Putjeot (풋젓) is made with shrimp harvested from the end of January through April. Also called deddeugi jeot (데뜨기젓) or dotddegi jeot (돗떼기젓).

Ojeot (오젓) is made with shrimp harvested in May.

Yukjeot (육젓, 六젓) is made with shrimp harvested in June and is regarded as the highest quality jeot. It is the saeujeot most preferred for making kimchi[2] because of its richer flavor and bigger shrimp than other saeujeot. The shrimp in Yukjoet have red heads and tails.

Chajeot (차젓) is made with shrimp harvested in July.

Gonjaeng-ijeot (곤쟁이젓) or jahajeot (자하젓, 紫蝦젓) is made from the smallest shrimp (actually the very small shrimp-like Neomysis awatschensis).  They are harvested in August and September. As it ferments, the jeot changes from transparent to light violet or brown in color and becomes soft in texture.

 Chujeot (추젓) is made with small shrimp harvested in autumn which are smaller and cleaner than the shrimp in yukjeot.

Dongjeot (동젓, 冬젓) is made with shrimp harvested in November. Dongbaekha (동백하젓 冬白蝦)is made with shrimp harvested in February whose bodies are white and clean.

(summary from Wikipedia)

http://en.wikipedia.org/wiki/Saewoo_jeot