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Newsletter and Technical Publications
<International Source Book On Environmentally Sound Technologies
for Wastewater and Stormwater Management>

Sanitary conditions of the fish

Microbiological analysis performed in the fish sampled in the breeding tanks between March and May, 1998 evidenced an average concentration of 1,386 heterotrophic bacteria and 10 fecal coliforms per gram of fish. Those values are well below the 10 million heterotrophic bacteria and 400 fecal coliforms considered by the ICMFS as limits for warm water fish. All the same, the values found are also below the values of 5,664 and 408 recorded in 1988-90 for the same parameters, showing that the Unit is currently producing fish with higher quality than at the beginning.

The analysis of cadmium, chromium, mercury and lead showed that there was no accumulation of those heavy metals, since the low concentrations detected in the raw wastewater are completely removed in the treatment process.

Fish production

The continuous distribution pilot program was maintained to serve the local market; to date, over 19,000 kg of tilapia between 250 and 600 g each were marketed for direct human consumption and 340,000 tilapia alevines to be bred in Peru farms. This permanent operation of the Aquaculture Unit has also maintained an important qualification program for professionals, teachers, university students and technicians working in other similar plants.

The investigation program carried out in the last years has led to the results disclosed in table 5.37.

a.            Comparative breeding of silver and red tilapia

Though no differences were found in the survival of both kinds, the silver tilapia showed a growth rate 2.44 times higher than the red tilapia. The silver tilapia productivity was also 2.6 times higher, reaching 24 kg/ha/day between 33 and 67 days. Those results could be due to the fact that the silver tilapia is more adapted to natural food, while the red tilapia is brought up only artificial feed only in Panama and Costa Rica.

b.            Comparative breeding of silver tilapia from Panama and San Juan

The preliminary results of up to 90 days of breeding show that the Panama tilapia has a growth rate 39% above the one existing in San Juan, possibly because of a better genetic selection of the first and greater consanguinity of the second. The combination of both, though leading to improved growth, does reach the Panamanian rates. In October the survival will be assessed and that trend will be definitively confirmed. Without doubt, the results already lead to believe that the Panama kind would replace the existing one to improve production.

Table 5.37: Results of the comparative breeding of red and silver tilapia in the treated water from the wastewater lagoons of San Juan (from Nov 21, 97 to Apr 6, 98)

Variety Unit Red Til. Grey Til.
Initial Population No. 1000 1000
Final Population No. 696 671
Survival % 69.6 67.1
Initial Density Fish/m2 1.25 1.25
Final Density Fish/m2 0.87 0.84
Initial Weight g/fish 35.13 34.04
Weight 136 days ahead G/fish 130.6 266.43
Increm. Weight g/fish 95.48 232.39
Growth rate g/fish.day 0.7 1.71
Initial Biomass kg/ha 439 425
Biomass 136 days ahead kg/ha 1,136 2,235
Increm. Biomass kg/ha 697 1,809
Productivity kg/ha.day 5.13 13.3
Results from the comparative breeding of tilapia of San Juan, PanamEand combined with treated water from the San Juan stabilization ponds (from Apr 20 through Jul 20, 1998)
  Unit San Juan Panama
Initial Weight g 2.0 1.6
Weight 90 days ahead g 29.6 40.0
Increm. Weight g 27.6 38.4
Growth Rate. g/dia 0.92 1.28
Biomasa Initial kg/ha 150 120
Biom. 90 days ahead kg/ha 2,220 3,000
Increm. Biomass kg/ha 2,070 2,880
Productivity kg/ha.dia 69.0 96.0

Conclusions and recommendations

Among the main achievements of the study, it may be said that the treatment of wastewater in wastewater ponds is appropriate to obtain effluent with levels of fecal coliforms below 100,000 NMP/100 ml, the quality limit established for the production of fish suitable for direct human consumption.

The fish production system presented encompasses the introduction of a "Nile Tilapia" Oreochromis niloticus population at the rate of two 60g fish per square meter. In four months, the system achieves a load capacity of 4,400 kg/ha of 250 g fish and a productivity of 30.8 kg/ha/day, without artificial feed.

The market survey of Tilapia carried out in the Greater Lima evidenced good acceptance of the tilapia, there being no evidence of reservations as to the origin of the product. The potential monthly demand in 1991 was 180 MT at US$1.00 per kilo of tilapia.

The research program carried out in the past years has led to the improvement of the productivity of the system. Thus, it was observed that the common carp (Cyprinus carpio) is not as resistant as the tilapia in the conditions of the treated wastewater of San Juan. It was also proved that the red tilapia grows less than the silver tilapia traditionally used in San Juan, and that the introduction of the new variety of tilapia from Panama is showing better growth than the existing variety, therefore it would be replaced to improve production.

CEPIS is currently designing integrated wastewater treatment and utilization units combining different agricultural, aquacultural and forestry elements to diversify the production, improve the efficiency and reduce the investment risks.

Investigation should be continued to optimize the fish breeding systems in treated wastewater, employing other species, assessing the quality of effluent from lagoons other than wastewater lagoons, and the production in other tropical areas. For that purpose, showcase units should be implemented in larger scale and in tropical areas, where a larger productivity is expected. Those units will support a dissemination and qualification program to ensure the repeatability of this alternative technological scheme.

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