Proceedings of the Third World Fisheries Congress: Feeding the World with Fish in the Next Millenium—The Balance between Production and Environment
Comparison of Grass Carp Ctenopharyngodon idella and Puntius Puntius gonionotus Using Paragrass Brachiaria mutica as the Primary Feedstock
Qingjun Shao, Joseph A. Gartner, C. Kwei Lin
Many studies on fish culture using low-cost materials, agricultural by-products, and animal feces as fishpond inputs have been conducted in the world (Cai 1987; Edwards 1987; Sattar 1987; Sritatera 1987; Zhang 1994). According to Sattar’s and Sritatera’s reports, one important problem at small-scale fish polyculture farms in Thailand was that the herbivorous fish puntius Puntius gonionotus had very poor growth response to the addition of paragrass Brachiaria mutica (grown widely in Southeast Asia) as the feed supplied in the pond (Humphreys 1978; Edwards 1987; Sattar 1987; Balasuriya 1988). In contrast, grass carp Ctenopharyngodon idella could have a much higher potential as a herbivorous species to use paragrass. Although a huge amount of data is available on grass carp culture using grasses and plant tissues, there is little on grass carp using paragrass.
Grass carp and puntius were grown separately, in a common polyculture of Nile tilapia Orechromis niloticus, common carp Cyprinus carpio, and snakehead Channa striata. The ponds were stocked with 10,000 Nile tilapia, 2,500 common carp, and 500 snakehead combined with 10,000 grass carp per hectare in the grass carp system (ponds A and C) or 10,000 puntius per hectare in the puntius system (ponds B and D). The initial body weights and body lengths were 2.0 g and 3.4 cm, respectively, for grass carp and 5.7 g and 6.5 cm, respectively, for puntius. The stocking density in each pond was 2.3 fish/m2. Those ponds were 200 m2 (10 m × 20 m) and 2 m deep, and the slope of the walls was 1:1.25.
The daily feed rations in the first month after each sampling were 7% of the total body weight of the herbivorous fish for the grass carp system and 5% for the puntius system. In the second month applied was 125% of the amount of the former month in both systems; the feeding level was determined by the pond with the higher herbivorous fish biomass. The paragrass was chopped and broadcast into a floating bamboo frame in ponds once a day between 6:00 and 7:00 p.m. The fish stocked in each pond were sampled (10% of each species in each pond) every 2 months during the trial period except the first sampling, which was after 1 month. Benzocain (ethyl-4-amino benzoate) was applied at a rate of 20 parts per million to anesthetize fish during the sampling process. The water depth in the ponds was kept at 1.6 m by water supplied from a nearby water channel.
The nutrient values of paragrass in different experimental periods were analyzed by AOAC (1984) methods, which are presented in Table 1. The results were compared according to Duncan’s multiple-range test.