YOU buy a cute little catfish around 6in long which fits perfectly in the modest fish tank in the living room.
Fast-forward several months and you realise you have bought a monster.
This week, The Deep transferred two large pangasius catfish to Bristol Zoo.
They are among several species, which The Deep has rescued from pet owners and hobbyists after they've outgrown their tanks.
These stunning fish heading south are now a whopping 60cm and 45cm in length and are still growing, something the owner did not bank on when they were purchased.
The problem has led to the launch of The Big Fish campaign to highlight the pitfalls of buying fish which can grow very large.
"These Pangasius were living in a cramped 4ft tank, which was nowhere near big enough for them," curator at The Deep Katy Duke said.
"The owner was simply not aware of the size they would grow to or what facilities and care they would need.
"Many of these 'problem species' will grow to more than a metre in length, which ultimately leaves owners with a huge problem in more ways than one.
"When there are so many species of fish to choose from, it really pays to do your homework first."
The Big Fish campaign aims to educate both businesses and consumers about how important it is to research and choose the right pet fish before buying.
Many fish which people think of as pets can quickly outgrow an average tank, leaving the fish cramped and in compromised conditions which can cause deformities and even premature death.
A lot of the time, people are simply unaware of just how big their "pet" will grow.
The most common problem species include freshwater fish such as pangasius, pacu, plecs and redtail catfish.
BBC's The One Show was on hand this week to film the pangasius leaving The Deep, which Mrs Duke hopes will boost the awareness campaign.
"It is fantastic to see The One Show covering this important issue and helping us spread the message," she said.
"Aquariums all over the UK get numerous phone calls every week from members of the public with the same problem – their fish has grown too big for its tank.
"While it may seem logical to contact a zoo or aquarium, the space in these facilities is limited and designed for the animals they already house.
"This, sadly, is the situation here, but we are delighted to see them going to a new home with our friends at Bristol Zoo where they will make up part of their Asian display alongside a variety of Asian fish including giant gourami, dragon fish and fly river turtles."
The British and Irish Association of Zoos and Aquariums(BIAZA) Aquarium Working Group is behind the campaign.
It carried out research showing that in just four months, 11 UK aquariums were asked to house 144 fish that had outgrown their owners' tanks. At the same time the BIAZA Aquarium Working Group has been asking pet stores to sign up and support the Big Fish Campaign which already has the support of many responsible retailers who only stock species that are suitable for the average home aquarium and provide accurate information to their customers.
Robert Nicklas, of Thearne Pet Store in South Street, city centre, believes lesson are being learnt but there remains a problem.
"Fish are deemed a lower life form than other pets but that doesn't mean people should be unnecessarily cruel," he said.
"People have to understand some fish grow very large and they will die if they don't have enough space.
"There are many varieties of catfish and people need to do their homework."
Mr Nicklas admits more still needs to be done within the pet store industry but believes it is improving.
"None of my suppliers are selling pangasius and knowledge has increased within the industry over the past few years.
"There have been practices going on for years, which are now being turned around.
"But I am convinced there are still pet shops, which aren't following the right advice."
There are catfish which are suitable for small tanks.
"There is a group of catfish called corydoras, which are quite small and don't grow much more than 6in," Mr Nicklas said.
"These are suitable for most household fish tanks."
You can help improve the welfare of pet fish by supporting the campaign. Visit www.bigfish campaign.org to find out more.
