Invertebrates, including <i>Asellidae</i>, are part of the natural ecosystem of the drinking water distribution system (DWDS) and are known to cause a nuisance to consumers. In addition, recently, the potential role of the species <i>Asellus aquaticus</i> (L. 1758) in the regrowth of <i>Aeromonas</i> bacteria was published. <i>Aeromonas</i> is included in the Dutch drinking water guidelines as a process parameter, and the guideline values are regularly exceeded. Although neither <i>A. aquaticus</i> nor <i>Aeromonas</i> is associated with health risks, the Evides drinking water utility shows a strong interest in the possible reasons for these exceedances and possible control measures. In surface waters, <i>Asellidae</i> feed mainly on decaying leaves that are abundantly present. These food sources are not present in the DWDS. Therefore, we determined suitable food sources for <i>A. aquaticus</i> in the DWDS. Laboratory experiments show that <i>A. aquaticus</i> individuals survive on biofilm on pipe wall material and loose deposits (sediments) collected from DWDS. Growth and survival rates on these loose deposits were even higher than on the positive control (decaying leaves). As the basis of these loose deposits is inorganic (iron deposits, sand, and pipe particles), the organic matter (living and decaying bacteria, protozoans, fungi, and invertebrates) must be their substrate. These experiments validate hypotheses that <i>Asellidae</i> can grow and survive on organic matter in deposits in DWDS.

An experiment were conducted to evaluate The effect of feeding frequencies and stocking size on growth and feed conversion ratio (FCR) of rainbow trout (O. mykiss) in brackish water for 102 days. Three stocking sizes (10, 25 and 40 g/fish) of rainbow trout and three feeding frequencies (feeding fish twice, three times and four times per day) were examined as the same time. Fish were fed at a restricted feeding program according to the rainbow trout standard table in the definite times during the light period. The results showed that in the group with 10 g initial weight increasing the feeding frequency, some growth factors like final weight, daily growth, and weight gain. But the other factors such as food conversion rate (FCR) and specific growth rate (SGR) decrease. It means in this group (10 g) two times feeding per day is not enough for an acceptable growth rate. In the two other groups with (initial weight 25 and 40 g) although by increasing the feeding frequency, some growth factors a little increase but these differences in 95% level (p،ـ0.05) are not significant. Therefore in rainbow trout culture with initial weight at least 25 g two times feeding per day was enough. The results of carcasses analysis of fish, showed that by increasing the feeding frequency there were no significantly difference at 95% level between the body compositions in all of treatments. With connivance of feeding frequencies, the best FCR was in the group with 10 g initial body weight and there was not any significant difference in SGR. So according to the results, it suggests that fish should be stocked with 10 g initial body weight.

The present paper reports on the results of a long-term field study on the simultaneous influence of 2 environmental factors (temperature and food supply) on annual growth rates in the tellinid bivalve Macoma balthica. For >30y (1978–2009) we monitored twice-annually the weight changes of soft parts of individuals of known age at several permanent sampling stations located at Balgzand, an extensive (50km2) tidal flat area in the western Dutch Wadden Sea. Monthly data were available on mean water temperature and chlorophyll a (chl a) concentration from a nearby site in the main tidal inlet. Mean individual ash-free dry weights at ages of nearly 1 and of nearly 1.5y were assessed in February/March and in August, respectively. Such weights show a consistent annual pattern: they increase between late winter and early summer to decline for the remainder of the year. Annual multi-station means of the spring/summer individual weight gains were higher as chl a concentrations in the water had been higher and water temperatures had been lower for the growing season. These correlations proved to be stronger at sampling sites that were situated low in the intertidal zone close to the main tidal stream than at those high in the intertidal near the coast (where M. balthica obtain their food primarily by deposit feeding on benthic material). At the low off-shore sites, suspended algae are available for longer daily periods and their concentrations in flood water may be less depleted by grazers. The negative correlation between weight gain and water temperature may have been primarily based on the shortening of the M. balthica growing seasons in warm summers. We conclude that the present simultaneous trends of global warming and declining stocks of pelagic algae may affect M. balthica in the Wadden Sea in a similar, negative, way.

The growth rates and yields of Listeria monocytogenes and Yersinia enterocolitica were determined in liquid culture media, and in model oil-in-water emulsions that contained 30, 70 or 83% (v/v) hexadecane. In emulsions with a mean droplet size of 2 pm containing 83% (v/v) hexadecane, the growth of both organisms resulted in decreased yields. Additionally, in these emulsions adjusted to pH 5.0 or 4.4 the growth rate of L. monocytogenes was significantly less than in other model systems which had an aqueous phase of equivalent chemical composition. Microscopic examination of the 83% (v/v) emulsion showed that its microstructure immobilized the bacteria, which were constrained to grow as colonies. Bacteria behaved similarly in model emulsions of either hexadecane or sunflower oil. Manipulation of the droplet size distribution of the emulsions changed the form and rate of growth of bacteria within them.