Hey Brian. I've been a member of many herp groups and this question seems to always come up. There have been reports of some very large Marine populations, but, to date, I haven't seen anyone produce them reliably. I've seen some extremely large ones, usually long term female captives. Or females caught in areas with new populations of these toads. It seems that the longer these guys inhabit an area, the smaller they get. It probably has something to do with the amount of prey available per toad, and maybe the HUMAN element (people don't seem to like them much) Big toads are easier to I.D., More likely to fall victim to a big car/shovel/foot. I'd say that if you want a really big B. marinus you have two options, 1.Buy a really big one from someone who is willing to unload it (everyone I know who has Biggun's wouldn't let them go for anything). Or 2. Get a female and raise her yourself. These critters seem to respond well to a good diet, healthy environment. I have yet to see any reliable growth rate charts for these guys. Hopefully I'll be getting a few Juvies soon. Every herp I've ever owned has grown larger/faster than the norm, I had a savanna monitor that grew from 6" to nearly 3 feet in 2 years (husbandry does make a difference), so hopefully I'll have some reliable data soon.
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How to get your wife to like toads; 1.Get a male toad. 2.Get him to hug your wifes wrist (amplexus). 3. Tickle him so he chirps in protest. 4.Say "Awww, he likes you". Note; Make sure he pees first or you may receive bodily harm during this procedure.