The fact that a DVM says so, don't make it so.
And before all the anti smokers go crazy, first off I no longer smoke, and haven't in years. I am also not referring to dogs, cats, or birds - but specifically about fish. How much, if any, second hand smoke may possibly affect a fish would depend on numerous factors, such as the amount of daily/weekly smoke exposure, air flow and filtration in home, filtration in tank, filter media used (such as carbon), how well the tank is sealed from the outside environment, frequency of water changes, and volume of same, growth stage of fish, species of fish, and probably a long host of other variables that I haven't considered.
One of the greatest fishkeepers (RIP Don) that I've had the pleasure of knowing over the years was a heavy smoker. His fish always grew well, bred like rabbits, and lived what would typcally be considered the norm as far as longevity for the species in question. His fish room always had an ashtray or two in it, usually full of butts, and his 2000+ gallon systems filtration was all via air.
Smoking indoors isn't a great idea for numerous reasons, I'm just not one to jump on the bandwagon over something that a DVM feels. Plenty of DVM's have plenty of opinions that have never been scientifcally proven, but are stated online as though they are fact.