Amino
acid requirements of fish larvae and post-larvae: new tools and recent
findings
L.E.C. Conceição, H. Grasdalen, I. Rønnestad
Aquaculture, 227(1-4): 221-232
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 14C-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 14CO2
(<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 13C-labelled live food and 13C-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 nitrogen molecular form(s). Estimates of
relative bioavailability of individual AA together with the IAA profile of
the larval protein allow to determine the ideal dietary IAA profile for a
given species.
(CCMAR, University of Algarve, Campus de Gambelas,
P-8000-117, Faro, Portugal, e-mail: lconcei@ualg.pt)