|Feeding ecology of penaeid shrimp in Kenyan mangrove ecosystems: implications for biological shrimp aquaculture|
Gatune, W.C. (2013). Feeding ecology of penaeid shrimp in Kenyan mangrove ecosystems: implications for biological shrimp aquaculture. PhD Thesis. Ghent University, Marine Biology Research Group: Gent. 153 pp.
Ghent University, Biology Department, Marine Biology, more
Aquaculture; Shrimp culture; Penaeidae Rafinesque, 1815 [WoRMS]; Marine
Feeding ecology, Mtwapa creek
Ecological shrimp aquaculture derives its feed input from the naturally occurring food sources. This practice has an environmental advantage of reducing the use of fish meal as the main food input. Use of fish meal in aquaculture has a negative effect on the coastal fisheries in the sense of depleting fish stocks. It also has a tendency to discharge wastes that pollutes the receiving coastal ecosystems. Ecological shrimp aquaculture therefore impacts low burden to the coastal ecosystems since it is integrated into the estuarine food chain. The potential of shrimp aquaculture in Kenya is high. However the initial development attempts heavily relied on the mangrove ecosystem and expensive technology. The environmental efforts to conserve the mangrove forest and the inability of the poor community to adopt the expensive technology led to the collapse of the shrimp aquaculture in Kenya. The potential approach to revive this practice therefore depends on defining ways which are not destructive to the mangrove ecosystem and which falls within the economic capability of the local community. Ecological shrimp aquaculture uses naturally generated and locally available inputs making it less costly to develop and manage. For instance, the food inputs can be derived from the estuarine ecosystem or enhanced by promoting microbial proteins. A microbial intercept would also prevent discharge of nitrogenous pollutants. However this would depend on the general setting of the shrimp ponds so that most appropriate inputs to enhance the supply of the natural food is optimised. The following study therefore attempt to explore to what extent the penaeid shrimp post larvae would rely on the natural food derived from the decomposing leaf litter of the mangrove, Rhizophora mucronata. It is hoped that the observations of this interaction can be employed in the design and management of an ecological shrimp culture practice in the Kenyan mangroves. The role of micro-biota such as the microbial community, micro-algae and meiofauna in supporting a potential food chain with the penaeid shrimp post larvae as an apex consumer is hereby explored. Specific attention is focused on the nutritional requirement of Penaeus monodon and Penaeus indicus. These penaeid shrimp species are of commercial food importance both globally and along the Kenyan coast. The study derives insight from recent studies on bacteria and micro-algae in the processing of nutrients resulting in the production of a potential diet for small invertebrates and penaeid shrimp. Moreover, an ecological approach to shrimp aquaculture cannot be accomplished without considering the policy issues governing the utilization of the coastal resources in Kenya. The motivation for this study is to recommend an ecological approach to shrimp aquaculture as a fishing activity in Kenya. It is visualised that this approach has a potential to increase income and food security to the local communities deriving livelihood from the Kenyan mangrove ecosystems. The overall aim of this PhD study was to understand the feeding ecology of penaeid shrimp in a mangrove system and to apply this knowledge to design an ecological shrimp aquaculture system which can derive biological food resources from the mangrove ecosystem. Five specific research themes were assessed: 1) the extent to which shrimp post larvae can ingest and assimilate organic matter from decomposing mangrove leaf litter given the option of a bacterial biofilm as a food source; 2) the microbial contribution to the nutritive value of the decomposing mangrove leaf litter and the associated biofilm to shrimp post larvae in comparison to an estuarine food source; 3) the temporal variation in the biota associated with the biofilm developing on the decomposing mangrove litter and their food-value-potential to support the growth of shrimp post larvae; 4) the effect of exposure to the different environmental conditions of sunlight and sediment to the temporal variation in the diversity and abundance of biota associated with the biofilm developing on the decomposing leaf litter; 5) the nutritive effect of the biofilm associated with the decomposing mangrove leaf litter on the physiological performance of shrimp post larvae.