FIsh and Gas seem to be useless compared to most other resources. Sure,they have their use,preventing morale loss,but they do not do much more. Take,for instance,coal. Coal is very important;we need it for railways and also to build Battleships and Railguns. Or Wheat,or the construction materials,or oil...without them you could not win
Gas just seems to have not much use;it is only used to build aerodromes and Observation Balloons. Of course,Aerodromes are important in the late game,but with the stock market,you could just set the resource slider for gas to the furthest right,thus increasing oil and coal production,and buy the gas for the Aerodromes instead.
As for fish,well,it's only use is to produce cavalry and sustain them. It may be important for an early game cavs rush,but other than that,it does not do much.