Induction of ovulation and spawning in the Mediterranean red porgy, Pagrus pagrus, by controlled delivery and acute injection of GnRHa

Gonadotropin-releasing hormone analogue (GnRHa) in the form of saline injections or sustained-release microspheres was used to induce oocyte maturation, ovulation, and spawning in captive red porgy (Pagrus pagrus). Individually tagged vitellogenic females (n = 9 or 10) were treated at the beginning of the spawning season (March) with 20 μg/kg body weight (bw) GnRHa-loaded microspheres, a single injection of 20 μg/kg bw dissolved in saline, or physiological saline (control). Females were placed in tanks (one tank per treatment) connected to overflow egg collectors and monitored for 11 days. In addition to the eggs collected from the tank overflow, eggs were stripped from the fish on a daily basis. Only one spawn was obtained from the control fish, probably from a single female, given the small relative fecundity (700 eggs/kg bw). On the contrary, treatment with a GnRHa injection produced two spawns (9 and 11 days after treatment) and 50% of the fish ovulated. Treatment with GnRHa microspheres induced seven spawns (3 and 6-11 days after treatment) and 100% of the females ovulated. Females did not spawn all the eggs ovulated on a particular day, evident from the significant number of eggs obtained by manual stripping. Egg quality did not significantly differ among treatments, whereas number of spawned eggs and total relative fecundity were significantly higher in fish treated with GnRHa microspheres (ANOVA, p<0.05). The results demonstrate the potential of GnRHaloaded microspheres to induce spawning in red porgy, as a method of overcoming spawning failures in commercial hatcheries

Recyclage de déchets d'aquaculture marine - Caractéristique d'un effluent de pisciculture : l'écume

Previously to its use as culturing medium for algae, we have studied the various characteristics of the sewage extracted from marine fish rearing ponds, through a purificating system called "foamer". Qualitatively, this sewage differs from the sea water which produced it on various points : It is richer than the water in Organic Carbon, Organic Nitrogen, Ammonia, particulate matters, phosphorus and varied metals. However the concentration factors are not constant and they change in time. This sewage is toxic for some group of animals and this toxicity varies with the concentration but also the age of the product. Finally, it is eutrophicant and this richness enables to the growth of algae for long periods but the boundary between toxicity and eutrophy Is narrow.Préalablement à son utilisation comme milieu de culture algale, nous avons étudié les diverses caractéristiques de l’effluent extrait de bassins d’ élevage de poissons marins, par le système d’épuration nommé "écumeur". Sur le plan qualitatif, cet effluent diffère de l’eau de mer de la­quelle il provient sur plusieurs points : il est plus riche que cette dernière en Carbone organique, Azote organique, ammoniaque, matières en suspension, Phos­phore et divers métaux. Cependant les facteurs de concentration ne sont pas cons­tants et évoluent dans le temps. Il est toxique pour certains groupes d’animaux et cette toxicité est fonction de la concentration mais aussi de l’âge du produit. Enfin, il est eutrophisant et cette richesse permet de maintenir des cultures algales en crois­sance pendant des périodes importantes mais la limite entre toxicité et eutrophie est étroite

Contribution à la connaissance du comportement et de la biologie des larves de marbré Lithognathus mormyrus (sparides) en élevage

International audienc

Evolution divergente de cultures phytoplanctoniques marines en relation avec la qualité des enrichissements

Four marine phytoplanctonic cultures from natural inoculum of Nannodito sp. have been submitted to different fertilizers in identical light and tem­perature conditions. The composition of enrichments has been studied to introduce Nitrogen as comparative factor. One tank without nutrients and three enriched cultures, the first only with sodium nitrate, the second with "Conway medium" and the last in which nutri­ents were provided by convenient dilution of "foam", have been followed for phy­sical, chemical, biological parameters during three months. Temperature, pH, dis­solved oxygen, optical density, particulate matters, Organic Carbon, Nitrogen, Phos phorus, Calcium, Magnesium, Sodium, Potassium, metal traces and biological parame­ters were analysed periodically. The first results of the experiments enable to show : - the unsteadiness of non enriched and mineral enriched cultures in which algal biomass falls quickly according to a competition between algae dil­ates, Rotifers and Copepoas ; - the steadiness of the medium enriched with foam during all the ex­periments due to the permanent richness of this selective medium and the delay of contamination by a relative toxicity of this type of culture versus tiny zooplankton as grazing agent. Finally It Is possible to anticipate the applicability of poor but selective media for mass cultures of marine planktonic algae.Quatre cultures phytoplanctoniques marines inoculées à partir de sou­ches naturelles de NanochlorelIes ont été soumises à des enrichissements diffé­rentiels dans des conditions d'éclairement et de température identiques. La composition des enrichissements a été calculée de manière à intro­duire comme facteur de comparaison l'Azote. Un témoin sans apport de nutrilites et trois cultures enrichies, I' une exclusivement par du nitrate de sodium, la seconde par une "milieu de Con­way", enfin une dernière dont les nutrilites étaient fournis par un apport d' écume convenablement diluée ont fait l'objet d'un suivi physico-chimique et biologique d'une durée de trois mois. L'évaluation des températures, pH, sali­nité, oxygène dissous, pourcentage de transmittance, matières en suspension ; les dosages quantitatifs de carbone organique, Azote, Phosphore total, Calcium, Magnésium, Sodium, Potassium, oligo-éléments traces et les comptages biologiques ont été effectués périodiquement. Les premiers résultats de cette expérimentation permettent de dégager : .1) Une instabilité du témoin et des milieux enrichis minéralement qui ne tardent pas à accuser une chute brutale de la biomasse algale due à une conta­mination rapide par des Ciliés, Rotifères et Copépodes ; 2) Une stabilité du milieu enrichi en écume, pendant toute la durée de l'expérience, due à la richesse constante du milieu sélectif et au retard ap­porté à la contamination par une toxicité relative du milieu vis-à-vis des zoo- planctontes de petite taille agents de cette contamination. Enfin, il est possible d'envisager dès à présent la réalisation de cul­tures phytoplanctoniques sur des milieux pauvres mais sélectifs

Abnormalities in finfish mariculture: An overview of the problem, causes and solutions.

Abnormalities of shape or color and bony I body deformities whether related to lack of swimbladder or not, are still a major problem for many Mediterranean finfish sea farms. Despite their high economical consequences, they remain difficult to eliminate, due to basic gaps of knowledge about their causes and sometimes management errors in the rearing technique. After a review of abnormalities in aquaculture, the authors targeted the mechanisms of their apparition and aimed to the main gaps of knowledge and the possible solutions. Until accurate cost effective conditions for prevention are found, strategies of early assessment and sorting are recommended. The role of the EU research in these actions is emphasized

Préférences alimentaires et comportement de la larve de daurade Sparus auratus face à du zooplancton congelé

International audienc

Rearing techniques for difficult marine fish larvae

In finfish mariculture, seed production and larval rearing still form the bottleneck for all ongrowing operations and are considered as the main limiting factor for industrial development. Through trial and error more than through biological understanding two opposite hatchery techniques have been developed which surprisingly control a multiparametric combination of different factors but aspire to the same objective of conformity with wild standards and the cost-effective production of larvae. In intensive aquaculture, the rearing technique is characterised by high initial larval densities in small tanks under strict hydraulic, thermic, and nutritional conditions. The light conditions are artificial. The temperature and quality of water are controlled. The food is restricted to an unchanging diet of Brachionus plicatilis and Artemia, two live prey that do not even occur in the natural environment of the cultured larvae. In this method, all parameters are potentially limiting and the requisite for success is a highly specific biological knowledge and know-how. When the technical milieu does meet the requirements of the biological demand, the fish must either adapt or die. Even when they adapt they sometimes remain deformed (non marketable) or display poor growth performances. Thus, only few marine species are reared on an industrial scale using intensive culture methods