Does Overlord DLC kill your fish?

I just defer buying my fish until after I get Kelly to commit to looking after them.  To do that, flirt with her during your first conversation (using the "I'd embrace you" line).  Tell her that you like her flirting with you during her second conversation.  After you recruit Garrus, talk with her and tell her that her therapy sounds good.  At that point she should say something about setting aside some time to really talk and get to know each other.  Then, after you get Samara, flirt with her again and invite her to your cabin for dinner.  The next morning, she'll offer to look after your fish... whether you have any fish or not.

After that point is when I start buying fish and I never have to worry about feeding them.  It's probably more "canon" to let a couple of groups of fish die, though since there are quips about Shepard killing fish during the Citadel DLC.  The only fish you really need to save are the Prejak Paddle Fish (since they give an extra upgrade at Liara's terminal if they make it into ME3).  However, a full aquarium looks nicer.

In ME3, I make sure to buy the Aquarium VI as soon as I get the fish back from Kelly (or if I buy new ones in ME3).  It costs 25,000 credits.

Understandable.  I sometimes do that as well... but then I'll usually lose a batch of fish or two because I simply forget to feed them.  The point I often seem to lose them is when the 5-mission time runs out and I'm whisked away to the Collector Ship, so be sure to feed them before hitting the CIC after you've finished the 5th mission after Horizon.

I would hold off buying the Prejak Paddle fish until the very end of the playthrough so that they carry over into ME3 and you can still get the associated bonus even if you do lose some batches of fish earlier in the game.

Yea but it's not like you need a fancy VI to pull of a food dispenser on a timer, either.

After all, in ME2, you can buy the feeder VI (for frigging 25.000 credits). We have 4 top notch engineers on this ship. Is the implication here really that none of them are competent enough to wire up a stupid automated fish feeder?