Small tropical reservoirs and fish cage culture: a pilot study conducted in Machakos district, Kenya

Abstract

The findings of this study provide useful insights into the key aspects of fish cage farming to be considered during setting and overall management of multi-purpose water resources so as to maximise their aquacultural potential. The study was conducted in Machakos District, Kenya, to characterise limnochemistry and algal composition of three small man-made reservoirs Ngeki, Ngei and Kavovi, used for cage culture of Nile tilapia (Oreochromis niloticus). In Ngeki, the open water was compared with areas in between the cages and significant differences in dissolved oxygen were found. For N, P and chlorophyll-a, no differences were noticed. In all the reservoirs, temporal variations were noticed for all parameters except NO 3 N and NH 4 N. Peak concentrations of nutrients occurred during the rainy season with lower values in the dry season (below detectable limits for SRP). All reservoirs were classified as hyper-eutrophic with a strong positive correlation between chlorophyll-a and TP. Algal abundances changed with season. Chlorophyta dominated at the start of the rainy season, while cyanobacteria prevailed at the onset of thermal stratification. Diatoms prevailed in the dry season but were notably absent in the rainy season. It was concluded that all the reservoirs are suitable for cage culture of Nile tilapia, but this should be undertaken with caution considering critical periods when anoxic conditions may occur.

Water quality in Ponte Pensa Aquaculture Park, Solteira Island Reservoir, SP, Brazil, where fish are cultivated under great-volume cage system

“…According to PCA results, the analyzed abiotic variables were influenced by seasonality. Other authors also pointed out seasonality as one of the factors influencing variations in abiotic factors, mainly water transparency, in studies similar to the current one (Alves and Baccarin, 2005;Borges et al, 2010;Kaggwa et al, 2011;Ayroza et al, 2013;Bartozek et al, 2014).…”

“…After the introduction of the first cages in the farming sites in February 2012, DO values dropped at Station 2, which was used for fish farming. Several studies (Demir et al, 2001;Veenstra et al, 2003;Alves and Baccarin, 2005;Bristow et al, 2008;Degefu et al, 2011;Kaggwa et al, 2011;Ayroza et al, 2013) have already recorded DO concentration reduction in cage farming sites.…”

Response of phytoplankton to an experimental fish culture in net cages in a subtropical reservoir

“…The magnitude of the effects of cage culture in the ecosystem depends primarily on the intensity of fish production, the residence time of the water and the environmental carrying capacity to assimilate nutrients input (Guo and Li, 2003;Kaggwa et al, 2011). These effects are generally stronger in water bodies with low water removal.…”

“…Despite of the low number of net cages employed, studies on the impacts of fish farming in water quality (Guo and Li, 2003;Guo et al, 2009;Kaggwa et al, 2011;Sipaúba-Tavares et al, 2014). Borges et al (2010), in an experiment with tilapia (Oreochromis niloticus L.) in net cages, in a Brazilian subtropical reservoir (Rosana Reservoir), observed an increase in total nitrogen and ammonium concentrations after the installation of the net cages.…”

Bioremediation using Gracilaria chouae co-cultured with Sparus macrocephalus to manage the nitrogen and phosphorous balance in an IMTA system in Xiangshan Bay, China

“…Wen et al (2007) reported that the N and P input by trash fish accounted for 70.62% and 83.11% of the total N and P input, respectively, in Daya Bay, China. Kaggwa et al (2011) showed that the maximum concentration of nutrients occurred during the rainy season in the fish cage culture area in Machakos District, Kenya, which suggested that rainfall was a contributor to the nutrient load. However, in the present study the contribution by rainfall was ignored because it represented such a small proportion of the total N and P input.…”