The mayor was absent from yesterday's meeting, but when asked later about ratepayers funding the trip said it would be "no junket".
"It's part of my work and I don't think the ratepayers will object to me doing my job," he said.
"If you think that it's any kind of holiday, spending 13 hours in the cheap seats at the back of a plane to go there and work your ass off for four days and then spend 13 hours cramped up coming back, that's no kind of junket.
"It's a straight working trip, the itinerary doesn't give us time for a cup of coffee for pleasure."
The mayor said the expansion project was one of the biggest the council was currently working on. As it was estimated to cost "somewhere between $25 and $35 million, if that money is going to be spent it needs to be well spent".
It was expected between March 26 and April 2, staff would be visiting, researching, and developing partnerships with four facilities between the Monterey Aquarium/Monterey Bay Aquarium, California Academy of Sciences, The Aquarium of the Pacific, and Birch Aquarium at Scripps.
"The fact is that taking the mayor with them simply opens doors," Mr Dalton said.
A paper before the committee noted Mr Dalton's expenses would cost a total "higher estimate" of $6170. The bulk of this cost - up to $3200 - would be for international flights, up to $2500, and domestic, $700.
Estimates put additional costs at $2100 for accommodation, $600 for meals, and $270 for car hire.
Funding would come from the National Aquarium Expansion Project budget.
Reacting to the news of Mr Dalton's trip, New Zealand Taxpayer's Union executive director Jordan Williams said, "whenever politicians used weasel words like 'build relationships' and 'international partnerships' it starts to raise suspicions".
"It seems to us a bit premature to be sending Mr Dalton overseas to 'build partnerships' before the decision has even been made about the aquarium expansion".
Mr Williams said sister city relationships were "an excuse politicians to travel the world on our dime".
"This looks similar. The promised economic benefits never eventuate."
"On the flip side, the Mayor of Hastings, Laurence Yule, goes on countless overseas junkets in his role as president of Local Government New Zealand. At least Mr Dalton, unlike Mr Yule, is transparent about how much this trip is costing ratepayers."
The council is leading the expansion project in partnership with Hawke's Bay Regional Council, Waikato University, and several public and research organisations.
The project also received central government support through Matariki - Hawke's Bay Regional Economic Development Strategy and Action Plan 2016.
At the strategy's June launch it was announced the Government would commit $50,000 toward scoping the proposal's feasibility.