GCG and glucose measurement: Daily administration of tilapia skin gelatin hydrolysate (750 mg/kg/day) for 30 days was more potent to improve the glucose tolerance in streptozotocin-induced diabetic rats than hydrolysates from halibut skin (750 mg/kg/day), inducing the inhibition of plasma dipeptidyl peptidase IV (DPP-IV) activity, enhancement of glucagon-like peptide-1 (GLP-1) and insulin secretion.