<p>Question: The young fish (were) very tiny, yet each of (them ate) many times (its) own (weight in) solid food every day. </p>
<p>Brackets () = Underlined parts</p>
<p>This question seems a bit weird to me. All the underlined parts and the parts that aren't underlined are correct to me except for "the young fish were" were is correct as it relates to them so I'd never change it to the "the young fish was" .... I'd change it to the "The young fishes were" .... I assumed they made an error/typo but after some research I realized that "fish" is actually singular or plural depending on the context.</p>
<p>My question: For the knowledge of people (including me) who aren't aware that words like "fish" could be both singular and plural.. what other words are there that can be both singular and plural depending on context?</p>