On the generous advice of a friend and mentor, Pedro Casas-Cordero, I decided to follow his example and use the fish nursery as a source of nutrients for seedlings prior to their transplant to the main grow area.
To keep a staggered rotation of tilapia, we must acquire new fingerlings every 2-3 months. These 2-5 grams fish are too small to place in the large tanks in the fish house, so we must raise them for 2 months or so until they reach 50-100 grams in weight. So during this growth period, we house them in a dedicated “nursery tank,” and use their waste products to feed the seedlings after they germinate.
At the germination stage, the developing plants need little or no additional nutrition. Everything they need is amazing stored in the cotyledons of the actual seed. Once secondary leaves form, and the plant begins to grow, external nutrients are required, and we will provide these by circulating the fish water over their roots.
And so, we built a platform on which the fish tank will sit, together with a solids settling filter and a biofilter. This latter device is where the magic happens as naturally occurring microbes break down ammonia and waste solids to form nitrates that the plants can feed on. The seedlings remove the nitrates from the water and it is returned to a sump tank and then pumped back to the fish in a continuous closed loop.