Nobody gets fat on 2 pieces of salmon sushi. People get fat on 12 plates of it. Kura lists a salmon plate at 93 calories, which sounds like a diet food until you do the kaiten maths. Ten plates is 930 calories and 1,200 yen, and 10 plates is a perfectly normal lunch for an adult man in Japan. Fifteen plates is 1,400. The conveyor belt is the reason the number matters.
The rice is the bigger half. Each nigiri sits on 18 to 20g of sushi rice seasoned with sugar and vinegar, about 30 calories. The salmon slice is 8 to 10g at chain shops, about 17 calories. That is why 'shari half' (half rice) options exist at Kura and Sushiro. Ordering half rice drops the plate to about 65 calories and lets you eat 15 plates for the calories of 10.
The variations are not equal. Plain salmon at 93 is the cheap one. Aburi cheese salmon at Kura is 120 for the plate, salmon with onion mayo is around 130, and anything with 'mayo' or 'cheese' in the name adds 30 to 50 per plate. Ten plates of the fancy salmon is 1,300 instead of 930, and it is the same fish.