In a nutshell: STFU about the fish and get on with the adventure.
The plot when there was plot was rivetting, and Verne's occasional comic relief through both Conseil and Ned Land was entertaining as well. I'm told that comprehensive detailing of the science in SF is characteristic of the period. If it were published today it would probably be half as long because as a modern reader that is tiresome and we like to be entertained by the non-fiction aspect don't we? The modern reader has access to books, journals like New Scientist, the internet if he/she desires to learn more. We don't need that level of detail. There is extensive discussion of maritime history, geography, specifics of longtitude and latitude, physics and waaay too much coverage of every single fish and lifeform encountered.
This reader understands that the narrator is a marine biologist but is this text written for the benefit of fellow scientists? The use of scientific names only in some cases was particularly annoying! The text would be at least a quarter if not a third as long if these piscine descriptions were pared back to the essentials.