In her poem “The Dolphins” Carol Ann Duffy lends voice to a dolphin to express its feelings living in a pool in its own words. The dolphin describes how their life of thraldom has been different from the life when they enjoyed complete freedom in the open ocean. In fact, the poem opens with the dolphin saying what true ‘world’ would be like:

World is what you swim in, or dance, it is simple.

This is the kind of world that the dolphin used to live in earlier. But now they are forced to live in a pool. Though they are in their element, i.e., in water, they are not free. Freedom is what the dolphin finds most important to be happy. There is a man constantly guiding their movements through hoops. There is a constant feeling of guilt in their life of bondage.
 
The dolphins don’t find the comfort and ease in the pool. They are now unhappy for being regulated and restricted by a man. They cannot do anything they like. Rather they have to work in the tunes of the whistle as the man wants them to perform to entertain people in the circus. The dolphin finds its life in the aquarium monotonous with no change at all. It repeats the words “same space” twice to highlight the monotony. 

It was the same space. It is
the same space always and above it is the man.

In the pool, the dolphins have got nothing but only a coloured plastic ball on which they have to balance. They can no more see the moon as they are not in the open ocean. They sing a “music of loss” and there is hopelessness everywhere. They sink to the limits of the pool, not only literally but also metaphorically. They know that they will eventually die here in the pool, as there is a man restricting their movements.

There is a man and our mind knows we will die here.

So, to conclude, through the voice of a dolphin the poetess has successfully painted how a life of suppression and slavery feels like as opposed to a free life. It is full of restrictions, monotony, artificial barriers, sense of loss and hopelessness, and of course, realisation of the importance of freedom, as the dolphin now realises.