Om Namo Narayanaya

There are very few temples dedicated to Matsya Avatara one such is Nagalapuram Veda narayana swami perumal temple

As you can see Sri Mahavishnu is in matsya roopi with fins(instead of ears) and holds sudrashana Chakra in prayoga(ready to release)

According to Matsya Purana
Devataa one day is one kalpa, one day at the end of kalpa Brahma deva felt sleepy and vedas slipped out of his mouth due to involuntary yawning a demon named somakudu stole the vedas from brahma. Vedas are necessary for creation.

As we know Pralayam occurs at the end of every Kalpa and creation is again started by Lord Brahma, it was necessary to collect all the plants, seeds, animals so that they would continue to exist in the new creation
Devatas prayed Lord Vishnu to get the Vedas back from the Demon

King Satyavrata a devotee of Sri maha vishnu who was later know as Manu was offering water during Sandhya vandanam
Sri Maha Vishnu in the form of a small fish came into his hands and pleaded to save its life. He drops it in his Kamandalam.

Over night the fish became too big to be in Kamandalam. By the request of the fish he moved it in to another big bowl, but soon fish became too big for the vessel also. Then Satyavrata then left the fish in a pond but in no time the fish grew as large as pond.