Hybridization between Tilapia zillii (Gervais) and Tilapia andersonii (Casteinau) at the Freshwater Fisheries Institute, at Nyegezi, Tanzania

As a part of an overall project on fishculture development techniques in Tanzania, hybridization between Tilapia zillii and Tilapia andersonii was carried out at the Freshwater Fisheries Institute, Nyegezi, Tanzania. T. andersonii, a plankton feeder, is not indigenous to Tanzania but was introduced in 1968 from Zambia for certain specific purpose. T. zillii, a macrovegetation feeder, is present locally and is common. In the present studies T. zillii (245.0 mm/260.0 g) female was hybridized with T. andersonii (288.0 mm/350.0 g) male. Under cement cistern conditions it was only after about four months of acclimatization that hybridization between the two occurred. About 1,637 interspecific hybrid fry were produced in a single brood. Eggs were adhesive and parental care shown by the female, the male being driven away. Growth under cistern conditions was slow, attaining a size of 134.8 mm/44.3 g in 10 months. But this growth rate need not be taken as ideal. In body shape, colouration and other morphometric characters the hybrids had inherited from both parents. The number of gill rakers among the hybrids was eighteen which was intermediate between T. zillii (12) and T. andersonii (27). Among one hundred and seventy two specimens (106.0 mm - 168.0 mm) cut and examined the sex ration was hundred per cent males and all of them were between II and IV stages of maturity. This is the first report of fish hybridization from Tanzania and possibly the first report on hybridization between T. zillii and T. andersonii. The full significanoe of the findings and its role in African fishculture is discussed.

Evaluation of external anchor tags for estimation of growth and survival in tilapia (Oreochromis shiranus chilwae Trewavas)

The effects of tagging with Roy FD-68B T-bar anchor tags on estimates of growth in Tilapia (Oreochromis shiranus chilwae) were investigated in a pond and in a field experiment. In the pond experiment, mean length increments of tagged and marked fish were compared. In the field experiment growth of tagged and "untouched" individual wild fish were compared by measuring scale circuli spacing (Circ.), which is correlated to instantaneous growth rate. Length increments of tagged and untagged/marked fish were not significantly different in either experiment. In the pond experiment, the total mortality rate in the small tagged fish was significantly higher than in the marked fish. The recoveries of tagged fish in the pond experiment increased with fish size. Recoveries exceeded 80% at lengths over 13 cm TL. The ratios of tagged to marked recoveries were 1.02 and 0.74 for large and small fish respectively. The study shows that tagging of Tilapia with Roy anchor tags does not in general alter the growth rates of the fish.

A note on recent advances in the genetic characterization of tilapia stocks in Lake Victoria region

Oreochromis esculenta, the original "ngege" is virtually extinct in Lake Victoria, and is limited to satellite lakes and reservoirs in the greater Lake Victoria region. Oreochromis variabilis can still be found in Lake Victoria and some satellite lakes in the Kyoga System, but in small numbers and only at a few localities (WANDERA and KAUFMAN, unpub. data). Little is known about the influence that species translocations have had on the genetic structure of these crucial fishery species, and even the source of the parent stocks for the introductions remain obscure. Genetic variability was examined within and among allopatric populations of three species in the tilapiine genus Oreochromis: O. esculentus (endemic to Lakes Victoria and Kyoga), and two exotic species introduced to Lake Victoria in the late 1950's to supplement the failing fisheries for native tilapiines, O. niloticus and O. leucostictus.

Growth rates of juvenile Nile perch, Lates niloticus L. in lakes Victoria, Kyoga and Nabugabo

The growth rates of Nile perch, Lates niloticus L. of 20 cm to 40 cm total length were estimated in lakes Victoria and Kyoga in 1991 and 1992 and Nabugabo in 1992 and 1993 by tagging. Fish grew faster in Lake Kyoga (mean growth rate 28.7 ± 1.3 cm S.E. per year, N = 49) than in Lake Victoria (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 each other (p = > 0.05). The faster growth rates in Lake Kyoga were attributed to improvement in food supply 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.

The past, present and projected scenarios in the Lake Albert and Albert Nile fisheries: implications for sustainable management

Lake Albert is one of the largest lakes in Uganda that still supports a multi-species fishery which as a result of variable adult sizes of the species, causes management challenges especially in relation to gear mesh size enforcement. Prior to the 1980s, commercial species were 17 large sized fishes especially Citharinus citharinus, Distichodus niloticus and Lates spp. that were confimed to inshore habitats of the lake and were thus rapidly over fished. Frame and catch assessment surveys conducted in this study revealed a >80% dominance of small size fish species (Neobola bredoi and Brycinus nurse) and a 40 -60% decrease in the contribution of the large commercial species. Sustainability of small size fish species is uncertain due to seasonal fluctuations and low beach value. At about 150,000 tons of fish recorded from Lake Albert and Albert Nile, the beach value was estimated at 55.3 million USD. Despite the noted decline in catches of the large sized fishes their contribution was more than 50% of total beach value. Therefore, management measures should couple value addition for the small sized species and maintain effort regulation targeting recovery of the large previously important commercial species.

Fisheries Department Annual Report 1969

During the year 1969, the fishing industry maintained a rate of increase that had been witnessed in the three previous years. The total catch landed was estimated at 125300 metric tons, valued at shs 130,500,000/-at the lakeside,and about shs 260,000,000/-in the retail market. This was an increase of 16,900 metric tons over the 1968 figure. The largest increases again came from the Lake Kyoga area, where the Nile Perch and the introduced Tilapia species are still expanding. Large numbers of fishermen from other regions (i.e. from Lake Victoria) moved to Lake Kyoga where catches were high and remunerative. This intensified fishing on this lake, resulting in the high figure of catches recorded. As in the previous year, there was a marked increase in the use of large-mesh gill-nets for catching Nile Perch and Tilapia. Individual Tilapia nilotica of up to 5 kg were quite common, and Nile Perch weighing over 50 kg were also regularly taken. The marketing and distribution side of the industry was as active as ever: 87 people took out specific licences, and 640 fishmongers were licensed by different urban authorities. Elsewhere in the Districts, 7,950 fishmongers were licensed. Host of the fish landed was consumed within Uganda and exports accounted for dnly a very small fraction of the market, mainly composed of frozen fiilets to Kenyai and salted fish to the Republic of the Congo. Kampala market was the most important one, serving also as a central market from where fishmongers bought fish for distribution to rural areas.

Annual Report of the Game Department for the year ended 31st December, 1947

) General (2) Legislation (3) Nets (4) Imports and Exports of Dried Fish (B) Economic:- (I) Lake Victoria (2) Lake Albert (including the Albert Nile (3) Lake Edward and Associated Fisheries (4) Lake Kyoga (5) Minor Lakes, Dams and the Victoria Nile (6) Introductions (7) Fish Transfers (8) Crocodiles:- (C) Angling Trout Nile Perch Barbel Tilapia Variabilis

Annual Report of the Game Department for the year ended 31st December, 1948

Fisheries section of the annual report covers the following A. ADMINISTRATION (1) General, (2) Legislation, (3) Nets (4) Imports and Exports of Dried Fish, (B) ECONOMIC :( 1) Lake Victoria, (2) Lake Albert (including the Albert Nile), (3) Lake Edward and Associated Fisheries, (4) Report by Fish Culturist, (5) Lake Kyoga, (6) Minor Lakes and the Victoria Nile, (7) Dams,(8) Introductions,(9) Fish Transfers (10) Crocodiles:(i) Control,(ii) Industry, (iii) General (ll) General Notes, (C) ANGLING:Trout, Nile Perch Barbei, Tilapia variabilis.

Aspects of migration, size structure and mortality of juvenile Nile perch in the Mwanza Gulf of Lake Victoria

A detailed study of the early life of fishes forms one of the very important aspects with respect to recruitment mechanism and proper uneterstanding of the dynamics leading to sustainance of fish populations. It should be the central theme of the fisheries biologist and managers to extract the bilogical information relevant to the proper understanding of this part of the population. A number of studies in the Mwanza gulf and Lake Victoria have emphasized the need to monitor the fishery by conducting observations of stock size, migration, catch effort data and growth of big specimen (Acere 1981, Goudsward et al 1984, Asila. Ogari 1988 and Okemwa 1984). The present paper discusses the preliminary information on the size structure, mortality and migration of juvenile Nile perch. The long term objectives of the programme is aimed at describing the size structure, growth, mortality, recruitment pattern and population dynamics of the Nile perch up to 30 cm total length in the, Mwanza Gulf.

Investigations of the present factors affecting the population characteristics and relative abundance of nile perch (Lates niloticus) at selected trawling sites of western part of Lake Victoria, Uganda, Kagegi Gulf

This report is based on the investigation of the factors affecting population characteristics and relative abundance of Nile perch in selected sites of Kagegi Gulf Lake Victoria Uganda in the month of November 2006. Nine (9) stations were sampled at depth strata of 0-10, 10-20, 20-30 and 30-40 m the mean catch rates were as follows; 8.75±5.5, 4.77±2.3, 6.33±0.3 and 1.34±1.1 tonnes per square kilometer respectively. The catch rates differed at various depth levels with p-value of 0.2940 at 5% level of significance. Limnological parameters were temperature 25.15±0.28, 23.68±0.20, 24.74±0.13 and 25.3±0.20°C; pH of 8.0±0.00, 7.7±0.11; 7.66±0.33 and 6.32±0.14, dissolved oxygen 7.37±0.24, 6.44±0.30, 6.32±0.14 and 6.22±0.14 mg/l; Total nitrogen 589.82±97.2, 514.34±68.8, 690.44±257.8 and 809.03±45.02 µgL-respectively with a p-value of 0.4392 at 5% level of significance. Prey type of Nile perch indicated 65.2% of haplochromine in 0-10 m depth and other strata >10 metre were dominated by Caridina nilotica. Generally investigations indicated that the catch rates of Nile perch at Kagegi gulf in various depth strata probably depended on both the physical and chemical parameters mentioned above.

The effect of hook size on the catch rate and size of the Nile perch Lates niloticus (Linne) fishery in the Napoleon Gulf, Lake Victoria, Uganda

This study was undertaken in Napoleon gulf, Lake Victoria Uganda from July – December 2009. It was conducted in four landing sites; Bukaya (0.41103N, 33.19133E), Bugungu (0.40216N, 33.2028E), Busana (0.39062N, 33.25228E) and Kikondo (0.3995N, 33.21848E) all from Buikwe district (Formerly part of Mukono district). The main aim was to determine the effect of both hook size and bait type on the catch rate (mean weight) and size composition of Nile perch (Lates niloticus) (LINNE) fishery in the Napoleon Gulf, Lake Victoria. The main hook sizes investigated during the experiment were 7, 8, 9, 10, 11 and 12 that were dominantly used in harvesting Nile perch in Napoleon Gulf, Lake Victoria. In this study length, weight and bait type data were collected on site from each boat at that particular fishing spot; since most fishermen in the Napoleon Gulf could sell their fish immediately the catch is caught there and then. The results indicated a total of 873 Nile perch fish samples collected during the study. Statistical tests, descriptive statistics, regression and correlation were all carried out using the Statistical Package for the Social Sciences (SPSS) in addition to Microsoft excel. The bait types in the Gulf ranged from 5-10 cm Total length (TL) haplochromine, 24.5-27 cm TL Mormyrus kannume and 9-24 cm TL Clarias species. The bait types had a significant effect on the catch rate and also on the size composition the fish harvested measured as Total length (ANCOVA F=8.231; P<0.05) despite the fact that bait type had no influence on mean weight of fish captured (ANCOVA F=2.898; P>0.05). Hook sizes used by the fishers had a significant effect on the both the size (TL) composition (ANCOVA F=3.847; P<0.05) and the mean weight (ANCOVA F=4.599; P<0.005) of the Nile perch captured. Investigations indicated hook sizes seven (7) and eight (8) were the ones that harvested the Nile perch above the slot size of 50 cm total length. In general hook sizes indicated to be the main drive in the harvesting of the Nile perch though bait type also contributed toward that. Generally there is need for management to put a law in place on the minimum hook size to be used on the harvesting of the Nile perch and also monitored by the Fisheries Management as a regulatory measure. In addition to that aquaculture should be encouraged to farm the fish for bait at a higher scale in the region in order to avoid depleting the wild stocks already in danger of extinction. Through this kind of venture, both biodiversity conservation and environmental sustainability will be observed in the Lake Victoria basin.

Age, growth, tagging of tilapia spp. and reproductive biology of siluroid catfishes in Lake Victoria

This report encompasses the time period 1 September 1973 through 31 July 1975. The research Officer's tour of duty officially terminated 30 September 1975, consisting of a regular 2-year tour of duty with three month extension of contract. During this time research into age and growth of several tropical species of fishes was conducted. In addition a closely related tagging program was initiated in order to determine both growth and movements of fishes. Lastly, some effort was directed towards aspects of the basic biology of several of the siluroid catfishes. This report delineates the relative effort into and success of the various research projects; presents results of research not previously offered, summarizes findings, and makes recommendations for future research endeavour. Two annual reports along with quarterly reports up to 30 June 1975 have been produced and are on file both at Headquarters in Jinja and the Kisumu Sub-station. These only will be referred to in some instances and built upon in others. Opinions offered, conclusions drawn and recommendation given within this report are solely those of the research officer employed in an official capacity for E.A.F.F.R.O.

An assessment of the impact of the Nile perch on the fisheries of Lakes Victoria and Kyoga

The combined effects of lack of effective management measures, over-exploitation with destructive fishing gears, and interspecific competition, particularly among tilapiines have had profound effects on the fish stocks of Lakes Victoria and Kyoga. It has been proposed that these have been more important in the decline of the indigenous fisheries than predation or competition from Nile perch. The purpose of this paper is to provide an assessment of the dramatic changes in the fisheries of Lakes Victoria and Kyoga . Both lakes have experienced almost similar changes for which Lates could not have been wholly responsible.

Impact of stability in prey supply to the stocks of the Nile perch in Lakes Victoria, Kyoga and Nabugabo

The food of the Nile perch has changed since its introduction into Lakes Victoria, Kyoga and Nabugabo and stabilized on Caridina nilotica, Anisopteran nymphs, Rastrineobola argentea, Nile perch juveniles, and tilapiines. For the Nile perch to sustain production in these lakes, its is important that these prey species are properly managed.