Are there any Job opportunities in Merchant navy for ECE Diploma Holders?????

You can join the merchant navy course and you are absolutely eligible for it. The minimum requirement for join merchant navy is 10 + 2 with PCM with at least 50% marks.

To become officers you need to have following eligibility:

3 year degree course in Nautical Science for (10+2) students
4 year degree course in Marine Engineering for (10+2) students
2 year course for Diploma Holders
3 month course for Deck Cadets for (10+2) students

Qualification to join as utility hand or Petty Officers (Fitters)

The qualification for joining the merchant navy as petty officers or utility officers include
Personal Survival Technique (PST)
Fire Prevention & Fire Fighting (FPFF)
Elementary First Aid (EFA)
Personal Safety & Social Responsibilities (PSSR)

There are many institutes which offer training for aspirants both in the public and private sector. The public sector organisations include:

Lal Bahadur Shastri College of advanced Maritime Studies and Research, Mumbai.
Marine Engineering & Research Institute (MERI), Mumbai.
Training Ship Chanakya, Navi Mumbai.
Marine Engineering & Research Institute (MERI), Kolkata.