Effects of micronutrients in the development of juvenile gilthead seabream (Sparus aurata)

Growth of gilthead seabream production is challenged by the need to develop economically and environmentally sustainable feeds low in fishmeal (FM) and fish oil (FO). Replacement of these ingredients by plant sources could also imply the modification of the feed micronutrients profile (minerals and vitamins) affecting their supplementation levels. However, nutritional requirements for these nutrients have not been established for gilthead seabream. The aim of the present study was to obtain information about the adequate levels of some of these minerals and vitamins in diets with low FM and FO levels. Six different vegetable based practical diets (FM: 15 per cent, FO:7 per cent) contained a micronutrients premix in ascending order. Gilthead seabream juveniles (weight 25.5 plus minus 2.7 g (mean plus minus S.D.)) were distributed in 18 tanks in triplicates and fed until apparent satiation three times per day for 155 days. Performance parameters including feed intake, thermal growth coefficient and feed conversion ratio were calculated. Biochemical analysis of whole body, vertebrae, plasma and blood cells; hematocrit; histological analysis; expression of several genes in liver and vertebrae; and whole fish X-ray were conducted. Increasing nutrient package affected fish growth, expression of molecular markers related with these nutrients, gill morphology, mineral content in different tissues, etc. Optimum levels for seabream were close to those determined in a similar study for Atlantic salmon, except for higher copper, iron and zinc. Optimum levels for B-vitamins, such as thiamin, were increased when using plant-based diets. The whole nutrient package regression method was useful to gain information about the seabream requirements for some micronutrients. However, nutrients interactions made it difficult to obtain clear results for some of these nutrients, and must be studied in more detail.