Fish

Of purifiers I am the wind; of the wielders of weapons I am Rāma; of fishes I am the shark, and of flowing rivers I am the Ganges.
(BG 10.31)

One who loves Kṛṣṇa will give Him whatever He wants, and he avoids offering anything which is undesirable or unasked for. Thus, meat, fish and eggs should not be offered to Kṛṣṇa. If He desired such things as offerings, He would have said so. Instead He clearly requests that a leaf, fruit, flowers and water be given to Him, and He says of this offering, “I will accept it.” Therefore, we should understand that He will not accept meat, fish and eggs. Vegetables, grains, fruits, milk and water are the proper foods for human beings and are prescribed by Lord Kṛṣṇa Himself. Whatever else we eat cannot be offered to Him, since He will not accept it. Thus we cannot be acting on the level of loving devotion if we offer such foods.
(BG 9.26 purport)

There is a Bengali proverb that “You go to catch fish, but don’t touch the water.” You see? If you are clever, if you have that rod to catch fish, take out the fish, but don’t touch the water. Similarly, for our Kṛṣṇa consciousness movement we have to go in so many places. They are all materialistic, but we cannot become materialistic. We will take some service from a person for Kṛṣṇa’s service. So we’ll do some good to him, but we don’t accept his quality. That should be our position.
(Lecture on SB 2.9.2 — Melbourne, April 4, 1972)

A fish that is taken out of the water cannot be happy by any arrangement on land. He must be supplied with water. In the same way, the minute sac-cid-ānanda living entity cannot be really happy through any amount of planning conceived by his illusioned brain in this material universe. He must therefore be given a different type of happiness which is spiritual in essence. Our ambition should be aimed at enjoying spiritual bliss and not this temporary happiness.
(EKC 2 Hard Struggle for Happiness)