改革开放初期,一户农民分到了一个鱼塘。他在鱼塘内只养一种鱼,收益不高。后来他发现各种鱼的生活习性不一样,有的生活在水底、有的生活在中层、有的生活在上层,鱼所吃的食料也不一样,因此他把几种鱼 In the early reform and opening up, a farmer was assigned to a fish pond. He raised only one kind of fish in the fish ponds, and his income was not high. Later, he found that different kinds of fish had different habits of life. Some lived on the bottom, some lived in the middle, some lived on the top, and the fish also had different foodstuffs. Therefore, he put several kinds of fish