Determination of dietary docosahexaenoic acid (DHA) requirements for senegalese sole (Solea senegalensis) post-larvae

Dissertação de mest., Aquacultura e Pescas, Faculdade de Ciências e Tecnologia, Universidade do Algarve, 2009 Docosahexaenoic acid (DHA) is an essential fatty acid for marine fish larvae, with effects on growth and larval quality. DHA requirements for Senegalese sole (Solea senegalensis), a species of high commercial interest, are poorly understood. On this thesis a dose–response design in conjunction with a methodology based on tube feeding of 14C-[DHA], was employed in order to determine the dietary DHA requirements for Senegalese sole post-larvae. The effect of dietary DHA was examined on growth, survival, pigmentation and Artemia intake (at low light conditions). From 22 to 35 days after hatching (DAH) - pre-weaning period - post-larvae were fed frozen Artemia that had been enriched using one of four experimental emulsions containing four graduated concentrations of DHA. Final levels of DHA in the enriched Artemia metanauplii were 0.0 mg g-1DW (DHA-0), 5.1 mg g-1DW (DHA-5), 14.1 mg g-1DW (DHA-14) and 30.2 mg g-1DW (DHA-30). Afterwards and during the weaning period (41 to 61 DAH) all post-larvae were fed with a same moist feed. Significant differences in dry weight (DW) were found at the end of the pre-weaning period. Treatment DHA-0, induced a higher larval growth (2.84±1.04 mgDW) than treatment DHA-5 (2.38±0.74 mgDW). Light intensity influenced both final DW and RGR and there was a positive correlation for a higher growth (DW and RGR) as the light intensity increased. On weaning period treatments DHA-0 and DHA-30 showed significant higher DW and total length values than those presented in DHA-5 and DHA-14. On the radiolabelled Artemia intake test, and after 30 min in presence of Artemia (T30), larvae ingested significantly higher amounts than observed at 10 min, and a positive correlation between dietary DHA levels and Artemia fed within the T10 groups was also found. Tube feeding of [1- 14C]DHA resulted in no significant differences for absorption, retention and catabolism between larvae submitted to different experimental treatments. However, a slight tendency for an increase in the percentage of catabolised DHA with increased DHA dietary supply was also noted, with an apparent increase in catabolism between treatment DHA-5 and DHA-14. No major effects of dietary DHA levels ranging from 0.0 to 30.2 mg.g-1Artemia DW between 22 and 35DAH could be observed on larval performance. However, light intensity probably had an impact on post-larvae performance, mainly at high intensities. Furthermore, the tube feeding trial suggested a possible DHA requirment between 5.1 and 14.6 mg g-1 of Artemia dry weight.