Using a sharp knife, chop the fish as finely as possible – do not mince the fish as it will result in tough fishcakes.
Form the mixture into 8 cakes, then refrigerate for 30 minutes.
Heat the butter and oil in a pan then fry the fishcakes for about 4 minutes on each side, or until golden and cooked through.
For the salsa, mix together the pineapple, lime juice and zest, and a little extra chopped chilli, to taste. Season with salt and pepper.
Serve the fishcakes topped with the salsa.