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Larval growth can be improved through the reduction of energy expenditure, which has been correlated with the rate of protein synthesis and hence to amino acid metabolism. Understanding the dynamics and regulation of the amino acid metab­olism may contribute to the formulation of larval diets. A model was developed to simulate amino acid fluxes in yolk-sac larvae. The model considers the flux of amino acids through three pools: amino acids in the yolk; free amino acids in the body; and protein-bound amino acids in the body. Each pool is subdivided into sub-pools of the individual amino acids. Yolk amino acids are absorbed into the body free pool, a process which is proportional to yolk volume and to the pool of amino acids in the yolk. The body-free pool is used for catabolism and protein synthesis, with the respective rates increasing with both body size and amino acid concentration. Amino acids are released into the free pool as a result of protein breakdown. Protein turnover was estimated during development of yolk-sac larvae. Results suggest that efficiency of protein retention is lower than 50% in yolk-sac larvae. Minimal values for fractional rates of protein synthesis were estimated to be 300% d -1 (Clarias gariepinus) and 30% d -1 (Hippoglossus hippoglossus). Different amino acids provided similar estimates for protein turnover. Article from Marine Science Symposia Vol. 201 - "Mass rearing of juvenile fish". Symposium held in Bergen, 21-23 June 1993. To access the remaining articles please click on the keyword "MSS Vol. 201".

Food uptake follows rules defined by feeding behaviour that determines the kind and quantity of food ingested by fish larvae as well as how live prey and food particles are detected, captured and ingested. Feeding success depends on the progressive development of anatomical characteristics and physiological functions and on the availability of suitable food items throughout larval development. The fish larval stages present eco-morpho-physiological features very different from adults and differ from one species to another. The organoleptic properties, dimensions, detectability, movements characteristics and buoyancy of food items are all crucial features that should be considered, but is often ignored, in feeding regimes. Ontogenetic changes in digestive function lead to limitations in the ability to process certain feedstuffs. There is still a lack of knowledge about the digestion and absorption of various nutrients and about the ontogeny of basic physiological mechanisms in fish larvae, including how they are affected by genetic, dietary and environmental factors. The neural and hormonal regulation of the digestive process and of appetite is critical for optimizing digestion. These processes are still poorly described in fish larvae and attempts to develop optimal feeding regimes are often still on a 'trial and error' basis. A holistic understanding of feeding ecology and digestive functions is important for designing diets for fish larvae and the adaptation of rearing conditions to meet requirements for the best presentation of prey and microdiets, and their optimal ingestion, digestion and absorption. More research that targets gaps in our knowledge should advance larval rearing. © 2013 Wiley Publishing Asia Pty Ltd., This study benefited from participation in LARVANET – COST action FA0801 (EU RTD framework Programme). I.R. received funding from the Research Council of Norway (CODE- 199482 and GutFeeling- 190019) and the EC FP7 (LIFECYCLE- 222719). M.Y. received financial support from the Spanish Ministry of Science and Innovation MICINN + FEDER/ERDF (projects AGL2007-64450-C02-01 and Consolider Ingenio 2010 Program-project Aquagenomics CSD2007-0002). C.B. received funding from the Italian Ministry of Agricultural, Forestry and Alimentary Policy (Law 41/82) (projects 5C49- 6C138).

Trabajo presentado en el World Aquaculture 2012, celebrado en Praga del 1 al 5 de septiembre de 2012.