Arbalete D.D.S. speargun

I think you will need to try it out to figure that out. I would start by not spearing anything over 5 lb (small snappers, grunts, hogfish) and see how well it works. Then you can move up if it is reasonable.
Questions to answer:
Does it penetrate all the way through with the tip?

If so, don't spear anything larger, because that is as much fish as you are likely to keep on the shaft.
Does it string a fish you shot (entire shaft go all the way through and leave just the shooting line through the fish?
If so, move up toward 8-10 lb and watch how it works.

If it doesn't penetrate all the way through a fish, then focus on small snappers and grunts (maybe 2 lb), and leave the larger fish alone. You'll just wound them.