Students of Somerville College, Oxford, whose alumni include Lady Thatcher, plan to boycott a college ball next month if plans go ahead to display a live shark in a tank as entertainment at the party.

Clare Phipps, who graduated in 2011 and is studying for a PhD in London, and Matthew Hawkins, a history graduate, have written, with 10 others, to the college principal, Dr Alice Prochaska, asking her to "please use your authority to prevent any live animals from being used at the ball", which is jointly run by the Somerville and Jesus colleges and is held in the former's dining hall.

"We're primarily concerned about the shark," Phipps said. "We don't know where it came from in the first place, whether it was bred in captivity or captured in the wild, and we can't find out as the committee won't give us the details of the company they hired it from. I am worried about the unnecessary stress for the animal of being transported and lots of people gawping at it.

"There is a difference from a shark in an aquarium because that has an educational purpose, informing people about conservation, and often zoos are involved in breeding programmes and so on. This is about nothing more than showing off. We've got so much money sloshing around we can hire a shark."

The cheapest tickets for the sold-out, black-tie event – billed as "one night of decadence, debauchery and indulgence" – cost £110.

The protesters say that when the Latin name for nurse shark, Ginglymostoma Cirratum, appeared on posters for the 4 May event, followed by the instruction "You should really go look that up", many took it as a joke. But in February Phipps emailed the ball committee chair, Sam Levin, a second-year biology student, to find out.

Levin and his committee were apparently unwilling to reveal more details, and several more emails were exchanged before Prochaska confirmed that a nurse shark was part of the plans. Anyone objecting was offered a refund.

Hawkins said: "It's worrying that a leading educational institution such as an Oxford college would allow that view of nature to be perpetuated, of animals as an extravagant, gaudy show. If the organisers won't cancel the shark then we won't attend and we will ask others to boycott the event as well.

"We know Oxford is old-fashioned, and there are things about it we don't agree with. But when we're trying in our day-to-day lives to do our little bit to save the planet, it's a bit galling to find your own college going in the opposite direction."

In a statement the college said staff were working with students to ensure "the highest standards of safety and ethics" and had insisted that the shark be housed in a quiet area and accompanied by a handler.

When contacted by the Guardian, Levin declined to reveal the source of the shark or the cost of hiring it, but said it had been with the company, which also supplies animals to the film industry, for five years. The area around the tank could be quickly cleared if the fish became distressed, he said.

He added that the idea of having a shark at the ball came from Baz Luhrmann's 1996 film Romeo and Juliet, in which the star-crossed teenagers meet while gazing through a fish tank.

Levin said: "As someone who cares a lot about animal welfare, I think we've ensured this shark is looked after. It will have a guard and caretaker with it at all times to look out for signs of stress, and we're keeping it there for only a short time. I feel confident that the shark will not suffer."

The RSPCA said: "Using sharks in any type of event would require very careful planning to ensure their welfare, particularly in terms of transportation, housing and the potential impact of the event itself. Like other fish, sharks are very sensitive to vibrations and low-frequency noise."