Effect of dietary vitamin C level during early larval stages in Senegalese sole (Solea senegalensis)

• This novel study evaluates the effects of dietary vitamin C level supplied through alginate microencapsulated diets in early larval stages of the flatfish Solea senegalensis.
• The new microdiet preparation enables effective entrapment of vitamin C when used in the ascorbyl palmitate form, leading to microdiets containing graded levels of vitamin C.
• Ascorbyl palmitate can be use as a vitamin C source in microdiets, remaining available to S. Senegalensis larvae and increasing ascorbic acid concentration in tissue in a dose response way.
• The influence of dietary vitamin C during first feeding on further development in Solea senegalensis was revealed. Low dietary vitamin C during early feeding of S. senegalensis larvae delayed development.
• The level of vitamin C during early stages of S. senegalensis plays a critical role in growth modulation, malformations, metamorphosis, stress and the antioxidant status in later developmental stages.

The aim of this work was to assess the effects of a dietary supplement of vitamin C (as ascorbyl palmitate, AP) delivered through new and optimized alginate microcapsules (MA) on larval performance, antioxidant status and gene expression profiles. For this purpose, three MA (referred to as MA-1, MA-2 and MA-3) with increasing AP content ranging from 1700 to 5700 μg AP g− 1 DW were assayed. Sole larvae were fed the three MA from first feeding to 7 days post-hatch (dph) and later replaced by Artemia from 7 to 28 dph. The experimental groups were performed in triplicate using a recirculation system. The efficiency of AP inclusion into MA was 55%. At 7 dph, larval ascorbic acid (AA) content was proportional to the AP concentration included in MA (p < 0.05). Larval growth until 7 dph was low but significantly higher in larvae fed MA-2 and MA-3. After Artemia supplying, a compensatory growth was detected in the three experimental groups whereas a faster metamorphic process and a higher weight at 28 dph in larvae fed MA with a higher AP content (MA-2 and MA-3) was observed (p < 0.05). Moreover, Artemia feeding substantially increased the larval AA content during development peaking at 18 dph and decreasing at the end of metamorphosis with significantly lower AA levels in larvae fed MA-3. This reduction coincided with a higher total antioxidant capacity and lipid peroxidation whereas no differences in catalase or total glutathione peroxidase were detected. Expression data revealed that MA diets significantly modified the transcript levels of 16 genes involved in antioxidant defence (gpx1), tissue structure (col1a1 col1a2 and col1a3), stress (hsc70-1, hsc70-2, hsc70-3, gr1, gr2, pomcb), glycolytic pathway (gapdh1 and pkm), osmoregulation (cftr, nkcc2 and nkcc1) and pigmentation (mc1r). All these data reveal novel new insights about role of vitamin C during early stages of S. senegalensis to modulate growth, stress and antioxidative status in later developmental stages.