Development of Techniques for the Cultivation of Fish in a Converted Wastewater Treatment Plant

The town of Davie, Florida, converted a defunct wastewater treatment plant into an aquaculture facility. A feasibility study was conducted of the facility and it was determined that tilapia would be best suited for growout at the facility. Oreochromis aureus and a hybrid of Oreochromis niloticus are the two fish currently being grown at the aquaculture facility. A review of fish culture suggests that a filtration system that influences water quality will be needed to grow healthy fish. Furthermore, harvesting will prove to be very difficult in the deep tanks, and a most practical methodology for harvesting must be devised. Two filters were built-one from PVC pipe, nylon cord, and plastic biobarrels, and the other from a PVC frame and wetland plants. Water was run through the filters for 10 days prior to taking water samples. Water samples were then collected, frozen, and transported to the lab for analysis. The water samples were analyzed for ammonia, nitrate, and phosphate concentrations. The results indicate that the filter made of the biobarrels caused a significant increase in nitrate concentrations in the water. The results also indicate that the biobarrel filter was significantly more effective than the hydroponics filter in influencing water quality. There was no significant difference in ammonia or phosphate levels between the two filters. Three separate harvesting nets were compared. One net was built of hog wire, the second net was made of a stretchable nylon mesh, and the third was made of a nonstretchable nylon mesh. There was no significant difference in the three nets used for harvesting, and, according to the catch per unit effort, it was determined that the nets were ineffective as harvesters. However, the nets did prove to be capable of crowding fish of a desired weight in such a way that facilitated catching the fish with a cast net. Two different sized cast nets were analyzed to determine their effectiveness in sampling. Each net was cast into the same depth of water 30 times and the catches per unit effort were compared. This was repeated for twelve depths. It was found that catch size was significantly different for the two nets and that catch per cast increased with decreasing depth until shallow water (\u3c5 \u3eft) prevented proper net closure. However, there was no significant difference in determining the number of fish per unit volume when comparing the catches of each net. Finally, a comparison was made between two species (Oreochromis aureus and Oreochromis niloticus hybrids) to determine which species was more suited for growth at the Aquaculture Center. Random samples of various sizes for each species were taken simultaneously for a period of time. This information was used to calculate and compare the growth rates of the two species. It was determined that, although the growth rate of blue tilapia was greater than that of hybrid tilapia, hybrid tilapia had a higher overall production rate, possibly because it could tolerate higher stocking densities. These results helped answer several questions about culture methods, and modifications to the facility, based on these results, were ultimately made