Fishery
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Item The Bulb Eelworm Disease of Narcissus in Kenya(1950) Nattrass, R.M.The Bulb Eelworm disease of Narcissus species has long been the cause of serious loss Europe. It has only recently (1949) been recorded in Kenya. In appearance the disease symptoms are similar to those usually associated with fungi or bacteria. It is, however caused by an elworm Anguillulina dipsacngItem The Cladocera of the Zanzibar Area of the Indian Ocean, With a Note on the Comparative Catches of Two Plankton Nets(1968) Wickstead, J. H.Three species of Cladocera are recorded from the Zanzibar area of the Indian Ocean, Pen ilia avirostris, Evadne tergestina and Podon polyphemoides; this last species was rarely taken. Two nets were worked at three stations for 13 months. Figs. 1 and 2 show the incidence of Pen ilia in the plankton, Figs. 4 and 5 the incidence of E. tergestina. Fig. 6 shows these two species as a percentage of the total plankton numbers during their periods of abundance. Fig. 3 shows the temperature conditions at the three stations. "Explosive" populations of Penilia are discussed, with the suggestion that a combination of the 0 0 content of the water and inherent progressive degeneration of parthenogenetic females are the limiting factors of a population. The coincidence of heavy diatom and Penilia populations is noted, with the suggestion that the former supplies 0" for the latter. Catches of two nets are compared. The CF 70 catches about 10 per cent less Pen ilia and about 20 per cent less E. tergestina per unit volume of water than the J.C.S.N., this latter being therefore the more efficient net under the conditions in which they were used.Item Conference on land management problems in areas containing game Lake Manyara, Tanganyika(1961) Pereira, H. C.; E.A.A.F.R.O., Muguga, KenyaThis group of admirably short and factual papers by members of the East African Veterinary Research Organization was introduced by Mr. Brocklesby, who began by stating firmly that the veterinary profession were not prejudiced against game: they did not believe that elimination of all game would eradicate any of the main cattle diseases from East Africa.Item The Culture of Carp (Cyprinus Carpio L.) In Ponds in Uganda: Preliminary Observations On Growth And Reproduction(1960/1961) Wurtz, A.G.; Simpson, C.J.H.; Food and Agriculture Organization ; Game and Fisheries Department, UgandaThe use of Tilapia as a culture fish throughout East and Central Africa is well known (Chimits 1955, 1957; De Bont et af. 1948; DeBont 1949, 1952). Tilapia have been extensively cultured in fish ponds at the experimental fish farm at Kajansi, near Kampala, since 1953. Monocultures of Tilapia present difficulties in management owing to their specialized food habits. Tilapia reach maturity in fish ponds at the age of between three to six months. Thereafter their growth rate slows appreciably and the reproductive cycle becomes rapid and continuous; this leads to overpopulation in the ponds. Various ways of overcoming these disadvantages have been suggested. They include monosex culture (De Bont and Hers 1950, Brown and Van Someren 1953; Van Somerenand Whitehead 1959) and the introduction of Predatory fish into the ponds (work in progress at Kajansi). It will take time to evaluate the Results and to design suitable techniques of management that can be adopted by African Peasant farmers. The problem of finding a pond fish to supplement the Tilapia under Uganda conditions is urgent, due to the fact that over 5,000 fish ponds have been built by Africans in the last few years.Item The Culture of Tilapia Nigra (Cunther) in Ponds IV-The Seasonal Growth of Male T. Nigra(1960) Someren, V.D.; Whitehead, P.J.The growth rate of male Tilapia nigra is neither constant throughout life, nor from month to month. It decreases asymptotically in length as the fish grows older, and varies from month to month according to fluctuations in external environmental conditions, weight being more affected than length in the latter instance. The most important external factor is undoubtedly the water temperature at which the fish live; rises and falls in mean temperatures of only a few degrees causing marked increases or decreases in weight achieved, respectively. Water temperature is in itself much affected by other weather conditions, and is not necessarily maximal in months of maximum sunshine owing to increased wind speeds and evaporation rate in such months. Rainfall may in itself also affect fish growth directly, though this is not fully established yet. In the environmental conditions present at Sagana, male T. nigra show two good growing periods and two poor growth periods every year.Item The Culture of Tilapia Nigra (Gunther) In Ponds Growth after Maturity in Male T. Nigra(1959) Someren,V.D; Whitehead,P.JFish cultural research at the Inland Research Station of this Ministry, at Sagana, has been concentrated mainly on the factors affecting the growth of T. nigra under controlled pond conditions.Item The Culture of Tilapia Nigra (Gunther) In Ponds Part Viii-The Effect of Cropping a Breeding Population by Trapping(1962) Vernon, D.In Part VI of this series the effect of selective cropping of a mixed breeding population of T. nigra in three different ways was described. In those experiments cropping was carried out by monthly seine netting with a t in. mesh nylon seine, and selection was effected by hand sorting the fish in one haul. The three methods employed were: (a) removal of all large fish, returning fry alive; (b) removal of only colored males, returning all females, immature males and fry alive; and (c) removal of fry only, returning all large fish alive. The results, which were different in each case, showed a profound effect on both the periodic crop taken and the final yield on draining.Item The Culture of Tilapia Nigra (Gunther) in Ponds V - The Effect of Progressive Alterations in Stocking Density on the Growth of Male T. Nigra(1960/1961) van Someren, V.D.; Whitehead, P.J. ; Fish Division (Research), Ministry of Forest Development, Game and FisheriesExperiments have shown that depression of growth always results with unfed fish in untreated ponds when the population density is increased, whether the density is increased at one time, or successively increased at short term intervals. The limiting factors are probably food supply available in the first place, but behaviour patterns of shoaling in themselves probably also introduce growth limitation by competition for feeding space. When, however, several different size groups of fish are stocked simultaneously, they do not affect each other's growth rate, and when two size groups of fish are stocked successively at much longer term intervals again depression of growth is not so marked. Generally, however, growth of male T. nigra shows great plasticity, and even at large sizes and long after maturity, such males can respond by increased growth to decrease in stock density, though there is an increasing limit to length increment possible as the fish grows larger; but this is offset by the fact that in larger fish small length increments correspond to considerable weight increase. The fattening of runted fish from overstocked conditions is entirely practicable when these can be given improved growth conditions by stock reduction.Item The Culture of Tilapia Nigra (Gunther) in Ponds VI-The Effect of Selective Cropping Methods on Breeding Populations(1960/1961) van Someren, V.D.; Whitehead, P.J.; Ministry of Forest Development, Game and Fisheries, Kenya ColonyIt is shown that cropping only large fish from a mixed breeding pond will in time lead to a diminution in availability of such large fish, not only because they have been cropped, but also because it leads to a greater survival of fry, which in turn leads to a denser population and therefore less growth of individual fish. The larger of the fry left under such cropping will never attain the former size of original stock fish. By contrast, cropping of fry only, leads to much greater total weight yields, though the majority of fish taken are of relatively useless trash size. It also leads, however, to a greater increase in size of the larger fish left. Cropping of mature males only on the basis of breeding colouration, these to be used for fattening in monosex ponds elsewhere, can be carried on perhaps for very long periods, since as breeding males are removed, so others colour up to take their place. Indications are that up to 44 coloured males per acre per month could thus be cropped, and such cropping does little more than reduce the normal preponderance of males in the normal sex ratio to parity with females. It probably leads also to higher fry production, and thus more males still over a long period. For the culture of good sized Tilapia nigra, therefore, a two-pond technique is recommended. In one of these, mixed breeding is allowed to occur freely; from this mixed pond, mature males are removed periodically on the basis of breeding colouration, and these are then fattened separately for marketing or consumption in another pond in which such males only are kept in monosex culture.Item The Culture of Tilapia Nigra (Gunther) In Ponds VII-Survival and Growth of Tagged and Untagged Males of Different Sizes(1961) van Someren, V.D.; Whitehead, P.J.Individual tagging of fish of sizes from 13.0 cm. upwards does not have any effect on either their subsequent growth rate or survival. Tagging of fish as small as 7.5 cm., however, appears to affect adversely both their chances of subsequent survival and their growth rate if environmental conditions are not optimal.Item The Culture of Tilapia Nigra (Günther) in Ponds: IV—The Seasonal Growth of Male T. Nigra(1960/1961) van Someren, V.D.; Whitehead, P.J.; Ministry of Forest Development, Game and FisheriesThe growth rate of male Tilapia nigra is neither constant throughout life, nor from month to month. It decreases asymptotically in length as the fish grows older, and varies from month to month according to fluctuations in external environmental conditions, weight being more affected than length in the latter instance. The most important external factor is undoubtedly the water temperature at which the fish live; rises and falls in mean temperatures of only a few degrees causing marked increases or decreases in weight achieved, respectively. Water temperature is in itself much affected by other weather conditions, and is not necessarily maximal in months of maximum sunshine owing to increased wind speeds and evaporation rate in such months. Rainfall may in itself also affect fish growth directly, though this is not fully established yet. In the environmental conditions present at Sagana, Male T. Nigra show two good growing periods and two poor growth periods every year.Item Dagaa fisheries in lake Tanganyika(1954) Lockley, G. J.; Department of Agriculture, Tanganyika TerritoryThe dagaa industry of Lake Tanganyika is the Territory's most valuable inland fishery. The small sardine-like dagaa are marketed in a sun-dried form and this product is in great demand by employers of fed labour, particularly in the sisal industry. Over the past few years, sales of the value of exports of dried dagaa from the Lake Tanganyika area has been of the order of £150,000 per annum and approximately one-third of this amount is usually obtained in hard currency from sales to the neighboring Belgian Territories. On the production side the industry is entirely in the hands of Africans and at least 6,000, using upwards of 2,000 canoes, are believed to be engaged in the fishery.Item The dam fisheries of Tanzania(1966) Bailey,R. G.; Ministry of Agriculture, Forests and WildlifeDams constructed for domestic and agricultural purposes in Tanzania have been successfully stocked with fish. The geographical distribution of dams is discussed with some consideration of their physical, chemical and biological characteristics. The use of Tilapia in stocking dams is described together with the present distribution of these and other self-stocked species. A review of the fisheries exploitation of dams in Tanzania is made and a few estimates of the annual crops from dams are presented.Item Development of Fish Farming in Uganda(1966) Stoneman, J.The Uganda Fisheries Department as a technical branch of the Game Department, was first established in 1949. Much of the early work was directed to the major lakes and rivers of Uganda, but even then interest in Fish Farms was increasing. Then, as now, protein deficiencies in the food of Ugandans were a subject of concern, and while the fish production from major lakes was being increased to help alleviate the problem, it was clear that for some time to come communication and marketing difficulties would hamper fish sales in many regions. Fish farms and ponds sited near the final consumer offered an obvious way around transport difficulties while large areas of Uganda offered suitable terrain and water supplies for fish ponds. Ponds could utilize otherwise worthless land, and family ponds, dug by farmers and their families as a spare time activity, would represent a "bonus" investment of manpower and time which might otherwise be frittered away. Finally, in certain difficult areas, such as north-west Uganda, the fish farm might produce a cash crop, badly needed in the area.Item Diagnoses and Key to the Juveniles of Tilapia (Pisces, CichliDae) In Lake Victoria(1964) Welcomme, R.L.Recent introductions of Tilapia species into the La~e Victoria basin have aggravated the problem of identification of the morphologically similar young fish of the genus which tend to occur together in similar habitats. Eight species, viz. T. nigra, T. nilotica, T. zilli, T. melanopleura, T. leucosticta, T. mossambica, T. esculenta and T. variabilis are now known from the basin of which only the last two occur naturally. Diagnoses of each species are provided, with a key to identification at the juvenile stage. Some remarks are added on the present habitats of both endemic and introduced species.Item The families of freshwater fishes of Tanganyika Territory, with a key to their identification(1949) Lockley, G. J ; Department of Agriculture, TanganyikaEvery specimen should be accompanied by a label giving details of locality, altitude, date, method of capture, sex (if known) and any other relevant items such as the colour of the fish in life. Such labels are best written on unsized paper with a 2B pencil or on parchment paper with waterproof Indian ink.Item The Fecundity of Tilapia Species(1956) Rosemary, H. L.Fecundity has been defined as the number of young produced by an individual during its lifetime. Factors influencing fecundity are: length of breeding season, frequency of spawning during a breeding season, the number of eggs laid at a spawning. and the care taken of eggs before and after hatching. 2. According to whether they care for their young outside or inside the mouth, Tilapia can be classified as "guarders" or "brooders". Generally, guarders produce many small eggs and brooders fewer, large ones. 3. Only four species are known to be guarders: T. sparrmani. T. guillasalla. T. melanopleura and T. zillii. The remainder are brooders. 4. Due to the different breeding biology of the two groups, the fecundity of guarders depends upon the number of paired fishes, whereas in brooders it is determined by the number of ripe females. 5. In the genus Tilapia. evolution appears to have been towards a reduction in the number of eggs produced, and towards the development of a brooding habit.Item Fishery research in the lakes of East Africa(1954) Beauchamp, R. S. A.; East African Fisheries Research Organization, UgandaFishery research is the study of fish in relation to their environment; little can be learnt about them until we have a fair knowledge of the conditions in which they live. The need for this knowledge is made very obvious to the biologist working on inland fisheries. Forxample,the same species of fish occur in anumber of East African lakes, in some theygrow to a considerable size. weighing several pounds, while in others they never exceed afew ounces in weight. No explanation of these facts is likely to arise from investigations confined solely to the study of the fish themselvesItem Fishes of the Genus Tilapia (Cichlidae) In Tanzania, With a Key for their Identification(1968) Bailey, R. G.By virtue of their interesting biology and importance in the development of inland fisheries, Tilapia have received considerable attention from both scientists and fisheries workers in Africa. In Tanzania, where they are widely acceptable as food, Tilapia are found in many lakes and rivers, making in some areas the largest contribution to the commercial catch. They have also been used for pond culture and for stocking, in attempts to broaden certain existing fisheries and to establish new ones in small lakes and dams.Item Fishes taken by purse - seine and dip net in the Zanzibar channel(1966) Losse, G. F.Two commercial fisheries exploit the pelagic fishes in East African coastal waters. Both are confined to the Zanzibar Channel, a shallow water bank extending from the Pangani Estuary (Latitude 50 26' S.) in the north to Dar salaam (Latitude 60 49' S.) in the south. Asardine purse-seine fishery was introduced into this area by Greek fishermen during 1961(E.A.M.F.R.O. Annual Report 1961), laser tuna seining was developed (E.A.M.F.R.O. Annual Report 1963). Japanese dip nets, or boke ami, came into operation off Dar es Salaam in 1964.Both sardine seining and dip netting depend essentially on the attraction of pelagic fish shoals to a source of artificial light at night; the tuna seine exploits the larger surface shoaling species during the hours of daylight
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