Vaccinations of fish start in aquariums to fight diseases
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On the first floor of Tokyo Sea Life Park in Edogawa Ward, rocksuckers were clinging to the walls of an aquarium, themed on the “coasts of southern Africa,” through ventral suction discs on their bellies.
The fish, also called giant clingfish, died one after another from around early 2018. They were healthy in breeding tanks. However, after they were placed into water tanks for exhibition, they died in a span of about three months. Other fish in the tanks also died.
Through a microscope in the laboratory of the park, fish veterinarian Madoka Yoshizawa spotted “scutica,” a parasitic insect found in rocksuckers. If fish are infected with the insect, their muscles become necrotic and they die.
“It is a terrible disease-causing agent because portions affected by it can spread as quickly as in one day. A sense of crisis was felt in our park,” she said.
In such difficult circumstances, the park staff decided to give the rocksuckers vaccinations.
A move to protect fish in aquariums against disease through preventative inoculations, which is rarely seen in the world, is spreading in Japan.
Okinawa Churaumi Aquarium in Motobu, Okinawa Prefecture, and Ehime University have started information exchanges or joint studies with several facilities.
“If they can show healthy fish to visitors through appropriate vaccinations, then vaccines will have played a significant role,” said Chihaya Nakayasu, head of the Research Center for Fish Diseases, which is part of the National Research Institute of Aquaculture of the Fisheries Research and Education Agency.
In a closed environment such as in a water tank, all the inhabitants could die if one fish contracts and spreads a disease. To prevent that, fish veterinarians are cooperating with researchers.
If fish contract diseases in an aquarium, its staff clean the tanks thoroughly and even disinfect them in some cases. In the tanks of the rocksuckers, however, other fish are also present. Strong medicines added to the water may adversely affect sea anemone residing in them.
Previously, there had been no other way except for transferring diseased fish to other tanks and putting medicines for treatment into the water.
The use of vaccinations had spread in aquaculture since the 2000s and had been found to be effective for such species as yellowtail and flounder. However, they had not been used in aquariums partly because the disease-causing agents are different.
The Tokyo Sea Life Park turned to Okinawa Churaumi Aquarium for guidance.
In the aquarium, when abnormal symptoms occurred among marine creatures exhibited there, veterinarians and other staffers formed a medical team to determine the causes and work out measures to prevent a recurrence.
Previously, when the team analyzed dead fish, it determined that scutica was the cause of their deaths.
In 2017, the aquarium started to vaccinate fish in cooperation with Ehime University, which had made progress in studies of scutica vaccines for the aquaculture of flounder.
When the aquarium gave vaccinations to snappers and other fish, their deaths resulting from scutica drastically decreased.
“If precious fish or difficult-to-catch fish die and we try to secure new fish of those kinds, we are concerned about the costs and harmful effects to the (natural) ecosystem,” said fish veterinarian Makio Yanagisawa.
“In the case of fish that we exhibit in a school, if we can reduce the number of their deaths from 100 to 10 (with inoculations), the effects are huge,” he said.
In Tokyo Sea Life Park, some fish contracted diseases even after they were vaccinated. Therefore, the park is still in the trial-and-error stages.
“In aquariums, it is easier to control (water) temperatures and the salt content than in aquaculture. So it will be possible to heighten the effects of innoculations,” said Shinichi Kitamura, associate professor of fish infectious diseases at Ehime University.
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