New perspectives for fish in the Scheldt Estuary

The integration of a 600ha floodplain to the stream corridor of the tidal freshwater Scheldt Estuary will increase populations of eurytopic and rheophylic b species

Introductions of fish and crabs in the Schelde estuary

Since 1991, we have systematically recorded the fish and crab fauna of the Schelde estuary in samples of power plants cooling water and of fyke nets. In this period, we found 71 species of which eight were introduced (table 1). Additionally, one native and three non indigenous crab speices were observed. All non native marine species recorded in the estuary arrived from North America. Probably, their presence is due to transport via the ballast water of ships docking at the port of Antwerp. All non native freshwater species in the estuary arrived from eastern Europe and Asia. The occurrence of these species in the estuary is almost invariably due to deliberate introductions. The most recent observations of non-indigenous species in the Schelde estuary date from October 2001 when two young Vimba vimba and an adult Micropogonias undulatus were caught nearby the Dutch-Belgian border (Stevens et al., submitted). These species have not been recorded yet in Belgium

PATHOGENIC EFFECTS ASSOCIATED WITH TRYPANOSOMA DANILEWSKYI STRAIN FCC 1 INFECTION IN JUVENILE COMMON CARP, CYPRINUS CARPIO L

ABSTRACT Mortality and pathological effects caused by Trypanosoma danilewskyi strain F Cc 1 in laboratory-infected single breed juvenile common carp were investigated in this study. The study was divided into two parts. In the first part, four groups (A-D) each containing 20 fish (4 months old) were inoculated intraperitoneally with various size of inocula; 1000, 25,000 and 50,000 live trypanosomes/fish in groups A-C respectively while group D was injected 0.2 ml of PSG (phosphate buffered saline with glucose, pH 7, filter sterilized)/fish as a control. Blood was examined at 10 days intervals to monitor the development of parasitemia. All dead fish were counted and their blood and body fluids were examined for the presence of trypanosomes. The second part of the study was conducted under the similar conditions as first part to measure the pathological effects induced by the infection of T. danilewskyi strain FCc 1. Two groups, (A & B) each containing 40 fish (5 months old) were inoculated with 50,000 live trypanosomes/fish in group A and 0.2 ml PSG/fish in group B (control). Blood was examined at 10 days intervals and used for the estimation of parasitemia, hematocrit, hemoglobin and thin blood smear preparations. In the first part of study no fish died in groups A & D, 12.5 % mortality was observed in group B and 50 % in group C. The second part revealed a significant decrease in hematocrit, hemoglobin, erythrocyte counts and significant increase in leukocytes counts was observed in infected fish (group A) when compared to the control (group B) at the same interval of time. Thus it is concluded that Trypanosoma danilewskyi strain F Cc 1 is a potential hemoflagellate pathogen of juvenile common carp as it causes mortality, anemia and altered blood parameters

Selected nondigestible carbohydrates and prebiotics support the growth of probiotic fish bacteria mono-cultures in vitro

To search for nondigestible but fermentable (NDF) carbohydrates and prebiotics with a potency to promote the growth of selected bacteria in vitro. The growth of three reference bacteria strains Bacillus subtilis LMG 7135(T), Carnobacterium piscicola LMG 9839, Lactobacillus plantarum LMG 9211 and one candidate probiotic bacteria Lactobacillus delbrueckii subsp. lactis was investigated over a minimum period of 48 h in the presence of beta-glucan, xylo-oligosaccharide, arabinoxylo-oligosaccharide, inulin, oligofructose and glucose. Besides the capability to grow on inulin and oligofructose containing media, a distinct high growth in beta-glucan based substrates and a low growth in (arabino)xylooligosaccharide containing media were evident for most bacteria tested. With the exception of B. subtilis and L. plantarum, other bacteria grew equally well or even better on different substrates than on glucose. The fermentation of studied carbohydrates by these micro-organisms was dominated by the production of acetic acid as the main short chain fatty acid. Selected bacteria are able to ferment and grow on NDF and prebiotic carbohydrates but in a substrate dependent manner. This study delivers a first screening of which NDF or prebiotic carbohydrates are the most promising for aquaculture feed supplementations

Fermentation of Arabinoxylan-Oligosaccharides, Oligofructose and their Monomeric Sugars by Hindgut Bacteria from Siberian Sturgeon and African Catfish in Batch Culture in vitro

The in vitro fermentation of two Non-Digestible Oligosaccharide (NDO) preparations, Arabinoxylan- Oligosaccharides (AXOS) and Oligofructose (OF), and their respective monomeric sugars, xylose and fructose, were investigated by hindgut microbiota of two major aquaculture fish species, Siberian sturgeon (Acipenser baerii) and African catfish (Clarias gariepinus). Inocula from the hindgut of both fish species were incubated for 48 h in bottles containing 1.0% of one of four substrates, i.e. AXOS, OF, xylose or fructose. Amounts and profiles of produced Short-Chain Fatty Acids (SCFAs) differed between the two fish species and substrates. The hindgut microbiota of Siberian sturgeon has a higher fermentation capacity than the microbiota from African catfish. Xylose was much easier fermented than AXOS by microbiota from Siberian sturgeon whereas OF was quicker fermented than fructose with African catfish inoculum. The SCFAs were dominated by acetic acid for both fish species and for all substrates. Fermentation of OF and fructose by hindgut microbiota of Siberian sturgeon also yielded high amounts of butyric and branched-chain fatty acids after 48 h incubation. Results of this study suggest that AXOS, OF, and their monomeric sugars have an impact on microbial fermentation activity of hindgut microbiota from Siberian sturgeon and African catfish in a substrate and species dependent manner

Genetics and aquaculture in Africa

Les poissons transgéniques ouvrent des perspectives intéressantes pour les études sur la biologie du développement et l'expression in vivo des gènes ; ils sont utiles comme modèles dans les recherches biomédicales et ils rendent possible l'augmentation de la production aquacole par sélection en manipulant des caractères commercialement importants. Cette revue s'attache aux buts, aux procédures et aux conséquences environnementales de la fabrication de poissons transgéniques. En général, le matériel génétique provient d'une autre espèce de poisson. Il est constitué d'une séquence promoteur qui contrôle l'expression, d'un transgène qui code pour le caractère désiré, d'un élément régulateur distant, et d'un vecteur plasmidien ou viral. Les transgènes peuvent être subdivisés selon la nature du caratère pour lequel ils codent : gain d'une nouvelle fonction, protéine de régulation, perte de fonction. La méthode de transfert pour une intégration stable dans le génome est concentrée sur le zygote ou le jeune embryon ; l'utilisation de massifs cellulaires est également envisagée. Habituellement, on procède par approximation successive pour insérer correctement le gène dans le génome parce que les méthodes de recombinaison homologue ne sont pas encore utilisables. La micro-injection est la principale méthode pour administrer le nouvel ADN. Les implications pour l'aquaculture sont principalement l'augmentation de la croissance, de la résistance au froid et aux maladies. La biosécurité et les problèmes environnementaux en relation avec les poissons transgéniques devraient être convenablement abordés avant chaque dissémination dans l'environnement naturel... (D'après résumé d'auteur

Biomass transport to and from an upper estuarine area by migration of juvenile Atlantic herring <i>Clupea harengus</i>

A model describing fish abundance resulting from fish migration and mortality in an upper estuary is presented. This model can be used to estimate biomass transports by fish migrations between estuary and sea and to assess production assimilated in the estuary. It was applied to herring Clupea harengus L., a marine species with 0+ juveniles that migrate during winter to temperate European estuaries. It was shown that different mortality regimes greatly affected the number of fish that eventually emigrated and, hence, the biomass that was exported during the seaward migration. The difference between imported and exported biomass was assessed under different growth conditions and varied from positive to negative as mortality rates increased. The discrepancy between export of biomass and in situ produced biomass showed that fish production was not necessarily transported to the sea when emigrating. It was tentatively concluded that export of biomass out of the estuary only occurs if populations move seaward before winter