An Indonesian fisherman caught with about 25 kilograms of shark fins has been fined $16,000 in the Darwin Magistrates Court.

Indonesian man La Deke has pleaded guilty to illegally fishing in the Australian fishing zone early this month.

The court heard a Navy patrol was forced to chase the fishing boat and at one point the two boats almost collided.

The prosecutor told the court when Navy officers boarded the boat, they found up to 30 shark carcasses and 25 kilograms of shark fins.

Deke was ordered to pay $16,000 in fines within a month.

He was told he would serve time in prison if he did not pay the fine or if he was caught illegally fishing again.