SB 3.9.19
tiryan-manusya-vibudhadisu jiva-yonisv
atmecchayatma-krta-setu-paripsaya yah
reme nirasta-visayo ’py avaruddha-dehas
tasmai namo bhagavate purusottamaya
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
O my Lord, by Your own will You appear in the various species of living entities, among animals lower than human beings as well as among the demigods, to perform Your transcendental pastimes. You are not affected by material contamination. You come just to fulfill the obligations of Your own principles of religion, and therefore, O Supreme Personality, I offer my obeisances unto You for manifesting such different forms.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The Lord’s incarnations in different species of life are all transcendental. He appears as a human being in His incarnations of Krsna, Rama, etc., but He is not a human being. Anyone who mistakes Him for an ordinary human being is certainly not very intelligent, as confirmed in Bhagavad-gita (9.11): avajananti mam mudha manusim tanum asritam. The same principle is applicable when He appears as the hog or fish incarnations. They are transcendental forms of the Lord and are manifested under certain necessities of His own pleasure and pastimes. Such manifestations of the transcendental forms of the Lord are accepted by Him mostly to enliven His devotees. All His incarnations are manifested whenever there is a need to deliver His devotees and maintain His own principles.