ONTOGENIC CHANGES OF LIPOLYTIC ENZYMES IN STRIPED BASS (MORONE-SAXATILIS)

Ontogenetic changes of triacylglycerol hydrolase (TAGH), wax ester hyd rolase (WEH) and phospholipase A(2) (PLA(2)) activities were determine d in the fertilized eggs and premetamorphosed larvae of striped bass a nd the larval food Artemia using radioassays. Maximum activities of th e three enzymes were observed at a substrate concentration of 500 mu M and in the presence of 5 mM Na-taurocholate. PLA(2) showed the major activity in the eggs, followed by TAGH and WEH. TAGH became the domina nt lipolytic activity after feeding was initiated at 7 days post-hatch ing (DPH). The proportions of TAGH:PLA(2):WEH in the fertilized eggs w ere 1.1:1.6:1.0. In 20 DPH fed larvae, however, the proportion changed to 6.3:1.9:1.0. In unfed larvae, the enzyme activities were significa ntly lower compared to feeding larvae (P < 0.05). The activities of PL A(2), TAGH and WEH in Artemia were in the order of PLA(2) > TAGH > WEH . The contribution of dietary enzymes to the total lipolytic processes is estimated to be less than 6.5% of the total enzyme activity throug hout the development. The results of this study indicate that first fe eding striped bass larvae have the capacity to digest 47% of their dai ly lipid ingestion.