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- Phaeodactylum tricornutum biomass in microdiets enhances Senegalese sole (Solea senegalensis) larval growth performance during weaningPublication . Barreto, André; Pinto, Wilson; Rodrigues, Andreia; Rocha, Rui J. M.; Unamunzaga, Carlos; Silva, Tome; Dias, Jorge; Conceicao, LuisMicroalgae are one of the most promising groups of functional ingredients for inclusion in microdiets for Senegalese sole (Solea senegalensis) larvae, supplying components with anti-oxidant effects that may be important during an accelerated stage of development where excessive reactive oxygen substance production leading to oxidative stress may occur. The diatom Phaeodactylum tricornutum complies with such potential since it is rich in fucoxanthin, a carotenoid with demonstrated antioxidant activity. This study aimed at determining the effect of dietary P. tricornutum supplementation on the growth performance, survival and levels of oxidative stress of Senegalese sole postlarvae. Four dietary treatments were tested: a commercial microdiet, used as control, and three experimental variants where P. tricornutum was included (1) whole cells at 5%-WP5, (2) broken cells at 5%-BP5 and (3) broken cells at 10%-BP10. At the end of the trial, no significant differences were found in growth performance of larvae fed diets where P. tricornutum was included at 5% (WP5 and BP5) and the commercial control. However, larvae from the BP10 treatment had a significantly higher dry weight than larvae from the remaining treatments. Moreover, the experimental diets had no significant effects on oxidative stress. Nonetheless, lipid peroxidation levels were significantly higher in smaller larvae fed diets where P. tricornutum whole cells were included, relatively to the commercial control. The results of the present study demonstrate that P. tricornutum broken cell biomass has the potential for inclusion in weaning microdiets for Senegalese sole, increasing larval growth performance at an inclusion level of 10 %.
- Towards an early weaning in Senegalese sole (Solea senegalensis kaup, 1858)Publication . Barreto, André Filipe Gonçalves; Conceição, Luís Eugénio da Castanheira; Pinto, Wilson Gabriel Poseiro CoutinhoThis Thesis aimed to contribute towards an earlier weaning in Senegalese sole which currently starts at larvae 25 days after hatching (DAH) with good results. Two trials were conducted using different weaning strategies and microdiet formulations, targeting full weaning after larval settling (15 DAH). On the first trial, seven different treatments were tested: the control treatment was suddenly weaned at 25 DAH to a commercial diet, while the remaining six treatments were co-fed each a different microdiet and Artemia until full weaning at 23 DAH. Larvae achieved RGR values of around 12.4%.day-1, FCR values around 1.0 and survival between 56 to 79%, which are great improvements to results obtained by other authors in Senegalese sole weaning studies. WinFlat and NCAP (WinFlat variant with mixture of encapsulated and non-encapsulated taurine instead of the microencapsulated version alone used in WinFlat) seem to be the most appropriate and cost effective microdiets used in this trial. The lowest growth performance was exhibited by the PH20 larvae that fed on a microdiet with increased inclusion levels of protein hydrolisates in relation to the commercial diet WinFlat. The control exhibited significantly inferior growth performances than all co-fed treatments, excluding PH20, and exhibited the lowest survival of all treatments. The results suggest that the use of a co-feeding regime is more appropriate when weaning larvae at such early stages of development. In the second trial, a total of seven different treatments were tested. All larvae were subject to a co-feeding regime, each with a different inert microdiet, until full weaning was performed at 19 DAH. Larvae achieved RGR values of around 11.1%.day-1, FCR values averaging 4.5 and survival between 45 to 61%. The overall growth results are superior to those obtained in the first trial at an approximate larval age and such good results had never been reported before. Nevertheless, the lowest survivals observed may be related to the more aggressive weaning strategy employed. The use of a mixture of encapsulated and non-encapsulated taurine instead of a microencapsulated version alone was beneficial to the larvae growth performance. The inclusion of the microalga Phaeodactylum tricornutum broken cells in the microdiets at an inclusion level of 10% produced superior growth performances than the commercial diet WinFlat. The inclusion of dietary tryptophan in WinFlat may enhance larvae growth performances. The use of a moist WinFlat variant, diluted in a 1:5 ratio, caused the larvae to exhibit inferior growth performances than all remaining treatments, probably due to insufficient nutrient intake. In conclusion, results from both trials conducted during this Thesis support that the age at which Senegalese sole currently starts to be weaned can be reduced from 25/30 DAH to 15 DAH. Nevertheless, results also suggest that improvements can still be made in weaning microdiets formulations and weaning strategies.