On the Identity of the Matsya Avatara of Visnu

pātālādutpatiṣṇormakaravasatayo yasya pucchābhighātā-
dūrdhvaṃ brahmāṇḍakhaṇḍavyatikaravihitavyatyayenāpatanti |
viṣṇormatsyāvatāre sakalavasumatīmaṇḍalaṃ vyaśnuvānā-
stasyāsyodīritānāṃ dhvanirapaharatādakṣriyaṃ vaḥ kṣrutīnām 1

The mention of Matsya jumping up (utpatisnu) from Patala in this opening verse of the Matsya Purana provides a great clue with regard to the identity of Matsya.

The impression one gets from these opening verses of the Matsya Purana is that Matsya, the primeval piscis, is the zoomorphic representation of the respiratory diaphragm. It is easy to understand why the diaphragm would be regarded as the very first descent of the Lord into the microcosm. Being the primary muscle of inspiration, the diaphragm is without doubt one of the most important entities of the cardio-respiratory framework. It supports the heart and the lungs and it is the inferior-superior movement of the diaphragm that provides the chief mechanism, from the point of view of respiratory mechanics, for breathing—inspiration as well as expiration—of the jiva. The respiratory diaphragm is thus, in this perspective, the very support of the jiva. It is Ananta; the jiva is Visnu. Ananta resides below Patala, the subterranean region; this is the region below the heart and the lungs.