The fish stocks of Lake Victoria, Uganda

An experimental bottom trawl survey was carried out in the Uganda sector of Lake Victoria from November 1997 to December 1998 to estimate the composition, distribution, and abundance of the major fish species. In 12 cruises, 295, thirty-minute hauls were taken in waters from 4-60 m deep. Nile perch, Lates niloticus (L) made up 95% of the catch by weight. Haplochromine cichlids and L. niloticus occurred in all areas sampled while Nile tilapia, Oreochromis niloticus (L.) and other tilapiines were restricted to waters less than 30 m deep. In waters deeper than 40 m, catches were generally near zero. Species diversity and abundance decreased with increasing water depth. In waters less than 30 m deep, the area where the artisanal fishermen operate, the mean catch was 126kg hr super(1)

An investigation of the effect of replacing fish meal with soyabean meal, groundnut cake and blood meal at varied proportion on growth and food utilization of the Clarias anguillaris fingerlings fed in outdoor hapas

Fingerlings of Clarias anguillaris obtained from a homogenous source through induce breeding and each with a mean weight of 2.8g were stocked in ten hapas each measuring 1.0x1.0m in outdoor concrete tank and were fed for eight (8) weeks. Results shows that the best growth rate was recorded among fingerlings fed fish meal as the only protein source (TD5) while DT2 containing soya bean, groundnut cake (40%), blood meal as the protein sources came next. The growth rate of fingerlings fed DT2 (40 % groundnut cake, 10% soyabean meal and 10% blood meal) was higher than those fed DT4 containing 10% fish meal but lower than those fed DT5 which has fish meal as its sole source of protein (53.0%). Analysis of various growth parameters like SGR, FCR and PER. shows that DT5 was the overall best diet but there was no significant statistical difference in weight gained by fish fed the five diets (P <0.05)

Aspects of ecology of Owena reservoirs: implication on fish production

The article gives physical description of Owana reservoir, Nigeria. The reservoir was chemically and thermally stratified partial mixing of the water was observed during the rains. The concentration of major ions in the water showed distinct peculiarities. The captions (Na super(+), K super(+)Ca super(H),Ca super(Z), Mg super(++)) SO sub(4) super(2-) were relatively low. The water had high dissolved oxygen, it was acidic and also had low values of alkalinity, conductivity and total dissolved solids. About 61 plankton taxa belonging to 21 species were identified. The reservoir supports a commercial fishery of about fifteen fishermen with about fifteen species of fish caught daily with the aid of traps set and cast nets. Effective management of the lake will enhance fish production

Intensive small scale cage, pen and enclosure fish production systems: towards 2010

A brief review of most of the publications by the author and other relevant workers on the three water-based fish culture systems was made. The present status of the culture systems in the National Food/Fish Programmes was highlighted. Strategies were advanced towards a successful implementation of the intensive water-based culture systems project as a contribution towards alleviating poverty, hunger and malnutrition under the concept of VISION 2010

Effect of fish meal in formulated diet on the growth of Heterotis niloticus in semi-intensive pond culture system

The aim of the investigation is to know the percentage of fish meal required to support the best growth of Heterotis niloticus in a semi intensive pond culture system. To achieve this, feed was formulated with equal percentages of blood meal, and corn meal and varying levels of fish meal. The experiment was in four treatments. Results showed that the mean weight gained was directly proportional to the quantity of fish meal made available to the fish fence 31.58g, 33.79g, 45.15g and 51.24g were recorded for treatments I, II, III and IV respectively. Result from this study when compared with previous works, shows that size of the water body to a greater extent affects the growth. The availability of fish meal in the feed made it more acceptable to the fish and hence a commensurate conversion in to flesh. The analysis of variance showed that there is significant difference in the growth performance in the treatments

26. Jahrestagung der WEFTA (Western European Fish Technologists´ Association) in Gdynia, Polen

Die 26. Jahrestagung der WEFTA fand vom 22. bis 26. September 1996 erstmalig in Polen statt. Gastgeber war P. Bykowski vom Institut für Seefischerei (MIR) in Gdynia, das im Jahre 1996 sein 75jähriges Jubiläum feiern konnte . Die Tagung wurde von etwa 70 Delegierten aus den 16 WEFTA Mitgliedsstaaten und Gästen aus den USA, Rußland, Israel und Litauen besucht. Die Konferenz wurde von Z. Polanski, dem Direktor des Institutes und von M. Brzeski, dem Zweiten Bürgermeister der Stadt Gdynia eröffnet. In 10 Vortragssektionen und einer Postersektion wurden den Teilnehmern insgesamt 38 Vorträge und 24 Poster geboten.

Pre-packaged fresh fish - Searching for quality descriptive criteria

32 Proben verpackten Frischfischs in Selbstbedienungspackungen, 16 Seelachs- und 16 Rotbarschproben aus deutschen Supermärkten wurden mit physikalischen, chemischen, mikrobiellen und sensorischen Methoden untersucht. Ziel der Untersuchung war dieWertung von Untersuchungsmethoden zur Qualitätsbestimmung. Es zeigte sich, daß neben der sensorischen Beurteilung die Bestimmung des TVB-N geeignet ist, die Qualität dieser Produkte zu beurteilen.

Fish transplantation as an ecological tool in boosting fish production: Tiga case study

The paper discusses the status of the Tiga Reservoir Fishery pre-and Clupeid transplantation. This was achieved by examining the species diversity, abundance and distribution with mitigating factors. It concludes with a verdict on the achievement of the transplantation exercise

Length-weight relationship and organ indices of pond raised and wild population of C. gariepinus (Burchell 1822) pisces-Claridae

Samples of C. gariepinus collected from the wild and cultured populations in Plateau and Niger States of Nigeria were analyzed for length-weight relationship and organ indices (Gonadosomatic index (GSI), hepatosomatic index (HSI), renalsomatic index (RSI) and somatic fat deposit index (PDI). High correlation and linear relationship between body length and body weight was observed in all sample population (P<0.05). A significant difference was observed between the GSI of males and females of both wild and cultured population and also between females of the wild and cultured population,(P < 0.05).There was no significant difference in HSI, CSI RSI and PDI of all the sample populations (P < 0.05).The importance of length-weight relationship and organ indices in fish production are discussed

The effect of long term exploitation by the gill net fishery on the multispecies fish stocks in Kainji Lake, Nigeria, 1969-1997

The findings are presented of an assessment made of the gillnet fishery in Kainji Lake, Nigeria from 1969 to the present, on the basis of data sets from commercial and experimental gillnet fishing, with the purpose to detect trends in some key fishery monitoring indicators. During this period, there has been an increase in the number of small meshed nets in the fishery resulting in a shift in the mode to lower mesh sizes; consequently, the average mesh size declined gradually in the fishery. This trend is found to be directly correlated with the decline in the CPUE and mean weight of the fish species. It is argued that the observed trend in CPUE and mean weight is forcing the fishermen to switch effort to gears such as traps which have very small meshes and can indescriminately take all sizes of the fish. It is shown that the catch composition by weight of Citharinus citharus, Lates niloticus and tilapias declined in the gillnet fishery in the late 70's and early 80's. Recent data, from 1994 to 1996, however indicates that C. citharus is recovering, but with declining mean weight. This suggests that the exploitation pattern is shifting to the smaller fish through the use of small meshed nets. In general, however, there has not been drastic changes in species bio-diversity in the Lake as a result of predatory effect and ecosystem overfishing as has happened in other great African Lakes. The species composition since lake formation continued to be dominated by fewer that 20 species. The potential yield for the lake has been estimated to be 32,166 tonnes (excluding clupeids) and the required optimum fishing effort to be 1,814 fishing canoes. In view of the relative stability of the species diversity in the lake and the current fish production level, it is proposed here that this MSY be adopted for all species. This would be achieved with the current effort level in the lake assuming that the efficiency of the fishermen and their gears do not improve. It should be reviewed after 10 or more years of catch and effort data collection. (PDF contains 65 pages)

Predictions of fish yields and the status of the Kainji Lake fishery, 1998

Length frequency data was collected for the 6 main species from the Kainji Lake fishery for up to 16 months. Growth parameters were estimated and used for virtual - population and length based cohort analysis. The results from cohort analysis suggest that before the ban on beach seines the maximum economic yield from the fishery was overshot by 70%. Yield per recruit analysis showed that the fish are caught far below their optimum size. Fishing gears and the timing responsible for this early mortality have been identified. After the eradication of seines from the lake a 10% increase in total catch revenue can be expected from the fishery. This is equivalent to an increase in income of Naira 18,300 per annum for each fishing entrepreneur using other methods. A scenario for the regulation of cast net mesh size together with the ban of beach seines has been presented. A further increase of Naira 142 million (N25,500 per entrepreneur) can be anticipated if this is implemented by the Kainji Lake Fisheries Management and Conservation Unit. It is expected that the annual increase in fishing effort presently experienced will cause future yields to decline. The rate of the decline has been reduced by the eradication of the beach seine fishery and will further fall if the minimum mesh size for cast nets is implemented. A recommendation is made to the Kainji Lake Fisheries Management and Conservation Unit to first consolidate the beach seine ban and then to implement a ban of undersized cast nets. (PDF contains 70 pages)

An evaluation of the pelagic primary productivity and potential fish yield of Kainji Lake, Nigeria

The environmental conditions of Kainji Lake from 1971/72 to date appear to have stabilized to a large extent, judging from the similarity of physico-chemical parameters investigated in this study over the period. Solar radiation (as reflected in variation in temperature) and pH have remained largely constant over the years, while conductivity (index of nutrient enrichment), though significantly higher in 1995/96, could be described as sporadic and needs further monitoring to ascertain its trend in the lake. While water transparency and dissolved oxygen were higher in 1971/72 compared to the other years, these increases cannot be said to be overwhelming. The lower transparency in 1995/96 was due to the exceptional flood of that year and may have also accounted for the poorer dissolved oxygen concentration compared to the other years due to its impact on photosynthesis. There is no evidence from this study to indicate that primary productivity has increased over the years. Consequently, the observed increase in fish yield by the KLFPP from CAS, which is corroborated by estimates from the MEI, cannot be supported on the basis of improved photosynthetic production. The phenomenal high levels of conductivity recorded during certain periods in 1995 (600 mu mhos cm super(-1)) are hitherto unknown in the lake and may indicate a trend towards nutrient enrichment. However, it is premature at this stage to conclude on its long-term impact on primary production and consequently, on fish yield. Secondly, the notion of overfishing in the 80s (Ita, 1993), may need to be further examined as low or dwindling catches could be due to a number of factors among which are the level of fishing effort, the type and efficiency of gears and the intensity of sampling. It would appear that with the intervention of KLFPP, the better management of the lake's fisheries would increase the current level of catch. It also needs to be examined how much of the clupeid fisheries, which is now known to account for a substantial proportion of the total fish yield in Kainji Lake, was included in the sampling of the 80s. (PDF contains 43 pages)

Potentials for marine fish hatchery production in Nigeria

The development of fish hatcheries and fish fingerling production in Nigeria has all along concentrated largely on the freshwater fish species without paying enough attention to the more numerous fish species that abound in our coastal/marine environment. This paper, therefore, tries to highlight some basic technologies (in term of design and management) of marine fish hatchery based on the author's experiences in Southeast Asia. Appropriate adaptable technologies for the production of our indigenous species such as the Snappers, Groupers etc. are also discussed. General recommendations are made for marine fish hatchery development in Nigeria

The electric field of a weakly electric fish

Freshwater fish of the genus Apteronotus (family Gymnotidae) generate a weak, high frequency electric field (< 100 mV/cm, 0.5-10 kHz) which permeates their local environment. These nocturnal fish are acutely sensitive to perturbations in their electric field caused by other electric fish, and nearby objects whose impedance is different from the surrounding water. This thesis presents high temporal and spatial resolution maps of the electric potential and field on and near Apteronotus. The fish's electric field is a complicated and highly stable function of space and time. Its characteristics, such as spectral composition, timing, and rate of attenuation, are examined in terms of physical constraints, and their possible functional roles in electroreception.

Temporal jitter of the periodic field is less than 1 µsec. However, electrocyte activity is not globally synchronous along the fish 's electric organ. The propagation of electrocyte activation down the fish's body produces a rotation of the electric field vector in the caudal part of the fish. This may assist the fish in identifying nonsymmetrical objects, and could also confuse electrosensory predators that try to locate Apteronotus by following its fieldlines. The propagation also results in a complex spatiotemporal pattern of the EOD potential near the fish. Visualizing the potential on the same and different fish over timescales of several months suggests that it is stable and could serve as a unique signature for individual fish.

Measurements of the electric field were used to calculate the effects of simple objects on the fish's electric field. The shape of the perturbation or "electric image" on the fish's skin is relatively independent of a simple object's size, conductivity, and rostrocaudal location, and therefore could unambiguously determine object distance. The range of electrolocation may depend on both the size of objects and their rostrocaudal location. Only objects with very large dielectric constants cause appreciable phase shifts, and these are strongly dependent on the water conductivity.

Substituting fish meal with grasshopper meal in the diet of Clarias gariepinus fingerlings

The effect of inclusion of grasshopper meal on the growth, feed conversion ratio and survival of Clarias gariepinus fingerlings of mean weight 9.71g was investigated. The results show that the best growth and food utilization indexes were recorded in the fingerling fed with 10% grasshopper meal and 30% fish meal, while the poorest growth and food utilization indexes were recorded with the diet containing 25% grasshopper meal and 15% fish meal. The best survival of 100% was observed in the diet containing 30% grasshopper meal and 10% fish meal while the worst survival of 73.3% was observed in the diet containing 25% grasshopper meal and 15% fish meal