YOU SAID:

there is plenty fish in the sea

INTO JAPANESE

海にはたくさんの魚がいます

BACK INTO ENGLISH

There are a lot of fish in the sea

INTO JAPANESE

魚は海にはいくらでもいる。

BACK INTO ENGLISH

There are as good fish in the sea as ever came out of it.

INTO JAPANESE

魚は海にはいくらでもいる。

BACK INTO ENGLISH

There are as good fish in the sea as ever came out of it.