Volume 2

Welcome to Ushimitsudoki Aquarium (丑三ッ時水族館へいらっしゃい, Ushimitsudoki Suizokukan He Irasshai) is the second volume of the Oumagadoki Zoo manga.

Chapter

 * Chapter 8: The Rabbit and the Unidentified Walking Object (ウサギと未確認歩行物体, Usagi to Mikakuninhokoubuttai)
 * Chapter 9: The Aquarium's Invasion (水族館の侵略, Suizokukan no Shinryaku)
 * Chapter 10: Zoo vs. Aquarium - The Outburst (動物園　ＶＳ　水族館勃発, Doubutsuen baasasu Suizokukan Boppatsu)
 * Chapter 11: Welcome to Ushimitsudoki Aquarium! (丑三ッ時水族館へいらっしゃい, Ushimitsudoki Suizokukan He Irasshai)
 * Chapter 12: Assault! The Local Aquarium (突撃！　隣の水族館, Totsugeki! Tonari no Suizokukan)
 * Chapter 13: Shiina and Isana (椎名と伊佐奈, Shiina to Isana)
 * Chapter 14: Zoo vs. Aquarium! It Begins! (動物園　ＶＳ　水族館、　開始, Doubutsuen baasasu Suizokukan, Kaishi)
 * Chapter 15: Willpower of the Underdog (負け犬根性, Makeinu Konjou)
 * Chapter 16: Duel of Honorable Men (漢の決闘, Otoko no Kettou)

Synopsis
An orca named Sakamata appears at the zoo asking if he could speak with Shiina, after the conversation they were been disagreeing with him which he uses violent and captured Igarashi. Shiina is with anger to the Ushimitsudoki Aquarium to rescue him. In the Aquarium they meet Isana the director of the zoo. While being separated by Isana's attack Hana then knows more about the Aquarium and the horrible director.