Does the crab actually keep time，or does its skin simply respond to the sun’s rays，changing color according to the amount of light that strikes it？To find out，biologists kept crabs in a dark room for two months．Even without daylight the crabs’skin color continued to change precisely on schedule．
This characteristic probably evolved in response to the rhythm of the sun，to help protect the crab from sunlight and enemies．After millions of years it has become completely regulated inside the living body of the crab．
The biologists noticed that once each day the color of the fiddler crab is especially dark，and that each day this occurs fifty minutes later than on the day before．From this they discovered that each crab follows not only the rhythm of the sun but also that of the tides．The crab’s period of greatest darkening is precisely the time of low tide on the beach where it was caught！
招潮蟹——活的时钟
招潮蟹是一座活的时钟。它以皮肤的颜色显示一天的时间，白天皮肤呈黑色，夜晚呈灰白色。招潮蟹变化着的肤色遵循着一个有规律的24小时周期，与太阳的每日律动正好吻合。
是招潮蟹真的会计时，还是它的皮肤对太阳光作出反应，按照射在它身上的光量来改变颜色的呢？为了弄清这一问题，生物学家们把招潮蟹放在一间暗室里生活两个月。即使没有日光，招潮蟹的肤色照样准时变化。
这一特征可能逐渐演化成为对太阳律动的反应，借以帮助招潮蟹免受阳光和敌人的侵害。经过几百万年，这一特点在招潮蟹活动的身体里变得完全规律化了。
生物学家们还注意到，招潮蟹的颜色每天有一次显得特别黑，而且这一情况每天总比头一天迟出现50分钟。他们由此发现：每只招潮蟹颜色的变化，不仅遵循太阳的节律，而且还顺着潮汐的涨落。招潮蟹颜色最深暗的那段时间，正是它落网的海滨的低潮时间。
The Trumpet Fish in the Waters
Near the Cape Verdes Islands
Our best companion in the reefs was tragicomic trumpet fish，which is found everywhere in great numbers in the waters near the Cape Verdes Islands．The trumpet fish has a head like a horse’s，a disproportionately tiny tail，and a long，pipelike body．
This hapless fish，sometimes called poisson flute，is wretchedly equipped for locomotion；his useless tail and stiff tubular body are handicaps for which he compen states by wildly agitating his pectoral fins to move forward and backward．Dozens of these unhappy creatures may be found sticking up from a rocky hole，like pencils in a cup．
Often a trumpet fish will abandon his fellow wall flowers and swim rapidly toward a larger animal，such as a parrot fish or rock bass．He will place himself alongside or on the back of the pass or by，barely touching it，and swim along in this tandem fashion as if seeking friendship，begging for tenderness，offering his heart．There is absolutely no hostility in this gesture The trumpet fish，unable to harm even a fish his own size，is in fact placing himself in danger by approaching the larger，more capable fish．
The gesture is never reciprocated．The larger fish goes about its affairs，heedless of the trumpet fish until it grows annoyed with this bore．Then it spurts forward to dislodge the nuisance，but the lonely one follows．The large fish accelerates to full speed，leaving the trumpet fish hanging morosely behind，rejected once again．
We watched this piscine social drama many times，torn between pity and laughter．
佛得角群岛附近水域的管口鱼
在礁石中，我们的最好伙伴是可悲又可笑的管口鱼。在佛得角群岛附近的水域，到处都能见到大批管口鱼群。管口鱼的头很像马头，小小的尾巴跟全身很不相称，身躯是长长的，像一根管子。
这不幸的鱼，有时被称作“长笛鱼”，它身上长的帮助运动的器官十分可怜。它那毫无用处的尾巴和僵硬的管形身躯是运行的障碍，它用以补救的办法是，猛烈摆动胸鳍以使身体前进或后退。人们可以看到几十条这样不幸的动物从一个石洞里竖起身来，就像插在茶杯中的铅笔一样。
一条管口鱼常常抛弃它的寂寞的同类伙伴，迅速游向一只较大的动物，如一条鹦嘴鱼，或一条岩阳鱼。它常与路过者相比肩，或游到路过者的背上，只不过去碰一碰它，然后便尾随其后，一前一后向前游，好像寻求友情、乞求爱抚和倾诉衷肠似的。这一举动决无敌意。管口鱼甚至难以伤害与其大小相仿的鱼，因此它在靠近较大的、更有能耐的鱼时，实际上已把自己置于危险之中。
这一举动从未获得回报。大鱼自顾自的事，对管口鱼不予理会，直到它对这一可恶的家伙感到厌烦时。接着，它便突然迅速向前游去，以摆脱这讨厌的家伙，但是这孤独者却紧随不舍。这时大鱼便全速向前游去，让管口鱼苦恼地滞留在后边，再次品尝遭受抛弃的滋味。
我们曾多次观察这一鱼类社会剧，既感到好笑，又产生同情。