Matsyasana: Fish
This asana eases tension and improves spinal flexibility. Steps:

1. On your back: Assume the Corpse Pose and, when you are ready, begin to come into the fish. Stay flat on your back, and bring your feet together. With your arms straight by your sides, lay your palms on the floor, then tuck your hands in underneath your buttocks. Starting Pose: Prepare yourself for this asana by relaxing in the Corpse Pose for as long as you need.
2. Head Back: Having arched your spine, tilt your head so that your crown rests on the ground. Hold for 30 seconds. To come out of the Fish, slide your head back and then lower your chest. To finish, relax by lying in the Corpse. Chest Lift: Press your elbows down on the floor, inhale, and arch your chest upward as far as you can.
3. Inhale and bend the left knee upward and place the left foot flat on the floor to the right of the right leg with the ankle touching the right thigh.
4. While turning the spine to the left straighten the right arm bringing it around to the outside of the left knee and grasp the left foot with the right hand.
5. Turn your head as far as possible to the left and bend the left arm behind your back. Keep your spine, neck and head aligned and continue to exert effort at turning to the left.
6. Repeat the posture the other side by reversing directions 2-6.

The fish is the stretch that counters the Plough. The name of the posture derives from the fact that if you adopt the position in water, you will float quite easily. The Asana does wonders for your respiratory systems; when you assume this position, your chest is stretched open and your bronchial tubes are widened to promote easier breathing. In time your ribcage will expand, and this will also encourage you to breathe more deeply. By lifting your chest and tucking your arms underneath your body, you will combat postural defects such as rounded shoulders and the cervical region of your spine, thus releasing pressure on your nerves. Try to hold the pose for half of the time that you spent in the Shoulderstand, in order to equalize the stretching effects on your spine ans muscles.

Fish Variations
Try this if you are flexible enough. In the Easy Pose, clasp your toes. Lie back, arch up, and rest your buttocks on your heels. Lay the top of your head on the floor.
Knees Bent - Sit cross-legged, then put your arms down behind your knees and catch hold of your toes.
Fish in Lotus - This pose is an advanced variation on the ordinary Fish. It is similar to the Easy Pose variation shown above, except that it begins with the Lotus. Practitioners of yoga use this variation for staying afloat in water. The Fish in Lotus pose should not be attempted by beginners, or even by more experienced yoga students, until the full Lotus position can be held comfortably for a long period of time.
At the end of the session one must do a deeper, final relaxation.