The nitrogen flow together with dissolved nutrients and other parameters are described in a large shrimp maturation operation in Ecuador. In summary, only 8.9% of the nitrogen input ended in animal tissue. Nitrate-N and dissolved organic nitrogen (DON) accounted for more than 95% of the nitrogen pool. The nitrogen dynamics in the system is driven by a nitrification based trickling filter attached population and a free living heterotrophic carbon limited in the sump. The average nitrification rate of TAN (total ammonia nitrogen) averaged 44.81 gd-1. The trickling filters worked as a nitrifier body and also reducing the organic load. There is also some evidence that the trickling filters might have also play some role in denitrification. Nitrate never reached high concentrations (<3.7 mg L-1 nitrate-N), hence did not present a danger to the productivity of the system. In general either inorganic or organic phosphorous did not undergo any major change during the study. BOD values in the sump were low averaging 1.1 mg L-1 d-1 more likely as a result of the carbon limitation of the system. A combination of low C:N ratio and high load of organic nitrogen in the trickling filter could be part of the key factors running this system. The semi closed recirculating system presented in this study has been used since 2004 providing a steady yield of nauplii without the seasonal effects typical of open system and without the accumulation of deleterious amount of waste nitrogen or the presence of pathogens. The present study demonstrates the feasibility of using a simple and inexpensive semi closed recirculating systems in a large commercial scale.