The reason most people are going to shoot in Raw is that aquarium lighting makes proper color balance very tricky. With a Raw photo, this can very easily be corrected, because you have the "raw" red green and blue data for each pixel. Once a photo has been converted to jpeg, that fidelity of data has been lost. Generally, we have plenty of time shooting aquaria, so you don't have to worry about how many shots you can get in a burst or taking time to swap out cards. If you're worried about space on the computer, you can still convert to jpeg after processing and then delete the raw file. . .but memory is pretty cheap, so I really don't see any reason for that.