The prosecutors have already charged two men who worked with the Culture Ministry publications department with "disparaging religion" and publishing a work offensive to public morals.
About 2,000 students took part in protests around Al-Azhar University in Cairo, and police used tear gas and rubber bullets to disperse them.
The 75 students released on Friday could be re-arrested because prosecutors have not closed the case, correspondents said, quoting security sources.
The prosecutors have already charged two men who worked with the Culture Ministry publications department with "disparaging religion" and publishing a work offensive to public morals.
On Thursday, one of the men, Ibrahim Aslan, a prominent novelist in his own right, said he had been questioned for eight hours by prosecutors for his role in recommending that the book be reprinted.
Intellectuals have defended the book, accusing the Islamists of inciting violence.
"Most of the students who demonstrated have said they didn't read the book," Mr Aslan said after his questioning.
Culture Minister Farouk Hosni, who has been strongly criticised by Islamists over the reprinting of A Banquet for Seaweed by the Syrian writer Haidar Haidar, said about 1,000 copies had been sold, but that the rest had been withdrawn from bookshops.
Arab dictatorships
The clashes were among the most serious to take place in Cairo since the protests against the Gulf War in 1991.
A Banquet for Seaweed, first published in Beirut in 1983, was released in Egypt last November by an institution affiliated with the Culture Ministry.
The plot centres on two leftist Iraqi intellectuals who fled the injustice of Iraqi President Saddam Hussein in the late 1970s.
The characters blame political oppression in the Arab world on dictatorships and conservative movements.
In one of the most controversial extracts, God is described as a failed artist.