For the video below, the official title is “The Behavioral Preferences of Opae Ula Shrimp in Varying Conditions.” It was uploaded to YouTube on 9 Jan. 2014 by Spencer Kiehm. The researchers are Shane Hayakawa, Kiehm, and Charlynn Yeung.
The results of this study reinforce the theory that opae’ula need both light and dark places in a tank. The researchers placed the tiny Hawaiian shrimps into a clear tube in direct sunlight, and after they covered one end to block the light, they found that the shrimps all moved to the darker end.
The generalization is that light is needed for the growth of algae, which the shrimp relies on for food, but when not feeding, they tend to prefer darker places.
The message for tank owners is to not be concerned if your opae’ula aren’t always visible. They’re hiding in the dark places in your tank. An equally important message is that you should factor dark hiding places into your tank design. An excellent, and apparently effective, method is suggested by Dennis Nakashima, who adds a mound of small coral rocks in one corner of his tank. I’ve followed his example in my tanks.
These mounds serve as a kind of apartment complex for the shrimp. The gaps between the unevenly shaped rocks serve as natural living spaces. According to Nakashima, dark private places are essential for breeding. In this respect, opae’ula aren’t much different from homo sapiens.