City sewage fish ponds in Hungary and India

Abstract

The management parameters and culture techniques followed in the production of fish in domestic sewage oxidation ponds in Hungary and in sewage-fed ponds in Calcutta (India) are compared, along with the physico-chemical parameters, and nutrient status in the context of biological productivity. The environment supporting healthy growth of fish was more stable in Hungarian oxidation ponds due to the daily introduction of sewage. The diel oxygen concentration ranged between 4 and 19 mg dm −3 in the Hungarian fish ponds and 3.2 and 16.4 mg dm −3 in the Indian ponds. The highest total ammonia was 0.9 and 3.6 mg dm −3, respectively. Of the natural fish food resources, zooplankton reached the same maxima (around 11 000 dm −3) but chironomids and oligochaetes were more abundant in Indian ponds with maxima of 22 000 and 35 000 m −2. A considerably higher fish production was realized in the tropical zone (21.3 kg ha −1 day −1) than in the temperate zone (12.0 kg ha −1 day −1) with production efficiency — in terms of percent primary production converted to fish — of 2.7 and 1.5 – 5.2 respectively. The results from both sets of ponds are presented, viz. choice of species, stocking structure and density, manipulation, period of rearing, and possibilities of implementing the technique in tropical and temperate urbanised areas with high sewage production.