In the sentence 'The fishermen have been fishing all night long' the tense form is?

The tense form in the sentence "The fishermen have been fishing all night long" is the present perfect continuous tense. This tense is used to indicate an action that began in the past and has continued up to the present, emphasizing the duration of the activity. The use of "have been" signifies that the action is ongoing, while "fishing" is the present participle.