The Keralan Curry was yummy! If using chicken or pork instead of fish would the concentrated fish stock still be used?
Nigella's Keralan Fish Curry (from Forever Summer and on the Nigella website) can be made with other meats, but you should make sure that you use quick-cooking cuts, such as chicken breast or pork loin. Chicken and pork may take a few minutes longer to cook than the fish, and make sure that they are cooked though before serving the curry.
If using chicken then it would be possible to use chicken stock concentrate as an alternative and if using pork then you can use vegetable stock concentrate or stick with the fish stock concentrate. The stock concentrate is fairly easy to find in the UK but can be more difficult to find elsewhere. If you cannot find it then you could use a good quality stock or bouillion cube dissolved in a little boiling water. You need to use enough stock cube to make the equivalent of 200ml/scant 1 cup stock (many cubes make 250ml/1 cup stock so you would need here to use just less than 1 cube).