In vivo studies of digestion and nutrient
assimilation in marine fish larvae
I. Rønnestad, C.R. Rojas-García, S.K. Tonheim,
L.E.C. Conceição-2001
Aquaculture, 201(1-2): 161-175
Abstract:
This paper describes a method for quantifying the
functionality of the digestive system in fish larvae. The system described
can provide data for the gut absorption, oxidation and retention
(assimilation) of nutrients. A tube-feeding setup (originally described in
Aquaculture 116 (1993) (341-352) using 14C-labelled dietary
nutrients formed the basis of a new incubation system. This permitted
unabsorbed nutrients evacuated from the gut to be distinguished from
molecules originating from catabolism of the absorbed nutrient, both of
which are present in the incubation water. The system is based on the
release, transfer and entrapment of metabolically produced 14C-CO2
through manipulation of the water pH. The efficiency of the trap has been
validated and tested, and provides 100.0±1.3% (S.D.) recovery. The
usefulness of the method is demonstrated in a study in which Atlantic
halibut post-larvae (46 days post first feeding) were fed a 14C-labelled
protein diet. These data show that this protein has a digestibility of 42%
for halibut post-larvae. If oxidation had not been measured through the use
of the CO2 trap, digestibility would have been greatly
underestimated (at about 25%).