Fender bass weights

Generally speaking, the brighter-sounding wood you use, the heavier it will be (dense wood = brighter tone = heavier). Here's a pretty good guide to different tonewoods:

http://www.warmoth.com/bass/options/options_bodywoods.cfm

 

Pretty funny how no one offered the straight info on this straight question. I'd say that's because Muscato's link puts it so well, but I'll admit that in all my years as a bassist I've wondered myself. As the former owner of a '61 P-Bass, I appreciate that real featherweight that marks some of Fender's best basses.
I recently bought a 2008 American Standard P-bass, which they say is alder, and it is a nice "mid-light" weight. I'd imagine that my '61 (which was much lighter) was alder as well, as the Warmouth link suggests. As my back is wrecked from 30 years of lugging mondo bass cabs, a light bass is a good thing indeed.

 

I tend to love the "woody/hollow/organic" tone a light weight bass tends to offer..they seem to have a lot more resonance and tactile feedback. Most of the lighter true Fenders tend to be alder, but I've experienced some very light swamp ash bodies too. I like a light body and a slightly robust/heavy neck...not so much that there is bad "neck-dive", but I think the combo of light body and heavier (usually "stiffer" and brighter) neck is terrific tone-wise.

 

I'm guessing my '76 is ash as it weights a ton. I like it though (no one else tries to play it) but I'm also keen to find out more about the effect of the wood on both the weight and sound... going to check out that link (from above) now.

 

One of my best sounding basses is a DIY SCPB using an Allparts maple/maple neck with a chunky profile and 1-1/2 inch nut width on a Guitar Mill Featherweight body made of paulownia.

The body weighs exactly 3 lbs and bass weighs 5-15. It sounds very full and even with no hint of any muddiness as mentioned in the Warmoth page, in spite of it's humbucking pickup.

I like it so much that I recently ordered a J bass body made of the same wood.

 

I have a 78 P. I sold it to my cousin on installments but he couldn't pay so I got it back and Im darn glad I did. It's a great sounding/playing bass.
But, weighing in at 9.5 lbs poses a problem if I haven't played it in awhile. It's ash I suppose.
I also have a MIM Jbass with a warmoth neck that is nearly as heavy though.

After 35+ years of Ice hockey (goalie) I'll probably get to a point soon enough where I'll have to sit down (Nooo!) or go to a lighter bass for gigs...

 

The Highway One P I just bought is the lightest bass I've ever held. I think the weight of the finish on my 78 Rick was heavier than this P.

 

My 1982 AVS '57 RI is a 3 piece alder body, just under 8 lbs.
I foolishly sold a 2000 Jazz 1 piece ash body 8 lbs even.
So, to answer your question, Ash or Alder.