Answer:
El pescado huele mal.
Step-by-step explanation:
"El pescado" is him (in English "it"), therefore we use the 3rd singular person verb form of the present tense of the verb oler (to smell) which is "huele".
This is verb is somewhat irregular, look at the present tense of oler:
- Yo huelo
- Tú hueles
- Él/Ella huele
- Nosotros olemos
- Vosotros oléis
- Ellos/Ellas huelen
Native speaker over here. I hope this is helpful.