Introduction
Requirements for the major nutrients have been described for several European Union (EU) cultured species including salmonids and carps, however, information related to minerals and vitamins is still scarce for Gilthead seabream (Sparus aurata) despite being a major marine species cultured in the EU. Recent studies have described the effects of increasing dietary levels of selenium (Se) (Dominguez et al., 2019a), manganese (Mn) (Dominguez et al., 2020a), copper (Cu) (Dominguez et al., 2019b), zinc (Zn) (Tseng et al., in prep), and their sources (Dominguez et al., 2017, 2019c; Mechlaoui et al., 2019; Tseng et al., 2021); as well as vitamin A (VA) (Dominguez et al., in prep), vitamin D (VD) (Dominguez et al., 2021, Sivagurunathan et al., submitted), vitamin K (VK) (Dominguez et al., 2022, Sivagurunathan et al., in prep), and B-vitamins (Dominguez et al., in prep) ) in gilthead seabream. The present abstract aims to describe the available knowledge on mineral and vitamin nutrition for gilthead seabream juveniles.
Materials and methods
A total of 8 trials were conducted in gilthead seabream juveniles with the aim of understanding the optimum dietary levels for Se, Mn, Cu, Zn, VA, VD, VK and vitamins B1, B9 and B12; an additional 4 experiments were carried out to understand the effects of several mineral sources. For the trials aimed at studying the optimum levels, a basal feed was supplemented with at least 5 different levels for each nutrient, and each feed was tested in triplicates, to give a total of 15 tanks per trial. For the experiments with the difference mineral sources, the same level of the mineral was tested using different sources. Fish were raised by natural spawning at the Aquaculture Research Group from the University of Las Palmas de Gran Canaria ECOAQUA institute, and for each trial the fish came from the same broodstock, so as to reduce the genetic variability. Samples for proximal and vitamin/mineral composition, gene expression, histology and other analyses were taken at the start and end of the trials.
Results and Discussion
Se supplementation up to 0.94 mg/kg promote growth of gilthead seabream juveniles (figure 1). On the contrary, dietary levels of 1.70 mg Se/kg were found to be excessive and caused growth reduction, increased catalase expression and hydropic degeneration in the liver. The Mn content present in the basal diet (19 mg/kg) covered the requirements in juvenile seabream, although results from oxidative status markers might point out the need to increase levels beyond this point when fish are under pro-oxidant conditions. Dietary Cu levels did not affect productive parameters, suggesting that no supplementation was needed. On the contrary elevation of dietary Cu levels up to 11.0-32.0 mg/kg reduced growth and increased the markers of hepatic damage denoting toxic effects of Cu (figure 2). Seabream fed with dietary Zn levels at 89 mg/kg of plant-based diet increased the growth. VA levels tested were several times above those described for other species, however, no effects of toxicity were observed. Increasing the VD level caused an increase in the prevalence of histological alterations in the cardiac muscle. On the other hand, VK supplementation affected growth, grp expression, and the reduced prevalence of skeletal disorders suggested that dietary VK levels for gilthead seabream fingerlings should be above 12 mg/kg. Moreover, in an interaction study between VK and VD showed, 0.04mg VD/kg and 12 mg VK/kg in diet reduced total anomalies by upregulating the bmp2 and pthr1 expression in vertebral column. Dietary B-vitamins showed no relation to productive parameters, nor were there external signs of vitamin deficiency or mortalities. After the trial, the level of vitamins in whole body had reduced in 50% for B1, 12% for B9 and 18% for B12 on fish fed the diet without supplementation when compared to the initial samples, whereas an increase in the deposition of the vitamins was observed as the dietary levels increased. The dietary increase in B9 and, particularly, B12 reduced the percentage of erythrocytes with irregular nucleus in blood. These results suggest the feeds for seabream should be supplemented with B-vitamins.
References
Dominguez, D., et al., 2017. Inorganic, organic, and encapsulated minerals in vegetable meal based diets for Sparus aurata (Linnaeus, 1758). PeerJ 5, e3710.
Dominguez, D., et al., 2019a. Optimum selenium levels in diets high in plant-based feedstuffs for gilthead sea bream (Sparus aurata) fingerlings. Aquac. Nutr. 26, 579–589.
Dominguez, D., et al., 2019b. Effects of copper levels in diets high in plant ingredients on gilthead sea bream (Sparus aurata) fingerlings. Aquaculture 507, 466–474.
Dominguez, D., et al., 2019c. Effects of zinc and manganese sources on gilthead seabream (Sparus aurata) fingerlings. Aquaculture 505, 386–392.
Dominguez, D, et al., 2020a. Dietary manganese levels for gilthead sea bream (Sparus aurata) fingerlings fed diets high in plant ingredients. Aquaculture 735614.
Dominguez, D., et al., 2021. Effects of vitamin D3 supplementation in gilthead seabream (Sparus aurata) juveniles fed diets high in plant based feedstuffs. Aquaculture 543.
Dominguez, D., et al., 2022. Effects of Menadione Sodium Bisulphite (Vitamin K3) Supplementation of the Diets Based on Plant Feed Ingredients on Growth and Bone Health of Gilthead Seabream (Sparus aurata) Fingerlings 2022.
Mechlaoui, M., et al., 2019. Effects of different dietary selenium sources on growth performance, liver and muscle composition, antioxidant status, stress response and expression of related genes in gilthead seabream. Aquaculture 507, 251–259.