The Aquarium biologists put an end to “terror”

The Aquarium biologists put an end to “terror”

The slow pace of life at the Ocean Abyss exhibit has been interrupted by maturing cobias. These distant relatives of remoras were added to the Aquarium's largest tank in late 2018. Then the cobias were very young and had a body length of up to 30 cm, -- but their ill temper manifested itself at once, for instance, they bit scuba divers in the fingers and cheeks during feeding sessions. As biologists expected, such behavior was only the beginning of what was to come. Within a year the predatory fish grew enough – some of them are more than one meter long – to cause troubles not only to people taking care of them but also to their tank mates. Spotted eagle rays and Javanese сownose rays got the worst of it – the cobias started stripping food from them.

“Aggression is an inherent behavioral trait of cobias,” said Alexander Volkov, Senior Specialist at the Tropical Marine Organisms Department. “While adjusting predators to a captive environment, we change their food habits – the fish take prepared feed from human hands and do not prey on the other residents of the tank. But natural aggression in cobias tends to increase as they age, and especially during the puberty period.”

“Not long ago we began hand-feeding bony fishes separately from rays and sharks,” said Mikhail Streltsov, Head of the Tropical Marine Organisms Department. “Thus, in addition to Dancing with Rays, one more feeding program – Underwater Swirl –  emerged. The cobias fitted in with the “swirl” of bony fishes rather well but after a while they resumed harassing their tank mates. To overcome this sticky situation, we have introduced a new feeding scheme. Now the cobias get their feed from the staff’s hands at the water surface an hour or an hour and a half prior to lunch for the other species inhabiting the exhibit. This time interval is chosen based on experience – the predatory fish have enough time to calm down and realize their being satiated.”

Forty cobias consume 15-18 kg of fish per feeding, their diet consists of char and saffron cod. Since in the wild cobias hunt for large prey, the husbandry kitchen staff cut fish for them into large pieces, and  medium-sized chars are swallowed whole by the predators.

General information:

— The species has a number of common names, including black kingfish, black salmon, crabeater, and lemonfish.

Its large pectoral fins are normally carried horizontally, so that, as seen in the water this fish may be mistaken for a small shark.

— Cobias can grow to a length of 2 meters. They are a solitary species and only gather in groups during breeding seasons.