Credit: Manuel Cano Alfaro (Guatemala)
The photo shows a grow-out tank for tilapia located in Lake Amatitlán, Guatemala. The lake is one of four major lakes in Guatemala. The water supply to tilapia tank is pumped from a depth then pass through a filter of volcanic rocks and geotextile to reduce its ammonia content before reaching fish tank. The biological filtration is of top importance especially when knowing that Lake Amatitlán receives waste water of more than 2 million people that live in the upper part of the basin of the lake. The water hyacinth, Eichornia crassipes which is epidemic to the lake and seen floating in tilapia tank has been introduced to provide food supplements to tilapia in the form of natural food as represented in the macro-invertebrates attached to the roots of this weed. On the other hand, the presence of the weed in tilapia tank reduces the water quality within the grow-out tilapia tank. The lake is furnished with fourteen 5-HP aeration pumps which target to reduce the accumulation of blue green algae in the shoreline of the lake and in the same time to enhance the level of dissolved oxygen within the lake.