Its only after giving birth that a female can take on new packets from other males, or if she is virgined, until then she holds the packets from the male that fertilized the current batch of young growing inside her, the males can sense this and are often very aggressive pursuers after a female has dropped. To my knowledge the female has no control over whether she accepts new packets or older packets, its just simple survival.

Cheers

well both females in that tank have never been pregnant so the little guy isnt doing his job to well

From the picture you can tell she is definitely pregnant or "gravid", if they have been in the same vicinity as any male guppy they usually are already "packet-ed", which basically means that they have been fertilized and will continue to drop fry every 4-6 weeks.

See that dark spot by her anal fin? that will grow and grow, until she looks like she will burst. That dark patch is actually all the little eyes of the fry growing inside her, clustered together in one spot. With any livebearer i use the same formula, plenty of high quality food (be careful not to over feed) and plenty of small regular water changes, plant your tanks out and watch the family grow.

Cheers

wow cool thanks for the info I have a spawning mop in the tank and also a cave made of stones and thats it I want to see if I can breed some really cool looking fish

Well if your ever down wellington ways, I'll be happy to give you a big handful of plants. I find plenty of plants in the tanks also help stabilize and regulate a healthy and natural environment. Mops are usually used for egg scatterers or non-annual killifish but i guess you could have it setup to simulate plants.

When I visited Australia ALL the guppies (male and female) were HUGE, like the size of mollies! Made our NZ available guppies look puny!

Both my girls are pregnant now so it will be interstiing to see what the offspring are like

I remember a few years back Wet pets in palmy used to always have ''giant'' guppy's but i found they where quite plain. I have some largish females, but nothing like the size the wet pet store had. Would be really keen to get my hands on some now actually.

The females are so busy having babies usually that they don't grow. I you keep them virgin you can get them to a good size before mating them.

my biggest female who is a decent size had the hugest growth spurt when she was carrying her first lot of fry. She just seemed to grow really fast once she became pregnant and she was quite young too.