There's a way to get Kelly (the lady that stands at those computers next to the galaxy map who alerts you about messages at your terminal) to feed them but I'm not exactly sure how to go about this. You have to invite her to your room for a private dinner and then her feeding them is for some reason brought up. I think this is shortly before you officially form a relationship with her so her agreeing to feed them probably doesn't happen until close to the end of the game.
You have to keep speaking to her after each main mission, especially recruitment and loyalty missions. When you get an extra option in the conversation regarding being nice to Kelly (positive comments about her, etc.), take it. Keep repeating this process and it won't take you long to get her to dinner. Then she'll offer to look after your fish.