NUTRITIVE VALUE OF Arthrospira platensis, (Gomont, 1892) AND Oocystis sp. AS PROTEIN SOURCES IN NILE TILAPIA FISH FEEDS

Abstract

Fish farming is a rapidly developing industry globally due to the increasing demand on protein for feeding the rapidly increasing human population. On the other hand, capture fisheries have significantly declined. One major impediment to aquaculture is access to affordable fish feeds, due to the expensive crude protein component. To address this challenge, this study investigated the potential of two algal species: Arthrospira platensis, and Oocystis sp. as sources of crude protein in fish feeds. The objectives of this study were to establish the most appropriate fertilizer regime that would allow for the optimum Oocystis sp. growth to generate adequate biomass, formulate fish feeds from the two algal species, analyse their proximate composition, and determine their efficiency in the growth of Oreochromis niloticus. Two experimental set-ups were made in the study, the first set-up involved the culturing of Oocystis sp., and determining its biomass and crude protein contents. The growth rate, doubling time, and divisions per day were determined from the changes in chlorophyll-a concentration. Proximate analysis was done on subsamples of Oocystis sp. and A. platensis. The second experimental set-up involved the assessment of the performance of O. niloticus fed on seven formulated diets namely, diet 1 was the control with Caridina nilotica as the protein source and the other six diets had 10%, 20%, and 40% replacement of C. nilotica with Oocystis sp. (diet 2-diet 4), and A. platensis (diet 5-diet 7). To achieve this, a ten-week experiment was conducted at the Agro-science Fish Park at Egerton University, where 21 hapa nets, each containing of 30 O. niloticus fry were subjected to the seven diets in triplicates. The results of the first experiment showed that there were no significant differences in the mean Oocystis sp. biomass (p> 0.05), growth rate (p> 0.05), divisions per day (p> 0.05), and doubling time (p> 0.05) from the different treatments. The overall body weight of the fish increased significantly (p < 0.05) from 0.240 g to 8.486 g. There were significant differences (p< 0.001) in the final body weight between diet 1 (7.778 ± 0.498 g) against diet 2 (9.985 ± 0.504 g) and diet 5 (9.937 ± 0.366 g). Therefore, this study showed that inorganic fertilizers can be used as cost-effective media in the mass scale culture of Oocystis sp. and that 40% substitution of C. nilotica as a protein source with either A. platensis, or Oocystis sp. enhances the growth of O. niloticus fry and reduces production cost, while having no adverse effects on the growth performance. In conclusion, the study revealed that there is great potential in the use of A. platensis, and Oocystis sp. as protein sources in fish feeds. This study recommends the potential inclusion of A. platensis or Oocystis sp. to lower the cost of production so that aquaculture not only becomes more profitable but contributes to increased food and nutritional security.