I would be tempted to report these people for animal cruelity. Not feeding the dragon for a month because they didn't want it anymore is cruel. They obviously didn't offer water either, given how much he dragon when you received him. I bet they had little or no UVB light either.
To bring your new guy up to shape, offer small amounts of food items. A well balanced salad (if you have a 24" male you know what foods the dragon needs
). As other have suggested, offer small amounts spread out over the day. 2-3 meals a day should be good. I would offer softer bodied insects, such as silkworms as well. They are easier to digest and are not very active, so your dragon doesn't have to waste energy chasing crickets. Giving his small size, I would offer small crickets, if you can't get ahold of silkworms, (for the silkworms, get the one inch ones for now.) smaller than you would normally offer a dragon his size. For the first couple days, just offer a few crickets (or silkworms), maybe 4-8 (more small crickets, less silkworms).
The ideal now is to make sure all his innards are working properly. I also recommend a vet check as well. He can better ac cess the condition of the dragon (if you are going to place charged for animal neglect/abuse on the previous owner, I would take the lizard to the vet right away, so they can take pictures and see the condition it was in when they handed it over to you. If you can't get to a vet in a few days, take pictures, digital or regular, preferibly one that can carry a date stamp).
Having no interest in a pet is not an acceptable reason to starve it to death. They should have still fed it properly (bad enough the petstore gave them wrong information about the care requirements in the first place. Make me really wonder, don't people have common sense? If I knew nothing about reptiles and decided to bought one, a meal once a week seems rather to little, enough so i would have questioned it, and researched it on my own. But then again I have alot of common sense and follow it, some people don't, or are just too trusting).
Once again I would suggest charging them for animal cruelity...if they are too good friends and you don't want to ruin that and if you haven't already, deffinitely explain to them what they did was very cruel and against the law. You can also explained the petstore lied, which many unethnical petstore employees do, either unintentionally (misinformation from manager/chainstore policies) or because they only want to sell to make a commission or just don't care. Proper education of the public is very important to make our herps happy. For a happier closing note, deffinitely ask them to contact you if they have any questions about reptile care in the future and to verify/disapprove petstore information either before or after buying another reptile. This way you can either tell the the correct care information or at least research it for them and give them the proper care information.
Sorry, post wound up being longer, but I hate to see people letting animals suffer because they lost interest in them. It's not just done with lizards, its done with all animals, common every day ones and exotic.
In this day and age, it's not that hard to find a new home for a pet. An ad in the local grocery store is easy and free to do. There are many online ad sites to use that are free or very low costs. There are also the 'auto trader' sized classified booklets available. Free to put up an ad in most of them, if nothing fancy. Newspapers will also put up free to low cost ads, especially for 'free to new home' type ads, or low cost items.
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PHLdyPayne