Browsing by Author "Nkalubo, Winnie"

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    Feeding ecology of the intensively fished Nile Perch, Lates niloticus, in Lake Victoria, Uganda
    (Aquatic Ecosystem Health & Management, 2014) Nkalubo, Winnie; Chapman, Lauren; Muyodi, Fredrick
    The diet of Nile Perch (8.0–121.0 cm total length [TL]) from the Ugandan waters of Lake Victoria was quantified through stomach content analysis of specimens collected from experimental catches and fish factory samples. A total of 7824 stomachs (5602 from experimental fishing and 2222 from factory samples) were examined, of which 34.8% contained food. Fish from the experimental catches were smaller (8.0–41.6 cm TL) and had a higher diversity of prey dominated by unidentifiable fish prey, haplochromine cichlids, Rastrineobola argentea, Odonata and Caridina nilotica, while larger fish (30.0–121.0 cm TL) from the factory samples had a predominance of fish remains and haplochromine cichlids. Nile Perch that had a high proportion of fish prey (versus invertebrates) in their stomachs showed a larger size for a given age, and were in a better condition (K = 1.24) than those that had primarily invertebrates (K = 1.10) in their stomachs. Nile Perch exhibited a much smaller size (15 cm versus 30 cm TL) at shift to piscivory in comparison to Nile Perch examined in earlier studies, when haplochromines were rare in Lake Victoria. The recovery of haplochromine cichlids coincident with declining Nile Perch densities illustrates the importance of developing sustainable management options that can define a proper balance between fishing mortality and Nile Perch predation.
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    Optimizing Selection of Sexually Mature Barbus Altianalis For Induced Spawning: Determination of Size at Sexual Maturity of Populations from Lake Edward and Upper Victoria Nile in Uganda
    (Fisheries and Aquatic Sciences, 2018) Aruho, Cassius; Ddungu, Richard; Nkalubo, Winnie; Ondhoro, Constantine Chobet; Bugenyi, Fredrick; Rutaisire, Justus
    Sexual maturity (L50), the length at which 50% of fish in a size class are mature, is a key aspect of domestication of new fish species because it guides the procedure for identification of appropriate broodstock size for artificial spawning. In this study, the L50 was determined for 1083 Barbus altianalis samples obtained from Lake Edward and the Upper Victoria Nile. Gonads of freshly killed samples were examined macroscopically and verified with standard histological procedures for the maturation stages that were used to determine L50. Oocytes and spermatogenic cell sizes were compared for fish obtained from both water bodies. Results indicated that there were no variations in macro gonad features observed for fish from Lake Edward and Upper Victoria Nile. Similarly, there were no significant differences in oocyte sizes (P > 0.05) between the two populations but significant differences in spermatogenic cell sizes were noted (P < 0.05) except for spermatozoa (P > 0.05). This however did not suggest peculiar differences between the two populations for staging the gonads. Consequently, no staging variations were suggested for both populations in determination of L50. Sexual maturity was found in the same class size of fork length (FL) 20–24.9 cm and 35–39.9 cm for males and females from both water bodies, respectively. At this FL, however, males were too small, and for good selection of vigor broodstocks for spawning and conservation purposes, they are better picked from class size of 30–34.9 cm FL and above. These findings were crucial for integration of appropriate breeding size in spawning protocol by farmers and fisheries scientists conserving wild B. altianalis populations.
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    Stock Assessment of Lates niloticus in Upper Victoria Nile and its Impact on Uganda’s Economy
    (Uganda Journal of Agricultural Sciences, 2019) Bassa, Samuel; Getabu, Albert; Balirwa, John Stephen; Musinguzi, L.; Nkalubo, Winnie
    This study investigated the growth, mortality, recruitment, and catch estimates of Nile perch, Lates niloticus (Linnaeus, 1758), in Upper Victoria Nile, basing on total catches and length-frequency data collected between 2008 and 2018. The asymptotic length (L∞) had a value of 93.45 cm TL, growth curvature (K) was 0.446 year-1, total mortality (Z) was 1.85year-1, natural mortality (M) was 0.79 year-1, fishing mortality (F) was 1.09 year-1, exploitation rate (E) was 0.59 and growth performance index(ᴓ) of (L∞) was 3.604. There were two peaks recruitment period, a minor one in March and a major one in August. These respectively accounted for 12.8 and 26.3 percent of the total catch. The optimum sustainable yield (E0.5), maximum sustainable yield (Emax) and, economic yield (E0.1) was 0.278, 0.421 and 0.355 respectively. The findings suggest that there is a decline in the population of Lates niloticus in Upper Victoria Nile. Therefore, strict management of the fishery by adhering to the recommended slot size of 50-85 cm TL and curtailing use of illegal gears is needed. This will be possible through enforcement of regulations, monitoring, control and surveillance in order to ensure sustainability of the Nile perch fishery and ecosystem restoration in the Upper Victoria Nile.