Psilogobius mainlandi Baldwin, 1972
This small goby lives on silty sand bottoms where it shares a burrow with either of two species of snapping shrimps. The nearly blind shrimp digs and maintains the hole, while the goby, with its keener senses, stands guard at the entrance. The shrimp, which labors underground clearing and extending passages, emerges at intervals pushing a load of rubble like a little bulldozer. When near the entrance it always keeps one antenna in contact with the goby's tail fin. At the slightest sign of danger, the goby twitches its tail signaling the shrimp to retreat. If danger is imminent, the goby follows. Sharp-eyed snorkelers in Kane`ohe Bay, O`ahu, or inside the reef at Hanauma Bay can easily observe shrimp and goby pairs. Their holes enter the sand at an angle and have a pile of excavated sand in front. The burrows are under constant construction and may shift location from day to day. Occasionally these gobies live in empty burrows made by other animals, such as mantis shrimps. Many species of shrimp gobies are known; this is the only one from Hawai`i. The name honors zoologist Gordon Mainland who drew attention to this fish while a student at the University of Hawai`i. The goby attains about 2 1/2 in., the shrimps about 1 1/2 in. Both are usually smaller. The goby is endemic; the shrimps have Indo-Pacific distributions. Photo: Hanauma Bay, O`ahu. 8 ft.. One appears to be a female swollen with eggs. (This photo is in my Hanauma Bay book, but not in Hawaii's Fishes.)