not exactly sure what youre attempting to do, but i saw a model train on ebay once where the cars were basically made to look like they had fish in them swimming about, like aquariums (fake little fish of course), sort of like the old circus trains that were like cages on wheels so the animals were seen when the train went by kind of a thing. is that what youre thinking of? or were you thinking of making each car shaped like a fish of some sort?