Hot-tempered eggs: bobtail squids can alter their colour even before they are born

Hot-tempered eggs: bobtail squids can alter their colour even before they are born

The biologists at the Primorsky Aquarium have obtained the first brood of the butterfly bobtail squid (Sepiola birostrata) – a tiny cephalopod found in the Sea of Japan.

“At the Aquarium we provide the mollusks with conditions similar to their natural habitat, including the opportunity to prey on live food, the opossum shrimp, and all these efforts have resulted in their breeding,” said Yuriy Nekotinev, Lead Specialist at the Department of the Russian Far East Marine Organisms. ““In our fish tanks the water temperature is constantly kept at 10°C throughout the year that is why the bobtail squids laid eggs without waiting for spring. In the wild females attach their eggs to some structure in well aerated places with good water circulation and always conceal them with sand. Our female picked an overflow pipe to lay eggs on and dusted its offspring with sand to hide them.”

Bobtail squids reproduce once in their lifetime. Using its modified arm, a male inserts sperm into the female’s mantle cavity. The female fertilizes eggs releasing them from the mantle cavity, and then attaches these eggs to some substratum in the site chosen for spawning. If considering that a female deposits several hundred eggs, one can understand how time- and effort-consuming this process is.

Eggs of the miniature cephalopod are minute, measuring about 1 mm in length. They are transparent but if disturbed, the eggs begin turning red inside -  bobtail squid’s embryos are able to change their colour before they even hatch. Bobtail squids have a complicated camouflage mechanism: to merge with the surroundings, they use their muscles and chromatophores – pigment-bearing and light-reflecting cells. The mollusk’s brain analyzes the environment and sends out signals to the cells to change the colour and to the muscles to alter the shape of the body. 

Some of the babies have already hatched. Immediately after emerging, they started hunting. The newborn predators are fed with brine shrimp -  planktonic crustaceans.

General Information

— The bobtail squids that spawned at the Aquarium had been collected during monitoring of ichthyoplankton in Zhitkov Bay in October 2019.

— An adult butterfly bobtail squid reaches a size of some 2 cm; its lifespan is about 1 year.

—The butterfly bobtail squid glows in the dark. Inside the mantle the mollusk has a two-horned sac containing mucus with bioluminescent symbiotic bacteria.