Various Forms of Fish Pose (Matsyasana) :

There are many forms or types of Fish Pose (Matsyasana), ( matsya meaning fish, asana meaning pose). If you’re not capable of comfortable with the full-fledged Fish Pose now, you can practice the easier forms or types.

It is very natural that everyone will not be as capable to follow full-fledged form. They should go for easier forms/types of Fish poses. Somebody may  feel problems in the ankles, some on other areas. So easier forms of fish pose is there to help you.