Eggs are cheaper than fish, even with recent volatility.

Is it feasible to farm sardines?

People repeat this thing about satiation but it's not really true. In fact, the most highly satiating food is potatoes. Fish is quite high up there, but other "protein" foods like meat, eggs and cheese are nowhere near the top. Oats and many fruits like apples are higher.

The really stupid thing about fad diets like keto is you either just start craving carbs because food is miserable without them, or you develop an eating disorder. The only thing anyone should do is eat normal, delicious, home-cooked food made from mostly plants.