A method for radiolabeling Artemia
with applications in studies of food intake, digestibility, protein and
amino acid metabolism in larval fish
S. Morais, L.E.C. Conceição, M.T. Dinis, I. Rønnestad-2004
Aquaculture, 231(1-4): 469-487
Abstract:
The present paper describes a method for
radiolabeling Artemia that has potential applicability in the study
of food intake, Artemia digestibility, protein and amino acid (AA)
metabolism in early stages of marine fish larvae. Artemia nauplii
were labeled by adding a uniformly labeled 14C protein
hydrolysate to its hatching or enrichment media. Both newly hatched and
enriched nauplii assimilated rapidly the radiolabel and a very high
proportion of the uptaken label was incorporated into the TCA precipitate
(mostly protein) fraction after a short period of time––84–91%, at the
end of the hatching period and 81–87%, after 12 h of enrichment. In
addition, it was observed that the amount of radiolabel per Artemia,
as well as its distribution between the TCA precipitate and soluble (free
AA) fractions, was relatively stable (up to 8 h) in conditions simulating
transfer to larval feeding tanks. During the radiolabeling trials a
substantial amount of the total initial radioactivity in the media was not
recovered at the end of the hatching or enrichment period (38% and 29%,
respectively). An experiment was designed to study the release of the
radiotracer into the atmosphere, as 14CO2. It was
concluded that although the Artemia catabolism may be responsible for
some release of the radiolabel into the atmosphere, bacterial activity in
the enrichment media has a major impact, being responsible for the loss of
19.2% of the total initial radiolabel from the system. The digestibility and
transfer rates of the labeled nutrients from Artemia to fish larvae
was analysed "in vivo" by feeding radiolabeled newly hatched
nauplii to herring (Clupea harengus) larvae and following the
metabolic fate of the label. The results revealed a high digestibility
(around 60%) of the Artemia, with 20% being retained in the body and
39% catabolised by the larvae, 24 h after feeding. The digestion process and
subsequent absorption of the digested radiolabeled nutrients were quite
rapid, given that 40% was recovered in the body only 2 h after feeding and
6% was found in the CO2 trap at this time.
(CCMAR, Universidade do Algarve, Campus de Gambelas,
8000-117, Faro, Portugal, e-mail: smorais@ualg.pt)