Metabolic budget of an essential and a non-essential dietary amino acid in herring ( Clupea harengus) larvae

Abstract

In comparison to mammals, juvenile and adult fish have a higher amino acid (AA) requirement and a lower adaptability of AA metabolism. This means that fish are more sensitive to diets with low protein levels or with an imbalanced AA profile. Fish larvae are thought to have even less control of their AA metabolism, leading to higher catabolic losses of AA, and thereby to higher AA requirements (Dabrowski 1986). Therefore it is important to know to what extent fish larvae have the ‘ydpacity to spare essential AA (EAA) at the expenses of non-essential AA (NEAA). ‘This study intended to estimate a metabolic budget both for an EAA and a NEAA, in herring (Clupen harengus) larvae. A nlix of crystalline amino acids containing either ‘“C-Glutamate or 14C-Lysine was tube-feed to first feeding and 47 days-old Ipre-metamorphosis) in herring larvae. The following components of the metabolic budget were estimated: AA digestive absorption, AA conversion into lipidic molecules, AA oxidation, and conservation of AA in the FAA and in the protein pools. l-‘lrst feeding herring larvae absorbed around 92% of both lysine and glutamate. However, 23 % of the tube-feed lysine was ouidised and 69% was retained while for glutamate oxidation was as high as 76% and retention only 16%. A similar picture was observed for 47 days-old larvae. Here oxidation was 22% and 62% and retention 63% and 32%, for lysine and glutamate, respectively. Therefore, herring larvae use glutamate preferentially to lysine for energy production from first feeding onwards. These results suggest that fish larvae may have a better capacity of regulating AA catabolism than previously believed (Concei@o et al. 1997, 1998). Conce@o, L.E.C. et al. (I 997) Amino acid metabolism and protein turnover in larval turbot (Scophthalmus mmimus) fed natural zooplankton or Artemia. Mar. Biol.29. 25526.5. Concei@o, L.E.C et a1.(1998). Amino acid profiles and amino acid utilisation in larval African catfish (Clurias gariepinus): effects of ontogeny and temperature. Fish Physiol. Biochem 19: 43-47. Dabrowski, K.R. (1986) Comp. Biochem. Physiol. &5J: 639-655.