These aren't exactly early signs of dehydration but take a look at his poop, specifically the whitish portion. That part should be a nice bright white. If it looks off-white, beige, brown, orange, or any other strange color then your cham isn't getting enough hydration. You cha also look at his Casque, that's the crown like part of his head. Some chams like Panthers have very well developed casques, others not so much. What you want to see especially in panthers, is a nice plump casque. If its flat or sunken it is a definite sign of dehydration and possibly even malnutrition as this is a fat pad that stores both calories and water.