The only thing that really is cause for concern with small guppies, reds and goldfish (depending on the size of your newt) is that they are prone to disease and parasites. If you do choose to feed your newt fish, which I feel is the most natural food for them and most entertaining to watch as they hunt, keep a separate small tank that is filtered with a *thin* layer of gravel that is cleaned frequently. Do not feed your newt with your recently purchased livestock until several days later when any ill fish will have passed and problem fish may be quarantined. Guppies frequently breed in captivity, and you can ensure a unadulterated feeding source of fish by breeding your guppies and removing the eggs/fry before they would have an opportunity to obtain any diseases carried by their parents. They will look like little specks in the water, and may be fed with brine shrimp and other very small aquatic foods. All in all, feeding fish can be a worthwhile but initially costly venture. It is definitely worth it, though, for a primarily aquatic creature. If you have a more terrestrial animal such as a sallie you may prefer to stick to dry foods...OH YEAH...and you can easily hand-feed larger newts fish. It helps the first few times to hold the fish out of the water for a while to weaken it a bit, as some of the larger ones can put up quite a fight and even continue to squirm once swallowed. Try tweezers to begin with, but soon you can put the fish up to kiss your newt's mouth and he'll take it right from your fingers! Best of luck! (I would not recommend feeding pinkies. While newts/sallies have much more effective digestive systems than reptiles, there is a lot of raw bone matter and difficult material in the mice, and they are rather large for anything other than a full-grown tiger as noted in earlier posts.) Bloodworms are a GREAT treat for newts/sallies as they do not die in the water, eat wastes in the gravel, and seem to be easy to digest. Much higher nutrition than waxworms, but you can't gut-load them like crickets. Ok, this post is way long enough. Let me know if you have any questions about the fish...