YOU SAID:

i must murder a fish from that lot of fish

INTO JAPANESE

私はそのたくさんの魚から魚を殺さなければなりません

BACK INTO ENGLISH

I have to kill the fish from that many fish

INTO JAPANESE

私はその多くの魚から魚を殺さなければなりません

BACK INTO ENGLISH

I have to kill the fish from that many fish