I flew to and from JNB in F in April and you should be ok, as there is the Loch Fyne fish dish, but only from London.

You could also have something to eat in the First lounge at Terminal 1, and hopefully there should be a decent vegetarian or fish dish, although I have not used it so cannot comment.

I have been reasonably lucky with immigration but you should allow time to clear immigration, pick up your luggage (which is not too quick, even with the First label) and go to the hotel to use the lounge. Just be a little careful with the inevitable people hanging around- just ignore them and move purposefully outside and towards the hotel.

I find Comair good in Business, but you may not get a fish meal, unless you specifically request a vegetarian alternative for this 2 hour flight.

Hope you enjoy your trip!