Can the Lord not come in animal forms?

[The Puranas mention the forms of a fish (Matsya), tortoise (Kurma) etc. that the Lord took and came to earth.] Matsya, etc. are the forms in which the Lord came temporarily to destroy demons. Such forms were not worshipped because they did not live along with human beings like Rama and Krishna [human incarnations]. Such animal forms could not preach the divine knowledge.