Fans were rewarded for their patience when "Finding Dory" - the sequel to the 2003 hit "Finding Nemo" - finally arrived to German movie theaters this Thursday (29.09.2016).

In the animated film, the friendly but forgetful blue tang Dory searches for her parents - but then gets trapped herself.

In the United States, the movie established a new record for an animated film opening when it was released in June.

The Disney animated film "Finding Dory" has grossed nearly $1 billion worldwide to date

Conservationists, though, see the movie's huge success with mixed feelings.

On the one hand, they hope that "Finding Dory" will raise public interest in preserving our oceans, and the species that live there.

On the other hand, they see an unfortunate side effect, as Nemo the clownfish became hugely popular in Germany.

Boost for pet shops

After the massive success of "Finding Nemo," demand for clownfish and home saltwater aquariums rose in Germany.

"Kids see this fish [in the cinema] and they want to have it," says Marius Tünte of the German Animal Welfare Association.

Aquarium shops ran advertisements featuring Nemo the clownfish, trying to convince costumers that it was an ideal pet.

"A lot of parents thought that this animal was easy to handle and also quite cheap," Tünte says.

Sadly, that is absolutely not the case.

Clownfish, or anemonefish, were popularized by the movie "Finding Nemo"

Nemos down the drain

A saltwater aquarium is highly time-consuming to maintain - not to mention, expensive.

Günter Hein is more thn 70 years old, and has been an aquarium enthusiast his whole life. He discourages people from purchasing a saltwater aquarium as an impulse buy.

"The equipment is quite expensive - you need skimmers, strong pumps, strong lighting," Hein said. "The water quality has to be controlled around the clock, you need instruments for that. The saltwater cannot be changed easily, and needs to be kept absolutely clean."

Günter Hein helps organize freshwater fish exchanges

Children are simply not able to handle such complex aquarium systems, Hein adds.

Tünte says a lot of clownfish and other seawater fish died in the tanks in German households because people simply couldn't properly care for the animals.

"Many clownfish were even flushed down the toilet. We got feedback from public utilities that they had found this kind of fish in the sewers."

Saltwater aquariums are only for specialists, not for the mass market, Tünte stresses.

But already in June, some retailers reported an increase in sales of blue tangs like Dory across the US and in other countries.

There was a spike in blue tang demand after the film "Finding Dory" was released

Fishing with poison

According to conservationists, more than 90 percent of all fish in the aquarium shops are caught in the wild.

"Most fish come from illegal sources in Southeast Asia, Indonesia, Sri Lanka, the Philippines and so on," Phillip Kanstinger, marine expert with the World Wide Fund for Nature, tells DW.

The fishermen use poisonous sodium cyanide to render the fish temporarily unconscious. The animals drift to the surface, where fishermen collect them.

But even low doses of cyanide can kill fish and other organisms on the reef. Cyanide fishing can devastate an ecosystem, Kanstinger says, adding that it is contributing to the decline of reefs around the globe.

"For every aquarium fish that is sold, one square meter of coral reef is destroyed by this fishing."

Coral reefs around the world have been hit by a mass bleaching event linked to global warming

Baby Dorys from the lab

Most marine fish have such complicated lifecycles, it is impossible to breed them in captivity.

Let's take Dory, the blue tang. Its eggs and larvae are tiny, says Matthew DiMaggio of the Tropical Aquaculture Laboratory at the University of Florida.

"When they hatch out, they don't even have a mouth yet - their eyes really aren't functional," he tells DW. "Once they are ready to eat, they are still less than 2 millimeters long. What do you feed a fish that's not even 2 millimeters long?"

Baby blue tangs eat tiny crustaceans

Young "Dorys" are "pretty picky" with what they eat, DiMaggio says. That's why they typically die during the first days of their lives when bred in the lab.

His team found that they only eat copepod, crustaceans less than a millimeter long, which live among plankton.

Growing copepods in the lab, though, is just as complicated.

"The copepods will only eat live microalgae. So we actually have to grow algae to feed to these live copepods, so that we can then feed those copepods to the larvae fish."

Using this newly found food source, DiMaggio and his team succeeded in breeding blue tangs in captivity for the first time ever.

Right now, though, their blue tangs are much more expensive than the ones caught in the wild.

This year, researchers have succeeded in breeding blue tangs in captivity for the first time ever

But DiMaggio is hopeful that they will be able to make their lab Dorys competitive with fish from the wild.

"We will see these fish commercially available in the coming years."

The nongovernmental group Rising Tide Conservation helps to finance the project. They hope that captive-bred blue tangs will help to save the reefs from further destruction.

Alternatives available

Owning a home aquarium doesn't have to harm the environment, though.

If you still want to have a home fish tank after watching "Finding Dory," go for a freshwater tank, conservationists and animal welfare activists promote. This is a far better option than saltwater.

Discus fish are colourful and beautiful - and they are sustainably caught from the Amazon river

About 90 percent of freshwater fish are bred in captivity, WWF's Philipp Kanstinger says. But even those taken from the wild can be caught sustainably.

"It depends how well the fishery is managed. There are some examples from the Amazon River where locals catch fish in a sustainable way with traps, and sell them. It is a good additional income."

Projects like those give locals an incentive to protect their river systems, including the wildlife there.

So you can enjoy fish and other aquatic animals at home - and still leave Dory and her friends in the open ocean, where they belong.