54 resultados para 20-195B


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Qualitative and quantitative characteristics of the reaction of certain fish to light were tested and reasons for the attraction of certain fish to light are discussed.

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The FIDAWOG workshop held at the Tom Mboya Labour College in Kisumu was the fourth stock assessment workshop held under the LVFRP programme. There were two main objectives: training in paper and report writing and presentation, and presentation of research results collected to date.

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The effectiveness of 17 α-hydroxy-20 β-dihydroprogesterone (17 α-20 β Pg) or of a trout hypophyseal gonadotrophic extract on the in vitro intrafollicular maturation of trout oocytes can be modulated by steroids which do not have a direct maturing effect; the effectiveness of the gonadotrophic extract is lowered by oestradiol and oestrone and increased by testosterone. As these steroids have no significant effect on maturation induced by 17 α-20 β Pg, the site of their activity is probably in the follicular envelopes. Corticosteroids, and Cortisol and cortisone in particular increase the effectiveness of the gonadotrophic extract, but increase the effectiveness of 17 α-20 β Pg even more strongly, suggesting that this 'progestagen' has a direct effect on oocyte sensitivity.

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Laboratory research was done in order to study the feeding of larval Cricotopus silvestris F. in relation to characters of structure of oral apparatus. Results of the experiments are summarised and the oral apparatus morhologically described.

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The morphology, increase and systematica of Sphaerotilus natans is studied and culture methods examined.

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Sampling was concentrated on the North Moor region and the series of ditches which drained this area to the Bristol Channel. Although most ditches were not deep the mud substratum precluded sampling from within the habitat. All samples were taken with a pond net from the banks. Efforts were made to sample each part of the habitat although in some ditches the macrophyte growth was so intense as to make sampling difficult particularly of the sediments. Organisms were identified on the 10 sampling sites.

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One additional Chalci campaign that, in line with the previous Chalci campaigns 78-01, 78-02, and 79/01, has as its major objective the trawl exploration of the Ivoirian continental shelf at the depth of 10 to 120 metres.