Amino acid requirements of fish larvae and
post-larvae: new tools and recent findings
L.E.C. Conceic¸a
˜
o
a,
*
, H. Grasdalen
b
, I. Rønnestad
c
a
CCMAR, University of Algarve, Campus de Gambelas, P-8000-117 Faro, Portugal
b
Department of Biotechnology, NTNU, N-7491 Trondheim, Norway
c
Department of Zoology, University of Bergen, Alle
´
gt. 41, N-5007 Bergen, Norway
Accepted 29 May 2003
Abstract
This paper reviews methodologies and recent findings in the study of the amino acid (AA)
metabolism of fish larvae and post-larvae, in order to better understand the AA requirements. The
larval indispensable AA (IAA) profile can be used as index of the IAA requirements. When turbot
larvae and live food IAA profiles are compared, the profile of the latter seems to be deficient in some
IAA. However, the larval IAA profile is only a rough indicator of AA requirements. A more precise
estimate of the ideal dietary IAA profile implies the knowledge of the relative bioavailabilities of the
individual AA, in particular, eventual differential rates of absorption and catabolism. Metabolic
budgets (including unabsorbed AA, AA oxidation and AA retention) can be estimated using an in
vivo method based on controlled tube-feeding of AA mixes containing a
14
C-labelled AA. Results
with fasted post-larval Senegal sole (Solea senegalensis) and fasted herring (Clupea harengus) larvae
show a high retention of labelled doses of IAA (>60%) in the body, compared to catabolism as
measured by liberated
14
CO
2
( < 25%). In contrast, dispensable AA (DAA) show a higher catabolism
(>40%) and a lower retention ( < 57%). So, from the onset of exogenous feeding, fish larvae have
high catabolic losses of AA, but use DAA preferentially to IAA as energy substrates. A new method
combining the use of
13
C-labelled live food and
13
C-NMR spectroscopy can be used to study
simultaneously the relative bioavailability of several individual AA in fish larvae. In larval gilthead
seabream (Sparus aurata) fed on rotifers, relative bioavailabilities (a combined measure of
absorption efficiency and rate of catabolism) vary between AA being high for aspartate, glutamate
and lysine and low for threonine. These estimates of relative biovailability of individual AA together
with the IAA profiles of the larval seabream indicate that rotifers are deficient in threonine and
leucine for larval seabream, threonine being the first limiting AA for protein synthesis. In order to
define ideal IAA profiles for larval fish, further studies are needed on the factors affecting the relative
bioavailability of IAA, such as species, age, developmental stage, temperature and the dietary
0044-8486/$ - see front matter D 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0044-8486(03)00505-2
* Corresponding author. Tel.: +351-91-7015872; fax: +351-289818353.
E-mail address: lconcei@ualg.pt (L.E.C. Conceic¸a
˜
o).
www.elsevier.com/locate/aqua-online
Aquaculture 227 (2003) 221 – 232