Death certificate question.

[HarrysMum]

Does anyone know if a child died on the way from England to Australia in 1855, would there be a death certificate anywhere?
There’s not one in Australia, even though his name is on a headstone with his brother who died here.

I have looked through the UK ones as much as I can but can’t find him and presume his death would not have been recorded in UK anyway.

Just wondering if there is a list of those who died at sea anywhere.