半深海带（英语：bathyal zone或bathypelagic）由希腊语：βαθύς（bathýs）衍生而来，这里也被称作午夜区（midnight zone）。这一区域位于海平面下1,000米（3,300英尺）至4,000米（13,000英尺）之间，平均温度大约为4 °C（39 °F）。 半深海带的动物密度较低。阳光到达不了这一区域，这也就意味着这里不可能有初级生产，因此这里才被称作午夜区。由于这里缺乏光线，这里仅有蝰鱼属与皱鳃鲨有眼睛。许多种类的自游生物生活中半深海区域，如鱿鱼、大鲸鱼和章鱼；海星、海绵多孔动物门、腕足动物、海胆也在这里很常见，但这个区域对于其它鱼类来说太难居住。因为这里很少会有有营养的食物，不易捕食，在这一区域中生活的鱼类便通过减缓新陈代谢来节省它们的能源。这里的鱼类没有天敌，因此它们有着无力的肌肉，柔软的皮肤与黏糊糊的身体。

The bathyal zone or bathypelagic – from Greek βαθύς (bathýs), deep – (also known as midnight zone) is the part of the pelagic zone that extends from a depth of 1000 to 4000 meters (3300 to 13000 feet) below the ocean surface. It lies between the mesopelagic above, and the abyssopelagic below. The average temperature hovers at about 4 °C (39 °F). Although larger by volume than the euphotic zone, the bathyal zone is less densely populated. Sunlight does not reach this zone, meaning primary production, if any, is almost nonexistent. It is known as the midnight zone because of this feature. Because of the lack of light, some species do not have eyes, however those possessing eyes in this zone include the viperfish and the frill shark. Many forms of nekton live in the bathyal zone, such as squid, large whales, and octopi, but this zone is difficult for fish to live in. Sponges, brachiopods, sea stars, and echinoids are also common in the bathyal zone. The fish in this zone have become very energy efficient, since it is especially hard to find nutrients. Many have slow metabolic rates to conserve energy. The fish here have weak muscles, soft skin and slimy bodies. Animals in the bathyal zone are not threatened by predators that can see them, so they do not have powerful muscles. Animals need to have the right adaptations to survive in this lethal area. There are no known plants because of the lack of sunlight necessary for photosynthesis. In the bathyal some of the world's largest whales feed. The adaptations of some of the fish that live there include small eyes and transparent skin.