Effects of low fishmeal diets on growth and gastro-intestinal luminal and digestive conditions of European sea bass (Dicentrarchus labrax L.) juveniles

Abstract

Feed ingredients are known to possess different buffer capacities which might influence pH ranges along the digestive tract. Fishmeal (FM) have one of the highest buffer capacities among raw materials and its decreasing content in aquafeed formulations might affect the ideal gastrointestinal environment for digestive enzyme action. In addition data on gastric and intestinal pH in carnivorous marine fish species under different feeding regimes are scarce. A study was undertaken, therefore, to assess growth response, gastric and intestinal pH of European sea bass (Dicentrarchus labrax L.) fed diets with low fishmeal levels added with or without buffering agents in comparison to a standard fishmeal diet. Three isonitrogenous (45% protein) and isolipidic (16% lipid) extruded diets containing 10% FM with or without buffering agent (FM10b, FM10, respectively) and one control diet containing 20% FM (FM20) were fed to triplicate fish groups of 80 individuals (initial weight: 23 g) to overfeeding over 64 days. At the end of the trial there were no significant differences between diets for final body weight, feed intake and feed conversion rate even if specific growth rate was slightly higher in FM10 compared to FM10b. Hepatosomatic index was higher in FM20 compared to FM10 while no significant differences were observed in the viscerosomatic index. pH was measured in the stomach and along the intestinal tracts (anterior, middle, posterior) of three fish per tank at 0, 4, 8 and 12 hours post prandial and correlated to the different diets. At the same time enzymatic activity of digestive enzymes and gut microbiota by next generation sequencing were also analysed. In conclusion, low FM diet (FM10) led to equal growth and feed utilization in comparison to standard FM level (FM20) and the inclusion of buffering feed agent did not seem to promote the overall growth performance.Trabajo presentado en el 18th International Symposium on Fish Nutrition and Feeding (ISFNF. 40 years of research in fish nutrition), celebrado en Las Palmas de Gran Canaria del 3 al 7 de junio de 2018.N