Optimizing the nutritional composition of commercial diets for flatfish larvae

• Autor(a) principal: Valente, Afonso Manuel Roberto
• Data de Publicação: 2022
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10400.1/19948
• topic: Senegalese sole; Turbot; Microdiets; Binders; Leaching; Physical properties; Domínio/Área Científica::Ciências Naturais::Outras Ciências Naturais

Aquaculture industry is the food sector with higher contribution to recent growth in global food supply. Atlantic salmon (Salmo salar) is the most commercialized species in Europe. Mediterranean aquaculture is dominated by seabass (Dicentrarchus labrax) and seabream (Sparus aurata). Senegalese sole (Solea senegalensis) and turbot (Scophthalmus maximus) are two flatfish identified with potential in aquaculture whose production recently increased significantly in Portugal, Spain and France especially due to research effort made for these countries, in subjects such as weaning strategy, larvae nutrition and disease control. There are important improvements still needed for these species because they are cultivated in recirculation systems and water quality should be kept under control. It is necessary to find formulations that comply with larval necessary nutritional requirements and allow reduce nutrient leaching into the water and adapted to the flatfish species-specific feeding behaviour. The type of binder and/or binding process selected in a diet formulation and feed production technology will influence the leaching and physical characteristics of the pellets. Ingredients that provide microdiets a higher capacity of sinking of the pellets are more suitable for Senegalese sole that feed on the bottom, while binders that will slow-down sinking should be used for turbot diets that feeds on the water column. This thesis aims to perform adaptations in microdiets formulation in order to improve their physical properties and leaching and evaluate how the new ingredients affect the Senegalese sole larvae growth performance. New binders and different combinations of them were used to reduce Turbot microdiets nutrient leaching, adjust the dispersion and sinking capacity and also correlate with the biological efficiency which was evaluated in two trials. On trial 1 Senegalese sole larvae were fed with four different microdiets. The used diets were a commercial microdiet as control, and 3 diets with different ingredients. B/C was a diet with high benefit/cost ratio composed of high quality fish and squid meals and a mixture of plant-proteins including wheat gluten and pea protein concentrates, LFAT a diet with a similar composition to diet B/C, but where the reduction of the crude fat content was targeted, and PL was a diet also with a similar composition to diet B/C, but where the inclusion of a higher phospholipid content was targeted. The growth performance from all treatments was not significantly different except on LFAT which had a significantly lower growth performance, but regarding the microdiets properties PL was the diet with lower protein leaching, B/C and PL were the diets with higher sinking capacity and B/C was the diet with higher dispersion capacity. Furthermore, the results suggest that PL and B/C can be considered the best treatments used on trial 1 essentially due to the growth performance results which are similar to the control treatment and represent a higher benefit/cost ratio, but because they also fulfil important requirements on physical properties. On the second trial four different microdiets were tested in Turbot larvae, a diet used as control and three experimental diets. CTRL was a commercial-like diet, being composed of high quality fish and squid meals and plant-proteins including wheat gluten. MIX was produced with a similar composition to CTRL but using a mixture of binders in its dietary composition, LOW was produced with a similar composition to CTRL, but using a novel binder at a low inclusion level, and HIGH was produced with a similar composition to CTRL, but using a novel binder at a high inclusion level. At the end of trial CTRL and HIGH were the diets with best results for growth performance. Despite HIGH and CTRL does not have the best results on leaching reduction and the physical properties tests were not the ones who best fit into the Turbot feeding behaviour, the growth performance obtained with this dietary treatment was higher than the remaining treatments. When compared with other treatments, MIX can be a good solution to reduce leaching but will result in a with lower growth performance. CTRL and HIGH were, therefore, the most advantageous solutions. In summary, B/C and PL microdiet for Senegalese sole was the best solution due to it high benefit/cost ratio, combined with a good growth performance and reduced protein leaching, regarding Turbot, the best treatments were CTRL and HIGH due to its best growth performance results.