Is it mentioned in the epic?

Today they show Krishna's Guru-matta asking for her son who drowned in the sea and Krishna going into the sea to fight off the demon who has held him captive. Is this mentioned in the epic?

Yes.. I have not watched the episode yet, but Krishna gave Sandipani his son as guru dakshina.. and he returned with Sandipani's son, a teenager, to complete his education at Sandipani's ashram..

Thank you. They show that he has ended his education anda s gurudakshina he brings backs his GUru's son.

And Krishna got his " Sankha" named PANCHJANYA from this ocean and He used that even during the Kurukshetra.

^^^True..it is mentioned in the epic.Also in Prem Sagar I think.