The Aquatic Commons is a thematic digital repository covering the natural marine, estuarine /brackish and fresh water environments . It includes all aspects of the science, technology, management and conservation of these environments, their organisms and resources, and the economic, sociological and legal aspects.
Subject = Fisheries
Mostrando recursos 1 - 20 de 12,849
Fish exploitation and changes in the fish community of Lake George, Uganda - Kamanyi, J.R.
Unlike Lake Victoria, the fisheries of Lake George have undergone gradual changes in the size and proportion of the major commercial fish species, the Nile tilapia (Oreochromis niloticus: cichlidae) in the last 40 years (1950-1989). The size decreased from an average weight of 900g in 1950 to 430g in 1989 while percentage contribution in commercial catches during the same period declined from 92% to 36%. The over all annual commercial catches though showed a steady increase from the period 1950 when the fishery was opened to intensive and controlled exploitation, consistently high catches were observed in the 1960s and 1970s...
A conceptualized fishing system for the African environment with a comparative approach - Ita, E.O.
The paper examines a conceptualized fishing system for the African Environment with a comparative approach. Although the fishing system has been conceived as a bio-economic complex, emphasis will be given to the explanation
of the detailed structure and functioning of the system. Subsequent synthesis involving the use of existing relationships for management etc. will also be undertaken. The proposed fishing system is conceptually feasible in an ideal environment with adequate monitored data and organized fishing, however it is anticipated that the African environment will not satisfy such conditions.
Key for the identification of the East African marine fishes to family level - Matthes, H.
The paper provides key for the identification of the East African marine fishes. Just like in most determination keys this one is based on the "either-or" principle, i.e. there is a single alternatIve at each point. A specimen either fits all the characters recorded, or fails to conform to one or more characters and you should then proceed to the next number, keeping this up until the fish to be identified does fit all the characters.
Preliminary observations on the feeding of Tilapia nilotica Linn. in Lake Rudolf - Harbott, B.J.
Tilapia nilotica is commercially very important throughout the Ethiopian region including the major rivers in West Africa, the Chad basin, the Nile and its associated
lakes. The Tilapia fishery of Lake Rudolf is at present small, but potentially important, particularly on the eastern shores of the lake where fishing intensity is low.
Preliminary results from observations on the feeding of Tilapia nilotica in Lake Rudolf are presented. The fish exhibit a regular diurnal feeding rhythm, commencing
between 05.00 hours and 08.00 hours and ceasing between 14.00 hours and 18.00 hours. The largest fish appear to feed longer. Quantitative estimates of the daily food
Comparative electrophoretic patterns of lactase dehydrogenase and malate dehydrogenase in five Lake Victoria cichlid species - Basasibwaki, P.
Biochemical techniques designed to compare species on the basis of protein differences were started by NUTTALL (1904) who used immunological methods to compare the serum of humans with that of other primates. Since then more refined techniques have led to better results at the protein level in taxonomy, The analyses of proteins are considered to be the simplest indirect approach to understanding the structure and function of the genetic material, deoxyribonucleic acid (DNA). Interest in these analyses
arises because of the close relationship between protein structure and gene structure. Thus by comparing the properties of homologous proteins from different taxa one...
Fish tagging experiments: a prelude to an extensive tag-recovery programme on Lake Victoria - Rinne, J.
The present study is an early stage of this programme and examines several species of fishes under controlled conditions to delineate responses to tagging as a function
of type of tag, species, size, and sex of fish, and position of tag placement. It is intimately related to another phase of research currently being conducted by the
author on age and growth of several species important to the fishery of Lake Victoria (e.g. Tilapia spp., and several catfishes, Clarias mossambicus Peters and Bagrus
docmac (Forskal). Data reported are both a reflection of growth studies and an attempt to achieve insight into tag loss, growth,...
A note on some parasites of Merluccius capensis (Pisces) and their zoogeographical significance - Meyer-Rochow, V.B.
During the Southeastern Atlantic Expedition of the German fishery research vessel "Walther Herwig" in 1967 the main emphasis lay on selective fishing of the South African
hake Merluccius capensis (von BRANDT 1967). Some of the fish were found to be infested by ecto-and endoparasites both of which were collected whenever possible. Large plerocercoids of Dibothriorhynchus grossum whose adult stage lives in the South Atlantic Ocean in Lamna cornubica (L.SZIDAT, personal communication) were quite common as were cysticercoids of a Tetrarhynchus sp., which had also been reported in Cynoscion striatus off the Argentinian
coast (MACDONAGH 1927, cited in Szidat, personal communication). Brownish nematodes...
The rediscovery of Notopoides latus Henderson in the western Indian Ocean (Crustacea-Decapoda, Raninidae) - Bruce, A.J.
The small brachyuran family Raninidae Dana is represented in the Indo-West Pacific region by eight genera, with only some twenty species. One of the least known genera is Notopoides, which contains only a single species. This genus was first described by Henderson (1888) on the basis of material collected by H.M.S. "Challenger" from the Kei Islands, in the Banda sea off Indonesia.
There have been no subsequent reports of this species in the ninety seven years since its original discovery.
During the course of the study of the benthic fauna off the coast of East Africa, the Fisheries Research Vessel "Manihine" obtained...
Improved facilities for marine biology in East Africa - Hartnoll, R.G.
In 1967 the then University College of Dar es Salaam built a small laboratory on the shore at Kunduchi, 16 km from the
main campus and 24 km north of Dar es Salaam. This was used for undergraduate field courses, and as a base for staff from the University to carry out research. It soon
became apparent that the urgent need for studies of the marine environment in the East African area, and the lack of existing facilities, necessitated the development of the Kunduchi Marine Biology station into a research establishment with its own staff of full time scientists. This operation began...
Possible fish stock size assessment and available production survey as developed on Lake Kariba - Balon, E.K.
This paper is an outline of methods practically useful for the evaluation of ichthyomass, fish abundance, available production and yield in lakes and rivers.
Terms and concepts are reviewed, and difficulties stemming from the use of "predetermined" mathematical models are discussed. Sampling with toxicants in blocked-off areas was found to be the most practical method and is described in detail. For the total estimation of ichthyomass the spatial ranges of fish distribution must be determined; the results of echo-sounding surveys for horizontal, vertical, topographical, seasonal and diel fish distribution are given.
Some of the most important methods for computing available production are...
Observations on the biology of Nothobranchius guentheri (Pfeffer) (Cyprinodontidae), an annual fish from the coastal region of East Africa - Bailey, R.G.
Nothobranchius guntheri is found in seasonal pools and streams in the coastal region of Tanzania. A population recurring annually in a pond near Kilosa has been studied. Growth in length was rapid and maximum mean lengths were attained within 11-12 and 7-8 weeks of hatching by
males and females respectively. Males grew larger and exhibited wider variation in length than females. N. guentheri shows clear sexual dichromatism.
No significant inequality in the sex ratio was found. Females with ripe eggs were found 7-8 weeks after hatching. Spawning continued throughout adult life and fecundity increased markedly with increasing length. In laboratory aquaria, aggressiveness...
Observations on the influences of codend mesh size on bottom trawl catches in Lake Victoria, with emphasis on the Haplochromis population - Cordone, A.J.; Kudhongania, A.
Codends of four different mesh size" were compared during exploratory bottom trawling on Lake Victoria. Small mesh sizes (19 and 38 mm) generally caught greater quantities of fish than large mesh sizes (64 and 76 mm) with haplochromis species responsible for the difference. The differences in catch rates were most pronounced where dense concentration of small haplochromis were found. This was generally in shallow water since the average size of haplochromis tends to increase with depth. Catch rates for species other than haplochromis were fairly similar for the codends tested, although there were indications of lower catches in small mesh...
Relationship between the water levels and the fish catches in lakes Mweru and Mweru wa Ntipa, Zambia - Williams, R.
The relationships between water level and catch per effort in two Zambian lakes are compared. In the relatively stable Lake Mweru, a positive correlation exists which can be used, with certain reservations, to predict the state
of the fishery two years in advance. The cause of the relationship is probably the effect of water level on the marshy and swampy breeding areas, where at least the most common species in the commercial catch (Tilapia macruchir) has definite limits for the depth of water in which it
will breed. For Mweru wa Ntipa, a consistant definite relationship does not exist, probably because the...
The commercial fishery of Lake George, Uganda (East Africa) - Dunn, I.G.
A shallow, highly productive, tropical lake is descrihed with a brief history of its commercial fishery. Three separate assessments of the present (1967-1970) yield are compared, with an apparent confirmation of the values derived from Fishery Department statistics over a period of 20 years.
The seasonal change in the catch is noted with, an apparent anomaly shown by ohservations of canoe landings. Long-term trends during the period 1950-1969 are considered with a brief discussion of possible future trends in the fishery.
The future prospects of the fish stocks of Lake Victoria, Uganda - Okaronon, J.O.
Experimental trawling during the period 1981/86 and analysis
of past commercial catch landings, mainly in the northern portion of Lake Victoria have indicated that the standing stocks and therefore, the estimates of sustainable yields of the most important fish species have unquestionably changed since the 1969/71 comprehensive lake-wide stock assessment survey.
Lake Victoria which was originally a multi-species fishery
now relies on two introduced species (Lates niloticus and
Oreochromis niloticus) and one indigenous cyprinid
(Rastrineobola argentea). Most of the traditional fish species, including the once dominant haplochromines, have either declined or disappeared. The catch rates in the experimental trawl catches declined from 797 kg/hr in...