That diet has no vitamins or minerals, especially calcium. Without the proper amount of calcium your caiman will begin to leech calcium out of its own bones (metabolic bone disease). He may not be eating for a variety of reasons (stress, parasites, improper husbandry, poor water quality, too small a cage etc...). I hope you are providing a sufficient amount of UV light. You should have researched what a caimen needs BEFORE acquiring one. Search the internet on caresheets for caimens, hit the forums and read books on the proper nutrition and captive care (husbandry) of the species of caimen you have. Good luck!
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