缩短养殖周期的办法？

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缩短养殖周期的办法？

答案

参考答案：

1.在湖泊、水库、海湾等大水体中发展网箱养鱼。以降低水质对鱼类生长的影响，增加投饵量，缩短养鱼周期。

2.发展工业化养鱼。建立人工小气候，为鱼类提供生长的最适温度和良好的生活环境，以缩短养成鱼周期。

3.培育或引进优良品种的养殖鱼类、其生长快，养殖周期短。

4.提早繁殖苗种，延长其生长期，缩短养殖周期。

5.提供最佳适口饵料和应用配合饲料，促进鱼类快速生长。

6.加强病害防治，改革养殖旧工艺，推广健康养殖新工艺加速鱼类成长，缩短鱼类的养殖周期。

阅读理解

A new study says that birds living in big cities sing shorter, faster songs that are higher-pitched (高音调的) than those sung by their brothers in the forests. The researchers think that the birds adjust their songs to allow themselves to be heard over the noises of the city, especially the low traffic noise.

To study how urban birds song, Hans Slabbekoorn and Ardie den Bore, biologists at the University of Leiden in Netherlands, travelled around Europe and recorded bird songs in ten major cities and in nearby forests. The species they focused on, the great tit (大山雀), is widespread across Eurasia and one of the few types of birds that thrives in big cities.

Singing is crucial (重要的) for males, which use their songs to attract mates and mark out their territory. The changing songs could play a role in eventually causing the city birds and the forest dwellers to evolve into separate species.

The findings could also help explain why usually only a few bird species thrive in cities. By contrast, many more bird species tend to be found in forests and other undeveloped habitats.

Studies like this could eventually help researchers predict how urbanization (都市化) will affect birds, using this knowledge could help urban planners design more pleasant city environments, study co-author Slabbe-koorn said. “You can make a city much more livable if you pay attention to where the noise goes and where the people go,” he said. “It would be easy to fit the birds into those models.” Then cities wouldn’t be strictly for the people, but also for the birds.