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The 31-year-old Made in China band member said the instrument, valued at about $10,000, was taken from his van after a gig at the Ra Bar in Dunedin's Octagon on Wednesday night.
"That was not just a bass; it was my livelihood. It's my only source of income and some b...... stole it."
Without it, Mr McMartin said it would be difficult for him to teach music from his Dalmore home, and he was worried he would not have his guitar back for his next gig at the Penguin Club in Oamaru next Saturday.
He bought the Fender at a market in Seoul, South Korea, in 2003 and since then has played it at hundreds of concerts.
"I can't imagine playing any other bass. Every time I've picked up someone else's, it's felt foreign. It just doesn't feel right. My Fender is just about a part of my body.
"It's completely distinctive. There isn't another one like it in New Zealand. Anyone trying to sell it in Dunedin is gonna be a schmuck, man. It's totally unique. Good luck to anyone trying to sell it."
The guitar was not insured, because it would cost about $1000 a year, he said.
"No insurance company is going to insure it. It's too valuable and my old van isn't considered secure enough to store it."
Dunedin police are investigating the theft and Mr McMartin has posted flyers around the city, offering a $500 reward for its return - no questions asked.