Respect and thanks to everyone for your answers, it wakes up my two inactive brain cells this time of morning...
The reason I asked dog, fish or human was to evoke a discussion around the innate abilities of fish (mainly) at being able to suss out a good meal in preference perhaps to a poor one, how this might compare to dogs (which most of us understand a little through better observation as pets) so that we as humans, the great hunter, might select the right kind of bait at the appropriate time and place.
I think we can agree to the extent as suggested, that fish are more capable in a watery environment at finding food, and a dog on land being better than humans breathing the same air and scents carried to find a good meal. A sight feeding trout may snatch at most things (but not all according to a film I've got which suggests they're more selective than first realised) passing by that resembles food. Even in total darkness, both the dog and fish are more than capable of finding something to eat using olfactory senses whereas we'd be pretty much left starving fumbling in the dark.
My dog, is a Russell (crossed with something or other, Patterdale I think according to the bloke who docked his tail illegally) and a very picky eater, spoiled on good quality food, knows the difference with what might look like a burger made of vegetable protein (soya) and a minced steak burger by smell alone. He also sticks his nose in the shopping bags and knows what's been brought home. We're all (all living creatures) stimulated by food scents which is largely an automatic response and its true to the extent that, given a choice; we all prefer only the best... a starving dog, fish or human will otherwise eat whatever it can get. I think this is significant to what kind of baits are preferred (or not) on a stuffed pond full of hungry fish, verses a river or lake with fewer fish present that largely feeds on naturals and a few anglers baits. Both will eat anything, whereas in times of plenty, like a hatch for example with less competition around, can afford to be a bit more selective.
I learned years ago some place that fishes senses are many hundreds of times more sensitive than dogs, possibly thousands depending on the species (the reason why you shouldn't over do it on the glug?) and that dogs have noses many hundreds of times more sensitive than humans - reason why my own dog can smell the difference a mile off between minced steak and veggie burgers and knows when there's a treat in the shopping bags (and which one), even though its at the bottom wrapped in plastic packaging.
If we had have evolved along with fish and stayed in the water we might have had a better nose and a lateral line or two, if we had grown up with wolves we might have had better hunting instincts and a nose for sniffing out our prey down wind. Genetically were all very similar (DNA) but a few percentage differences means we are worlds apart even to our nearest descendants - the chimpanzee!
A comparative study I read on the chimp genome says that humans and chimps diverged approximately five million years ago. The results suggest (surprising to them?) that humans do not appear to rely strongly on smell to survive. Finding food and sensing whether it is edible or noxious are possible selective pressures driving the evolution of human olfaction. Another study, detailed in the January 2004 edition of the journal Public Library of Science Biology, argues that, perhaps like the victim of a sense-robbing disability, humans and other apes may have sacrificed some sense of smell to develop full-colour vision.
Humans, mice and the other great apes all have a similar number of olfactory receptor genes. Yet up to 60 per cent of these are
inactive in man, compared to only 30 to 40 per cent in great apes and 20 per cent in mice and dogs.
