Have Reptile Veterinary Questions? Ask a Reptile Expert.
My name is ***** ***** I have been a Vet tech for 30+ years with special interest in Reptiles and reptile rescue.
You can try supplemental feeding beside crickets. Meat flavored baby food mixed with calcium works well and you can add some Flukers Repti Boost for insectivores http://www.petco.com/shop/en/petcostore/flukers-reptaboost-insectavore-and-carnivore-high-amp-boost This may help get the gecko jump started . You can also do a soak in a 50/50 warm water and Pedialyte soak. Do this is a shallow bowl and only has to cover the Vent area.
For feeders silk worms and Phoenix worms are very nutritious feeders and may be welcomed by your Gecko. Short of this there is not a lot that can be done at home. The Vet could give a vitamin shot and check the fecal for parasite that could be causing the weight loss. You would also want an acid fast stain to check for crypto which is a wasting disease.
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How is your Gecko doing. I wanted to check back in with you since he was so thi to see if the information supplied was of help.