Browsing by Author "Chande, Abdillah Ismail"

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    The Biology and fishery potential of the crab portunus pelagicus (Linnaeus, 1766) along the coast of Dar es Salaam.
    (University of Dar es Salaam, 2000) Chande, Abdillah Ismail
    The blue swimming crab, Portunus pelagicus Linnaeus, is of great potential for fishery expansion in Tanzania. This study investigated some aspects of the biology and fishery potential of P. pelagicus. The study also established the species composition and diversity of portunid crabs along the coast of Dar es Salaam. Samples were obtained from artisanal fishermen operating beach seine nets and basket traps. Studies on reproductive biology revealed that immature crabs dominated between December and June. There were two peaks of percentage mature crabs, one was between February and April while the second between July and November. Females attained sexual maturity slightly earlier (8.5 cm) than males (8.7 cm). The breeding cycle was continuous throughout the year with two peaks, a minor between January and April and a major one was between July and October. Studies on fecundity revealed that the number of eggs laid ranged between 112,300 and 1,061,000 for crabs of 6.73 cm and 12.22 cm carapace width, respectively. The incubation period was nine days at a temperature of 27° C. Investigations on the food and feeding habits of P. pelagicus showed that the food items taken comprised mainly sessile and slow moving invertebrates. The major food items included molluscs (51.3%), crustaceans (24.1%), and fish bones (18%). There was no significant difference in the percentage occurrence of the food items in relation to sex, crab size, season and habitats. However, non ovigerous females fed more frequently than ovigerous females. Studies on moulting and growth revealed that, P. pelagicus moults continuously throughout the year and in all size classes with some distinct peaks. Moult increments were higher in males (23.99% for immature and 9.77% for mature individuals) than in females (21.88% for immature and 7.94% for mature individuals). The modal progression analysis for males and females recorded more or less the same growth rate, 0.86 and 0.80 cm/month, respectively. It was concluded that P. pelagicus is a fast growing species. Production studies of P. pelagicus showed that there were seasonal variations in catch rates with a peak between December and May. The harvestable biomass for Dar es Salaam coast, was estimated as 34.5 tonnes/year while the contribution of recruitment to the biomass was about 20.2 tonnes/year. Data on species composition of portunid crabs showed that there were 11 species, with P. pelagicus being the most abundant in all study sites, followed by P. sanguinolentus, and the least represented was Charybdis natator. P. pelagicus and P. sanguinolentus were abundant in shallow sub-littoral waters while C. natator was abundant in deep waters. For P. pelagicus small individuals prefer shallow waters while large ones prefer deep waters. Development of P. pelagicus fishery is mainly hampered by the exploitation of juvenile crabs. The study concludes with recommendations for further studies and management of the crab fishery.
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    Post-harvest losses and insect infestation of fish in Tanzania
    (University of Dar es Salaam, 1991) Chande, Abdillah Ismail
    A study of the insect pests and fungi causing post-harvest losses in four important cured inland fish species in Tanzania was conducted. Attempts to evaluate the extent of losses and to establish the lowest possible salt concentrations which can be used to minimize the losses in fish, caused by insect infestation were made. The fish species dealt with included Lates niloticus L. {Centropornidae, Rastrineobala. argentea {Cyprinidae} both from Lake Victoria, stolothrissa tanganicae (Clupeidae} from Lake Tanganyika and Tilapia species from different parts of Tanzania. Data collection inwolved field work {survey of Dar-es-Salaam markets} and laboratory experiments, The market survey revealed that the common insect pests are beetles, Dermestes maculatus {Degeer} and Necrobia rufipes {Degeer}. Larvae of these beetles were by far more numerous than the adults. D. maculatus were common in Tilapia species and L. niloticus, whereas N. refipes were dominant pests of R. argentea and S.tanganicae. D. maculates and N. rufipes were reared in the laboratory and fed with L. niloticus and S. tanganicae respectively. Fish samples used in these experiments were treated with salt (NaCl) concetrations of 5, 10, 20, and 40% for 10 and 30 minutes prior to drying. L. piloticus treated with 40% salt concentration for 30 minutes showed a significant decrease in loss in Weight. However, treating with 20% salt concentration for more than 30 minutes is recommended for use on costs and palatability considerations. Treating S. tanganicae with 20% salt concentration for 30 minutes was found to be more effective against N. rufipes. Fungi isolated from dried L. niloticus belonged to three genera, Rhizopus, Aspergillus and penicillium. Rhizopus was the most prevalent mould while Penicillium was rare. Finally, recommendations on areas for improved fish preservation have been given. These include the use of fungal inhibitors such as Potassium Sorbate, Sorbic acid and Propionic acid in the treatment of fish prior to drying. Also the importance of hygienic handling of fish during processing particularly sundrying needs to be emphasized.