Usually when fish lie on the bottom its a water quality issue and this should be checked first before the swim bladder. Need to know the size of tank, what and how many other tank mates, test results for ammonia, nitrite, nitrate and ph. You may notice fish lying on the bottom of the tank more if the water is not aerated. This is likely to be a problem if the water is too warm or too cool. While cool water cannot absorb much oxygen, and water that is too warm will release more into the atmosphere. Female live bearing fish do not have pregnancy and delivery issues like mammals. Eggs develop inside the female with no placental connection, and the fry are fully functioning versions of the adult fish. Since the molly has been in your aquarium for only a week, she may be experiencing stress from being moved. molly fish with gill flukes can be seen gasping for air at the surface of the tank or in the bottom of the tank. Gill worms are usually introduced into the aquarium via new plants or new fish, so make sure you always quarantine new fish. feed your fish some flake food soaked in garlic juice (or just straight mashed garlic, if theyll eat it), and dose a half-dose of anti-parasitic water treatment to make sure to get the parasites, if that is what is going on. Some fish get afraid of the new lights and movement and settings and just hide on the bottom. Another possibility is he has something wrong, it could even be internal parasites and you wouldnt know unless you observed him for a period of time. your molly may be sick so i would keep watching with the temp raised. If she does not show any change or any signs of disease within the next week, there are a few other possibilities i can think of. 2) mollies are a bit large for a 10 gallon tank and she might feel cramped.