The phrase "a certain fish" is correct and usable in written English.
It can be used when referring to a specific type of fish without naming it directly, often in a context where the identity of the fish is either known or implied.
Example: "While fishing at the lake, I caught a certain fish that I had never seen before."
Alternatives: "a particular fish" or "a specific fish".
A "fishery" describes the complete habitat of a certain fish, embracing everything in the ocean from fish eggs to full-grown fish to their predators, as well as the fishermen who catch it and the freshwater streams and lakes that grow plankton to feed it.
Then there was this question of a certain fish, the "steelhead trout," that was purportedly threatened by our wedding preparation.
If you have, let's say, a fascination with a certain fish, you should develop that interest.
Jason had to work even harder to net it, finesse the hook back out of its hard, wide mouth while studiously avoiding rows of ice-pick teeth, present it properly to a certain fish-photo-crazy aunt and get the thing back in the lake in time to provoke an annoyed but healthy tail-thwapping departure for safer waters.
A new study in the journal Nature reports that a genetic defect in certain fish may have stunted fin growth and led to the development of limbs and the emergence of land dwelling creatures.
In studying this tooth wear on museum specimens, the scientists realized that two members of the Arthrodira added new teeth to the end of a row, a pattern seen today in certain fish.
Many studies -- though not all -- have concluded that low levels can have subtle negative effects as well if certain fish are a major part of the diet.
The researchers have given their data to state health officials, who can decide whether to issue a public advisory against eating certain fish from these areas.
You can't drink alcohol, eat cold cuts (unless they're heated), and certain fish are a no-no.
At the end of her brief lectures, she threw in a piece of trivia or a random thought: She had just read that cosmetic companies were thinking about using an antifreeze protein produced by certain fish.
Certain fish live about a year.
