No description available.

No description available.

No description available.

The effects of group size on aspects of stoneloach foraging behaviour were examined in laboratory experiments. Fish were observed under dark conditions, using infra red illumination and video equipment. Experiments were timed to coincide with the stoneloach's natural time of maximum activity, immediately after a period of artificially simulated dusk. Individual stoneloach located a concealed food source more rapidly when group size was increased from one to five fish. Large quantitative differences were observed between fish, and those which were slow to locate food when alone remained poor when conspecifics were present. Over a 900 sec period, individuals in groups of five fish spent a greater proportion of available time searching, and appeared to sample the environment more, when compared with individuals in groups of only two. An increase in sampling may have counteracted the observed reduction in the number of feeding attempts by the fish in the larger groups, which resulted from the increased emphasis on searching. Groups of both six and twelve fish, foraging in tanks comprising two feeding areas each containing a patch, and a central area where no food was available, distributed themselves roughly in accordance with the predictions of an ideal free distribution when patches were equally profitable. When the patches differed in profitability in a ratio of either 2:1 or 5:1, the number of fish found in the low profitability area was as predicted. However, the number found in the high profitability area fell below that predicted, due to the presence of some individuals in the central area of the tanks. It is suggested that the latter individuals were found in the central area as a result of non-aggressive interference between individuals in the high profitability area. Finally, the marginal value theorem was used to predict the optimal patch residence time. The prediction was met in experimental tests at a group size of one, but at group sizes of two or five fish the observed time was significantly lower than that predicted.

The life-cycle of Rhipidocotyle campanula (Dujardin, 1845) has been experimentally demonstrated and the species identity confirmed. Sporocysts were recovered from digestive glands of the freshwater-mussel Anodonta anatina, and in heavily infected 'hosts from the reproductive, system. Both cercariae and glochidia are released simultaneously in mussels where the reproductive system is partly invaded by sporocyst tubules. The development of the cercariae in the sporocyst tubules has been studied briefly fusing histological and histochemical methods. The liberation of cercariae varied- between >1000/mussel/day to none, and is intermittent. Behaviour of the cercariae including swimming, response to light and gravity, survival and entry, into the secondary host, is described. The morphology of the cercaria has been studied in detail using electron microscopy, histochemistry and histological methods and its significance analysed in relation to free-living existence. This is the first attempt to study the cercaria of R. campanula in any detail. Cercariae enter the secondary host passively and encyst in the subcutaneous fatty tissue beneath the lining of the pharynx, and in some cases in the gill arches. This is the only species of bucephalids where cercariae enter the secondary host passively. Encysted metacercariae attain maximum development after 5-6 weeks and survive nearly 200 days, but spontaneous excystation takes place only in cysts 80-90 days old. Adult flukes were recovered from the posterior intestine and rectum of the perch (Perca fluviatilis) six weeks after feeding fully developed metacercariae. Spermatogenesis and oogenesis were studied in the adults until egg formation. Miracidial development could not be observed. External morphology using SEM of cercaria, metacercaria and adult has been studied and compared. This is the first report of SEM study of these stages of R. campanula. A brief review of the literature is given and the problems of systematics and taxonomy of the family Bucephalidae the taxonomic position of R. campanula are discussed.Tabular summaries are given for the previous life-cycle studies of bucephalids, synopses of bucephalid trematodes and all previous reports of bucephalid cercariae.

M.Sc. / At present large scale extensive cropping of fish populations of impoundments is being undertaken by the agricultural departments of the government of the Republic of Venda and selfgoverning states of Lebowa and Gazankulu. Parasitological surveys coinciding with the cropping program revealed that Clarias gariepinus (Burchell, 1822) and Oreochromis mossambicus (Peters, 1852) were infested by fish lice of the genus Dolops (Crustacea: Branchiura). A study was therefore initiated to examine the extent of these infestations and other impoundments in Transvaal were also included. A total of 14 localities in Transvaal extending from Bloemhof Dam in the Southwest to Luphephe and Nwanedzi Dams in the Northeast were surveyed during 1982 and 1983. At these localities fish were collected by means of gill nets, seining and electrofishing techniques. The collected fish were examined in a field laboratory at the collection localities for the presence of ectoparasitic Dolops. The fish were weighed and measured and the site of attachment of the parasites, if present, were recorded. The parasites were removed and fixed in either hot formalin or AFA. A number of parasites were transported alive to the laboratory in Johannesburg where they were kept in glass aquaria and their life cycle studied. A morphological description based on light microscopy as well as scanning electronmicroscopy of the eggs, larvae and adults were made, and comparative body dimensions of parasites from various localities recorded. It was found that only one species of Dolops that is D. ranarum (Stuhlmann, 1891) occurred in Transvaal. This parasite was found in only five of the 14 examined localities of which all were situated in Northern Transvaal, north of the watershed.

No description available.

No description available.

Fish meals, particularly British Columbia herring meals, and condensed herring solubles have been studied for their nutritive properties as supplements in poultry rations. Both commercially and experimentally prepared herring meals were used in the study. Protein quality in fish meals was investigated to ascertain what degree of variability exists in commercial samples and to obtain information regarding the effects of raw material, processing temperature and storage. On the basis of the Protein Index Values commercial fish meals appeared to vary in the quality of their protein content. Much of the variability amongst different meals could be ascribed to the nature of the raw material. Experiments were carried out in which herring meals prepared under controlled conditions from material of known origin were compared. It was shown that the value as a protein source for the growing chick of meals produced under a considerable range of drying temperatures was similar. Differences in the vitamin content of fish meal were found to be responsible for differences in the rates of growth of chicks fed herring meals which had been dried at high and low temperatures. With the basal rations employed, folic acid was the limiting nutrient when herring meal was used as the sole source of supplementary protein. The folic acid content of meals prepared from similar raw material was found to be markedly affected by the temperature at which the meals were dried. Chicks and poults fed rations formulated to be complete in the known nutrients grew at a faster rate when 2.5 to 5.0 percent of herring meal was added to the rations. It was concluded that herring meal contains a factor(s) not identified with any of the known vitamins. Condensed herring solubles was shown to be an effective vitamin supplement to practical type poult rations whether or not the ration contained herring meal. Extraction of the oil from herring meals did not improve the growth response of chicks to the use of the meals as protein supplements. Normal and extracted commercial flame-dried meal and experimentally prepared low-temperature-dried meal were compared in this regard. Storage of herring meals for one year at -25°, 21° and 37°, respectively, did not appear to affect the nutritive value of the meals as protein supplements for chick rations. Chemical changes did occur in the fat present in herring meals during storage. The amount of ether-soluble material decreased with the length of the storage period and the iodine value of the ether extract decreased. The addition to the meal of 0.15 percent butylated hydroxytoluene before storage prevented any decrease in ether extractability of the fat during a 9-month storage period and considerably reduced the drop in iodine value of the extract. / Land and Food Systems, Faculty of / Graduate

Both field and laboratory experiments have shown lethal effects from the deposition of silt on incubating salmon eggs. Because silting appears to deprive the eggs of sufficient oxygen, theoretical limits of flow and oxygen content of sub-surface water were studied. Data have been gathered on temperature, oxygen content, and rate of flow of water twelve inches below the surface of the gravel at Nile creek. Field determinations of oxygen consumption of pink, chum and coho eggs have been made. In heavily-silted portions of the bed there was an insufficient supply of oxygen for pre-eyed chum salmon eggs. A field method for determining oxygen content and apparent velocity of gravel water is presented. / Science, Faculty of / Zoology, Department of / Graduate