In aquaculture, feed constitutes over 50% of operational costs, with fishmeal being the primary, yet increasingly expensive, protein source. Spirulina (Arthrospira sp) is a highly nutritious cyanobacterium which is rich in protein, vitamins, minerals, and antioxidants. Thus, it is suitable for human consumption, animal feed among other uses. Despite the conviction that the superfood holds the keys to unlocking the future of nutritional and food security challenges, its large-scale cultivation is often constrained by high production costs and resource-intensive methods. Further, little has been done to exploit the natural alkaline lake water, for Spirulina cultivation. This study investigates the potential of cultivating Spirulina using nutrient-rich alkaline water from Lake Simbi as a sustainable, cost-effective protein alternative for fish feed.
The experiment, conducted at KMFRI Sangoro in Kisumu County, evaluated Spirulina growth under varying concentrations (0%, 25%, 50%, 100%) of Zarrouk’s medium—both targeted and untargeted. Water samples were analyzed for physico-chemical properties to determine limiting nutrients.
Results indicated that while Lake Simbi water alone supported Spirulina growth, nutrient levels, particularly nitrogen, phosphorus, and potassium were significantly lower than literature values. Highest biomass yields, 1.22 g/L, were recorded in tanks with 100% Zarrouk and 50% untargeted feed, while cost-efficiency was highest in tanks with 0% feed. However, nutrient depletion limited long-term productivity in feedless setups. Moderate supplementation (50% Zarrouk) provided sustainable yields and maintained a healthy culture.
The study findings suggest that Lake Simbi water can partially support Spirulina cultivation, offering potential for localized, low-cost fish feed production. Further studies are necessary to explore alternative cost-effective nutrient enhancement for sustained productivity.
Key words: Spirulina; alternative protein source, sustainable production, alkaline lake water