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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.

In order to investigate the effects of dietary protein hydrolysates (PH) on larval growth performance, skeleton quality and proteome expression, triplicate groups of white seabream (Diplodus sargus) larvae were co-fed from first-feeding with live feed and three microencapsulated diets differing in the molecular weight of their PH fraction (Control – inclusion of CPSP-90; H – inclusion of a high amount in 0.5–30 kDa hydrolysates; L – inclusion of a high amount in

Reliable juvenile production or recruitment requires high numbers of healthy fish larvae. Despite considerable progress in marine fish farming in the past 20 years, juvenile fish production is still fraught with problems which arise during the larval phase. In fisheries, juvenile recruitment in some populations has not recovered despite long-term moratoria on captures and protection of the broodstock. These issues highlight the growing importance of multidisciplinary fish larval research.

Submitted by Paulo Gavaia (pgavaia@ualg.pt) on 2014-06-06T09:52:10Z No. of bitstreams: 1 PepT1 in a coldwater marine teleost larvae atlantic cod cloning and preliminary studies of expression and phylogeny.pdf: 92089 bytes, checksum: 29d7c838f8ab20cd979bf7fa808abca9 (MD5) Approved for entry into archive by Pedro Sousa (a19661@ualg.pt) on 2014-06-25T12:43:54Z (GMT) No. of bitstreams: 1 PepT1 in a coldwater marine teleost larvae atlantic cod cloning and preliminary studies of expression and phylogeny.pdf: 92089 bytes, checksum: 29d7c838f8ab20cd979bf7fa808abca9 (MD5) Made available in DSpace on 2014-06-25T12:43:54Z (GMT). No. of bitstreams: 1 PepT1 in a coldwater marine teleost larvae atlantic cod cloning and preliminary studies of expression and phylogeny.pdf: 92089 bytes, checksum: 29d7c838f8ab20cd979bf7fa808abca9 (MD5) Previous issue date: 2006

Functional characteristics of marine fish larvae digestive system at the onset of exogenous feeding have long been a subject for discussion. Absorption of digested proteins in vertebrates has been shown to include transporter systems for single amino acids and small peptides.

Fish embryos develop while utilizing yolk nutrients supplied by the (...). There normally exists a "first feeding window" between when the larvae (...) able to ingest exogenous feed,and the "point of no return" where (...) exhausted its yolk reserves and also irreversibly degraded critical tissues (...) energetic purposes it feeds is not ingested.

The H+-coupled peptide transporter 1 (PepT1) belongs to SoLute Carrier family 15 (SLC15A1) and is responsible for the absorption of di/tripeptides in enterocytes. Beside its nutritional role, it has been hypothesized that PepT1 functions as a transceptor, i.e. a peptide sensor/transporter involved in gut hormone release from entero-endocrine cell(s)1, 2. Studying the role of PepT1 in peptide absorption in the gut is relevant for the direct relation between dietary protein availability and fish growth3. In salmonids, PepT1 gene has been duplicated and two transporters, i.e. PepT1a and PepT1b, have been found in the intestine. The partial and complete transport cycle of the two PepT1-type transporters of Salmo salar, ssPepT1a and ssPepT1b, heterologously expressed in Xenopus laevis oocytes, were studied using Two Electrode Voltage Clamp technique. The pre-steady state currents of ssPepT1b were like that of other fish orthologs4 but differed from those of ssPepT1a. ssPepT1a showed a slower decaying currents, and the charge vs voltage (Q/V) and time constant vs voltage (τ/V) curves shifted to more positive potentials behaving as the mammalian transporter4. In both transporters, reducing external pH from 7.6 to 6.5 slowed the transients decay, shifting to more positive potential the Q/V and τ/V curves (Fig. 1). To evaluate the transport activity of ssPepT1a and ssPepT1b, the transport-associated currents were recorded in presence of 1mM of lysine(Lys)-containing peptides (KcPeps) as Lys is a limiting amino acid for animal growth3. KcPeps elicited transport-associated currents of different amplitudes, for e.g. ssPepT1b generated large currents when exposed to peptides carrying Lys in the N-terminus (KG, KM), while ssPepT1a produced small currents independently of Lys position (Fig. 2). The current vs voltage (I/V), in the presence of KcPeps, showed small and similar currents at two different pH (6.5, 7.6) in ssPepT1a. Conversely, in ssPepT1b the I/V curves differed at the most negative potentials with larger currents recorded at pH 7.6. KG dose-response experiments were also conducted, and while fitting with logistic equation allowed to obtain the kinetic parameters (K0.5 and Imax) at each voltage for ssPepT1b, only an estimation was possible for ssPepT1a at -140 and -120mV. The analysis on the transient and transport currents indicated important functional differences between ssPepT1a and ssPepT1b transporters. The dissimilar substrate specificity for KcPeps supports the idea of distinct roles in peptide recognition and transport for ssPepT1a and ssPepT1b.