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International audience

International audience

Although carbohydrates and sugars are not considered indispensable dietary nutrients for fish or shrimp, they contribute in a significant manner as a source of digestible energy. This chapter addresses different aspects of the issues related with inclusion and utilization of dietary carbohydrates by aquatic animals. Raw complex carbohydrates are poorly digested by many species of fish, but utilization can be significantly improved by appropriate technological treatments of the feedstuffs or the feeds themselves. Utilization of absorbed glucose is known to differ from that in terrestrial vertebrates and to vary between species of fish. Much progress has been made over the past decades to obtain insights on various aspects of glucose metabolism and homeostasis. Identifying the fine balance between endogenous glucose production and glucose utilization in different species of farmed fish and shrimp is a challenging and promising area of research and can provide the basis for taking full benefit of the potential of all sources of digestible carbohydrates.

This chapter presents current knowledge, methods, and applications of nutritional energetics in an aquaculture setting. All organisms ingest and metabolize macronutrients that supply dietary energy and the nutrients have different fates. The different aspects of energy flow from feed to fish or shrimp are similar to those known in land animals or birds, but the aquatic mode of life imposes challenges and confers advantages both at the cellular level and at the whole organism level. Energy gain and losses are governed by the efficiency with which the macronutrients are utilized. The application of net energy system as prevailing in monogastric land animal nutrition is also valid for aquatic organisms. The large number of species reared by aquaculture is a real challenge, but many of the basic principles are valid across species. There is a need for precisely quantifying the partition of dietary digestible energy for somatic growth, reproduction, and other physiological changes due to environmental factors.

International audience

Environmental factors such as nutritional interventions during early developmental stages affect and establish long-term metabolic changes in all animals. Diet during the spawning period has a nutritional programming effect in offspring of gilthead seabream and affects long-term metabolism. Studies showed modulation of genes such as fads2, which is considered to be a rate-limiting step in the synthesis of n-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA). However, it is still unknown whether this adaptation is related to the presence of precursors or to limitations in the pre-formed products, n-3 LC-PUFA, contained in the diets used during nutritional programming. This study investigated the combined effects of nutritional programming on Sparusaurata through broodstock diets during the spawning period and in broodfish showing higher or lower fads2 expression levels in the blood after 1 month of feeding with a diet containing high levels of plant protein sources and vegetable oils (VM/VO). Broodfish showing high fads2 expression had a noticeable improvement in spawning quality parameters as well as in the growth of 6 month old offspring when challenged with a high VM/VO diet. Further, nutritional conditioning with 18:3n-3-rich diets had an adverse effect in comparison to progeny obtained from fish fed high fish meal and fish oil (FM/FO) diets, with a reduction in growth of juveniles. Improved growth of progeny from the high fads2 broodstock combined with similar muscle fatty acid profiles is also an excellent option for tailoring and increasing the flesh n-3 LC-PUFA levels to meet the recommended dietary allowances for human consumption.