How can I tell the sex of my Dalmatian and silver Molly fish?

Yes Mollies can interbreed. All the variations came from a "basic " wild Molly, so it is basically the same species. Since you would be crossbreeding there will be an unpredictable phenotype, ie they could all look very different from their parents. So you could end up with babies that have the spots of a Dalmatian Molly but also a sailfin.

Thanks for reaching out about Black molly, but a good photo would help. White spots can be infections, parasites, over-active mucus cells, and some other conditions. If the white spot is the anus and is slightly protruding, she could be gravid but maybe intestinal parasites. If concerned, seek the attention of an aquatic veterinarian. Good luck.

Mollies do come in gold or orange colorations, but it is difficult to determine from that angle. If you can repost a broadside picture in a new question, that may make identification easier. If it is an egg laying species of fish, the third image could be an egg but I have reservations saying definitively without something for scale. It looks too large to be an egg. As an aside, if you leave the Molly fry in with adults, they will likely be eaten. You can separate the out, remove the adults, use a breeder screen or provide plenty of cover for them.

If they are less than a year old, it is difficult to reliably determine sex. Males will be more streamlined than females and, during breeding season, will develop white "dots" (tubercles) on the gill covers. Their vents will also be smaller and more oval shaped. Females will have larger, deeper bodies (for carrying eggs) and their vents will be rounder and more pronounced.

Hard to say from your description whether she is pregnant or ill. You can tell male from female Mollies by looking in the area of the anus. A male Molly has a so-called gonopodium. The gestation period of a molly fish is about 60 days. Female mollies can store sperm for months and may fertilize eggs as often as every 30 days, even without a male in the tank. Mollies may release 10 to 60 live babies at a time. Here is an illustration of sexing Mollies (and other live bearers)(credit: Mwahahahaa) http://photobucket.com/gallery/user/Mwahahahaa/media/bWVkaWFJZDoyMDk0MTEzNw==/?ref=

Thanks for your question about your guinea pigs, and congratulations on getting new members to your family. The photos are mildly blurry, but both of the pigs look like females. One thing you can do to confirm - the lighter colored guinea pig photo is more clear and is a female. The darker one is a bit harder to tell - if you compare them and they look the same then they are both females. If you are unsure, you can also post additional photos. I would recommend taking your new pets to the veterinarian for a wellness exam. They can provide you with husbandry and diet advice so that your new friends can stay happy and healthy. Thanks for using Petco Pet Education Center, formerly Petcoach!

The picture is not good, it's difficult to tell for sure from this angle. if i had to guess it would be a male though. maybe the following picture will help: https://breedingbusiness.com/wp-content/uploads/2017/07/determining-sex-of-puppies-male-female-800x800.png