Anne Feltham, the council's portfolio holder for business and leisure, confirmed: "One of the staff actually gave mouth to mouth resuscitation on some of the larger fish, which was an absolute eye-opener to me.
"Had our Park Gardeners and Park Rangers not responded so quickly this morning, then we would have lost many more, and I cannot praise them enough for their response in reviving some of the fish and quickly setting up new water tanks to contain the survivors.'
Experts however treated the apparent miracle with suspicion. They pointed out that fish breathe by gulping water into their mouths and passing it through their gills. Oxygen is absorbed from the water and dissolved into the blood.
Dr Rod Wilson, Associate Professor of Integrative Animal Physiology at the University of Exeter, told the BBC: "I'm doubtful mouth-to-mouth resuscitation would be that useful in this case, but it would be unlikely to have a negative impact on the fish.
He said carp were "famously good at surviving in water with little oxygen, or even out of water for a fairly long time.
"The fish might have survived anyway, especially in cold weather conditions like we have at the moment - it slows their metabolism right down and so they need less oxygen and will survive longer in air."
Colchester Castle Park attracts over 1 million visitors a year, and plays host to a variety of festivals and events.
An 18-year-old man was charged with theft and causing unnecessary suffering to a protected animal, and will appear at Colchester Magistrates' Court on 22 November.
A 16-year-old boy who was also arrested was released without charge.
