Eat loads, buy them bulk from Costco. Sardines, mackerel and less so of the Tuna in water/oil. When I can get it, also a fan of Costco smoked mackerel and kippers.
Mix in with sweet potato hot with chilli and spring onions, with rice instead of egg, easy (any fish) nicoise (hot or cold), in pitta breads with salads stuff. ciabatta sarnies with pickelled beetroot, or saurekraut.
With beans and flash-boiled courgetted ribbons with lemon and olive oil .
Pasta, stir fry's etc. you name it, the worlds your fishy oyster.
High calorie/protein so on calorie restriction days a half tin is enough, but needs a lot of restraint not to eat the rest!
When I can buy fresh fish cheap I'll freeze or use it, but don't touch Irish Sea and wary of southern north sea fish, both due to level of pollution. Morrissons do cheap salmon heads, fish head soups are common in Asia, but but I guess that's something you have to get used to eating in the UK.