Claude Soyez

Influence of dietary carbohydrate on the metabolism of juvenile Litopenaeus stylirostris

The effect of dietary carbohydrates (CBH) on glucose and glycogen, digestive enzymes, ammonia excretion and osmotic pressure and osmotic capacity of Litopenaeus stylirostris juveniles was studied. The increase of CBH, ranging between 1 and 33%, stimulates activities of alpha-amylase and alpha-glucosidase in the hepatopancreas. High levels of glucose in hemolymph and of glycogen in the hepatopancreas were reached at the highest level of dietary CBH; however, the kinetics of accumulation is different. Shrimps fed with low level of CBH needed 3 h to reached glucose peak, whereas only 1 h is necessary for high CBH levels. A saturation curve was observed in glycogen level and alpha-amylase activity with maximum values in shrimp-fed diets containing 21% CBH. This level could be used to be included as a maximum shrimp dietary CBH level. Pre-prandial glycogen levels were observed in shrimp fed a diet containing 1% CBH, indicating an important gluconeogenesis, which affected the protein metabolism. The present results show that a diet containing 10% CBH may not be enough to cover the CBH requirement, which could be satisfied by dietary protein content. The low osmotic capacity observed in shrimp fed on a diet containing 10% CBH coincided with a relatively low post-prandial nitrogen excretion which reflects a low concentration of amino acids circulating in hemolymph, which affected the osmotic pressure and the osmotic capacity. These results reflect the high plasticity of shrimp species to use protein to obtain metabolic energy from food and its limited capacity for processing dietary CBH.

Effect of molt stage and hypoxia on osmoregulatory capacity in the peneid shrimp Penaeus vannamei

The osmoregulatory capacity (OC) was used to study the effects of hypoxia in Penaeus vannamei. Since OC varied with molt stages with a tendency for animals to show a reduced OC before and after ecdysis, only shrimps at stages C-D0 were consequently used. Hyper-OC and hypo-OC, respectively, measured at low salinity and in seawater, were both depressed after 1–2 days exposure to low oxygen tension (PO2) ranging from 4 to 8 kPa. Low PO2 effect was time-dependent. OC recovered fully after 24 h in an O2 saturated medium. OC measurement is confirmed as a convenient tool to monitor the physiological condition and the effect of stress in crustaceans.

Osmoregulatory capacity according to nutritional status, molt stage and body weight in Penaeus stylirostris

Abstract Hypo-osmoregulatory capacity (or hypo-OC, i.e., the difference between the osmolality of the haemolymph and that of sea water), haemolymph glycemia and haemolymph sodium and chloride concentrations of Penaeus stylirostris were studied in experimental tanks according to the size, the molt stage and the nutritional status of the shrimp. Osmolality and haemolymph glycemia of fed and starved P. stylirostris were also studied in earthen ponds in fluctuating sea water according to time. In experimental tanks, the absolute hypo-OC of shrimp decreased linearly with increasing wet weight for each molt stage considered. For specimens weighing 16.6±1.7 g, the absolute hypo-OC was maximum in stage C (217±17 mosm kg −1 ) and significantly lower in stages B (165±16 mosm kg −1 ), D 0 (181±18 mosm kg −1 ), D 1 (146±20 mosm kg −1 ) and D 2 (135±13 mosm kg −1 ). The hypo-OC and haemolymph glucose concentration varied significantly after the food supply. No variations in haemolymph sodium and chloride concentrations were observed. In earthen ponds, haemolymph osmolality and haemolymph glucose concentration of molt stage C shrimp increased shortly after the food supply. When shrimp were kept starved for 24 and 48 h, haemolymph osmolality remained constant and haemolymph glucose concentration varied only slightly according to time. In light of these results, the use of shrimp hypo-OC (and/or haemolymph osmolality) and haemolymph glycemia in aquaculture as potential physiological indicators of disturbance in the aquatic environment is discussed.

Determination of gender in the pearl oyster pinctada margaritifera

ABSTRACT The pearl industry in French Polynesia is based on exploitation of natural stocks of the blacklip pearl oyster (Pinctada margaritifera). It generates an annual turnover of €90 million. Improvements in pearl quality need genetic studies to improve the populations. This pearl oyster is a protandric species, in which the sex ratio normally is biased toward males. There is an increasing interest in gender control to find the mechanisms to augment female proportions for management purposes. This review summarizes information on exogenous and endogenous factors regulating gender in this and other bivalves, and concludes that P. margaritifera is a protandric hermaphrodite, developing as a male during the first 2 y, and without evidence of an effect from abiotic and biotic factors on gender during this phase. Later, pearl oysters progressively change to females, reaching a sex ratio close to 1:1 in specimens older than 8 y. At this stage, gender is apparently influenced by environmental parameters, but particularly by stress. Future research should seek to determine accurately the effect of temperature and food on sex ratios. Studies should be performed to characterize genes responsible for expression of gender. The use of hormones is a path that might be explored to influence the gender of pearl oysters.

Temperature and food influence shell growth and mantle gene expression of shell matrix proteins in the pearl oyster Pinctada margaritifera.

In this study, we analyzed the combined effect of microalgal concentration and temperature on the shell growth of the bivalve Pinctada margaritifera and the molecular mechanisms underlying this biomineralization process. Shell growth was measured after two months of rearing in experimental conditions, using calcein staining of the calcified structures. Molecular mechanisms were studied though the expression of 11 genes encoding proteins implicated in the biomineralization process, which was assessed in the mantle. We showed that shell growth is influenced by both microalgal concentration and temperature, and that these environmental factors also regulate the expression of most of the genes studied. Gene expression measurement of shell matrix protein thereby appears to be an appropriate indicator for the evaluation of the biomineralization activity in the pearl oyster P. margaritifera under varying environmental conditions. This study provides valuable information on the molecular mechanisms of mollusk shell growth and its environmental control.

Influence of temperature and pearl rotation on biomineralization in the pearl oyster Pinctada margaritifera

ABSTRACT The objective of this study was to observe the impact of temperature on pearl formation using an integrative approach describing the rotation of the pearls, the rate of nacre deposition, the thickness of the aragonite tablets and the biomineralizing potential of the pearl sac tissue though the expression level of some key genes. Fifty pearl oysters were grafted with magnetized nuclei to allow the rotation of the pearls to be described. Four months later, 32 of these pearl oysters were exposed to four temperatures (22, 26, 30 and 34°C) for 2 weeks. Results showed that the rotation speed differed according to the movement direction: pearls with axial movement had a significantly higher rotation speed than those with random movement. Pearl growth rate was influenced by temperature, with a maximum between 26 and 30°C but almost no growth at 34°C. Lastly, among the nine genes implicated in the biomineralization process, only Pmarg-Pif177 expression was significantly modified by temperature. These results showed that the rotation speed of the pearls was not linked to pearl growth or to the expression profiles of biomineralizing genes targeted in this study. On the basis of our results, we consider that pearl rotation is a more complex process than formerly thought. Mechanisms involved could include a strong environmental forcing in immediate proximity to the pearl. Another implication of our findings is that, in the context of ocean warming, pearl growth and quality can be expected to decrease in pearl oysters exposed to temperatures above 30°C. Summary: Observation of the rotation of pearls in grafted oysters indicates that the movement of pearls is independent of temperature. But an excessive temperature of 34°C hinders the formation of pearls.

Low energy cost for cultured pearl formation in grafted chimeric Pinctada margaritifera

The pearl oyster is one of the rare animal models that support two distinct genomes, through the surgical graft process operated for culture pearl production. This grafted organism is assimilated to a chimera whose physiological functioning remains poorly known. The question of the energy expenditure comparison between chimera and non-chimera animals arises. To answer this question, grafted and non-grafted pearl oysters were evaluated for their energetic needs by the indirect calorimetry method. This method made it possible to measure the energy expenditure based on the respiration rate (RR) measurement, reflecting the basal metabolism. The results showed that the RR values for grafted and non-grafted pearl oysters were not significantly different (p < 0.05). The estimated cost of pearl calcification including CaCO3 and proteins synthesis was 0.237 ± 0.064 J h−1, representing 0.64% of the total energy expenditure of grafted pearl oysters. This study made it possible, for the first time, to see the energy cost of cultured pearl formation in P. margaritifera and the little impact in the energetic metabolism of the chimera organism.

Phenome of pearl quality traits in the mollusc transplant model Pinctada margaritifera

The bivalve Pinctada margaritifera exhibits three main transplant phenotypes derived from the donor (from which a mantle graft tissue, the saibo, is excised), the recipient (into which the saibo is implanted with a nucleus, leading to the formation of a pearl sac “chimera”) and the cultured pearls themselves. This first phenome study on the species derived from a large experimental graft. Transplant phenotype was assessed at three scales: 1) macro, pearl size, colour, grade, 2) micro, pearl surface microstructure, and 3) molecular, biomineralisation gene expression level in saibo and pearl sac tissues. From donor to pearl, the phenome revealed fine variations of quality traits dependent on the position on the mantle where the saibo was cut, whose variation could overlap with inter-individual donor phenotype differences. A single donor phenotype could therefore produce multiple pearl phenotypes at the scale of the saibo position, mirroring its original activity at the mantle position level and the colour and shape of the shell. This phenome study provides essential information on phenotypic trait architecture enabling us to explore and explain the main biological functions and pave the way for a phenomic project on P. margaritifera that could benefit the pearl industry.

Conditionnement de l’huître perlière Pinctada margaritifera en laboratoire : première approche descriptive de la croissance en bassins contrôlés

Dans le cadre du programme Reproduction de l’huitre perliere Pinctada margaritifera, dont l’objectif est la maitrise des croisements, le conditionnement en laboratoire des reproducteurs est une etape necessaire pour esperer controler et synchroniser la maturation de ces reproducteurs. Les facteurs presumes qui permettront de controler la maturation sont d’ordre environnemental : l’alimentation et la temperature. Cependant avant d’esperer etablir la relation entre la fonction physiologique et les facteurs qui controlent cette fonction, il est indispensable de mettre en œuvre une zootechnie adaptee aux besoins vitaux de facon a assurer la survie et une bonne croissance. Cette etude a pour objectif de tester la survie et la croissance des huitres perlieres dans une enceinte experimentale que nous cherchons a valider. L’enceinte testee est un raceway ou les conditions hydrodynamiques satisfont les besoins environnementaux des huitres. L’experience consiste a mettre en elevage pendant une periode de 3 mois des huitres de petite taille d’environ 5 cm de hauteur exterieure, a les alimenter avec des algues et a observer la croissance par une approche biometrique. Un echantillonnage hebdomadaire est fait pour determiner la croissance coquilliere et somatique. Le lot mis en elevage en laboratoire est compare avec un autre lot de meme origine place dans le lagon. Un autre aspect de l’objectif de cette etude qui est un preliminaire au Projet Conditionnement est d’obtenir des informations d’ordres statistiques sur la variabilite de la reponse. Les plans experimentaux a venir seront concus en fonction de la variabilite obtenue, permettant ainsi d’optimiser les cheptels en experimentation. Cette experimentation a dure 3 mois. Les animaux ont ete fournis par l’antenne du service de la perliculture de Takapoto. Pour des raisons pratiques, nous avons choisi de travailler avec des petites huitres puisque la consommation alimentaire est moins importante que celles des grandes, et surtout pour la plus forte amplitude de croissance.