Method
Lie down straight on your back for matsyasna. Keep both legs together touching heels and toes. Place both the hands sideways facing palms downwards. First of all bend right leg and keep it on left thigh and left leg on right thigh (while lying this is the position of padmasana) you can do by sitting in padmasana and lie down backwards while taking support of hands and elbows.
You It can be done according to your convenience. After keeping both legs on thighs take your hands over the head and raise your head and bend it try to touch the head from where hair starts touch it at the back on ground. Now take both hands from there and try to touch the toes with your hands. Place elbows on ground. Those practitioners who cannot hold toes or cannot place elbows on ground can keep their hands on knees. Keep your eyes and mouth closed. After being in this position for 10-15 seconds slowly leave this asana. First bring hands on floor make your head straight and straighten your left then right leg loose your body. Rest in savasana for sometime then do it again.
Benefits
Matsyasana is very good for stomach related problems. It overcomes constipation helps in blood circulation at back. This asana is compliment of sarvanasna.
Time
In first week do one cycle and with time you can increase it three times. In the beginning start with 15 seconds. The time which you give to sarvangasana if you give one third to matsyasna only then it will be completely beneficial.