Advances in tropical aquaculture

If warmwater finfish protein requirements as level in diet is low, absolute intake per day is similar to those of coldwater species. But relation to this requirement with specific growth rate differs for strictly warmwater fishes as tilapia. Analysis of partition between protein and non-protein energy provided and consequently improve their protein retention. Better carbohydrate digestibility and metabolism are propunded as part of the exploration. (Résumé d'auteur

Coarse-grained DEM-CFD simulation of a pilot-scale gaz-fluidized bed

Abstract: Recent studies point CGDEM (Coarse-Grained Discrete Element Method) as a valuable tool to circumvent the cost of original DEM (Discrete Element Method) simulations for large-scale industrial applications such as fluidized beds. In this approach, cost savings are ensured by decreasing the number of particles in the domain, while increasing their size. In the present work, CGDEMLES (Large-Eddy Simulation) numerical simulations are carried out on a 3D cylindrical pilot-scale fluidized bed in the bubbling regime and gathering 9.6M Geldart B-type particles. A macroscopic analysis is performed and allow observing the effects of coarse-graining on the bed behavior qualitatively and quantitatively. Among them, a global homogeneization of the fluidized region, characterized by higher bed surfaces, lower solid velocity and solid fraction gradients, is reported, along with a drop in the bubble population. These effects are observed to intensify as the coarse-graining factor increases. Some of the reported issues can be alleviated by employing additional mechanisms from the literature, aiming at dissipating the extra amount of energy inherently present in coarse-grained systems. However, these are barely sufficient to retrieve DEM results with the smallest coarsegraining factor tested.Communication présentée lors du congrès international tenu conjointement par Canadian Society for Mechanical Engineering (CSME) et Computational Fluid Dynamics Society of Canada (CFD Canada), à l’Université de Sherbrooke (Québec), du 28 au 31 mai 2023

Diel cycles in Hoplosternum littorale (Teleostei) : entrainment of feeding activity by low intensity colored light

Low intensity colored light is very often used to observe or manipulate fish during the scotophase. According to data on fish vision, most species can perceive these wavelengths of light since their cone pigments have maximum absorption peaks around 455, 530 and 625 nm. To test whether #Hoplosternum littorale$ can detect low intensity red or blue light, we attempted to entrain feeding activity, known to be nocturnal and synchronized by the circadian light/dark alternation, to such light. Feeding activity was entrained with either red or blue light, indicating that these fish can perceive these lights. In all cases, the fish fed during the darker phase of the light cycle. (Résumé d'auteur

Entrainment of the circadian rythm of food demand by infradian cycles of light-dark alternation in Hoplosternum littorale (Teleostei)

#Hoplosternum littorale$ (Hancock, 1828) shows a marked circadium rhythm of food demand. Feeding activity is mainly nocturnal, with two peaks, and is synchronized whith the diel light cycle. We tested the effect of infradian (period > 28h) light dark cycles on this rhythm in fish with demand-feeders : fish subjected to a 13.5 L/22.5 D light dark cycle for 8 days and a 25.5 L/10.5 D cycle for a further 8 days showed a strictly nocturnal feeding activity a response that only passively reflected the cycle alternation of light and dark. (Résumé d'auteur

Postprandial utilization of energy susbtrates by a tropical catfish, Holosternum littorale : indirect calorimetry analysis

Indirect calorimetry method was used to measure postprandial utilization of energy substrates by atipa, #Hoplosternum littorale (#Callichthyidae, Siluriform). A model was adjusted to the data on respiratory exchanges and nitrogen excretion for this purpose. As for other fish species, protein was actively catabolized after feeding during the 60 hr measurement time. As long as carbohydrates were available, atipa was also able to use these substrates for its energy metabolism. A gradual increase of contribution of lipids was then noticed. Over a 24 hr period following the food intake, a 30 g fish catabolized 90 mg of proteins and 43 mg of carbohydrates. At the same time, the results led to a synthesis of 3.7 mg of fat. An estimation of the increase of the global metabolism associated to food intake was obtained from integration of the exponential terms of the models. (Résumé d'auteur