Dynamiques du phosphore chez la truite arc-en-ciel (Oncorhynchus mykiss) : impacts de la chélation intestinale et adaptations physiologiques en cas de carence

L’aquaculture dans le monde est la production animale qui connaît la plus forte croissance ces vingt dernières années. Cependant, cette croissance est freinée par des considérations d’ordre environnementales parmi lesquelles la pollution associée au phosphore (P) occupe une place importante. L’excès de P dans les écosystèmes d’eau douce dû à l’excrétion des poissons, augmente la production primaire qui, non contrôlée, peut conduire à une eutrophisation, accélérant le processus de vieillissement des cours d’eau récepteurs. Ainsi, beaucoup d’efforts ont été déployés dans la recherche afin de réduire la pollution au P. Pour limiter les émissions de P résultant de l’alimentation des poissons, nous proposons d’incorporer des agents chélatants micro-encapsulés dans les aliments de la truite arc-en-ciel. Dans une première expérience, l’alun et le sulfate de fer ont été encapsulés dans une matrice lipidique hydrogénée par pulvérisation et refroidissement rapide « spray chilling ». Ces éléments actifs incorporés dans les aliments permettent une réduction de plus de la moitié du P inorganique remis en suspension par les fèces. L’incorporation de ces éléments actifs encapsulés n’a pas montré ni une baisse des performances de croissance avec ces aliments, ni une intoxication liée à la présence de ces métaux. Ces observations montrent la pertinence de l’utilisation de l’encapsulation comme approche visant à cibler l’endroit de libération d’un ion. Confronté à la nécessité de déterminer la composition proximale des poissons lors des expérimentations, la précision du DXA (dual-energy X-ray absorptiometry) comme outil de mesure a été testé. Les résultats montrent une bonne précision de cet appareil pour déterminer la composition en protéines, cendre, eau, P, et en calcium (Ca) chez les truites arc-en-ciel en pré-grossissement. Il a été ainsi possible de déterminer avec précision la rétention en P pour chaque type d’aliment et évaluer les rejets pour cet élément. Pour réduire les rejets en P dans les fermes salmonicoles, le teneur en P dans les aliments a été réduite considérablement. Cette approche peut induire des carences en P chez les truites arc-en-ciel en élevage. Ainsi, la capacité des truites arc-en-ciel carencées en P à absorber le P dans le milieu ambiant a été investiguée. Cette adaptation a été considérée comme inexistante du fait des niveaux faibles de cet élément dans le milieu naturel. En soumettant des truites arc-en-ciel carencées à des niveaux de P inorganique élevés dans l’eau, il a été mis en évidence une absorption significative corrélée à une surexpression de cotransporteurs de sodium-phosphates dans les branchies. Les résultats présentés dans cette thèse apportent à la fois des outils pratiques dans les efforts de réduction de la pollution au P dans les fermes aquicoles et des connaissances dans la compréhension pour l’intégration de l’ensemble des maillons entrant dans l’homéostasie de ce nutriment chez la truite arc-en-ciel.Aquaculture is the world’s fastest growing animal production. This growth is limited by environmental concerns, among which P pollution is a major concern. Excess phosphorus (P) released into freshwater ecosystems from feeding fish increases primary production; left uncontrolled, this can lead to eutrophication, accelerating the aging process of the receiving streams. Significant research efforts have been undertaken to understand and reduce P pollution. To limit P emissions from feeding fish, we propose incorporating microencapsulated chelating agents into rainbow-trout feed. In the first experiment, alum and iron sulfate were encapsulated by spraying a molten hydrogenated lipid matrix followed by rapid cooling (spray chilling). The active elements incorporated in fish feed resulted in a reduction by more than 50% of the soluble P released from the feces. The incorporation of these encapsulated agents did not show either a decrease in the fish growth performance or a toxic effect related to the presence of these metals. These observations demonstrate the relevance of using encapsulation as an approach to target the release of a compound of interest. In order to have a precise and simplified tool to determine the whole-body proximal content of fish under study, the accuracy of dual-energy X-ray absorptiometry (DXA) was evaluated. The results revealed that DXA provided accurate estimates for protein, ash, moisture, P, and Ca content of juvenile rainbow trout carcasses. Furthermore, using the established models, it was possible to accurately determine the P and Ca retention for each diet used in the trout growth study. Reducing P-dietary is the main approach used to reduce phosphorus pollution in fish farm sector. This stategy can lead to P-deficiency in fish. The ability of fish to absorb P from the environment is considered non-existent due to the low level of this element in freshwater systems. Our study showed that rearing P-deficient trout in water having a relatively high Pi concentration, revealed that P-deficient fish develop the ability to absorb P from the water. This regulation was highly correlated with overexpression of sodium phosphate cotransporters in gills of P-deficient trout, suggesting that fish can actively absorb Pi from their environment. The results presented in this thesis provide both practical tools in the efforts to reduce P pollution in fish farms and knowledge in understanding for the best integration of all the links involved in the P homeostasis in rainbow trout

In situ chelation of phosphorus using microencapsulated aluminum and iron sulfate to bind intestinal phosphorus in rainbow trout (Oncorhynchus mykiss)

Excess phosphorus (P) in freshwater ecosystems increases primary production which, left uncontrolled, may lead to eutrophication, accelerating the ageing process of receiving water bodies. To limit phosphorus release resulting from freshwater aquaculture, we propose to incorporate microencapsulated P-chelating agents into fish diets. In a first trial, alum (Al2SO4) and ferrous sulfate (FeSO4) were encapsulated by spray-chilling in a hydrogenated lipid matrix. Two practical diets incorporating one of these two chelating elements (6 g/kg) were fed to fish for five weeks (w), and P release from resulting feces was compared. In a second trial, a similar approach was used to evaluate the impact of increasing supplementation of encapsulated alum (3, 6, 15 g/kg of diet). Feces from the fish fed with the diets incorporating alum and ferrous sulfate released 62 % and 54 % respectively less P than feces from fish fed with control diets. The second experiment revealed a negative correlation between the level of encapsulated Al2SO4 included in the diet and phosphorus released by the feces (y = 0.18x2 ˗ 4.78x + 62.7; R2 = 0.93). Feces from feed incorporating Al2SO4 at 0, 3, 6 and 15 g/kg released 62 %, 52 %, 39 %, and 32 % of the total fecal P after 14 days respectively. Fish fed encapsulated Al2SO4 have similar growth performance and mineral status. Incorporation of encapsulated P-chelating agents into fish feed offers an opportunity to manage P release from fish feces. Long-term feeding studies are required for validation of dietary Al2SO4 and FeSO4 impacts on potential toxicity and growth/environmental performance following chronic feeding of encapulated P chelating agents

Methanogenic and fertilizing potential of aquaculture waste: towards freshwater farms energy self‐sufficiency in the framework of blue growth

International audienceThe fisheries sector, particularly aquaculture, is a fundamental source of nutrition for humans, particularly in developing countries. The modern development of fish farming requires energy for production systems. This study investigates the potential of using organic wastes derived from fish fattening to produce on-farm energy through the process of methanization. Oreochromis niloticus faeces methanogen potential was determined with (IFF) and without (UIFF) methanizer microbial inoculum. At the end of the manure methanation trials, the resulting digestates were tested as organic fertilizers for agriculture. The tests showed that inoculated fish faeces had faster biogas kinetics production compared with uninoculated fish faeces. In both cases, the produced biogas contained more than 60% methane (CH4) from the second week of incubation, indicating that it was of good quality. Furthermore, the total CH4 volume was twice as larger in IFF compared with UIFF. Biofertilizer tests showed no significant differences for most of the growth parameters in onion and tomato when compared to the unfertilized control, except in one case for tomato plants, which significantly increased its aboveground biomass. The results show that fish faeces are good methanogenic substrates conducive to energy recovery that could facilitate farm autonomy; however, valorization of the digestates as biofertilizer still requires extensive agronomic optimization. Based on our results, we estimate that equivalents of energy need of almost ten millions of people could be covered using the aquaculture potential in freshwater fish faeces biogas worldwide or that at least aquaculture farm energy self-sufficiency could be fostered

A study on the variation of nutritional profiles of seaweeds along the Senegalese coast

International audienc

A study on the variation of nutritional profiles of seaweeds along the Senegalese coast

International audienc

Safety considerations of seaweed in Senegal: heavy metals hazards

International audienceTo meet the challenge of feeding a global population estimated to reach 9.7 billion by 2050, alongside addressing the impact of climate change on food production and utilization, there's been a suggestion to expand the use of seaweed. This approach holds promise for long-term development in West Africa. However, the presence of hazardous heavy metals such as arsenic (As), mercury (Hg), lead (Pb), and cadmium (Cd) in seaweed raises concerns, as they can accumulate and become toxic above specific thresholds. Between April and July 2022, researchers gathered 41 samples of 25 different seaweed species along the Senegalese coast, spanning from the Cap-Vert peninsula to the Petite Côte. Microwave Plasma Atomic Emission Spectroscopy and XRF-fluorescence spectrophotometry were employed to determine metal concentrations. The findings reveal that 36% of the studied specimens exceeded the threshold of 10 mg kg-1 of dry seaweed for arsenic concentration, as set by the Norwegian National Institute of Nutrition and Seafood Research (NIFES, 2016). Additionally, all specimens surpassed the toxicity threshold of 0.5 mg kg-1 of dry seaweed for cadmium, as established by French health agencies. While 97% of the samples had cadmium values below 10 mg kg-1, which is the minimum concentration determinable with acceptable uncertainty. Hypnea musciformis, a seaweed species found in significant quantities along Senegal's coastline, exhibited lead concentrations exceeding four times the maximum suggested limit by French health agencies. The study originally aimed to extend its scope to cover the entire coastline over two years, intending to identify seasonal variations in heavy metal concentrations

A study on the variation of nutritional profiles of seaweeds along the Senegalese coast

International audienc

Safety considerations of seaweed in Senegal: heavy metals hazards

International audienceTo meet the challenge of feeding a global population estimated to reach 9.7 billion by 2050, alongside addressing the impact of climate change on food production and utilization, there's been a suggestion to expand the use of seaweed. This approach holds promise for long-term development in West Africa. However, the presence of hazardous heavy metals such as arsenic (As), mercury (Hg), lead (Pb), and cadmium (Cd) in seaweed raises concerns, as they can accumulate and become toxic above specific thresholds. Between April and July 2022, researchers gathered 41 samples of 25 different seaweed species along the Senegalese coast, spanning from the Cap-Vert peninsula to the Petite Côte. Microwave Plasma Atomic Emission Spectroscopy and XRF-fluorescence spectrophotometry were employed to determine metal concentrations. The findings reveal that 36% of the studied specimens exceeded the threshold of 10 mg kg-1 of dry seaweed for arsenic concentration, as set by the Norwegian National Institute of Nutrition and Seafood Research (NIFES, 2016). Additionally, all specimens surpassed the toxicity threshold of 0.5 mg kg-1 of dry seaweed for cadmium, as established by French health agencies. While 97% of the samples had cadmium values below 10 mg kg-1, which is the minimum concentration determinable with acceptable uncertainty. Hypnea musciformis, a seaweed species found in significant quantities along Senegal's coastline, exhibited lead concentrations exceeding four times the maximum suggested limit by French health agencies. The study originally aimed to extend its scope to cover the entire coastline over two years, intending to identify seasonal variations in heavy metal concentrations

Safety considerations of seaweed in Senegal: heavy metals hazards

International audienceTo meet the challenge of feeding a global population estimated to reach 9.7 billion by 2050, alongside addressing the impact of climate change on food production and utilization, there's been a suggestion to expand the use of seaweed. This approach holds promise for long-term development in West Africa. However, the presence of hazardous heavy metals such as arsenic (As), mercury (Hg), lead (Pb), and cadmium (Cd) in seaweed raises concerns, as they can accumulate and become toxic above specific thresholds. Between April and July 2022, researchers gathered 41 samples of 25 different seaweed species along the Senegalese coast, spanning from the Cap-Vert peninsula to the Petite Côte. Microwave Plasma Atomic Emission Spectroscopy and XRF-fluorescence spectrophotometry were employed to determine metal concentrations. The findings reveal that 36% of the studied specimens exceeded the threshold of 10 mg kg-1 of dry seaweed for arsenic concentration, as set by the Norwegian National Institute of Nutrition and Seafood Research (NIFES, 2016). Additionally, all specimens surpassed the toxicity threshold of 0.5 mg kg-1 of dry seaweed for cadmium, as established by French health agencies. While 97% of the samples had cadmium values below 10 mg kg-1, which is the minimum concentration determinable with acceptable uncertainty. Hypnea musciformis, a seaweed species found in significant quantities along Senegal's coastline, exhibited lead concentrations exceeding four times the maximum suggested limit by French health agencies. The study originally aimed to extend its scope to cover the entire coastline over two years, intending to identify seasonal variations in heavy metal concentrations

DNA-sequencing-based assessment of seaweed biodiversity and distribution along the Senegalese coast

International audienc