When to start worrying?

Ok, so my 2 yr old has always been a good and regular feeder since we brought him home in march, 2010. Around December he stopped eating. Still shows no interest. Other than not eating, he seems healthy. Normal routine, hiding all day, explores at night. Drinks water. Of course losing weight. Offering one sm rat about once a week with no results. Has no interest. When should we start worrying?

How much weight has he lost? If it's dramatic then you should be worrying. It's totally normal for breedable males to go off feed around this time of the year. But they don't lose alot of weight during that time. If he is losing alot of weight quickly I'd check temps, husbandry, then vet. I've had males go
Off feed for 6 months and barely lose 100g.

My het pied male decided to skip eating for 5 months at that age. I didn't really start worrying until he'd lost 30% of his original weight, and started to look really triangular with slightly flabby skin. But he started eating a couple weeks before I started worrying enough to try offering live, or take him to the vet.

What were his weight prior to the fast and now? Have any before and after shots? Change around his habitat at all? Temps, humidity, hides, etc?