Effects of sand extraction on the macrobenthos of the Belgian Continental Shelf: a comparison of long-term datasets: Thesis summary

Stations sampled on the Kwintebank in late seventies, mid nineties and 2001 were used to detect possible changes in macrobenthic communities related to the impact of sand extraction. The community analysis based on data covering the entire sandbank in the nineties, failed to detect a difference between stations subject to high sand extraction and stations subject to low sand extraction on the sandbank. Comparing the community analyses of the seventies and 2001 no real community shift could be detected, except the indications in the depression. But an overall decrease in density and diversity is defined at all stations in 2001 relative to the seventies. The most intensive sand extraction is situated at the centre and the northern part of the sandbank, where both geomorphological and granulometric as meiofauna communities are affected by sand extraction. For macrofauna there is no clear evidence for a change in community structure in the north and the centre due to the impact of sand extraction, although some clear changes in density, diversity and sediment grain size are recorded in these two most impacted areas. Although methodological problems enhanced the difficulties in comparing the results of the seventies with the nineties and 2001, Hesionura elongata was considered to be a suitable indicator for human disturbances

Knelpunten in aquacultuur: enkele risicovolle aspecten van de vroege levensstadia van de vis.

&lt;p&gt;Aquacultuur is een zeer snel groeiende sector, maar er zijn nog talrijke knelpunten bij het opkweken van larven (larvicultuur) en van adulte vissen. Veel van deze knelpunten zijn van nutritionele aard. Het voedingsregime is nog vaak onvoldoende afgesteld op de behoeften van specifieke vissoorten waardoor uithongering een grote invloed blijft hebben. Deze problemen kunnen opgelost worden door de ontwikkeling van het gastro-intestinale stelsel per vissoort in kaart te brengen. Parameters, zoals de enterocytenhoogte, de aanwezigheid van supranucleaire vacuoles in de enterocyten en ‘the point of no return’ kunnen als maatstaf gebruikt worden om uithongering te monitoren en te voorkomen. Aan de hand van deze gegevens kan een optimaal voedingsregime met rotiferen (radardiertjes), Artemia&amp;nbsp; (pekelkreeftjes) en Copepoda (eenoogkreeftjes) uitgewerkt worden.&lt;/p&gt; &lt;p&gt;Aquaculture is a fast growing sector. However, during larviculture and fish husbandry, many bottlenecks still occur. Many problems concern nutritional factors and can be avoided by a clear understanding of the development of the gastrointestinal system of the various fish species. Parameters, such as enterocyte height, the presence of enterocytic supranuclear vacuoles and &#039;the point of no return&#039;, can be used to monitor and prevent food deprivation. This information can also be used to compose a feeding regime with rotifers, Artemia en copepods.&lt;/p&gt;</p

Surface area assessment of the murine intestinal tract as a prerequisite for oral dose translation from mouse to man

In many pharmacological and toxicological studies knowledge about the intestinal absorption, which is dependent upon the surface area of absorptive epithelia, is indispensible. Although mice are often used in such preclinical studies, very few quantitative data about their intestinal surface area are available. Especially for locally acting candidate drugs in development, this information is crucial for dose translation towards humans. Therefore, the surface area of the intestinal tract of CD-1TM IGS mice was assessed in the present study. The intestinal tracts of 12 mice were collected after euthanasia. From six animals, histological sections from the duodenum, jejunum, ileum, caecum and colon–rectum were made according to common stereological principles. Using these sections, the volumes and surface areas of each intestinal segment were estimated applying stereological counting procedures. In the other six animals, the density and surface area of the microvilli present in each intestinal segment were determined by means of scanning and transmission electron microscopy to assess the increase of the intestinal surface area attributable to the presence of microvilli. The mean total volume and surface area of the intestinal tract were 1.34 cm3 and 1.41 m2, respectively. The relative intestinal surface area (intestinal surface area divided by the body surface area) was 119. The relative intestinal surface area of mice is very similar to that of humans. The results of this study are important for the appropriate dose translation of candidate therapeutic compounds in drug development from mouse to humans

Effect of germ-free rearing environment on gut development of larval sea bass (<i>Dicentrarchus labrax</i> L.)

A gnotobiotic feed chain (Artemia-European sea bass) has been developed recently. To investigate the extremely complex and poorly understood modes of action of putative probiotics and pathogens in vivo, we quantified the effect of a germ-free controlled culture on survival and gastrointestinal tract development from day after hatching (DAH) 0 till DAH15. The larvae were kept in a germ-free static and rotating set-up, next to the conventional static group. They were sampled on DAH1, DAH6, DAH9 and DAH14. The survival of sea bass larvae on DAH14 from both germ-free treatments was not significantly higher (93 ± 3% and 82 ± 5%) compared to the conventional (51 ± 19%) group (p = 0.058). Morphometric data revealed a significant growth on DAH14 in germ-free static larvae (4.84 ± 0.07 mm) compared to that of conventional (4.55 ± 0.06 mm) and germ-free rotating larvae (4.54 ± 0.08 mm) (p = 0.002). However, histological analysis showed minor variations in regional morphology of epithelial cell types observed in the gut in individual larvae between and within treatment groups. These presented techniques combined with the germ-free sea bass model can be used as a standardised model system to study in vivo the mode of action of probiotics

Development of a bacterial challenge test for gnotobiotic sea bass (<i>Dicentrarchus labrax</i>) larvae

The use of probiotic microorganisms in aquaculture is gaining a lot of interest. Gnotobiotic model systems are required in order to fully understand the effects and modes-of-action of these microorganisms, as the native microbial communities present in non-sterile animals can lead to false conclusions. In this study, a gnotobiotic sea bass larvae (Dicentrarchus labrax) test system was developed. In order to obtain bacteria-free animals, the eggs were disinfected with glutaraldehyde and subsequently incubated in a solution of rifampicin and ampicillin. Axenity was confirmed using culture-dependent and -independent techniques. The gnotobiotic larvae were fed axenic Artemia sp. from 7 days after hatching onwards. In the challenge test, one of the three opportunistic pathogens, Aeromonas hydrophila, Listonella anguillarum serovar O1 and O2a, was added to the model system via the water and encapsulated in Artemia sp. Only serovar O2a led to increased mortality in the sea bass larvae. The presented gnotobiotic model can be used for research on, among others, reciprocal metabolic effects between microorganisms and the host (e.g. as measured by gene expression), immunostimulants, pharmacological research and the histological development of the gastrointestinal tract and growth of larvae

Siberian sturgeon (<i>Acipenser baerii</i>) larvae fed <i>Artemia</i> nauplii enriched with poly-beta-hydroxybutyrate (PHB): effect on growth performance, body composition, digestive enzymes, gut microbial community, gut histology and stress tests

The effects of feeding Artemia nauplii enriched with or without poly-ß-hydroxybutyrate (PHB) and/or highly unsaturated fatty acids (HUFA) on Siberian sturgeon (Acipenser baerii) larvae were investigated. Feeding larvae with PHB-enriched nauplii (PHB, PHB + HUFA) decreased the growth performance of the larvae. PHB affected the body composition by increasing the lipid content of the whole body and decreasing total saturated, monoenoic, n3, n6 and decosahexanoeic acid (DHA) in the larvae, indicating that the PHB addition affected lipid metabolism. A high activity of pepsin was observed in the digestive extracts of PHB treatments (PHB, PHB + HUFA), while PHB suppressed amylase activity in the intestine of the larvae. Based on molecular analysis, PHB changed the microbial community in the distal intestine of the larvae. The highest counts of goblet cells were observed in the HUFA-containing treatments (HUFA, PHB + HUFA), indicating that HUFA addition may improve the mucosal barrier defence system. The overall quality of the larvae was evaluated by exposing them to different salinities and ammonia stress levels. PHB decreased survival rates in these challenges. Our results show that optimal PHB doses for bio-encapsulation into Artemia remain to be determined for further application at the earliest larval stages of sturgeon

Light and transmission electron microscopy of <i>Vibrio campbellii</i> infection in gnotobiotic <i>Artemia franciscana</i> and protection offered by a yeast mutant with elevated cell wall glucan

Luminescent vibrios are amongst the most important pathogens in aquaculture, affecting almost all types of cultured organisms. Vibrio campbellii is one of these most important pathogens. In this study, the effects of feeding mnn9 yeast cell wall mutant and wild type yeast strain were investigated in the digestive tract of brine shrimp nauplii, Artemia franciscana, after experimental infection with V. campbellii (LMG 21363). Gnotobiotic A. franciscana nauplii were fed daily with dead Aeromonas hydrophila LVS3, and with either wild type strain of baker's yeast, Saccharomyces cerevisiae, or mutant strain mnn9, of which the cell wall contains elevated chitin and glucan and lower mannose levels. After three days of feeding, some nauplii were challenged with V. campbellii. Mean survival (%), individual length (mm) and total length (mm) at one day and two days after challenge were significantly higher in the group fed mnn9 than in the group fed wild type yeast (81 ± 1.50 and 63 ± 0.49, 1.56 ± 0.07 and 1.13 ± 0.02, 38.21 ± 3.11 and 21.26 ± 0.81 respectively for one day and 50 ± 2.37 and 20 ± 1.41, 2.33 ± 0.01 and 1.24 ± 0.04, 34.97 ± 5.56 and 7.45 ± 1.63 for two days after challenge). Histological examination revealed that the luminal diameter and enterocyte height of both mid- and hindgut were larger in the mnn9-fed group. Colonization of the gut lumen by V. campbellii could be observed by transmission electron microscopy for the group of nauplii fed with wild type yeast. Furthermore, it was observed that V. campbellii caused damage to the gut epithelium including shortening and disappearance of the microvilli, destruction of the apical cell membrane and cell lysis in the nauplii fed wild type yeast. The gut epithelium remained intact in challenged nauplii fed mnn9 yeast. The morphological findings of the present study further substantiate previous studies reporting a protective effect of this yeast cell wall mutant