什么叫迴游鱼类在水中的运动,大体上可分为两种,一种是没有一定规律的,如临时躲避敌害的袭击、追逐俘获物;或其他偶然性的运动等等。这类运动有时连续发生,有时则很长时间没有出现;移动的距离或持续的时间一般较短,而且没有一定的方向和周期性,因而被称为“不定向移动”。另一种则刚好相反,运动是有目的性的,时间和距离相当长,路线和方向也有一定,而且在一年或若干年中的某一时间、某些环境条件下,作周期性的重复,因而形成了所谓“定向移动”,这就是通常所说的迴游。 What is called the movement of migrating fish in the water can be roughly divided into two types. One is that there is no certain rule, such as temporary avoidance of enemy attacks, pursuit of captured objects, or other accidental movements. Such movements sometimes occur continuously, sometimes for a very long time; the distance or duration of movement is generally short, and there is no certain direction and periodicity, so it is called “non-directional movement.” The other is just the opposite. The movement is purposeful, the time and distance are quite long, the route and direction are also certain, and it is periodically repeated at certain times of the year or years and certain environmental conditions. , thus forming the so-called “directional movement”, which is commonly referred to as back.