AN 18-YEAR-OLD KOALA IS EUTHANIZED AT THE ALBUQUERQUE BIOPARK. ZOO OFFICIALS SAY THE MALE NAMED ZAKI WAS ONE OF THE OLDEST KOALA'S IN CAPTIVITY. THEY HAD BEEN MONITORING HIM IN RECENTLY WEEKS AS HE HAD LOST A SIGNIFICANT AMOUNT OF WEIGHT AND BECAME WEAK. VETS COULD NOT FIND A MEDICAL CAUSE FOR HIS DECLINE OTHER THAN OLD AGE. KOALAS ARE KNOWN TO LIVE AS MANY AS 20 YEARS IN CAPTIVITY. ZAKI HAD BEEN AT THE BIOPARK SINCE 1997.