean), a small fish species endemic to Mexico and currently threatened with extinction are presented. Three zooplanktonic prey, viz. Brachionus calyciflorus (Pallas) , Moina macrocopa (Goulden) and Daphnia pulex (Leydig) were tested. The mean size (standard length ± SE, mm) of the larvae ranged from 9.0 ± 0.1 mm at week 1 to 18 ± 2 mm at the end of the experimental period (8 weeks). The gape size (mean ± SE) increased from 0.125 ± 0.002 mm at the first week to 2.300 ± 0.361 mm by the eighth week. Capture success (capture/attack) ranged from 0.80 to 0.98 with Brachionus , 0.72–0.94 with Moina and 0.17–0.46 with Daphnia . Prey preference experiments were conducted using B. calyciflorus, M. macrocopa and D. pulex at a fixed ratio of 5 : 2 : 2 ind. mL−1 , respectively, and revealed a positive selection for rotifers and Moina , but avoidance of Daphnia . The results are discussed with reference to conservation efforts for Allotoca dugesi . 相似文献
257.
Effect of culture system on the nutrition and growth performance of Pacific white shrimp Litopenaeus vannamei (Boone) fed different diets 总被引:2,自引:0,他引:2
A.G.J. TACON J.J. CODY L.D. CONQUEST S. DIVAKARAN I.P. FORSTER & O.E. DECAMP 《Aquaculture Nutrition》2002,8(2):121-137
Two 8-week feeding trials were conducted with juvenile Pacific white shrimp, Litopenaeus vannamei (Boone) to compare the growth and performance of animals fed a series of experimental and commercial pelleted shrimp and fish feeds and dietary feeding regimes within an indoor running-water culture system and an outdoor zero-water-exchange culture system. The best overall shrimp growth performance was observed for animals fed the experimental shrimp diet and all-day feeding regime under outdoor zero-water-exchange culture conditions. Final body weight and average weekly growth rate under these conditions were 2.8 and 3.4 times greater, respectively, than animals of similar size fed with the same diet under indoor running-water culture conditions. Although direct comparison between indoor and outdoor culture systems is difficult because of the lower indoor water temperatures, and consequently lower mean daily feed intake of animals, it is believed that the higher growth and feed performance of animals reared under outdoor `green-water' culture conditions was primarily due to their ability to obtain additional nutrients from food organisms endogenously produced within the zero-water-exchange culture system. The most promising features of zero-water-exchange culture systems are that they offer increased biosecurity, reduced feed costs and water use for the farmer, and by doing so provide a potential avenue of moving the shrimp culture industry along a path of greater sustainability and environmental compatibility. 相似文献
258.
Biological control is proposed as an ecological strategy to manage the threat of invasive plants, especially in natural areas. To pursue this strategy, we need to know that the host specificity criteria used to evaluate ecological risk with deliberate introduction of an exotic insect for biocontrol are sufficient to predict potential impact on native species. Host specificity is defined by adult feeding and oviposition preferences and larval development. One way to evaluate the criteria is to re-examine case histories where ecological effects are recorded, such as that of Rhinocyllus conicus Frölich. This flower head weevil, released in North America in 1968 to control exotic thistles like Musk thistle (Carduus nutans L), is now reducing seed production by multiple native North American thistle species (Cirsium spp.), and local population density of Platte thistle (Cirsium canescens Nutt.). We hypothesized that host specificity of R. conicus has changed since pre-release testing, providing an explanation for the unexpected magnitude of the documented ecological effects. Instead, when we re-tested host specificity of weevils naturalized over 28 generations, we found that host specificity has not changed. Naturalized adults of R. conicus showed strong feeding and oviposition preference for Musk thistle over Platte thistle. In addition, larval development by these weevils was faster and more successful (to larger size) on Musk thistle than on Platte thistle. Thus, our results indicate that a change in host specificity cannot explain the unexpectedly large build-up of R. conicus and significant ecological effect on Platte thistle. We conclude that accurate prediction of the potential level of impact on native host plants in the field requires further ecological information in addition to host specificity. 相似文献
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在工厂化循环水养殖中,准确识别鱼类摄食强度是实现精准投喂的前提和关键。水质、视觉、声音等单模态数据均可用于评估摄食强度,但单一模态往往具有片面性,难以完全反映全局特征,存在识别精度低、可移植性差等问题。多模态方法通过融合不同模态的特征,可为摄食强度量化提供新的手段。基于此,为融合鱼类摄食中的“水质-声音-视觉”信息,实现高精度的鱼类摄食强度量化,该研究在多模态Transformer(multimodal transformer,MulT)的基础上,提出一种多模态融合的鱼类摄食强度识别算法Fish-MulT。首先,从输入的水质、声音和视觉数据中提取特征向量;其次,利用多模态转移模块(multimodal transfer module,MMTM)对输入的特征向量进行融合,得到3种融合向量;然后对融合向量添加自适应权重并相加,得到融合模态;最后,利用融合模态将MulT算法中各模态分支的跨模态Transformer(cross-modal transformer)从2个优化为1个。试验结果表明,与MulT算法相比,本文算法的鱼类摄食强度识别准确率由93.30%提高到95.36%,参数量减少38%。与水质、声音和视觉单模态相比,准确率分别提高68.56%、21.65%和3.61%。可用于制定精准投喂策略,并为开发智能投喂系统提供技术支持。 相似文献
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