Blue whale

整個句子我會寫成:
The blue whale feeds on krill. It opens its mouth widely during swimming. Then the krill will be driven into the blue whale's mouth by the water currents.

用feeds on 係啱嘅，冇錯架。
YAHOO字典解釋得好清楚，feed
用作vt. (=verb transitive 及物動詞)
1. 餵(養);飼(養)[(+on/with)]
We feed the birds every day.
我們每天給鳥餵食。
They fed him on biscuits.
他們用餅乾餵他。
用作vi. (=verb intransitive 不及物動詞)
1. 吃;以...為食物;以...為能源[(+on)]
Sheep feed on grass.
羊吃的是草。
http://hk.dictionary.yahoo.com/search.html?q=1&s=feed

另外係網上好多關於藍鯨嘅文章，都係用“feed on”架。
例如係呢個介紹藍鯨嘅網頁 http://trillian.com/animals/whale.htm
FOOD & HUNTING 一段就咁寫:
In the Antarctic, blue whales feed on vast quantities of a plankton called krill. In Arctic waters, they feed on only three species of crustacean (shelled) plankton.

Krill在這句子裡解作磷蝦，不論單數或複數都不用加“s”。
如加“s”寫作“Krills”，就會成為一句街頭俚語(slang)解作毒品。如果想知多啲，可到Urban Dictionary睇下，呢個網頁專查街頭俚語。 http://www.urbandictionary.com/

呢句句子你唔可以用 feed on ,因為feed 即係餵咁解 ,只可以用這樣用 eg. We feed the birds every day. 所以如果將句句子改做 :
The blue whale eats krills .It opens its mouth when it swims.The krills follow the water current and run into the whale's mouth.
我覺得咁樣啱d!