Nutrient content of on-farm formulated Nile tilapia (Oreochromis niloticus) feeds: Implications for the aquaculture industry in Kenya

Due to the high costs and the unavailability of good quality fish feeds in Kenya, farmers have opted to use cheaper, locally available on-farm  formulated feeds. In spite of this, farmers continue to incur losses probably due to poor nutritive quality of these on-farm feeds. Furthermore, literature on the proximate composition and appropriateness of on farm formulated feeds for raising farmed fish in Kenya is scanty. Motivated by these reasons, this study sought to investigate the proximate composition of on-farm formulated Nile tilapia feeds and selected commercial fish  feeds used in Bomet, Kericho and Nakuru Counties of the Rift Valley Region of Kenya and compared the proximate composition with the official nutrient composition of fish feeds. The method of feed formulation used was also investigated using semi-structured questionnaires. The study also estimated the weight of fish harvested at the end of a production cycle. The results revealed a significant difference between the sampled feeds’ moisture, crude protein and mineral contents and the legislated nutrient levels of the commercial feeds commonly used in the counties. There was also a significant difference between the crude protein content of feeds in the three counties (P < 0.05). More than 50% of respondent farmers in the three counties used Pearson Square Method for fish feed formulation, while the rest used the trial and error method. The mean weight of fish during harvest was 311.5±155.8 g with fish from Kericho County weighing significantly lower than those from Nakuru and Bomet Counties (P < 0.05). Most of the on-farm formulated feeds from the three counties do not meet the recommended nutrient requirements for raising Nile Tilapia. This may be contributing to the observed low weights of the fish harvested, the low fish production and the apparent stagnation of the aquaculture sub-sector in Kenya. The study recommends the formulation of good quality fish feeds through the use of proper methods and appropriate ingredients. This could be achieved through monthly farmers’ trainings on best aquaculture practices. Key words: On- farm formulated feeds, fish feed quality, Nutrients, Nile tilapia, Kenya&nbsp

Effects of pH and salinity on the sedimentation of clay particles in turbid lakes of the rift valley of Ethiopia and Kenya

Some lakes in the Rift Valley of East Africa are among the most productive in the world, while others are dystrophic, possessing a stable, opaque suspension of fine silt or clay. Understanding the causes of flocculation and sedimentation of this material could provide insight into why these lakes are so turbid. We collected samples of suspended clay from three turbid lakes (Langano and Abaya in Ethiopia, and Baringo in Kenya), measured the size-distribution and organic content of their suspended sediment, and performed laboratory studies of sedimentation rate as a function of pH and salinity. Most of the turbidity in the two Ethiopian lakes was due to particles between 0.5 and 1.5 μm, and the suspended material had a low organic content and C/N ratio in all the three lakes. Sedimentation velocity of the material increased with both salinity and pH, with velocities varying from near 0 at neutral pH and low salinity, to 3 cm h-1 as pH approached 12 or salinity approached 25 ppt in the case of Lake Abaya. These results may explain why it is only freshwater lakes that demonstrate these turbid clay suspensions, and suggest mechanisms through which their turbidity might be altered