Collins Muhangi

Background: Aquaculture intensification generates nitrogenous and phosphorus-rich effluents that threaten aquatic ecosystems. Fermented plant-based feeds are increasingly used to enhance nutrient digestibility and protein availability, yet their impact on effluent water quality remains poorly understood. Understanding how substrates such as banana, jackfruit seeds, and sweet potato influence ammonia, nitrite, BOD, and phosphates is critical for developing sustainable feeding strategies and minimizing environmental pollution in intensive African catfish (Clarias gariepinus) culture. Objectives: This study aimed to evaluate the effects of solid-state fermented ripe banana, jackfruit seeds, and sweet potato tuber feeds on effluent water quality in African catfish (Clarias gariepinus), focusing on ammonia, nitrites, phosphates, BOD, copper, EC, and microbial composition to identify environmentally safer feed options. Methods: African catfish (Clarias gariepinus) fingerlings were stocked in 50 L glass aquaria and fed either fermented ripe banana, jackfruit seeds, sweet potato tubers, or commercial feed as control. Each treatment was triplicated in a completely randomized design. Effluent water was sampled weekly for four weeks to measure total ammonia nitrogen (TAN), nitrites, phosphates, biochemical oxygen demand (BOD₅), copper concentration, electrical conductivity (EC), pH, and microbial composition. TAN and nitrites were determined using colorimetric HS aqua test kits, phosphates and copper via Palin 7100 photometer, BOD₅ with a magnetic stir BOD system, and microbial counts on nutrient agar. Statistical differences were assessed using Kruskal-Wallis and Dunn's post hoc tests (p < 0.05). Results: Effluent water from tanks fed fermented banana and sweet potato exhibited lower total ammonia nitrogen (0.2–0.3 mg L⁻¹) and nitrites (0.01–0.12 mg L⁻¹) compared to jackfruit seeds (TAN 1.3 p < 0.05 mg L⁻¹, nitrites 0.75 p < 0.05 mg L⁻¹) and commercial feed (TAN 2.7 mg L⁻¹, nitrites 0 mg L⁻¹). Phosphate concentrations and biochemical oxygen demand (BOD₅) exceeded regulatory limits in all treatments except partial reduction in sweet potato tanks. Copper concentrations and electrical conductivity remained below permissible limits across all feeds. Microbial analysis revealed dominance of Bacillus and Lactobacillus species, with highest Bacillus counts in jackfruit seed tanks and Lactobacillus in banana tanks. Kruskal-Wallis tests confirmed significant differences (p < 0.05) among treatments for TAN, nitrites, phosphates, BOD₅, copper, EC, and microbial counts. Conclusion: The study demonstrated the potential of specific fermented plant-based feed ingredients to mitigate nitrogen pollution in aquaculture systems. In particular, the inclusion of fermented ripe banana and sweet potato tubers in fish diets was shown to reduce ammonia and nitrite concentrations in culture water and effluent. However, high BOD and phosphate persisted, revealing a knowledge gap on nutrient release and effluent dynamics, guiding future sustainable feed research.

Background: Fermentation is defined as a biochemical process that produces energy using microorganisms from various raw material substrates. It is an ancient form of bio-preservation of food and improvement of its nutrient content. In addition to enriching the nutritional components of plant materials and preserving food, fermentation promotes the growth of beneficial microbes that play a role in human and animal health, especially in the digestive tract, commonly known as probiotics. Objectives: The current study investigated the fermentation of ripe banana, jackfruit seeds and sweet potato tubers to produce Bacillus subtilis and also examined the effect of fermentation on the biochemical properties of the plant materials used in the current study. The mentioned plant materials are the most cultivated crops in many parts of Uganda and generate a lot of food waste. Methods: The study was carried out at the soil laboratory of Mountains of the Moon University in Fort Portal tourism western Uganda. The solid fermentation of ripe bananas, jackfruit seeds and sweet potato tubers in this study was a natural process hence no inoculation of microbes onto the sample was done. Solid fermentation involved the putting the solid substrates into fermentation vessel with limited moisture. In every 3 days, temperatures, relative humidity and pH were monitored in the fermentation vessels to establish the conditions in which microbes are growing. Gram staining was done on the sub cultured microbial colonies to view the shapes of the cells and endospore structures of the Bacillus species. There were 2 biochemical tests performed on sub cultured colonies i.e. catalase test and starch hydrolysis to confirm the presence of the presence of Bacillus in the fermented samples of ripe banana, jack fruit seeds and sweet potato tubers. For catalase tests: the microbial colonies from nutrient agar on petri-dishes of ripe banana, jackfruit seeds and sweet potato tubers cultures were transferred and smeared on microscope slides. For starch hydrolysis tests, the sub cultured microbial colonies from ripe banana, jackfruit seeds, sweet potato and mix petri-dish were transferred to starch agar. Results: There was decrease in carbon-nitrogen ratio due to fermentation effect except the ripe banana which experienced an increase in carbon content from 2.44 carbon: 2.8 nitrogen to 3:12 carbon: 1.7 nitrogen. In additional to that, ripe banana produced high population of microbes with colony forming units of 1.6 · 104 on day 3.4 · 104 on day 6, 1.05 · 105 and 1.08 · 105 on day 12. Conclusion: All the fermented samples ripe banana, jackfruit seeds, sweet potato tubers and mixed samples contained Bacillus since their microbial colonies displayed rod shaped cells and gram positive and they tested catalase. Fermentation improves the biochemical properties of ripe bananas as evidenced by increase of crude proteins and fats and carbon. For samples jackfruit seeds, fermentation negatively affect the biochemical properties since they lost carbon, crude proteins and fat.