An animal rights group is challenging Bedford's bid to bring the world's largest aquarium to the town.
An aquatic habitat science centre aims to boost conservation
The National Institute for Research into Aquatic Habitats said the science centre will attract 2m visitors a year.
But Justina McLennan, of Bedford Animal Action, said research has shown that fish suffer stress in aquaria.
Both the borough council and the county council support the £160m project, and the town is in competition with Merseyside and South Wales.
The project would have a domed structure four times the size of Cornwall's Eden project and would be built on the site of abandoned brick factory pits at Stewartby on the edge of Bedford.
But the Bedford Animal Action group said they have deep concerns about the proposed project.
Ms McLennan said: "Fish and reptiles shouldn't be kept in a confined environment.
"We're afraid that what is being marketed as a conservation project will in fact be nothing more than an animal-testing facility."
The backers of the aquarium project said it would be a unique global reference point for pioneering research and the study of freshwater habitats.
A National Institute for Research into Aquatic Habitats (NIRAH) spokesman said: "A number of inaccurate claims have been made about the ability to successfully keep fish, amphibians and reptiles in captivity.
"The fact is, nearly all species of 'freshwater' fish, amphibians and reptiles have far longer lives in captivity than they would ever have in the wild.
"Internationally acclaimed zoos and public aquaria continue to breed species that would have, otherwise, gone into extinction years ago.
"NIRAH will be able to provide captive conditions in which different species will live out longer and healthier than normal life-cycles whilst displaying their normal
range of behaviour, and so provide the basis of valid and highly valuable scientific research."