A Comparison of Three Methods of Pike (Esox lucius L.) Removal from a Lowland Trout Fishery

The seine netting, gill netting and angling techniques used at Grafham Water for the removal of pike are described and assessed, and the effectiveness of the various methods compared. It was found that a combination of summer gill netting and seine netting was most effective, but it was concluded that angling was worthwhile during the autumn months.     

Earthworm communities in native savannas and man-made pastures of the Eastern Plains of Colombia

 The structure and seasonal changes of earthworm communities were evaluated in a natural savanna and in a improved grass-legume pasture in a Colombian oxisol over a period of 18 months. One plot of 90×90 m was isolated in each of the systems and each month five samples of 1 m²×0.5 m and ten of 20×20×20 cm were randomly selected from a stratified block design. Species richness was similar in the two evaluated plots (seven species), whereas diversity measured by the index, H (Shannon and Weaver 1949) was clearly different, i.e. H=2.89 in natural savanna and H=1.29 in pasture. This is explained by differences in earthworm community structure. The average annual density in the savanna was 49.8, ranging from 10.8 to 135.8 individuals (ind) m^–2, and biomass was 3.3 g m^–2 (hand-sorting method), ranging from 0.9 to 11.5 g m^–2. In the man-made pasture, density was 80.1 ind m^–2 on average, ranging from 24 to 215.8 ind m^–2 and biomass was more than tenfold higher, ranging from 29.2 to 110.4 g m^–2. This was especially due to the presence of a large glossoscolecid anecic species, Martiodrilus carimaguensis Jiménez and Moreno, which has been greatly favoured by conversion of savanna to pasture. Endogeic species were dominant in the natural savanna whereas the anecic species accounted for 88% of total earthworm biomass in the pasture. Total earthworm density and biomass were significantly different in the two systems studied (t-test). The results indicate a clearly positive response of earthworm communities to improved pastures, a type of land use that is being increasingly adopted in moist neotropical savannas. Received: 20 October 1997     

Humoral and cellular immunoresponsiveness of stanchioned cattle infested with Psoroptes ovis

Bovine scabies in a clinical problem during the cool autumn and cold winter months. In south Texas it is necessary to stanchion animals in order to elicit patent infestation during summer months. Environmental factors and grooming have been purported to account for summer resistance to infestation. However, stanchioned animals exhibit varied levels of susceptibility to infestation, suggesting that the noted variability may be influenced by the host immune response. In this study, animals were infested with Psoroptes ovis while in stanchions. The development of anti-P. ovis antibody activity was measured by the enzyme-linked immunosorbent assay and cellular immune function was monitored with mitogens and P. ovis antigens. A correlation was noted between the development of anti-P. ovis antibody activity and the increase in mite numbers and dermatitis. Coincident with the developing infestation was a suppression of T-cell function that appeared to be stress-related as a result of stanchioning. A working hypothesis is presented that attempts to correlate the developing humoral response and the depressed T-cell response with both an increasing dermatitis and mite population.     

Microbial diseases of cultured lobsters: A review

Six microbial diseases of cultured American lobsters (Homarus americanus) determined to be of significant concern to commercial aquaculture are discussed in relation to present knowledge of characteristics of the causative microorganisms, lobster susceptibility, environmental influence, severity, gross and microscopic recognition, physiological changes, contagion and control. The diseases reviewed here include shell disease, Gaffkemia, microbial epibiont disease, Lagenidium disease, Haliphthoros disease, and Fusarium disease.