Caught. For example, I caught a bird. She caught the train. The prisoner was caught.
The plural form 'fishes' is used for the creatures, but many people do use the singular 'fish' as the singular (I caught a fish.), and the plural (I caught three fish.). The plural form, 'I caught three fishes.' is a correct use. Apparently, most people find the 'singular only' use is just fine.The uncountable (mass) noun 'fish' is the word for the food, a substance, with no plural form. Both fish and fishes are plurals to fish.
The plural form of the noun 'trout' is trout.The singular and plural form are the same.The singular and plural possessive forms are also the same: trout's.
The singular form of the demonstrative pronoun 'these' is this.
The word squid is usually used as singular or plural, examples: Singular: A squid was caught on my line. Plural: The restaurant had a tank of live squid on display. That being said, some people do squids as the plural form.
The singular form of feet is foot.
The singular form of "hypothysis" is "hypothesis."
The singular form is ombudsman.
it is already in its singular form.
The singular form is hilum.
The singular form is money.
The singular form of "cuffs" is cuff.
The singular form in stimulus.