Abstract
Keywords : live food, rotifers, protozoa, phytoplankton, fertilisation, earthen ponds Surveys of naturally-occurring live food for fish in Makoba earthen ponds, Zanzibar were conducted from November 2001 to August 2002. This involved identification of dominant plankton in the water column as well as the composition of algal mats. The effect of nutrients on the composition and abundance of the organisms was also assessed. Protozoa were found to be the dominant zooplankton in the water column, followed by rotifers. The most abundant phytoplankton genera were Prorocentrum (13.4%), followed by Coscinodiscus (10.4%) and Diplopsalopsis (7.5%), while the benthic algal mats were dominated by cyanobacteria, mostly Spirulina (22%) and Oscillatoria (18.4%). To complement the surveys, a time-series experiment was conducted for 21 consecutive days to assess the dynamics of plankton in earthen ponds and simulation containers, using a fertilisation rate of 83 kg dry matter/ha/day. Protozoa were the most dominant zooplankton in the earthen ponds. Fertilisation with chicken manure was effective in increasing the number of rotifers in simulation containers, but not in the earthen ponds; this was probably because, unlike the earthen ponds, the simulation containers were sheltered from external influences such as rain, flooding by tide water, etc. The phytoplankton genera Pyramimonas (16.7%), Biddulphia and Microcystis (8.3%) dominated the fertilised ponds. Chlorophyll-a concentration ranged from 1.8 to 16.9 mg/l, whereas soluble reactive phosphorous (SRP) and ammonia-N reached maximum concentrations of 1.4 mg-at.P/l and 9.7 mg-at.N/l respectively. Overall, salinity and fertilisation played a major role in controlling the abundance of live/natural food in the system. Western Indian Ocean Journal of Marine Science Vol.2(1) 2003: 45-56
Highlights
Food availability is one of the most important biotic factors affecting the success of fish culture
Preliminary studies conducted between 1999 and 2001 at Makoba, Zanzibar have revealed that fertilisation of earthen ponds using chicken manure, while maintaining low salinities could provide optimal conditions for the production of various live food types, especially rotifers, for fry and fingerlings (Kyewalyanga & Mwandya, 2002; Kyewalyanga et al, unpublished data)
In cases where significant differences were detected at P < 0.05, the ANOVA was followed by a Posthoc comparison of means—Tukey honest significance difference (HSD) test—applied to determine which means were different (Table 2)
Summary
Food availability is one of the most important biotic factors affecting the success of fish culture. The type and nature of the food is of paramount importance to any aquaculture operation. Preliminary studies conducted between 1999 and 2001 at Makoba, Zanzibar have revealed that fertilisation of earthen ponds using chicken manure, while maintaining low salinities (between 20–30 ‰) could provide optimal conditions for the production of various live food types, especially rotifers, for fry and fingerlings (Kyewalyanga & Mwandya, 2002; Kyewalyanga et al, unpublished data). KYEWALYANGA food with time and the role played by environmental variables, nutrients; (ii) examining the importance of fertilisation (with chicken manure) in increasing the quantity of the food; and (iii) comparing outcomes from simulation containers with those from natural ponds. The results obtained are discussed in light of their usefulness in establishing and maintaining fish nurseries, under mesocosm conditions
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