Last weekend, detergent was poured into the fishpond in Trinity College's Fellows' garden, killing all but one of the fish.
The pond will need to be drained and cleaned as a result.
In an email to the college, Nick Barber, the Dean of Trinity, stated that he was "saddened" by the "cruel act of vandalism."
He told JCR members that after a "swift and effective investigation by the Dean of Balliol, a group of students from that college has owned up to the act."
Alastair Travis, Balliol JCR President, commented, "A few individuals from Balliol, meaning no serious harm, planned a prank to put some washing up liquid in a fountain in Trinity. They found their access to the fountain blocked - instead finding the pond (which, in the darkness, they were not aware as being a fish-pond). After the damage was reported to the dean, they quickly owned up to the incident and the associated financial and decanal punishments.
The Dean of Trinity warned students at the college that "Trinity will not tolerate any ‘reprisals' against Balliol. Any action of this type will lead to significant fines - well beyond the ordinary punishments I have levelled for bad behaviour in the past."
Students at Trinity have expressed distress at the attack.
Damien Conyngham-Hynes commented, "I'm disgusted and outraged. It frankly sickens me. Trinity have moved with the times and moved on from our rivalry. Bailliol palpably have not."
"There's the banter of college rivalry - and then there's taking it too far. They're so far past the line, they can't even see the line!" stated another Trinity student, Fay Lomas.
