Alix, M., Blondeau-Bidet, E., Grousset, E., Shiranghi, A., Vergnet, A., Guinand, B., et al. (2017). Effects of fasting and re-alimentation on gill and intestinal morphology and indicators of osmoregulatory capacity in genetically selected sea bass (Dicentrarchus labrax) populations with contrasting tolerance to fasting. Aquaculture, 468, 314–325.
Résumé: Fasting and refeeding occur naturally in predators but this is largely ignored when dealing with farmed fish. Therefore,the effects of 3-week fasting and re-alimentation (2.5% of the individual body mass) were investigated using two genetically selected populations (F2 generation) of 250 g juvenile sea bass (Dicentrarchus labrax L.). Blood osmolarity, gill and intestinal morphology and expression of the sodium pump (Na+, K+-ATPase, NKA) were studied on two phenotypes showing different degrees of body mass loss during food deprivation: one group losing body mass rapidly during fasting (F+) and the other one limiting body mass loss during the same period (F-). Blood osmotic pressure significantly decreases due to re-alimentation in both groups, but this is compensated in the F+ group. In this group, gill ionocytes are smaller and less numerous, but a significantly higher NKA gene expression is noted in the gills in comparison to the F- individuals 48 and 72 h after re-alimentation, and also in the posterior intestine 72 h after re-alimentation. This most probably occurs to compensate for a higher salt intake during nutrient absorption in comparison to the F- group. Furthermore, refed F- fish absorb more lipids along the proximal anterior intestine, and take longer to digest than the F+ group, and show enterocyte vacuolization in the posterior intestine. Therefore, the two selected populations have different postprandial digestive strategies: the F- fish optimize feed efficiency first at the cost of optimal hydromineral adjustment, while the F+ group invests in osmoregulatory performance at the expense of digestive physiology. Statement of relevance: Our paper is highly relevant to the general field of commercial aquaculture. There is an increasing number of research articles dealing with fasting and refeeding in commercial fish and how to improve fish nutrition based oh these physiological data and genetic selection. (C) 2016 Elsevier B.V. All rights reserved.
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Castro-Ruiz, D., Mozanzadeh, M. T., Fernández-Méndez, C., Andree, K. B., García-Dávila, C., Cahu, C., et al. (2019). Ontogeny of the digestive enzyme activity of the Amazonian pimelodid catfish Pseudoplatystoma punctifer (Castelnau, 1855). Aquaculture, 504, 210–218.
Résumé: The aim of the study was to evaluate the functional ontogeny of the digestive system of Pseudoplatystoma punctifer through the analysis of the activity of the main intestinal (alkaline phosphatase, aminopeptidase N, maltase and leucine-alanine peptidase), pancreatic (trypsin, chymotrypsin, total alkaline proteases, bile-salt activated lipase and amylase) and gastric (pepsin) enzymes. Larvae were raised in triplicate in a recirculation system from 4 to 27 days post fertilization (dpf) at an initial density of 90 larvae L−1, 27.8 ± 0.7 °C and 0 L: 24D photoperiod. Larvae were fed from 4 to 17 dpf with Artemia nauplii and weaned onto an experimentally formulated feed (crude protein content ~ 45%; crude fat content ~ 10%; crude carbohydrate ~ 8%) within 3 days, then continued with the same diet until the end of the trial. P. punctifer showed an exponential growth pattern with two different growth rates: a slower one from hatching to 12 dpf followed by a faster one from 12 to 27 dpf. The specific and total activities of the pancreatic and intestinal enzymes were detected from hatching. The digestive system was functional at 12 dpf, indicating the transition from the larval to the juvenile stage (alkaline to acid digestion). Therefore individuals could be weaned from that day onwards. The variations observed in the enzymatic activity from 17 dpf reflected the adaptation of the enzymatic machinery to the new diet supplied. P. punctifer larvae showed a fast digestive system development with an enzymatic profile typical of a tropical and carnivorous species.
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Charmantier, G., & Anger, K. (2011). Ontogeny of osmoregulatory patterns in the South American shrimp Macrobrachium amazonicum: Loss of hypo-regulation in a land-locked population indicates phylogenetic separation from estuarine ancestors. Journal of Experimental Marine Biology and Ecology, 396(2), 89–98.
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Ituarte, R. B., Lignot, J. - H., Charmantier, G., Spivak, E., & Lorin-Nebel, C. (2016). Immunolocalization and expression of Na+/K+ -ATPase in embryos, early larval stages and adults of the freshwater shrimp Palaemonetes argentinus (Decapoda, Caridea, Palaemonidae). Cell Tissue Res., 364(3), 527–541.
Résumé: The euryhaline shrimp Palaemonetes argentinus exemplifies an evolutionary transition from brackish to freshwater habitats that requires adequate osmoregulatory capacities. Hyperosmoregulation is functional at hatching and it likely begins during the embryonic phase allowing this species to develop entirely in fresh water. Here, we investigated the Na+/K+-ATPase alpha-subunit gene (nka-alpha) expression using quantitative real-time PCR and localized Na+/K+-ATPase (NKA) in ion-transporting epithelia through immunofluorescence microscopy. We reared shrimps from spawning to juvenile stages at two salinities (1, 15 aEuro degrees) and maintained adults for 3 weeks at three salinity treatments (1, 15, 25 aEuro degrees). nka-alpha gene expression was measured in: (1) embryos at an early (SI), intermediate (SII) and late (SIII) stage of embryonic development; (2) newly hatched larvae (Zoea I, ZI); and (3) isolated gill tissue of adults. The nka-alpha expression was low in SI and SII embryos and reached maximum levels prior to hatching (SIII), which were similar to expression levels detected in the ZI. The nka-alpha expression in SIII and ZI was highest at 15 aEuro degrees, whereas salinity did not affect expression in earlier embryos. In SIII, in ZI and in a later zoeal stage ZIV, NKA was localized in epithelial cells of pleurae, in the inner-side epithelium of branchiostegite and in the antennal glands. Gills appeared in the ZIV but NKA immunolabeling of the cells of the gill shaft occurred in a subsequent developmental larval stage, the decapodid. Extrabranchial organs constitute the main site of osmoregulation in early ontogenetic stages of this freshwater shrimp.
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Orgeret, F., Cox, S. L., Weimerskirch, H., & Guinet, C. (2019). Body condition influences ontogeny of foraging behavior in juvenile southern elephant seals. Ecol. Evol., 9(1), 223–236.
Résumé: Ontogeny of diving and foraging behavior in marine top predators is poorly understood despite its importance in population recruitment. This lack of knowledge is partly due to the difficulties of monitoring juveniles in the wild, which is linked to high mortality early in life. Pinnipeds are good models for studying the development of foraging behaviors because juveniles are large enough to robustly carry tracking devices for many months. Moreover, parental assistance is absent after a juvenile departs for its first foraging trip, minimizing confounding effects of parental input on the development of foraging skills. In this study, we tracked 20 newly weaned juvenile southern elephant seals from Kerguelen Islands for up to 338 days during their first trip at sea following weaning. We used a new generation of satellite relay tags, which allow for the transmission of dive, accelerometer, and location data. We also monitored, at the same time, nine adult females from the colony during their post-breeding trips, in order to compare diving and foraging behaviors. Juveniles showed a gradual improvement through time in their foraging skills. Like adults females, they remarkably adjusted their swimming effort according to temporal changes in buoyancy (i.e., a proxy of their body condition). They also did not appear to exceed their aerobic physiological diving limits, although dives were constrained by their smaller size compared to adults. Changes in buoyancy appeared to also influence their decision to either keep foraging or return to land, alongside the duration of their haul outs and choice of foraging habitat (oceanic vs. plateau). Further studies are thus needed to better understand how patterns in juveniles survival, and therefore elephant seal populations, might be affected by their changes in foraging skills and changes in their environmental conditions.
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