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

Do the visual conditions at the point of escape affect European sea bass escape behavior?

European sea bass (Dicentrarchus labrax), an important species for the Mediterranean aquaculture industry, has been reported to escape from sea cage installations. Fish escapes are caused mainly by operational and technical failures that eventually result into a creation of a tear. Escapees may interact with wild stocks through interbreeding, transfer of pathogens and competition for food. The aim of this study was to examine at which extent the presence of a visible obstacle close to a tear on the net have an influence on sea bass propensity to escape. Fish were initially confined into small sea cages, with a tear at one side. The escape behavior was tested under experimental conditions. It is clearly demonstrated that sea bass was able to locate a tear on the net pen, immediately after its appearance. Crossings occurred in all cages, in singles or in a series of up to seven individuals. The presence of an obstacle close to the net tear altered the escape behavior of D. labrax resulting in a delay that eventually reduced the escape rate. Concluding, it is highly recommended that sea bass cages should be kept internally the culture array. Furthermore, the placement of artificial obstacles close to the sea cages could be an efficient practice that mitigates the escape risk after severe environmental conditions

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

International audienc

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

Growth and feed efficiency of sea bass (Dicentrarchus labrax) juveniles reared in different stocking densities and feeding levels

National audienc

European sea bass growth and N and P loss under different feeding practices

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