A histological description of ovarian recrudescence in two Labeo victorianus populations
- Authors: Booth, Anthony J , Hecht, Thomas
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123564 , vital:35455 , https://doi.org/10.2989/16085910409503813
- Description: The ovaries of Labeo victorianus are paired organs situated in the peritoneal cavity and suspended on either side of the midline by a mesovarium. A capsule, composed of dense, regularly-arranged collagen and elastic fibres mixed with a few smooth muscle cells, enclosed the ovaries and gave off connective tissue septa, forming the ovigerous lamellae, which contained germ and follicle cells. Eight discrete stages of recrudescence were identified: oogonia, chromatin nucleolar oocytes, perinucleolar oocytes, primary yolk vesicle oocytes, secondary yolk vesicle oocytes, tertiary yolk vesicle oocytes, post-ovulatory follicles and atretic oocytes. Ovulation seemed to be synchronised with the onset of rainfall, with some deviations in the Sio River population. Gonadosomatic index variation followed a bimodal pattern, with maxima between January–February and between September–October for both populations. The same pattern was exhibited for both rainfall and water levels at the two study sites. Successful ovulation was followed by the formation of post-ovulatory follicles and Type I atresia, while failed spawning was characterised by Type II atresia. Clearance of post-ovulatory follicles was by phagocytosis and formation of melanomacrophage centres. There were variations in post-ovulatory changes between the two populations. Reproductive patterns in the Kagera River population conformed to the ‘norm’ in African labeines of the synchronisation of spawning with rainfall. Slight deviations from this pattern were, however, observed in the Sio River population where spawning occurred prior to the onset of rainfall.
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An assessment of a light-attraction fishery in southern Lake Malawi
- Authors: Weyl, Olaf L F , Kazembe, Jacqueline , Booth, Anthony J , Mandere, D S
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123683 , vital:35472 , https://doi.org/10.2989/16085910409503787
- Description: This study provides the first quantitative assessment of the light-attraction component of a small-scale purse seine, locally known as a chilimira net, fishery in two areas of southern Lake Malawi. For monitoring purposes the shoreline of Lake Malawi is divided into a number of statistical strata. Two strata (‘2.1’ in the southeast arm and ‘3.1’ in the southwest arm of the lake) were selected for this study. Catch per unit effort in stratum 2.1 was generally lower than that recorded in stratum 3.1 but nets in stratum 2.1 fished more frequently, leading to similar annual catches in the two strata. Annual catch was estimated as 19.4 (CI = 15.9–23.5) tons net–1 year–1 in stratum 2.1 and 23.5 (CI = 19.5–28.1) tons net–1 year–1 in stratum 3.1 respectively. A total of 62 species from 28 cichlid genera, and 13 species from nine non-cichlid genera, were identified from the samples. Of the 37 genera identified, only five; Copadichromis, Dimidiochromis, Engraulicypris, Oreochromis and Rhamphochromis, contributed more than 5% to the total annual catch in either stratum. Their combined contribution to the annual catch was in excess of 85% in both strata. Comparisons showed that catch-composition was dependent on area. Length-frequency distributions of major target species in the catch showed that the fishery targeted juveniles in stratum 2.1, while in stratum 3.1 most individuals were harvested after reaching their lengthat-maturity. The dependence of catch-composition and size-selection on area indicates that management interventions for this fishery need to be area-specific. Since the fishery targets a diverse species assemblage, effort limitation or area closure may be the only viable management options, until such time as additional biological and fisheries data are available for the application of stock assessment models.
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Evolution of Labeo victorianus predates the Pleistocene desiccation of Lake Victoria: evidence from mitochondrial DNA sequence variation
- Authors: Rutaisire, Justus , Booth, Anthony J , Masembe, C , Nyakaana, S , Muwanika, V B
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:6762 , http://hdl.handle.net/10962/d1007924
- Description: Geological data show that Lake Victoria dried out some 15 000 years ago. These data suggest that the entire faunal diversity within the lake has evolved since this time. However, mitochondrial DNA sequence diversity in the endemic cyprinid fish, Labeo victorianus, was high (24 haplotypes in 38 individuals; percentage sequence divergence of 0.74%), suggesting that the evolution of this species predates this Late Pleistocene climatological event. This finding is consistent with what has been reported earlier for cichlid fishes in the lake.
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Induced ovulation, spawning, egg incubation, and hatching of the cyprinid fish Labeo victorianus in captivity
- Authors: Rutaisire, Justus , Booth, Anthony J
- Date: 2004
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124789 , vital:35697 , https://doi.10.1111/j.1749-7345.2004.tb00102.x
- Description: Ningu Lubeo victorianus is the only labeine fish within Lake Victoria and its catchment (Greenwood 1966; Reid 1985). This species, once widely distributed in the Lake Victoria basin and supporting a commercial fishery until the late 195Os, has declined due to overfishing (Cadwalladr 1965; Ogutu-Ohwayo 1990; Seehausen 1996). The L. victorianus fishery has not only collapsed but the species has also disappeared from some of its former habitats. Recent surveys in Uganda have only found two distant populations-one in the Sio River on the Uganda-Kenya border (0” I3’53”N, 34”00’30’E), and the second in the Kagera River on the Uganda-Tanzania border (0°56’28.1”S, 3 1’46’ 18”E) (Rutaisire 2003) (Fig. 1). Currently, there is growing interest to breed the fish for wild stock enhancement and culture as a food fish.
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