Owner of the attraction Marita Iverson said she will be handing keys to the premises over on 14 October but that the fish will have to be released or rehomed earlier than that.
'I'm going to do a sale but for the Aquarium I need to rehome everything and will have to let the local fish go.'
'The last chance to go into the Aquarium will be Thursday 3 October because then on Friday I will be releasing the local fish back to the water.'
Ms Iverson said the shop sale will then continue until closer to the date of closure to sell remaining stock which includes fish keeping equipment, food, teas and Guernsey merchandise including Guernsey jumpers.
'It's due to lack of tourism and a lack of support, it can no longer sustain itself.'
However Ms Iverson said she was grateful for the visitors and islanders who had supported the Aquarium.
'I want to thank so so much all those who have supported us over the years.
'Nobody is sadder than me.'
Ms Iverson has been finding new homes for the more exotic species but said there were still a few left and that anybody interested should come and speak to her at the Aquarium in La Vallette.
Having been involved with the Aquarium for five-and-a-half-years, Ms Iverson has made a number of changes to the site in order to attract more visitors including a complete refurbishment in 2017, a cafe area and an arcade room.
She had dreamed of one day setting up an ormer hatchery project to help conserve the Guernsey population.
Earlier this month Ms Iverson said she worried the attraction would have to close if business did not pick up because the number of visitors had been so low this year.