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Notes: A standardized method was developed for artificially infecting the European eel with Anguillicola crassus, a parasitical swim bladder nematode. For this purpose, an intermediate host, Paracyclos fimbriatus, and a paratenic host, Cyprinus carpio, were used. Parasite prevalence in the artificially infected eels was very high, although there was a large variation in the number of worms per eel. Compared to other methods of artificial infection described in the literature, this method apears to be more efficient and reliable; there were also more infectious larvae that were recovered and tRe mortality rate of eels under treatment was lower.〈section xml:id="abs1-2"〉〈title type="main"〉RésuméUne méthode améliorée pour l'infection artificielle de l'anguille européenne Anguilla anguilla par Anguillicola crassus (Nematoda, Dracunculoidea)Une méthode standardisée a été développée dans le but d'infecter artificiellement l'anguille européenne par Anguillicola crassus, un nématode parasitique qui se trouve dans le vessie natatoire de l'hôte. Dans ce but, un hôte intermédiaire Paracyclops fimbriatus et un hôte paraténique Cyprinus carpio ont été utilisés. La prévalence du parasite dans les anguilles infectées artificiellement était haute, bien que le nombre de vers retrouvés ingviduellement était trés varié. Comparé sà d'autres méthodes d'infection artificielle décrites dans la littérature, cette méthode démontre êre plus efficace: le nombre de larves contaminantes rassemblées était plus élève, la mortalité parmi les anguilles traitées était moins importante et la méthode était plus fiable.〈section xml:id="abs1-3"〉〈title type="main"〉ZusammenfassungEine verbesserte Methode der künstlicben Infektion des Europäiscben Aales, Anguilla anguilla, rnit Anguilhcola crassus (Nematoda, Dracunculoidea)Es wurde eine standardisierte Methode zur Infektion des europäischen Aals rnit dem Schwimmblasenwurm Anguillicola crassus entwickelt. Zu diesem Zweck wurden ein Zwischenwirt, Paracyclops fimbriatus und ein Wirt, Cyprinus carpio, eingesetzt. Die Häufigkeit des Parasiten in den künstlich infizierten Aalen war sehr hocg, jedoch konnte eine hohe Variabiliät individuellen Wurmbefdls festgestellt werden. Im Vergleich zu anderen Infektionsmethoden, die in der Literatur beschrieben sind, erscheint die mir erprobte Methode effizienter: die Wiederauffindungsrate infektiver Larven war höher und die Mortalitätsrate der behandelten Aale geringer. Die Methode wird auch als zuverlässiger angesehen.

Notes: Plant growth rate has frequently been associated with herbivore defence: a large investment in quantitative defence compounds occurs at the expense of growth. We tested whether such a relationship also holds for growth rate and pathogen resistance. For 15 radish (Raphanus sativus L.) cultivars, we determined the potential growth rate and the resistance to fungal wilt disease caused by Fusarium oxysporum. We subsequently aimed to explain a putative negative relationship between growth rate and resistance based on plant chemical composition. Both growth rate and resistance level varied greatly among cultivars. Moreover, there was a strong negative correlation between growth rate and resistance, i.e. there are costs associated with a high resistance level. Roots of slow-growing, resistant cultivars have a higher biomass density. Using pyrolysis mass spectrometry. we part1y explained variation in both growth rate and resistance in terms of the same change in chemical composition. Leaves of slow-growing, resistant cultivars contained more cell wall material. Surprisingly, roots of slow-growing, highly resistant cultivars contained significantly less cell wall material, and more cytoplasmic elements (proteins). We speculate that this higher protein concentration is related to high construction and turn-over costs and high metabolic activity. The latter in turn is thought to be responsible for a rapid and adequate resistance reaction, in which phenols may be involved.

Notes: Leaf, stem and root material of wild-type and gibberellin (GA)-deficient mutants of tomato (Lycopersicum esculentum L.) were analysed by pyrolysis-mass spectrometry for possible differentiation in chemical allocation pattern among cell wall and cytoplasm. GA-deficiency is accompanied by changes in the relative growth rate (RGR). RGR-correlated changes were found in leaves in the comparative amounts of cellulose- and protein-derived fragments. The low-RGR genotypes contained more protein and nucleic acid, the high-RGR ones more cellulose. In root material, a higher contribution of cellulose, hemicellulose and G- and S-lignin was found for the lower-RGR plants and comparatively high protein in the high-RGR genotypes. For stems, less clear results were obtained, possibly because of variation in the ratio of syringyl- and guaiacyl-lignin. Part of the results might be explained by a GA-dependent change in cell size.

Notes: Previous experiments have shown that the anatomy and chemical composition of leaves of inherently fast- and slow-growing grass species, grown at non-limiting nitrogen supply, differ systematically. The present experiment was carried out to investigate whether these differences persist when the plants are grown at an intermediate or a very low nitrogen supply. To this end, the inherently fast-growing Poa annua L. and Poa trivialis L., and the inherently slow-growing Poa compressa L. and Poa pratensis (L.) Schreb. were grown hydroponically at three levels of nitrate supply: at optimum (RGRmax) and at relative addition rates of 100 and 50 mmol N (mol N)−1 d−1 (RAR100 and RAR50), respectively.As expected, at the lowest N supply, the potentially fast-growing species grew at the same rate as the inherently slow-growing ones. Similarly, the differences in leaf area ratio (LAR, leaf area:total dry mass), specific leaf area (SLA, leaf arear:leaf dry mass) and leaf mass ratio (LMR, leaf dry mass:total dry mass) disappeared. Under optimal conditions, the fast-growing species differed from the slow-growing ones in that they had a higher N concentration. There were no significant differences in C concentration. With decreasing N supply, the total N concentration decreased and the differences between the species disappeared. The total C concentration increased for the fast-growing species and decreased for the slow-growing ones, i.e. the small, but insignificant, difference in C concentration between the species at RGRmax increased with decreasing N supply.The chemical composition of the leaves at low N supply, analysed in more detail by pyrolysis–mass spectrometry, showed an increase in the relative amounts of guaiacyl lignin, cellulose and hemicellulose, whereas those of syringyl lignin and protein decreased.The anatomy and morphology of the leaves of the four grass species differing in RGRmax were analysed by image-processing analysis. The proportion of the total volume occupied by mesophyll plus intercellular spaces and epidermis did not correlate with the amount of leaf mass per unit leaf area (specific leaf mass, SLM) at different N supply. The higher SLM at low N supply was caused partly by a high proportion of non-veinal sclerenchymatic cells per cross-section and partly by the smaller volume of epidermal cells.We conclude that the decrease in relative growth rate (and increase in SLM) at decreasing N supply is partly due to chemical and anatomical changes. The differences between the fast- and slow-growing grass species at an optimum nutrient supply diminished when plants were growing at a limiting nitrogen supply.

Notes: On two shrimp farms in East Java, Indonesia, a total of 16 tambaks stocked with Penaeus monodon (Fabricius) were monitored for water quality during one growing season. The water quality parameter values were compared with production characteristics. Ranges of parameter values remained between acceptable reference values. Influences of farm, tambak and time on water quality were significant. Tambak production was explained for 25% by water transparency. Observed water quality parameter values could not be a reason for recently described decreased production. Therefore, other factors should be investigated.

Notes: Shrimp farmers in South-East Java have recently observed a decline in Penaeus monodon (Fabricius) production. To stabilize overall production, some farms have switched partially to biculture of P. monodon and P. merguiensis (de Man). The production from 33 ponds in two of these farms was analysed. In addition, the water quality in 10 ponds was monitored over the entire culture period. Information was also available on the post-larvae (PL) source and feed used per pond. Water quality remained stable during the culture period and there was no accumulation of organic material during the second half of the culture period. Stocking P. merguiensis 2 months after P. monodon partially compensated for the low production of P. monodon, thereby stabilizing overall production. When the production of P. monodon is low, the production of P. merguiensis is high and vice versa (P〈0.001). Feed source had no effect on production when stocking density was included as a covariable in the analysis (P 〉 0.05), while P. monodon PL source caused production to differ by a factor of three (P〈0.001). It was concluded that biculture of P. monodon and P. merguiensis is an effective way to stabilize overall shrimp production.

Notes: The influence of salinity and dietary composition on blood parameter values (haematocrit, leucocrit, immature lymphocytes, mature lymphocytes, granulocytes, plasma osmolarity and total plasma protein) of red hybrid tilapia, Oreochromis niloticus (Linnaeus) x O. mossambicus (Peters), was studied. Two groups of tilapia were fed a high-protein diet while kept in fresh or brackish water, respectively, and compared with two groups fed a low-protein diet under similar environmental conditions. Treatments were executed in duplo. Results show that salinity influenced all cellular blood parameters except the haematocrit. Dietary composition influenced the total plasma protein and haematocrit, while all parameters changed as time progressed during the experiment. It was concluded that the environmental parameters investigated in the present study should be considered when estimating fish health based on blood parameter values.

Notes: The relationships between Penaeus monodon production and three crop characteristics in 107 ponds on nine shrimp farms in East Java were studied. Overall differences of production (Mt ha-1 year-1), survival rate (%), stocking density (number m-2) and mean weight at harvest (g) between regions and between farms were significant, while the difference of production between farms was also significant within regions. Overall analysis revealed that production was positively correlated with survival rate, stocking density and mean weight at harvest, while there was a negative correlation between stocking density and survival rate. Results imply that more attention should be paid to improving shrimp survival. The higher on-farm production in South East Java is linked to higher survival rates and higher post-larvae stocking densities than in North West and North East Java, while similar individual weights at harvest to North West East Java are reached. In this context, the relationship between coastal estuarine water quality and yield needs further investigation. Other parameters which need further investigation are farm management, post-larvae origin and duration of the culture period.