Let me start with what I know or seen/heard. Those other descriptions which I can't appreciate, I will leave them to the experts.
On giant spawns
1. The fry grow a lot faster than normal betta spawns. Never experienced it myself since I have never bred giants before. For those who have bred, can you share with us whether this is true, and whether you have done anything differently for a normal sized betta spawn? Kept the spawn in larger tanks for example?
2. I have seen "giants" which I was told are 3 months old, but they look comparable in size to, or even sometimes bigger than, those which are 5-6 months old normal-sized betta. Again, I have no way of verifying this fact.
