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A manta ray -- immense -- five metres across from the tip of one wing-like fin to the tip of the other.
巨大的鳐魟鱼，两翼张开有5公尺长。
It's travelling economy, wasting as little energy as possible, as it glides through the waters of the tropics.
它的活动非常省力，会在热带水域中滑行，以减少热量的消耗。
The remora fish that accompany it travel more economically still -- by hitching a lift.
搭便车跟着它移动的鲫鱼当然是更省力了。
Their host is searching for food -- plankton, the minute fish and invertebrates that float near the surface.
它们的宿主寻找着猎物，也就是浮在水面的微小鱼类及无脊椎动物等浮游生物。
It needs lots of them and may cruise for days before it finds a good feeding ground.
鳐魟鱼的需求量极大，可能会游好几天的时间来寻找适合的进食地点。
Dusk, at the edge of a Pacific island, three thousand miles from the nearest continent. Here surgeon fish have assembled to spawn.
在太平洋小岛边缘的黄昏，离最近的大陆有3000英里远。这里有粗皮鲷群聚产卵。
As they perform their nuptial dances, they discharge clouds of eggs and sperm into the water.
它们在表演求偶舞的同时，会释出烟雾一般的卵及精子。
The manta must have known this was about to happen, for it arrived at exactly this critical moment.
鳐魟鱼大概早已预知产卵期的发生，所以在最重要的时刻抵达。
And it is not the only one to do so. Others are here too.
而且不只一只。其他的也来了。
Now all they need to do is to sweep the water into their mouths and sieve out the eggs.
现在只需将海水扫入口中，挑出里面的卵就可以了。
Within an hour, the whole event will be over.
整个事件将在一个小时以内结束。
Any surviving eggs will be so dispersed that they are not worth collecting.
所剩的卵散布海面，已不值得搜食。
But other perils await them as they join the clouds of eggs and larvae and tiny fish that drift through the surface waters of the open ocean.
但是其他的危险正等着它们，它们渗入了一团飘过远洋海面的卵群与幼鱼中。
These are the eggs of yellow fin tuna. If the hatchlings survive, it will take them two years to become adults.
这些是黄鳍鲔的卵。如果成功孵化，它们需要两年的时间长成成鱼。
In three years, they could be nearly two metres long and weigh two hundred kilograms.
三年内它们就会长到2公尺长，重达200公斤。
Perhaps only one in a million will live as long as that.
幼鱼要存活可能只有百万分之一的机会。
They and the other animals and microscopic plants of the plankton constitute the basis of all life out on the open ocean.
它们及其他微生动植物等浮游生物，是所有远洋中生命的基础。
