Fast moving tiny bugs sounds like lice. They usually leave whitish clumps of eggs at the base of feathers. Permethrin 5%spray (available in concentrate for diluting, available at TSC and other feed stores) is very good to spray just the affected area around the vent to kill lice. Check again in 7 days and use again. The coop may need to be emptied and treated as well as the other chickens.
Look for some threads on ascites at the search box above for information and pictures of draining a swollen tight abdomen. An 18 gauge needle inserted just under the abdominal wall is used. If the belly is not tight like a drum, there could be something other than fluid in there. Internal laying incidence is increased at this age, and may be a reason for the swollen belly.
Look for some threads on ascites at the search box above for information and pictures of draining a swollen tight abdomen. An 18 gauge needle inserted just under the abdominal wall is used. If the belly is not tight like a drum, there could be something other than fluid in there. Internal laying incidence is increased at this age, and may be a reason for the swollen belly.