Fishery
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Browsing Fishery by Subject "Breeding"
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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 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 A Preliminary Note on the Breeding And Growth of Tilapia in Marine Fish Ponds On Zanzibar Island(1956/1957) Talbot, F. H.; Newell, B. S.The following notes describe an initial experiment in the stocking of marine fish ponds operated by the Organization with a species of wild Tilapia found in the estuarine reaches of the Mzinga Mzinga stream, at the north-western end of Zanzibar Island. This species had been collected twice previously from Zanzibar. It is closely allied to Tilapia mossambica (Peters) and to Tilapia pangani Lowe, being fairly similar to the latter but differing from it in the lateral line scale count. It is possibly a distinct species, and Dr. Trewavas of the British Museum is working on its systematic position.Item A study of the fecundity of some mormyrid fishes from lake Victoria(1970) Okedi, J.; East African Freshwater Fisheries Research Organization, Jinja, UgandaThe need for a rational exploitation of the fish stocks in the Lake Victoria Basin has, during recent years, necessitated further investigation of the breeding potential of the species of commercial importance. Because of their greater commercial importance in East Africa, the fecundity of species belonging to the families Cichlidae and Cyprinidae is better known than that of the Mormyridae. Lowe (1955) has described the breeding potential of a number of Tilapia and Cadwalladr (1965) has published some notes on fecundity in the cyprinid fish, Labeo victorianus Boulenger.The only available reference to fecundity in the Mormyridae, is that of Nawar (1959b), who made some observations on Hyperopisus bebe Lacepede from the Nile. Although members of the Mormyridae at present make up a relatively small part of the total landings offish from Lake Victoria, the group is nevertheless becoming one of increasing commercial importance to the fishery of the affluent rivers, Okedi (1966).
