This is a yoga pose. It is a hard pose to do if you're a beginner. Traditionally Fish Pose is performed with the legs in Padmasana. Since Padmasana is beyond the capacity of most noobs, here you will have to do the knees bent, feet on the floor, or with the legs straight pressed against the floor.
Lie on your back on the floor with your knees bent, feet on the floor. Inhale, lift your pelvis slightly off the floor, and slide your hands, palms down, below your buttocks. Then rest your buttocks on the backs of your hands (and don’t lift them off your hands as you perform this pose). Be sure to tuck your forearms and elbows up close to the sides of your torso.
Inhale and press your forearms and elbows firmly against the floor. Next press your scapulas into your back and, with an inhale, lift your upper torso and head away from the floor. Then release your head back onto the floor. Depending on how high you arch your back and lift your chest, either the back of your head or its crown will rest on the floor. There should be a minimal amount of weight on your head to avoid crunching your neck.
You can keep your knees bent or straighten your legs out onto the floor. If you do the latter, keep your thighs active, and press out through the heels.
Stay for 15 to 30 seconds, breathing smoothly. With an exhalation lower your torso and head to the floor. Draw your thighs up into your belly and squeeze.
The benefit you get from this pose are improved posture and helps strengthen the muscles of the upper back and back of the neck. It also stretches the deep hip flexors (psoas) and the muscles (intercostals) between the ribs, stretches and stimulates the muscles of the belly and front of the neck and the organs of the belly and throat.
That's not all. It is said that if you perform this pose in water for a few minutes, you will be able to float like a fish. So, you wanna give it a try? Anyone?