[tadeus]

To expand drewlt's answer:

Code:

local total = 0
local inv = Inventory("itemid="..fishID)
if (inv) then
  for k,item in pairs(inv) do
    total = total + item.count
  end
  d("------------"..fishName..": "..total)
  fishmanager.fishNamelabel = fishName
  fishmanager.fishCount = tostring(total)
end

I think that's pretty close to what you're looking for.