World Aquaculture September 2018

WWW.WA S.ORG • WORLD AQUACULTURE • SEP TEMBER 2018 63 S everal trends put contradictory pressures on the aquaculture industry. Reliance on scarce and costly rawmaterials such as fishmeal and the optimal use of alternative ingredients constitute a main challenge in aquaculture. Consumer awareness about environmental sustainability encourages producers to improve production performance through sustainable aquaculture practices. However, the use of less costly protein sources and low-nutrient dense diets most likely leads to lower protein digestibility, higher amino acid imbalance, higher carbohydrate and fiber content in feeds. Consequently, this can lead to inefficient nutrient use, resulting in increased feed usage, greater susceptibility to disease and higher ammonia emissions — raising production costs and increasing the ecological footprint. Improving Gut Performance Is Key It is no secret that optimum animal performance encompasses a number of factors, including genetic characteristics of the species, diet quality, environmental conditions and absence of disease outbreaks. Add to this competitive industry pressure and the need for efficient use and/or replacement of increasingly expensive raw materials, and the picture becomes even more complex. A focus on good gut performance and gut health can help to successfully navigate this large set of considerations and set the foundation for better growth. Phytogenic feed additives, consisting of herbs, spices, essential oils and extracts have gained considerable attention as an answer to these challenges. The active ingredients, such as phenols and flavonoids, can exert multiple effects in animals, including improvement of feed conversion ratio (FCR), digestibility, growth rate, reduction of nitrogen excretion and improvement of the gut microbiota and health status. Examples of these ingredients with major active compounds are provided in Table 1. Dietary Essential Oils Supplementation: A Powerful Tool to Minimize Nitrogen Losses Rui Gonçalves, Vera Rodrigues, Rita Colen, Laura Ribeiro, Gonçalo Santos and Jorge Dias How Phytogenics Work Phytogenics can stimulate digestive secretions, increase villi length and density and increase mucous production through an increase in the number of globlet cells. Through different strategies such as matrix-encapsulation, volatile essential oils can be stabilized and may remain active throughout a greater section of the gastrointestinal tract (GIT), thus ensuring that positive effects are not only restricted to a smaller GIT section. Do Phytogenics Work onMarine Species? Phytogenics have been successfully used in pigs, cows and broiler chickens, among others, and have great potential for fish aquaculture due to various beneficial biological effects, such as growth promotion, gut function improvement, appetite stimulation, antioxidant effects, and antibacterial, antiparasitic, antistress, and anesthetic activities (Franz et al . 2010, Reverter et al . 2014). Although the positive effects of phytogenics are broadly accepted for freshwater fish performance such as tilapia Oreochromis mossambicus and trout Oncorhynchus mykiss (Karásková et al . 2015), the beneficial properties and efficacy of phytogenic essential oils for marine fish species is still scarce. Recently we assessed the effect of a commercial blend (Digestarom ® ) of anise ( Pimpinella anisum ), citrus ( Citrus sinensis ), and oregano ( Origanum vulgare ) essential oils and its encapsulation in a plant protein-rich diet on the growth performance, nutrient utilization and protein digestibility of juvenile seabream (Rodrigues et al. 2018). Reduced Fishmeal Content vs. Feed Efficiency Three isonitrogenous (crude protein, 45.4 percent DM), isolipidic (18.5 percent DM), and isoenergetic (gross energy, 21.4 kJ/g DM) diets were formulated. The control diet (CTRL diet) included ( C O N T I N U E D O N P A G E 6 4 ) TABLE 1. Important constituents of selected essential oils (adapted from Tisserand and Young 2014). Name (Botanical name) Source Important constituents Anise (Pimpinella anisum) Seeds trans-anethole, methylchavicol, anise aldehyde Caraway (Carum carvi) Seeds carvone, limonene Oregano (Origanum vulgare) Leaves carvacrol, thymol, p-cymene Peppermint (Mentha arvensis) Leaves menthol, isomenthone, limonene Rosemary (Rosmarinum officinalis) Leaves 1-8-cineol, α - and β -pinene, borneon Thyme (Thymus vulgaris) Leaves thymol, p-cymene, carvacrol