A STUDY OF ACTIVITIES OF ENZYMES HYDROLYSING SUCROSE AND STARCH AND OF OXYGEN UPTAKE IN A SEQUENCE OF SOILS UNDER TUSSOCK GRASSLAND

Biochemical activities were studied at three sampling dates in a sequence of four soils, ranging in altitude from 275 to 1,520 m, on schist parent material in a tussock-grassland association on the Old Man Range, Central Otago. Activities were similar under different tussock species. The uppermost part of the soil appeared to be most affected by seasonal changes because fluctuations at different sampling dates were greater in samples of topsoil from depth 1 to 7.5 cm than in samples of A, AB, and B horizons at depths approximately 4, 13, and 28 cm. Activities of enzymes without added substrate and of enzymes hydrolysing sucrose or starch generally increased with increasing altitude of the soils and were strongly correlated with organic C content and, to a lesser extent, with soil moisture content. In previous pasture surveys, enzymes hydrolysing sucrose had not been significantly correlated with organic C. Although oxygen uptakes were also positively correlated with these factors, and with numbers of viable bacteria, consistent differences between soils were not found. Differences between A and AB horizons were usually greatest in the soil at the highest altitude but, otherwise, rates of regression of biochemical activities with depth of soil were generally similar in all soils. Results may be indicative of biochemical activities in other mountain-soil sequences.     

Water-soluble vitamin requirements of tilapia: ascorbic acid (vitamin C) requirement of Nile tilapia, Oreochromis niloticus (L.)

Abstract. The quantitative dietary ascorbic acid requirements of fingerling Nile tilapia, Oreochromis niloticus L., were assessed by feeding seven diets containing graded supplements of this vitamin (0, 50, 75, 100, 125, 300 and 400mg/100g dry diet) to triplicate groups of fish for 12 weeks. Fish fed the diet devoid of ascorbic acid exhibited significantly ( P < 0·01) poorer growth and higher condition factor. Food conversion and protein efficiency ratios were improved with increasing dietary ascorbic acid level up to 125mg/100g of dry diet. Protein utilization, haematocrit, haemoglobin level and tissue ascorbate concentrations were depressed in fish fed the ascorbic-acid-free diet. Tissue ascorbate concentrations, especially for liver, were highly correlated with dietary ascorbic acid level. Fish fed the ascorbic-acid-free diet exhibited deficiency signs including erratic and convulsive swimming, anorexia, lethargy, caudal fin erosion, skin haemorrhages and mortality. Based on the nutritional and pathological parameters investigated, the recommended dietary inclusion level is 125mg/100g dry diet, which is equivalent to a net requirement (after processing and storage) of 42mg/100g diet.     

Histopathology of snakehead, Channa striatus (Bloch), experimentally infected with the specific Aphanomyces fungus associated with epizootic ulcerative syndrome (EUS) at different temperatures

Abstract Snakeheads, Channa striatus (Bloch), were inoculated with a spore suspension of the specific pathogenic Aphanomyces , isolated from fish affected by epizootic ulcerative syndrome (EUS), in South East Asia. Fish were held at three different temperatures: 19, 26 and 31 °C. Histological changes induced by the infection are described. In the early stages of the disease, degenerative changes were observed in all samples, but inflammatory infiltrate was much more marked in fish kept at 26 and 31 °C. By 8 days post-injection, extensive mycotic granulomatosis was observed in the samples kept at 26 and 31 °C. The fish kept at 19 °C developed a severe invasive myonecrosis with limited macrophage response. From 14 to 28 days post-injection, healing became well established at 26 and 31 °C and surviving fish kept at these temperatures recovered completely by 28 days. The lesion was still progressing at 21 days post-injection in fish kept at 19 °C, and all such fish succumbed by this time. Thus, mortalities in the fish kept at 19 °C were considerably higher than in the groups of fish kept at 26 and 31 °C. The findings help to explain why mortalities from EUS occur when water temperatures are low.     

Strawberry disease in rainbow trout, Salmo gairdneri Richardson

Abstract. Strawberry disease is a subchronic, non–debilitating, and non–fatal inflammatory skin disease of rainbow trout that has been recognized for the past 25 years. Morbidity ranges up to 80% and the disease affects fishes from 15cm in length to brood stock size. Epizootiological data indicate that strawberry disease usually appears, first in the autumn and reaches peak incidence during the following winter and spring. Data also indicate that the disease is found only in certain trout farms in the western and Pacific north–western regions of the United States. Although the cause of strawberry disease is unknown, the normal clinical course of 8 weeks can be reduced by oral treatment with oxytetracycline. Clinical signs include appearance of bright red, raised, circumscribed, ulcerated and indurated lesions in the skin that usually range up to 3 cm or more in diameter. Microscopically, the disease is characterized as a subchronic, focal, non–suppurative dermatitis with ulceration and extensive infiltration of mononuclear inflammatory cells.     

The effects of the use of potassium alum adjuvant in vaccines against vibriosis in rainbow trout, Salmo gairdneri Richardson

Abstract. A formalized bacterin of Vibrio anguillarum , with and without alum adjuvant, was administered intraperitoneally to rainbow trout under farm conditions. Compared with the normal bacterin the adjuvanted preparation caused pathological changes indicative of chronic peritonitis, substantial early mortalities in 3 cm fish, and to a lesser extent in 20 cm fish, and depressed growth rate. No additional degree of protection against artificial challenge was obtained from its use.     

The effects of feeding fodder beet to dairy cows offered silage ad libitum

In a 16-week winter feeding experiment, 48 autumn calving cows and heifers were used to compare a control diet, with two diets including fodder beet at a low and a high level. The control diet was ad libitum silage and 6 kg d^-1 of concentrates (13.4 MJ (kg DM)^-1 of ME and 197 g (kg DM)^-1 of CP). The cows offered fodder beet were fed the control diet (C) plus fodder beet at either 2 (L) or 4 (H) kg DM d^-1. Soya bean meal was offered with the fodder beet at 0.5 or 1.0 kg d^-1 for diets L and H, respectively.
Total dry matter and metabolizable energy intakes were 15.2,16.4 and 17.3 kg DM d^-1; 177, 195 and 211 MJ d^-1 for treatments C, L and H, respectively. The mean milk yields were not significantly affected by the feeding of fodder beet. There was a significant improvement in the fat and protein content of the milk and yield of constituents. The milk composition and yield of solids were: fat content 42.3,44.2 and 45.9 (s.e.d. 1.25) g kg^-1; protein content 33.0, 34.5, 35.3 (s.e.d. 0.76) g kg^-1; fat yield 964,1027,1095(s.e.d. 63.2); protein yield 757, 801, 841 (s.e.d. 48.8) for treatments C, L and H, respectively. The treatments had no significant effect on live weight or condition score change.     

The population genetic structure of the rust fungus Melampsora lini as revealed by pathogenicity, isozyme and RFLP markers

Isozyme and RFLP markers were used to investigate genetic variation underlying the racial structure of populations of Melampsora lini occurring on the Australian endemic host species, Linum marginale . Previous studies of the pathogenicity of isolates occurring in a series of discrete but interconnected populations detected an overall structure characterized by linkage disequilibrium—indicative of a pathogen population reproducing asexually as a number of clonal lines (Burdon & Jarosz, 1992), Using samples from that study, we detected two isozyme multi-locus phenotypes. One of these was restricted to two closely related races which appear to be examples of recent migrants into the area. Variation was also detected among and between races of the pathogen using two RFLP markers. Differences detected by one of these markers suggested the occurrence of a previous migrational event. Variation in the other marker detected two phenotypes within three common, widespread races. However, not all possible phenotypes were recovered, suggesting that the variation detected was not generated by recent sexual recombination.