ummm.... try a half assed proper diet- iguanas dont just eat lettuce carrots and bananas.
lettuce- if you mean iceberg is worthless and if thats all he's eating- you're going to have more problems than you know what to do with.
some igs dont like carrots or bananas-
If you're going to keep the poor thing- at least do it right and get a book and get educated. or else- give the thing to a rescue for its sake.
Iguanas eat:
collard and mustard greens- romaine lettuce, green and red leaf lettuce (NOT ICEBERG AKA HEAD LETTUCE- THIS IS WORTHLESS- PURE WATER- NO NUTRIENTS. its not even suitable for human consumption IMO.)
They need a combo of AT LEAST 2 of the above leafy greens- and there are other greens available- those are the most common.
This should be the bulk of the diet. DO NOT GIVE THEM SPINACH-
Veggies:
most anything will do- you'll have to put forth some effort and try new things- chunking a carrot in a cage and expecting it to eat isn't going to cut it. Get out a potato peeler and shred the veggies up for him so they are thin and bite size.
zuchini, squash, sweet potatoe, celery, parsley, cilantro, bell pepper, things like that- ours get a combo of 2 or 3 of these.
Fruit:
strawberries, bananas, pears, apples, peaches, mango, plums, and really about anything else- AVOID CITRUS fruits.
There shouldn't be a ton of veggies- think of it as making a salad for yourself- lots of leafy greens and a handful of veggies and a few peices of fruit- just make it iguana size.
you will also need a calcium suppliment as well as proper lighting- UVA/B lights and a heat lamp- this will cost you around 30 bucks- around 60 to do it properly. you also need some kind of thermometer to tell you the temp of the basking spot. - he will need a good size cage and will require a HUGE cage as an adult- invest in a large one now.
you also need to find a vet- and from the sounds of it- he needs to go ASAP!
a good book to buy is iguanas for dummies- simple- to the point- gets the job done- i have 2 copies- i have had well over 200 iguanas through this rescue and only ever lost 2- one was in a surgery and by no means my fault- I have brought many back from the brink of death and I have also asked for advise on this forum and gotten good answers. It takes a lot of hard work and dedication to keep an iguana healthy- they aren't fish.
good luck
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The rescue site: www.freewebs.com/okreptilerescue