5 sentences

1. 鱼类是冷血动物。

   yú​lèi shì lěng​xuè dòng​wù.

   Fish are cold-blooded animals.

   Source: Tatoeba

2. 海洋中生活着各种各样的鱼类。

   hǎi​yáng zhōng shēng​huó zhe gè​zhǒng​gè​yàng de yú​lèi.

   All kinds of fish live in the ocean.

   Source: Dong Chinese Dictionary

3. 这些鱼类通过排放精子来繁殖后代。

   zhè​xiē yú​lèi tōng​guò pái​fàng jīng​zǐ lái fán​zhí hòu​dài.

   These fish reproduce by releasing sperm.

   Source: Dong Chinese Dictionary

4. 在汉字构造中，“鲜”字左边的“鱼”部代表鱼类。

   zài hàn​zì gòu​zào zhōng,“ xiān” zì zuǒ​bian de“ yú” bù dài​biǎo yú​lèi.

   In the construction of Chinese characters, the 'fish' radical on the left of the character 'xian' represents fish.

   Source: Dong Chinese Dictionary

5. 由于环境污染，湖里的鱼类种群数量大幅减少。

   yóu​yú huán​jìng wū​rǎn, hú lǐ de yú​lèi zhǒng​qún shù​liàng dà​fú jiǎn​shǎo.

   Due to environmental pollution, the fish population in the lake has decreased significantly.

   Source: Dong Chinese Dictionary