Mecanismos implicados en la eficiencia del proceso de digestión en peces marinos cultivados

Laburpena

The ongoing expansion of aquaculture production relies on improvement of the digestion efficiency to enhance the suitability and the commercial viability of the sector. The efficiency of hydrolysis and absorption is determined by several factors related to the gastrointestinal tract. Besides, feeding behaviour and digestion function are driven by external (e.g. light-dark and feeding-fasting cycles) and internal signals, and exhibit circadian patterns. However, many of the aquaculture practices, including feeding-fasting cycles are not synchronized with the species internal rhythms. The main hypothesis of this study was that a better knowledge of daily digestive function might help to improve the feeding efficiency in farmed fish species. Therefore, the principle objective of the present Doctoral Thesis was to determine the digestive capacity of gilthead seabream (Sparus auarata) and Senegalese sole (Solea senegalensis) juveniles, in relation to different feeding conditions, by adapting an integrative approach (comprised of in vivo and in vitro experiments) and considering the whole daily cycle. The selection of these species was based on their importance for Mediterranean aquaculture and their different feeding habits and digestive system morphologies. To achieve this, in several in vivo experiments, daily postprandial pattern of pH, enzymatic capacity, food transit rate, and apparent digestibility were determined in relation to feeding protocols in target species. Using the data generated by the in vivo experiments, in vitro models were used for further assessment of the mentioned parameters and for prediction of the fish response to combination of different factors. According to our findings, while peripheral oscillators were entrained by certain feeding protocols in Senegalese sole, in gilthead seabream these oscillators were strongly synchronized with the light-dark cycles. In both species, production and/or temporal organization of the enzymatic activity were significantly affected by the tested feeding protocols. Nevertheless, occasional daily acidification of the stomach and its general asynchrony with pepsinogen production, casted doubt on a major role of this organ in protein hydrolysis in gilthead seabream early juveniles. Different daily feeding protocols led to important changes in daily food transit, residence times, and apparent digestibility in the gut of both species, depending on the interspecific differences in anatomy and physiology of the digestive system. Our results from the in vivo experiments suggested that exclusively nocturnal and five diurnal daily meals are the most adequate feeding protocol for Senegalese sole and gilthead seabream juveniles, respectively. Finally, the findings from the in vitro experiments were highly comparable to the fish physiological responses, and allowed for a better understanding the results from in vivo experiments, suggesting the usefulness of this methodology for future studies.