Malaria prophylaxis, even in an endemic area, is controversial. Malaria is caused by a parasite (plasmodium sp.) passed in the saliva of mosquitos of the anopheles species. The percentage of anophelene mosquitos that carry the plasmodium parasite varies with location. Usually from 0 to 10%. So if your are just passing through your chances of becoming infected are fairly low. The CDC recommends prophylaxis but they also recommend immunization against rabies, measles, japanese encephalitis, polio etc. for many areas. I would not take preventative medication in the Bahamas
or the Caribbean
. That said it's good policy to avoid getting bitten in these areas due to dengue more than malaria.