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Aspects of the biology of the Lake Tanganyika sardine, Limnothrissa miodon (Boulenger), in Lake KaribaAfrican Journal of Tropical Hydrobiology and FisheriesJuveniles of limnothrissa miodon (Boulenger) were introduced into the man-made Lake Kariba in 1967-1968. Thirty months of night-fishing for this species from Sinazongwe, near the centre of the Kariba North bank, from 1971 to 1974 are described. Biological studies were carried out on samples of the catch during most of these months. Limnological studies were carried out over a period of four months in 1973. Limnothrissa is breeding successfully and its number have greatly increased. It has reached an equilibrium level of population size at a lower density than that of Lake Tanganyika sardines, but nevertheless is an important factor in the ecology of Lake Kariba.The growth rate, size at maturity and maximum size are all less than those of Lake Tanganyika Limnothrissa. A marked disruption in the orderly progression of length frequency modes occurs in September, for which the present body of evidence cannot supply an explanation.
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Nutritive value of fishes of Lake Tanganyika: II. Mineral compositionAfrican Journal of Tropical Hydrobiology and FisheriesThe composition of the minerals in three economically important fish species of Lake Tanganyika was determined. From the analyses there does not appear to be significant difference in the composition for the three species. Beside the major elements: Ca, P, K, Na, Mg, Cl, Fe, Al and Zn, eighteen trace elements were determined. The presence of the bones in the fish is especially nutritionally importantfor the following elements: Ca, P, Br, Sr, Mn and Mg.
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The taxonomy of the genus Synodontis (Pisces: Siluroidea) in Lake Kainji, NigeriaAfrican Journal of Tropical Hydrobiology and FisheriesThis paper considers the taxonomy of most of the synodontis spp. present in the main drainage basins of West Africa. The first section consists of a key to the sixteen species known to occur in Lake Kainji. Nigeria. A second section considers species which are reputed to live in the area and thereforemight occur in the lake. It is suggested that several of the latter group are synonymous with better known species.
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The role of macrophytes in the economy of the lower Sondu-Miriu river of Lake VictoriaAfrican Journal of Tropical Hydrobiology and FisheriesThis paper highlights the results of a 12 month's ecological study of macrophytes and their role in the economy of the lower Sondu-Miriu river of Lake Victoria. A total of 34 species of aquatic macrophytes were identified. These were grouped as emergent, floating leaved, free floating and submersed. The major community type identified were dominated by Cladium jamaicanse (Crantz) Kurk., Cyperus paprus (L.) and Cyperus latifolius (Poir). The study observed an over dependence on macrophytes by the local community for the supply of bedding, grazing fields, fuel, roofing and other building materials. The white (heart) of Typha shoot, Nile cabbage (Pistia stratiotes and a legume solanum nigrum traditionally known as "osuga" are used as vegetables by local community. The only source of protein in this arid region is the fish caught in the swamps and birds which inhabit the swamp. The swamp provides the only source of green pasture in the dry season for the animals. An export oriented economy has developed involving mat making and basket weaving with exports reaching as far as Japan. The study proposes a rational and sustainable exploitation of the littoral zone to support the adjacent rural community.
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A note on the commercial and sport fishing for some of the major scombroid fishes and wahoo on the Kenya coastAfrican Journal of Tropical Hydrobiology and FisheriesCommercial seerfish and wahoo catches were examined monthly during 1973 and 1974 at Malindi fish market where also fishfrom Ngomeni, Nambrui, Watamu and Kilifi were landed. Annual commercial catch data was compiled from Kenya Government Fisheries records at Malindi for 1973 and 1974. Sport fishing data was compiled from Angling Club log books at Bakari and outrigger clubs at Mombasa.
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Movements of haplochromines (Pisces: Cichlidae) in Lake George, UgandaAfrican Journal of Tropical Hydrobiology and FisheriesIn Lake George, the abundance of haplochromines in inshore regions during the day and at night differs significantly. Futhermore, while by day there are more haplochromines in the lower than the upper layers, at night these fishes appear to be uniformly distributed throught the water column. Regions of the lake near river mouths had fewer haplochromines during the wet than the dry season, while the reverse was true of regions distant form the river mouths. Possible causes of these movements are discussed.
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Plankton identified in stomach contents of Oreochromis niloticus (Pisces, Cichlidae) and the water system of Lakes Edward, George, and Kazinga channel - UgandaAfrican Journal of Tropical Hydrobiology and FisheriesThe samples were collected from Lake Edward at Rwenshama, Kisenyi and Katwe, and from Lake George at Mahyoro, Kashaka and Kasenyi and in Kazinga Channel at Katunguru. The organisms identified from the water samples obtained irrespective of station or depth were mainly the phytoplankton (diatoms, blue-green algae and green algae). Of the phytoplankton, blue green-algae were the mostabundant both in quantity and number of species especially in L. George. In order of importance were Microcystis spp,Planktolyngbya spp and Anabaenopsis spp were the dominant blue greens. Diatoms and green algae were present but less abundant. The estimated proportions of different types ofphytoplankton identified in O. niloticus stomach contents indicate that bluegreen algae were the most abundant followed by the diatoms and green algae.
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The potential of Nakivubo swamp (papyrus wetland) in maintaining water quality of inner Murchison bay - Lake VictoriaAfrican Journal of Tropical Hydrobiology and FisheriesNakivubo swamp (papyrus wetland) is located in the south east of the city of Kampala, Uganda. This swamp has been receiving waste water from Nakivubo channel for more than two decades. This investigation was aimed at monitoring the level of pollutants (nutrients and faecal coliforms) as the waste water filtrates through the swamp and the flow patterns of waste water through the swamp.From this preliminary investigation it was found out that the waste water is not evenly distributed over the swamp. Also high levels of pollutants seem to filtrate through the swamp and enter Inner Murchison Bay - Lake Victoria. Further research is under way to investigate in more detail the capacity of Nakivubo swamp to remove nutrients/pollutants from waste water flowing through it and the dominant mechanisms/processes involved.
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Current composition, distribution and relative abundance of the fish stocks of Lake Victoria, UgandaAfrican Journal of Tropical Hydrobiology and FisheriesAn experimental bottom trawl survey was carried out in the Uganda sector of Lake Victoria during the period May 1993 through May 1995 with the aim of establishing the current composition, distribution and abundance of the fish stocks. A total of 205 successful one-hour hauls were taken using the 25.4mm mesh size codend trawl net during the 19 cruises. Fourteen fish taxa (excluding the haplochromines) were recorded with Lates niloticus constituting the bulk (97 %) of the fish retained. Haplochromines and L. nilolicus were encountered in all areas sampled while Nile tilapia (Oreochromis niloticus) and other tilapiines were restricted to waters less than 20 metres deep. An average catch of 154 kg/hr was obtained in waters less than 30 metres deep. Species diversity and relative abundance varied with depth. Only two of the fifteen fish taxa (haplochromines and L.niloticus) were recorded in waters deeper than 30 metres and the bulk of the fish by weight (92 %) was obtained in waters less than 30 metres.
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Growth rates of juvenile Nile perch, Lates niloticus L. in lakes Victoria, Kyoga and NabugaboAfrican Journal of Tropical Hydrobiology and FisheriesThe growth rates of Nile perch, Lates niloticus L. of 20 cm to 40 cm total length were estimatedin lakes Victoria and Kyoga in 1991 and 1992 and Nabugabo in 1992 and 1993 by tagging. Fishgrew faster in Lake Kyoga (mean growth rate 28.7 ± 1.3 cm S.E. per year, N = 49) than in LakeVictoria (18.9 ± 1.4 cm per year, N = 20) and Lake Nabugabo (19.0 ± 0.7 cm per year, N = 43).There were significant differences in growth rates between the lakes (F2 109 = 24.037, P < 0.001).Growth rates in Lake Kyoga were significantly higher than those of lak'es Victoria and Nabugabo(p < 0.001) but those of lakes Victoria and Nabugabo were not significantly different from eachother (p = > 0.05). The faster growth rates in Lake Kyoga were attributed to improvement in foodsupply due to increases in stocks of haplochromine prey. Growth rates in Lake Kyoga were significantly higher, but those of lakes Victoria and Nabugabo were within the ranges of those reported in several native habitats of Nile perch.
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Studies on induced breeding of Clarias gariepinus (Burchell, 1822) in hapa pensAfrican Journal of Tropical Hydrobiology and FisheriesInduced breeding of Clarias gariepinus was conducted monthly in hapa pens, set up in Otamiri river for nineteen months (June 1993 - December 1994). Results of natural fertilization were unsatisfactory as few eggs were fertilized. Mean relative fecundity, percentage fertilization, percentage hatching and percentage fry survival were: 15.86 ± 1.95 x 10', 18.92 ± 5.28%, 13.50 ± 3.8% and 6.42 ± 0.72%. Results from artificial fertilization were as follows:Mean relative fecundity, 13.80 ± 2.85 x 10', percentage fertilization, 81.91 ± 2.28%, percentage hatching, 86.10 ± 2.46% and percentage fry survival, 21.40 ± 1.89% respectively. The success of artificial fertilization depended largely on the latency period of 9-11 hours and this suggests that induced breeding in pens is feasible. The poor results from natural fertilization were attributed to lack of adequate substrate for the male fish to display courtship and subsequent fertilization of eggs.
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Analysis of competition in the wholesale and retail markets for fish in Kisumu, KenyaAfrican Journal of Tropical Hydrobiology and FisheriesThis study analyses competition in the wholesale and retail fish marketing system in Kisumu, which is Kenya's largestfish market. It is based on cross sectional and time series primary data collected in a survey involving 88 retailers and 47 wholesale traders of fish in the town. Stratified random sampling method was used in selecting the respondents, Concentration ratios, Lorenz curves and Gini coefficients are derived and evaluated for both markets. They demonstrate that market shares are unequally distributed among the wholesalers and retailers. The Gini coefficients are 0.37 and 0.45 for the whole and retail markets respectively.Based on a Gini coefficient cut-off level of 0.4, it is concluded that the wholesale fish market exhibits effective competition while the retail outlet has oligopolistic tendencies. The implication of this level of competition to price efficiency is discussed. Intervention measures to enhance competition in the market are recommended.
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Fishery methods and fish diversity in the Kilombero River in south-eastern TanzaniaAfrican Journal of Tropical Hydrobiology and FisheriesAssessment of common fishery methods and of fish diversity was undertaken in two fishing camps on the Kilombero Riverin south-eastern Tanzania in surveys towards the end of the dry season, 1994. Fishermen identified 23 different types offish that they caught on a regular basis. Only 19 species of fish, belonging to 17 genera and 11 families were, however, identified according to Linnean taxonomy. Hooks, nets, traps and spears were used to catch fish. Fish were either sold fresh. or preserved for storage and long-distance tranport by smoking or frying. based un frequency distributions of the numbers of fish landed over a 4 day period at one of the camps, a Shannon-diversity index of 1.95 was calculted. The fork (or total) length of 480 fish and the weight of 413 fish were measured and length frequency distributions as well as length-weight relationships determined for the six most common species. It is concluded that local fishing methods applied in the Kilombero River allow for sustainable fish production.
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The distribution and concentration levels of trace metals in water and sediments of Lake Victoria, KenyaAfrican Journal of Tropical Hydrobiology and FisheriesThe water and bottom sediments of Lake Victoria (Kenya) were analysed for A1, Fe, Mn, Zn, Pb, Cu, Cr and Cd. The total metal concentrations were determined and their mean variations and distributions discussed. The bottom lake waters showed higher concentration levels than the surface waters. The range of values (in mg/l) in the bottom and surface lake waters were as follows:Surface Waters: A1(0.08 - 3.98), Fe(0.09 - 4.01), Mn(0.02 - 0.10). Zn(0.01 -0.07),Pb(0.001- 0.007), Cu(not detected - 0.006), Cr(not detected - 0.004).Bottom Waters: A1(0.1 0 - 6.59), Fe(0.23 - 9.64), Mn(0.04 - 0.39),Zn(0.01- 0.08), Pb(0.002 - 0.009), Cu(not detected - 0.03). Cr(not detected -0.002).River mouths and shallow areas in the lake showed higher total metal concentrations than offshore deeper areas. Apart from natural metal levels, varied urban activities and wastes greatly contribute to the lake metal pollution as shown by high Pb and Zn levels in sediments, around Kisumu and Homa Bay areas. Other comparatively high values and variations could be attributed to the varied geological characteristics of the lake and its sediments. Compared to the established W.H.O (1984) drinking water standards manganese, aluminium and iron levels were above these limits whereas zinc, lead, chromium, copper and cadmium were below.
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Helminth fauna of Oreochromis leucostictus (Pisces: Cichlidae) from a tropical lake, Lake Naivasha, KenyaAfrican Journal of Tropical Hydrobiology and FisheriesThe helminth fauna of Oreochromis leucosticus (Trewavas) from Lake Naivasha is described. The study was carried outon 1,050 gillnetted fish caught over a period of 24 months at different sites within the lake. Oreochromis leucosticuswhich is a commercially important fish was observed to be a host of four helminth parasites. These were anacanthocephalan polyacanthorhynchus kenyensis (Schmidt and Canaris), a nematode contracaecum sp.. a trematodeclinostomum sp. and a dilepidid cestode Amirthalingamia sp.Seasonal variation in prevalence, intensity of infection, organs infected and the variation in infection with the size, sex and body condition of the host are described. There was no seasonal variation in prevalence but intensity of infection was observed to increase with the age of the fish. Although male fish were observed to be more heavily infected, the parasites did not seem to have any significant effect on the body condition of the fish.
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Population parameters of Oreochromis leucostictus from Lake Naivasha, KenyaAfrican Journal of Tropical Hydrobiology and FisheriesLength-frequency data collected from fish landings on Lake Naivasha were used to estimate the growth parameters: total mortality (Z), growth performance index (Ø’), exploitation rate and recruitment pattern in Oreochromis leucostictus. The asymptotic length (L∞) was 38 cm and K 0.48 yr -1 Z was estimated as 3.5 yr -1, M was 0.19 yr -1, F was 2.6 yr -1 and E of 0.74. Recruitment occurs throughout the year, with a peak in January to March, while entry into the fishery occurs at a mean length of 15.9 cm. Existing restriction on the maximum number of gill nets allowed per fishing licence (10 per boat) and a minimum mesh size (10 cm) in the lake are not adhered to. Poaching using illegal mesh size nets as small as 5 cm and use of more than 10 nets per boat are common in the lake.
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Analysis of fish catch data from 1985 to 1994 in the Kenyan inshore marine watersAfrican Journal of Tropical Hydrobiology and FisheriesFish landing data collected by the Kenyan Fisheries Department from the nearshort coastal marine waters from 1985 to 1994 were statistically analyzed to determine trends in the traditional fisher's catch. Over the ten year period a significant decline occurred for total catch and for catches of seven commercially important fish families: Lethrinidae, Siganidae. Lutjanidae, Scaridae, Carangidae, Scombridae and Mullidae. 1994 registercd the lowest catch over ten years. The total catch for all the fish declined from a mean annual catch of 6150 metric tonnes in the 1980's to a mean of 5141 metric tonnes in the 1990's with the catch for 1986 being 2 times higher than that of 1994. Although Mombasa district had the highest mean annual landing, its total landings like that of Lamu and Kwale districts decreased over the years. However, Kilifi district showed a steady increase in catches over the years. The changes in fish landings is thought to be caused by lack of appropriate fishing regulations, leading to overfishing of the lagoonal reefs beyond their maximum sustainable yields.
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Methodology for valuing wetlands in UgandaAfrican Journal of Tropical Hydrobiology and FisheriesThe wetlands in Uganda are undergoing rapid degradation. Swamps provide a habitat for birds, fishes and other animals. They have many ecological functions and, furthermore, supply people with multiple resources, such as reeds, herbs, fish and agricultural products. Although some'uses of wetland are sustainable, others lead to rapid deterioration. The main threat to swamps are human activities. One reason for the progressive destruction of wetlands is that the people may not appreciate the existence of and the treasures represented by wetlands even if they live in arm long distance from them. Another reason is that the two most important user groups of wetlands, farmers and fishermen, although having conflicting interests concerning the wetlands, hardly interact. A study, done as part of the Ecotone Project at the Fisheries Research Institute (FIRI), tries to evaluate in monetary terms how much Uganda loseswith progressive destruction of wetlands. The study looks first at which uses of the wetlands are of importance and thereafter it examines, what data is needed and available to calculate the values of those uses.
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Morphometrics, length-weight relationship and condition of Rastrineobola argentea (Pellegrin 1904) in the Winam Gulf of Lake Victoria (Kenya)African Journal of Tropical Hydrobiology and FisheriesCorrelation between total length (TL), fork length (FL) and standard length (SL) of Raslrineobola argentea (pellegrin1904) in the Winam Gulf of Lake Victoria indicate that FL = 0.92 TL - 0.74 and SL = 0.90 TL - 1.74. Length-weight relationship of log-transformed data shows that the slopes of the regression lines were 3.06 to 3.22 for juveniles, 2.70 to 3.05 for males and 3.24 to 3.71 for females. The slopes were significantly different between groups at at a =0.05. The Fulton's condition factor (K) was highest in December (1.019-1.073) and March/April (1.015-1.030) but lowest in June (1:00-1.025) for all stations. Significant differences between groups demands for the use of different growth models for juveniles, males and females especially for the von Bertalanffy growth equation which uses length-weight relationship. Observed cyclic viationsin condition factor suggests two peak breeding seasons for this species in the Winam Gulf. The practical lmplicationsof these results in stock assessment using length-based fish stock assessment methods is briefly discussed.
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A decline in fish catches and the size of Oreochromis niloticus in Lake Wamala (Uganda) following human exploitationAfrican Journal of Tropical Hydrobiology and FisheriesThe fishery of Lake Wamala has declined since the lake was stocked in 1956 and opened to fishing during the 1960s.Surveys were conducted on the lake during 1975/78 and 1988/92 to investigate the causes of declining fish catches. The lake produced an average of 4000 - 6000 tonnes of fish annually from 1960s through 1970s. Total fish catches decreased from a maximum of 7100 tonnes in 1967 to less than 500 tonnes by 1990s. Catch rates decreased from about 8 kg in the 1960s to less than 1 kg per net per night by 1975. During the 1970s the catch was dominated by Oreochromis niloticus (67%) followed by Clarias gariepinus (17%), and Protopterus aethiopicus (15.1 %). By 1990s the proportion of O. niloticus had decreased to 45.1% while that of P. aethiopicus had increased to 37.6%. These changes seem to have been caused by overfishing resulting from increased fishing effort from the recommended 250 to about 1000 boats and the additional increase in effort through driving fish into the nets by beating water. The maximum size of O. niloticus in the fishery decreased from 32 cm total length in 1975/78 to 22 cm in 1988/92 while the size at first maturity decreased from about 21 cm to 14 cm during the period. This has been concurrent with a shift in the mesh size of gillnet used from 127 mm (5") in 1960s to 64 mm by 1990s. Environmental changes, especially in lake level in 1980, may also have affected the fishery.
