The phrase "a significant fish" is correct and usable in written English.
It can be used in contexts where you want to refer to an important or notable person or entity, often in a metaphorical sense.
Example: "In the world of finance, he is considered a significant fish, influencing major market trends."
Alternatives: "a big player" or "an important figure".
"Commissioner Vella has shown global leadership in implementing the EU's tough illegal fishing regulation against such a significant fishing state".
The port, with oil-bunkering facilities, is on the main shipping routes between Europe and South America and is entered annually by thousands of ships, which also contributes to a significant fishing trade.
There is a significant fishing industry, some tourism along the coast, a fertile valley around Culiacán (in which a good portion of all the tomatoes, eggplants, and melons consumed in the United States is grown), and, east of this, a scraggly, steep, and serrated mountain range.
The waters off Senegal particularly those at some distance from the shore have an abundance of economically significant fish.
Even if the racing developers could carve a track away from those protected marshes, it will still sit on one of 15 sites in the metropolitan area designated as a significant coastal fish and wildlife habitat.
Although not significant, fish trained at constant-velocity showed a trend towards higher survival than fish trained at either short or long intervals.
At stake in these sea disputes are vital economic interests, including vast oil and gas reserves, significant fish stocks, and vital trade routes -- as well as national pride.
In Africa, for instance, many coastal states licence vessels from distant water fishing nations such as China, Taiwan, Korea, the EU and Russia to fish in their waters, and there is a significant illegal fishing problem from many of these vessels [6].
