Demand for organic products for human consumption has been on the increase due to the belief that organic products are safer and healthier to the consumer and the environment. In developing countries, Nile tilapia (Oreochromis niloticus) is usually grown in low-input organically fed ponds with little or no high protein supplementary feeding, an environment suitable for production of organic fish. However, Nile tilapia from such production systems do not attain large sizes which leads to low pond yields. This paper presents results of an attempt to improve the performance of organically farmed tilapia through selection for growth in organically fertilised earthen ponds. The selection environment consisted of earthen ponds fertilized daily with 50 kg dry matter (dm)/ha chicken manure. Body weight increased with selection and substantial response was recorded. Gut length increased with selection for body weight. Moreover, gut length and body weight were genetically highly correlated indicating that tilapia selected for growth on a herbivorous diet may develop longer guts as a mechanism for increasing capacity and efficiency for nutrient absorption. Taken together, these results demonstrate the feasibility of selection for growth of organic Nile tilapia. Meanwhile, organic certifications for Nile tilapia should be instituted for better prices and increased profits of organic fish.