The race for Barker will be a crowded one at the federal election on May 18, as Liberal MP Tony Pasin will face at least six challengers.
Five minor-party candidates have already launched their campaigns, and Labor is expected to name a candidate "in the next day or so", according to a party spokeswoman.
Mr Pasin received 46.6 per cent of first-preference votes at the 2016 election, and saw off his nearest rival James Stacey of the Nick Xenophon Team, now the Centre Alliance by 54.7 to 45.2 per cent.
The Liberal-National coalition and its predecessors have held Barker since its creation in 1903.
Murray Bridge Councillor Karen Eckermann will represent the Animal Justice Party at the election, she announced at the council's meeting last week.
"My aim is to raise the profile of the Animal Justice Party and the values it promotes: kindness, equality, rationality and non-violence," she said.
"We can all be quite confident I won't be elected, but I am thrilled at the opportunity to do something important for an issue I care so much about."
She described living in a distict where animal agriculture was so prevalent as "a big challenge".
Her candidacy would not affect her commitment to serving the ratepayers of Murray Bridge, she said.
Keith farmer and Tatiara councillor Miles Hannemann will have another go for the National Party, he announced on Friday, after his unsuccessful 2013 campaign.
He said he was interested in regional development and addressing skills shortages.
"I have four boys and I want to create opportunities for them in our communities, here in Barker," he said.
"We need to provide secure local jobs and bring people back to our regions so we can secure our way of life for future generations.
"We have a strong story to tell: lower cost of living, affordable housing, cheaper industrial land, fantastic amenities and ideal locations to raise families."
The United Australia Party, led by Queensland billionaire Clive Palmer, will also field a candidate at the election: Rupert Bacher, a retired welder and timber worker from Mount Gambier.
Mr Bacher said he had joined the party to give back to the country he loved, the one in which he had arrived with 24 in his pocket in 1963.
Health services and the River Murray will be priorities for Centre Alliance candidate Kelly Gladigau.
She said Barker deserved a representative who would keep the government accountable.
"We must address the funding and infrastructure shortages that have plagued the electorate for years, particularly around healthcare and transport and roads," she said last week.
"More investment in mental health services, including for drug and alcohol addiction, is a top priority for me, along with addressing the cost of living."
Ms Gladigau, formerly a state candidate, entered the federal fray in October.
As well as fighting for a better deal for the Murray-Darling Basin, Meningie artist and river advocate Rosa Hillam would like to see better engagement with regional communities and more services in the areas of domestic violence, substance abuse, aged care and mental health.
She launched her campaign in Murray Bridge in January.