The Effect of Detopping the Field Bean Plants (Vicia faba L. minor) and Lack of the Pod Setting on the Symbiosis with Root Nodule Bacteria

The plants of field bean var. Nadwiślaνski were detopped after about 1 month since the beginning of flowering and after that all flower buds were removed from some plants. The effect of a change in the trophic balance on the setting and subsequent growth of root nodules was studied.
The removal of pods had the greater effect on the increase in the weight of the remaining organs than the detopping of plants. Detopping retarded the ageing of the plants and delayed the phase of the greatest reduction of the number of pods. The detopping of plants revealed their considerable compensative possibilities in terms of production of the pod weight and the potential of leaves for biomass production. The data obtained indicate that plant detopping may disturb the root–bacteria exchange of signals, necessary to initiate the nodule development, while the further growth of nodules depends, above all, on the amount of available photosynthates.
A very high correlation between the dry weight of the whole plant to the dry weight of leaves ratio and the weight of nodules was observed. It proves the importance of the trophic balance of the plant for the root nodule weight production.     

Prevalence and Aetiology of Mastitis in Cows from Two Major Ethiopian Dairies

The study was undertaken to determine the aetiology and prevalence of mastitis in hand-milked cows (n = 186) in two major Ethiopian dairies. The California Mastitis Test and culturing for bacteria revealed that 21.5% of the cows were clinically infected and 38.2% had subclinical mastitis. Most mastitis pathogens isolated from milk samples testing positive by the California Mastitis Test were Gram-positive cocci. Staphylococci constituted 57% of the isolates, of which the predominant cause of bovine mastitis was Staphylococcus aureus (40.5%). Other mastitis pathogens isolated include streptococci (16.5%), coliforms (9%) and corynebacteria (5%). Retrospective analysis of farm records indicated that mastitis was the second most important cause of culling and accounted for 27% of the cows removed from these two dairies.     

Use of marine yeasts as an available diet for mass cultures of Moina macrocopa

A 4‐week feeding trial was conducted to test the use of marine yeasts purified from seawater and sediments as a dietary source in cultivating a cladoceran, Moina macrocopa, a potential alternative live food for fish larvae. Optimal growth conditions of two yeast strains were obtained for NaCl concentration, pH and temperature. Moina macrocopa was cultivated using different diets: marine yeasts (Debaryomyces hansenii Yeast‐14 and Candida austromarina Yeast‐16) and a commercial diet (Erythrobacter sp. Sπ‐I). The essential amino acids of both the yeast strains were nearly as great as those in M. microcopa. Further, the yeast‐fed M. macrocopa had essential amino acid profiles similar to the documented values for rotifers and Artemia enriched in microalgae and commercial diets. Erythrobacter sp. Sπ‐I lacked n‐3 polyunsaturated fatty acids, 20:5n‐3 and 22:6n‐3, which were also low but detected in both yeasts. An increase in the 20:5n‐3 [eicosapentaenoic acid (EPA)] and 22:6n‐3 [docosahexaenoic acid (DHA)] levels, compared with the levels in yeast strains themselves, was more pronounced in the 22:6n‐3 level of Moina fed the C. austromarina, resulting in a high DHA:EPA ratio. When the Moina diets were switched, their δ¹³C values shifted gradually towards the values of the switched diets. Diet switch from Erythrobacter sp. Sπ‐I to C. austromarina Yeast‐16 resulted in a more rapid turnover of Moina tissue carbon than that in the inverse case. When fed a mixed diet, the δ¹³C values of Moina tissue approached the value of marine yeasts immediately. These temporal changes in the δ¹³C values of Moina tissue indicate the preferential ingestion of marine yeasts and a selective assimilation of the carbon originated from marine yeasts. These findings suggest that marine yeasts, particularly C. austromarina Yeast‐16, are highly available to mass cultures of M. macrocopa, providing better nutritional and dietary values than the commercial diet (Erythrobacter sp. Sπ‐I).     

Detection of Flexibacter maritimus in fish tissue using nested PCR amplification

A nested polymerase chain reaction (PCR) system was developed for the detection of Flexibacter maritimus from fish tissue. The total procedure for the diagnosis of marine flexibacteriosis, from the point of DNA extraction to the electrophoretic analysis, can be performed in < 4 h. This was achieved by the combination of a short thermal cycling programme with a rapid DNA extraction procedure. The assay was extremely sensitive, capable of detecting as few as 75 cfu mg(-1) fish tissue. The accuracy of the nested PCR was confirmed under field conditions using tissue samples recovered during 1993-2002 from fish suffering marine flexibacteriosis. The nested PCR method proved to be efficient for the rapid and sensitive detection of F. maritimus from fish tissues and can be used for routine diagnosis of the disease caused by this pathogen.     

Nutrient composition and metamorphosis success of Atlantic halibut (Hippoglossus hippoglossus, L.) larvae fed natural zooplankton or Artemia

Atlantic halibut larvae were fed docosohexanoic acid- (DHA) selco enriched Artemia (RH-cysts) or wild zooplankton in duplicate tanks from first-feeding and 60 days onward. The zooplankton were collected from a fertilized sea water pond and consisted mainly of different stages of Eurytemora affinis and Centropages hamatus . There were no differences in survival, or in growth during the first 45 days of feeding, between larvae fed the two prey items, but the larvae fed Artemia showed much higher incidence of malpigmentation and impaired eye migration than larvae fed zooplankton. The prey organisms contained similar amounts of dry matter and protein, but Artemia was higher in lipid and glycogen than the zooplankton. Larvae fed Artemia were higher in both glycogen and lipid than the zooplankton-fed larvae towards the end of the feeding period. There were large differences between the prey organisms in the concentrations of essential fatty acids (% of total fatty acids) which was reflected in the fatty acid composition of the larval body. It is concluded that the macronutrient composition of Artemia in the present study was probably within the optimal range for promotion of growth and survival in young Atlantic halibut. The concentration of n-3 HUFA, and especially DHA, is however, very much lower in enriched Artemia than in copepods, and may be one of the factors triggering developmental errors in Atlantic halibut.     

Optimization of the protein fraction of microcapsules used in feeding of marine fish larvae using in vitro digestibility techniques

The development of artificial feeds for marine fish larvae is demanding and, taking into account the difficulties and costs associated with the rearing of the larvae of some fish, preliminary evaluation of feed ingredients using in vitro techniques may be an alternative to in vivo assays. Some proteins used in microfeeds for marine fish were tested in vitro for examination of their effect on the proteases of seabream larvae. Casein and cuttlefish meal did not affect protease activity of crude larval extracts, whereas ovalbumin produced a 60% inhibition. The use of a pH-stat for the assessment of the degree of hydrolysis (DH) of proteins confirmed the low nutritive value of ovalbumin, since a much lower value was obtained for microcapsules prepared using this protein source when compared with those prepared using casein or cuttlefish meal (3.2 vs. 7.3 and 7.6, respectively). Products resulting from such hydrolysis were analysed using sodium dodecyl sulphate–polyacrylamide gel electrophoresis (SDS–PAGE). Image analysis of such gels led to the formulation of an index named the coefficient of protein degradation (CPD) which expressed the extent to which the main protein fractions were hydrolysed by larval proteases in a given time. A significant correlation ( r ² = 0.98, P  < 0.05) was obtained between DH and CPD values measured for either protein sources or microcapsules. The combination of protease inhibition assays with measurements of DH and CPD is proposed as a preliminary evaluation of protein ingredients used in the formulation of artificial feeds for larval fish.     

Isolation of a highly pathogenic Vibrio pelagius strain associated with mass mortalities of turbot,Scophthalmus maximus (L.), larvae

A bacterial strain, characterized as Vibrio pelagius (Hq 222), was isolated from a turbot, Scophthalmus maximus (L.), larvae mass mortality in a commercial fish farm in Spain. Turbot larvae, post-larvae (0.2 g) and juveniles (5 and 15 g) were experimentally infected. The bacterium appeared to be very virulent for larvae and post-larvae, LD50 being < 5 bacteria mL(-1) for larvae 1 week post-infection and 3.9 x 10(5) bacteria mL(-1) in post-larvae at day 12 post-infection. The bacterial strain was recovered in pure culture from the internal organs of infected fish. Histological lesions in post-larvae exhibited swelling and necrosis of gill secondary lamellae, sloughing of intestinal mucosa and necrosis of haematopoietic tissue in the kidney. Vibrio pelagius (Hq 222) was able to grow in sterile sea water when incubated at room temperature or at 15 degrees C. Vibrio pelagius (Hq 222) was more adherent to the turbot cell lines TV-1 and TF than Escherichia coli. In both cell lines, the number of adhered bacteria increased with incubation time.