Assessment of protein digestive capacity and metabolic utilisation during ontogeny of Senegalese sole larvae: A tracer study using in vivo produced radiolabelled polypeptide fractions

Dietary indispensable amino acids profile affects protein utilization and growth of Senegalese sole larvae

“…Since the sole digestive system at such young stages is still very immature, not having any pepsin activity, it relies proteolysis on pancreatic endoproteases (such as trypsin and chymotrypsin) activity, which may not be as efficient to access the cleavage sites of partially folded 6.8 kDa peptides as those of 1.0 kDa peptides. However, it was a little surprising that there was no major increase in the larvae capacity to absorb larger molecules throughout development, though similar results have also been observed in other studies with same-sized model peptides (Engrola et al 2013;Richard et al 2015). Perhaps an increase would be noticed at later stages, as it was observed in 34 DAH sole larvae by Richard et al (2015).…”

“…However, it was a little surprising that there was no major increase in the larvae capacity to absorb larger molecules throughout development, though similar results have also been observed in other studies with same-sized model peptides (Engrola et al 2013;Richard et al 2015). Perhaps an increase would be noticed at later stages, as it was observed in 34 DAH sole larvae by Richard et al (2015). The 20 % decrease in the 6.8 kDa absorption rate during the metamorphosis climax (19 DAH) is comparable to (Engrola et al 2009b) previous results, according to which Senegalese sole reared upon a co-feeding regime from an early stage displayed a reduced capacity to digest Artemia during the metamorphosis climax.…”

“…An alternative explanation may be the lower growth rate and metabolism of older larvae (Conceição et al 1998a), making them less efficient in using fastabsorbed lower molecular weight peptides, due to transient AA imbalances. The 6.8 kDa polypeptide fraction could also be better adapted to the AA anabolic and physiological need of young sole juveniles rather than younger larval stages as it was suggested by Richard et al (2015). These authors have also obtained an increasing trend of 6.8 kDa peptide retention throughout the ontogeny.…”

“…The effect of dietary amino acid profile on the digestion, absorption and metabolic utilization capacities of larvae throughout the metamorphosis was assessed through the metabolism of 14 C labelled model peptides with different molecular weights, 1.0 and 6.8 kDa (Richard et al 2015), at 13 DAH (premetamorphosis), at 19 DAH (metamorphosis climax) and at 25 DAH (metamorphosis completed).…”

“…metanauplii for 30 min. Then eight larvae (with guts well filled with Artemia) from each dietary treatment were anaesthetized with 150-330 lM of MS-222 (depending on larvae age) and tube-fed two doses of 13.8 gL of the test 14 C-labelled model peptide (193 gg of 1.0KDa peptide; 635 gg of 6.8KDa peptide) through a 0.19-mm-diameter plastic capillary inserted on a nanoliter injector (World Precision Instruments, Sarasota, USA) firmly attached to a micromanipulator (Richard et al 2015). After capillary withdrawal, each larva was gently rinsed for spillage in two successive wells filled with clean seawater and transferred into incubation chambers filled with 7.5 mL of seawater.…”