Since the salty fish is the direct object shouldn't it be in the accusative form? as in 'Piscem salsum ei placet'
In the Latin the salty fish is the subject, the thing doing the pleasing. Piscis salsus ei placet is more literally "The salty fish is pleasing to me."
" Pisces salsi ei placent " was given as the correct answer. Neither " pisces " nor " placent " were among the available words.
Instead you had "piscis" and "placet", which were correct. You're talking about the plural fish. Yeah, it would be right too, but there was already a correct answer
PISCEM SALSUM EI PLACET should also be correct since there is no way to tell in English whether plural or singular is meant in "the salty fish"
No, it should not be accepted. 'The salty fish' is the subject in the Latin sentence using placet thus it must be piscis salsus (nominative singular).