Depending on the form of pleasure that beings desire and the evolutionary cycle of species, they reincarnate from one body to another.
It is written in the Vedas, the original holy scriptures, that aquatic beings are inferior to plants.
A living being (human, animal, or plant) is originally a spiritual entity or spirit soul, and its desire to taste the pleasures of this material world causes it to fall from its position.
We can understand that the incarnated soul first assumes a body in human form, but gradually, due to its degrading actions, it falls among the lower species, animal, plant, or aquatic.
Beings incarnate in various material bodies, but all these envelopes of dense matter are foreign to them. Depending on the form of enjoyment they desire and the evolutionary cycle of species, they transmigrate (reincarnate) from one body to another, passing from aquatic to plant forms, from plant forms to insect forms, then to reptiles, from reptiles to birds, from birds to terrestrial mammals, and finally to human form.
It is by His own power that God created the material cosmos.
The power of Krishna, the Supreme Personality of Godhead, has several aspects.
For example, it includes the Sudarsana, the discus, the weapon of the Lord whose phenomenal power destroys the demonic disbelievers, but also the gaze of Godhead through which everything was created. The material cosmos was created by the power of the gaze of Krishna, the Supreme Personality of Godhead. The Lord looked upon the total material energy, and when it was stirred by the power of this divine gaze, all things came into existence.
Sudarsana is the manifestation of the supreme transcendental power that God holds in His sublime hands, and the original vision through which everything was created well. This is the manifestation of the power of Krishna, the Supreme Personality of Godhead. That is why God is called “the all-powerful.”
All beings were created together, simultaneously.
Contrary to a widespread misconception, during Creation, God created all 8,400,000 living species—celestial, human, animal, and plant—at the same time, simultaneously.
True evolution does not occur at the level of the physical envelope, but at the level of consciousness. Therefore, if a spiritual being incarnates within a lower species, animal or even plant, they must gradually evolve to higher species, human or even celestial.
Of these two energies, life and matter, or life and the soul, the latter represents the higher, original energy. As for matter, which is the lower energy, it comes from life. They exist simultaneously.
For the well-being and harmony of all spiritual beings who were to live in the material universe, God gave them all a body according to each person's karma. Their respective bodies were all created by Krishna, the Supreme Personality of Godhead, together, at the same time, simultaneously.