The waterfalls of “That country” are crowded with salmon fish. Besides, the seas there are teeming with mackerel fish. All these creatures (birds and fish) listen to sensual music and do not indulge in intellectual or artistic activity.In lines 7 to 8, the poet says these creatures listen to sensual music without caring for intellectual activity, which (intellectual activity) is ageless and so of a permanent value. Great works of art never die. Sensual music is that which appeals to the senses as distinguished from the mind or the intellect. The intellectual achievements are supposed to be ageless and immortal and so of permanent value. The reference is to things of beauty that are a joy forever,