In a food processor, blend the cod until finely minced.
In a large mixing bowl mix together the minced cod, chopped salmon and lime zest.
Add the chopped fennel, chopped coriander, green chillies, spring onions, fennel seeds, coriander seeds, salt, two tablespoons of oil, garlic paste, ginger paste, two teaspoons of crushed black pepper and lime juice and mix well.
Mould the fish mixture onto 12 skewers, forming 12 fish kebabs.
To make the cucumber raita, squeeze out any excess water from the grated cucumber.
Mix together the cucumber and yoghurt, and stir in the dill, the remaining black pepper and the garlic.
Heat one tablespoons of oil in a small frying pan and fry the mustard seeds, cumin seeds, asafoetida and curry leaves for 2-3 minutes, stirring, until fragrant.
Mix the fried mustard seed mixture into the raita.
Either grill the kebabs on a barbecue until golden brown on both sides or heat one tablespoon of oil in a large frying pan and fry the kebabs until golden brown on both sides.
Serve the freshly cooked kebabs with cucumber raita and basmati rice.