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Polyculture of Grass Carp and Nile Tilapia with Napier Grass as the Sole Nutrient
Input in the Subtropical Climate of Nepal
Feeds and Fertilizers Research 3 (10FFR3)/Experiment/Thailand
Asian Institute of Technology, Thailand
C. Kwei Lin
Institute of Agriculture and Animal Science, Nepal
Madhav K. Shrestha
University of Michigan
James S. Diana
1) Evaluate the growth of grass carp and tilapia fed with napier grass in polyculture.
2) Evaluate the nutrient and water quality regimes of pond water.
3) Determine the composition of foods consumed by Nile tilapia.
4) Determine the optimal ratio of grass carp to Nile tilapia in polyculture.
Grass carp Ctenopharyngodon idella, a herbivorous species, is a commonly cultured species in many parts of the world, especially in East Asia. In China, polyculture of grass carp with other species of different feeding habits is traditionally practiced, whereas grass carp consume low value vegetative waste and increase natural food production in the pond by nutrient recycling and fecal production (Yang et al., 1990; Li and Mathias, 1994). The effectiveness is depicted in a Chinese saying "one grass carp raises three silver carp." It was reported that a 5:1 stocking ratio by weight is most suitable for grass carp and filter-feeding species in a polyculture system consisting of silver carp Hypophthalmichthys molitrix, bighead carp Aristichthys nobilis, and common carp Cyprinus carpio (Yang et al., 1990). However, as grass carp are known to feed on a wide variety of plants, the quantity and quality of natural food production derived from recycling of grass carp wastes depend largely on the type and input of forage provided.
In Nepal, pond fish culture is mostly conducted in the southern subtropical region, where pond water temperature falls between 15-20 C during winter period from mid-November to mid-February (Shrestha 1999). Polyculture of herbivorous carps is a common practice in Nepal. The major constraints for small-scale, resource-poor farmers are fish feeds and chemical fertilizers, which are expensive and unavailable, while livestock manure is traditionally used for land crops (Shrestha and Yadav, 1998; Shrestha 1999). Exploration of easily available or easily grown plant material that is not used in human food production is a prime need to solve the problems of these fish farmers. Napier grass Pennisetum purpureum is a high yielding and perennial tropical grass (Humprey, 1978; Edwards, 1982) that is accepted by grass carp and can produce a reasonable yield (Venkatesh and Shetty, 1978; Shrestha and Yadav, 1998; Shrestha, 1999). As in Chinese polyculture systems, a major portion of plant biomass consumed by grass carp returns to the pond as organic manure which stimulates plankton production for other planktivorous fish in the same ponds (Woynarovich, 1975).
Recently, Nile tilapia Oreochromis niloticus was introduced to Nepal and has been cultured in experimental scale (Shrestha and Bhujel, 1999). Nile tilapia is an excellent candidate to be polycultured with grass carp to utilize the natural foods derived from plants fed to grass carp. Polyculture of grass carp and Nile tilapia may have an additional advantage due to the fact that large grass carp can prey to some extent on tilapia fry spawned in the pond (Spataru and Hepher, 1977). To fully utilize available resources, this system should be tested and the ratio of grass carp to Nile tilapia should be evaluated in polyculture ponds.
The results of this study will investigate a new polyculture system in Nepal as an alternative strategy to culture of grass carp by small-scale farmers. It will not only apply to Nepalese systems, but may also benefit fish
culturists in many other countries where grass carp and Nile tilapia are commonly cultured.
Location: Institute of Agriculture and Animal Science (IAAS), Nepal
Methods: Pond research
Pond Facility: 15 cement tanks (5x4.8x1.5 m) will be used.
Culture Period: 180 days
Stocking Density: Grass carp (100 g size) at 0.50 fish/m2, Nile tilapia (10 g size) at 0, 0.25, 0.50, 1.0, and 2.0 fish/m2.
Test Species: Grass carp Ctenopharyngodon idella and Nile tilapia Oreochromis niloticus
Nutrient Inputs: Chopped napier grass Pennisetum purpureum ad libitum
Water Management: Maintain at 1.5 m depth
Water quality: standard CRSP protocol, biweekly water quality sampling and monthly analysis of diel conditions at various depths.
Fish growth: monthly and total harvest
Gut contents: ten grass carp and ten Nile tilapia from each pond will be sampled randomly from fish removed at harvest and used for gut content analysis.
Partial budgets will be estimated to assess costs and value of fish crops.
Statistical Design, Null Hypothesis, Statistical
Analysis: Experimental design: The experiment is a
randomized complete block design. There will be a constant stocking density of grass carp, and a control and
four stocking ratios of Nile tilapia. Each treatment will be triplicated. The treatments will be as follows:
A) grass carp only at 0.5 fish/m2 (50 g/m2) (control)
B) grass carp plus Nile tilapia stocked at 0.25 fish/m2 (2.5 g/m2)
C) grass carp plus Nile tilapia stocked at 0.5 fish/m2 (5 g/m2)
D) grass carp plus Nile tilapia stocked at 1 fish/m2 (10 g/m2)
E) grass carp plus Nile tilapia stocked at 2 fish/m2 (20 g/m2)
Fish growth and water quality trends will be analyzed for significant differences among treatments
using ANOVA. Also, feed conversion efficiencies and nutrient utilization efficiency will be evaluated over
the entire culture period for differences among treatments.
The null hypothesis is that stocking ratio of grass carp to Nile tilapia has no effect on the growth of grass carp and Nile tilapia, nutrient utilization efficiency, or water quality.
Nile tilapia is commonly cultured throughout Asia, while grass carp is regarded as high valued fish in China, Thailand, Vietnam and Laos. The successful polyculture of grass carp and Nile tilapia using napier grass will provide an alternative strategy for small-scale resource-poor farmers. It will be used by the AIT outreach program as a possible extension method to regional farmers.
April to October 2002
Report submission: January 2003
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Humprey, L.R., 1978. Tropical Pastures and Fodder Crops. Longman Group Limited, Longman House, England, 145 pp.
Li, S.F. and J. Mathias (Editors), 1994. Freshwater fish culture in China: principles and practice. Elsevier, Amsterdam.
Shrestha, M.K., 1999. Summer and winter growth of grass carp (Ctenopharyngodon idella) in a polyculture fed with napier grass (Pennisetum purpureum) in the subtropical climate of Nepal. J. Aqua. Trop., 14(1):5764.
Shrestha M.K. and R.C. Bhujel, 1999. A preliminary study on Nile tilapia (Oreochromis niloticus) polyculture with common carp (Cyprinus carpio) fed with duckweed (Spirodela) in Nepal. Asian Fisheries Science, 12:8389.
Shrestha, M.K. and C.N.R. Yadav, 1998. Feeding of napier (Pennisetum purpureum) to grass carp in polyculture: A sustainable fish culture practice for small farmers. Asian Fisheries Science, 11:287294.
Spatatu, P. and B. Hepher, 1977. Common carp predating on tilapia fry in high density polyculture fishpond system. Bamidgeh, 29:2528.
Venkatesh, B. and H.P.C. Shetty, 1978. Studies on the growth rate of grass carp Ctenopharyngodon idella (Valenciennes) fed on two aquatic weeds and a terrestrial grass. Aquaculture, 13:4553.
Woynarovich, E., 1975. Elementary Guide to Fish Culture in Nepal. Food and Agriculture Organization of the United Nations, Rome, 131 pp.
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