Stimulation of bacterial exoproteolytic activity by fish farming in coastal marine ponds: Effect on dissolved protein cycling

The effect of fish farming on dissolved amino acid concentrations, bacterioplankton abundance and exoproteolytic activity was assessed in 3 experimental marine ponds. Different standing stocks of fish were introduced (semi-intensive pond: 250 g.m(-2); semi-extensive pond: 50 g.m(-2) control pond: 0). Sea bass farming increased dissolved combined amino acid (DCAA) concentrations only in the semi-intensive pond. Bacterial standing stock was unaffected by fish food supply. However, bacterial exoproteolytic activity was strongly stimulated by aquaculture intensification; the average maximal rate of dissolved protein hydrolysis (V-m) increased with intensity (control pond: 1 500 nM.h(-1); semi-extensive pond: 2 600 nM.h(-1) semi-intensive pond: 5 100 nM.h(-1)). DCAA fluxes through bacterial exoproteolytic activity ranged between 16 (semi-extensive) and 11% (semi-intensive) of the daily nitrogen input by fish food. Bacterial exoproteolytic activity allowed a substantial part of the increased supply of dissolved amino nitrogen to be incorporated into bacterial biomass, then available for transfer to higher trophic levels within the ponds. It also significantly decreased dissolved organic nitrogen export from the ponds to the surrounding environment.

Apport d'un programme de génétique à une filière de production aquacole : l'exemple de l'ostréiculture

Two oyster species are currently present along the French coasts : the indigenous European flat oyster (Ostrea edulis), and the Pacific cupped oyster (Crassostrea gigas), that has been introduced from Japan since the beginning of the 70ies. The flat oyster successively suffered from two protozoan diseases during the 60ies and its production decreased from 20 000 tons/year by that time to 1 500 tons/year nowadays. Consequently, the oyster production is principally (99%) based upon the Pacific oyster species with approximately 150 000 tons/year among which 90% are grown from the natural spat. However, the hatchery production of this species is developing and was estimated to 400 to 800 millions spat in 2002. Moreover, strengthened relationships between IFREMER and the 5 commercial hatcheries, that all joined the SYSAAF (Union of the French poultry, shellfish and fish farming selectors), allow to plan for new genetic breeding programs. At the end of the 80ies, IFREMER initiated a genetic breeding program for the resistance of the European flat oyster to the bonamiosis, and obtained strains more tolerant to this disease. After two generations of massal selection, molecular markers had identified a reduced genetic basis in this program. It was then reoriented to an intra-familial selection. However, we were confronted to a zootechnic problem to manage such a scheme and we compromised by an intra-cohorts of families selection scheme managed using molecular markers. The program has now reached the transfer level with experimentation at a professional scale. Concerning the Pacific cupped oyster, and in parallel with the obtaining and the study of polyploids, performance of different Asian cupped oyster strains were compared to the one introduced in France thirty years ago and currently suffering from summer mortalities. The local strain exhibited better performance, certainly based upon a good local adaptation. In other respects, although early growth is a relevant criteria for selection for growth to commercial stage, it is not to be privileged in the context of an oyster producing region with a limited food availability. Contrary, the spat summer mortality became a priority for numerous teams (genetic, physiology, pathology, ecology,...) joined in the MOREST program. The first results showed important survival differences between fullsib and halsib families. They indicate a genetic determinism to this character "survival" and promote for its selection.

VIVALDI, A H2020 European Project aiming at preventing and mitigating farmed bivalve diseases

The European shellfish industry enjoys a privileged position on the global scene. Its social dimension is essential, as it employs a high number of people in more than 8000 companies, mostly micro-companies. Shellfish production in Europe is little diversified and mainly relies on the industrially produced mussels, oysters and clams. Over the recent years, this sector has grown more slowly than other fish farming sectors, notably because it depends a great deal on the environmental quality and the emergence of diseases. Mortality events, linked to pathogen organisms such as viruses, bacteria and parasites (protozoa), tend to weaken the production’s sustainability. In this context, the European project VIVALDI (PreVenting and mItigating farmed biVALve DIseases) aims at increasing the sustainability and competitiveness of the shellfish industry in Europe, developing tools and approaches with a view to better preventing and controlling marine bivalve diseases. VIVALDI is a 4-years European Horizon 2020 project coordinated by Ifremer (2016-2020): 21 mostly European, public and private partners are involved, representing the diversity of the European shellfish industry landscape

Sampling design optimization for EROD measurements in fish

Activity of 7-ethoxyresorufin-O-deethylase (EROD) in fish is certainly the best-studied biomarker of exposure applied in the field to evaluate biological effects of contamination in the marine environment. Since 1991, a feasibility study for a monitoring network using this biomarker of exposure has been conducted along French coasts. Using data obtained during several cruises, this study aims to determine the number of fish required to detect a given difference between 2 mean EROD activities, i.e. to achieve an a priori fixed statistical power (l-beta) given significance level (alpha), variance estimations and projected ratio of unequal sample sizes (k). Mean EROD activity and standard error were estimated at each of 82 sampling stations. The inter-individual variance component was dominant in estimating the variance of mean EROD activity. Influences of alpha, beta, k and variability on sample sizes are illustrated and discussed in terms of costs. In particular, sample sizes do not have to be equal, especially if such a requirement would lead to a significant cost in sampling extra material. Finally, the feasibility of longterm monitoring is discussed.