The Sea Life aquarium in Bray, Co Wicklow, is to close in December after more than 25 years.
A statement on the Sea Life website said it was a "difficult decision" and their priority now would be finding suitable homes for the animals and helping staff with career opportunities.
Speaking on RTÉ's Morning Ireland, marine biologist and Social Democrats TD for Wicklow Jennifer Whitmore said the closure was "sad and shocking" and that the aquarium was "so important" for education and tourism.
Ms Whitmore said 20 staff are affected.
"It was somewhere everyone would bring their children to learn and experience the love of nature and marine," she said.
"This is really disappointing for families in Wicklow and all of the east coast and across the country."
Ms Whitmore said Sea Life needed investment and it was a financial decision to pull out.
She added that it would be her preference that entities like these are State-owned and not at the whims of the financial markets.
Sea Life Bray was the only aquarium on the east coast and it will be a "huge loss", Ms Whitmore said.
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Minister for Higher Education and Fine Gael TD for Wicklow Simon Harris said the decision to close Sea Life is a "blow to tourism and education" and called on the owners, Merlin Entertainment Group, to reconsider.
"This decision seems to have come as a bolt from the blue and it was widely recognised that visitor numbers were increasing again since the difficult pandemic days," Mr Harris said.
"Sea Life is still currently operating and I would call on Wicklow County Council, Fáilte Ireland and all relevant State agencies to see if they can assist in having this decision reversed.
"I would encourage the company to engage in a meaningful way to see if a resolution can be found."
