I use a SB700 on my wife's d5100 and although I mainly shoot with a Canon, I'm pretty impressed with quality of that camera.
There are some things to consider... What's your budget and what else to you plan to take pictures of? If budget wasn't a concern I would go with a full Nikon system. If you want to take a risk and get the best bang for your buck? Check out the wireless triggers from amazon like the ones from Yongnuo. Also, if you plan on using this system for other things like portraits, parties and gigs. Make sure the trigger and the flash has TTL or else you will have to calculate the flash output for each shot. The cheaper triggers and manual flashes aren't too bad if you're only taking shots of the tank and fauna, due to the controlled lighting environment.
Sorry, but I can't go to in depth about flashes and camera but if you want to know more, there are many books and online articles about them.
I hope this helps and remember practice, practice, practice.