These Notices of Publication announce recently published work carried out under PD/A CRSP sponsorship. To receive a full copy of a report, please contact the author(s) directly unless it is otherwise noted.

Research Report 01-172

Management to minimize the environmental impacts of pond effluent: Harvest draining techniques and effluent quality

C. Kwei Lin, Madhav K. Shrestha, and Yang Yi
Aquaculture and Aquatic Resources Management
School of Environment, Resources and Development
Asian Institute of Technology
PO Box 4, Klong Luang, Pathumthani 12120, Thailand

James S. Diana
School of Natural Resources and Environment
University of Michigan
Ann Arbor, MI 48109-1115, USA

An experiment was conducted to evaluate the amount of wastes discharged from fish ponds during harvest and to assess pond draining schemes and harvest techniques that may reduce waste loading in effluent water. Nile tilapia (Oreochromis niloticus) were cultured for 113–119 days in twelve 200 m² ponds with fertilization and supplementary pelleted feed. There were four treatments with three replicates each: (A) ponds were treated with teaseed cake at a rate of 10 ppm to partially anaesthetize tilapia 1.5 h prior to harvest by three seinings without draining ponds; (B) ponds were limed at a rate of 75 ppm calcium hydroxide 24 h prior to harvest and drained by sequential complete draining, and then tilapia were collected from a harvesting pit; (C) ponds were drained by sequential complete draining and tilapia were collected from a harvesting pit; and (D) ponds were drawn from 100 to 50 cm and tilapia were harvested by two seinings, followed by complete draining and collection of the remaining tilapia from a harvesting pit. Treatment D is the common practice in Thailand. The harvest efficiency was 97% in treatment A. Comparing the harvest efficiency for the first two seinings, there were no significant differences between treatments A and D. Liming in treatment B resulted in significantly higher concentrations of 5 day biochemical oxygen demand, total settable matter, total solids and total phosphorus (TP) in the water discharged from the last 25 cm depth than those at both 100–50 and 50–25 cm depths, while there were no significant differences in effluent quality parameters among different depths in both treatments C and D. Concentrations of all effluent quality parameters in the water discharged from the last 25 cm depth in treatment B were higher than those in treatments C and D. Seining in treatment D resulted in the highest concentrations of all effluent quality parameters except TP at middle depth. Compared with the common draining practice, adoption of the sequential complete draining schemes (treatments B and C) caused 33–86% reductions for different effluent quality parameters except total nitrogen and TP in the discharged wastes. The present experiment showed that the use of teaseed cake to anaesthetize tilapia could allow effective harvest by seining, without draining the pond. Alternatively, the discharge of potential pollutants from ponds into the environment could be reduced by sequential complete draining of ponds and collecting fish from harvesting pit (treatments B and C), and can be further reduced by modification of sequential partial draining of pond water level to 25 cm above pond bottom and seining fish without further draining. The present experiment demonstrated that appropriate management in pond draining and fish harvest could minimize the environmental impacts of pond effluents.

This abstract was based on the original paper, which was published in Aquacultural Engineering, 25(2001):125–135.

Research Report 01-173

Developments in integrated aquaculture in Southeast Asia

C. Kwei Lin and Yang Yi
Aquaculture and Aquatic Resources Management Program
School of Environment, Resources and Development
Asian Institute of Technology
P.O. Box 4, Klong Luang, Pathumthani, Thailand

Integrated aquaculture is inclusive of interactive utilization of resources and ecosystems in the artificial rearing of aquatic animals and plants. By the nature, purpose and scale of the operation, integrated fish culture can be categorized into five major modes. One is the traditional small-scale subsistence farming where fish are produced by recycling on-farm wastes in ponds or rice field, two is recycling of human excreta, three is the “industrialized” commercial operation by integrating medium and large-scale poultry or livestock farms with ponds for fish production, four is integration of aquaculture with natural ecosystems, e.g., shrimp culture with mangroves, cage and pen culture in lakes, cove culture in reservoirs. The fifth is environmental-oriented integration, where waste effluents from intensive aquaculture ponds are recycled to improve water quality and to grow filter feeder/herbivores or macrophytes as secondary crops. This paper presents concepts and practical examples for some of these systems.

This abstract was based on the original paper, which was published in L.M.B. Garcia (Editor), Responsible Aquaculture Development in Southeast Asia, Proceedings of the Seminar-Workshop on Aquaculture Development in Southeast Asia, 12–14 October 1999. Southeast Asian Fisheries Development Center (SEAFDEC), Iloilo, Philippines, pp. 77–88.

Research Report 01-174

Sex reversal: The directed control of gonadal development in tilapia

Ronald P. Phelps
Department of Fisheries and Allied Aquacultures
Auburn University, Auburn, AL 36849

Tilapia are becoming the most widely produced species of freshwater fish in the world. They can be produced in a variety of settings using a range of nutrient inputs. Males are the preferred sex to culture as they grow faster and divert less energy into reproduction. Males can be obtained using a variety of procedures but the most practical is through controlling gonadal development. Recently hatched tilapia fry have gonads that have not differentiated into ovaries or testes. It is possible to give such fish an exogenous source of hormone (androgen or estrogen) to control the development of the gonad. Fry less than 12 mm long can be harvested by seining along the edge of a spawning pond or from specialized spawning ponds where the pond is drained and harvested after 16-21 days. Proper size fish can also be obtained through a more intensive management approach where eggs are collected from the mouths of incubating females. Most commonly used approach to obtain male tilapia is to feed fry for 28 days or less a feed containing the androgen methyltestosterone. When fed properly the frequency of females in the population can be reduced to less than 5%. The short treatment duration very early in the fish’s life history and rapid metabolism of metyltestosterone helps insure that tilapia are free of MT before fish reach the consumer. The production techniques associated with sex reversal are efficient and straight forward enough so that sex reversal has become the commercial procedure of choice to produce male tilapia fingerlings and has been a significant factor in the rapid growth of the tilapia industry.

This abstract was based on the original paper, which was published in D. Meyer (Editor), 6to Simposio Centroamericano de Acuacultura Proceedings: Tilapia Sessions, 22–24 August 2001. Tegucigalpa, Honduras, pp. 35–60.

Research Report 01-175

Nutrition and feeding of tilapia

Daniel E. Meyer
Panamerican Agriculture School
Zamorano, Honduras

According to the most recent estimates, world production of cultured tilapia (Oreochromis sp.) is in excess of 1 million metric tons. Tilapia are cultured in a great variety of aquatic environments and with many different management protocols.

The management of modern commercial tilapia production systems is an aquatic analog to North American feedlots used for beef production. The fish are held in cages and raceways at stocking densities that can exceed 100 fish/m³. The fish are fed to satiation several times each day using specially formulated feeds, and then promptly sacrificed and filleted, for shipment to market.

Modern manufactured fish feeds are not well assimilated by tilapia. Typically only a small fraction (<30%) of the total content of N and P in the diet is incorporated into the fish’s biomass (= growth). The remaining amounts of each macronutrient are never ingested (feed not consumed), excreted into the pond water, lost as part of fecal material, or used for maintenance.

There are several commercial farms in Central America that are successfully growing tilapia to export fresh fillets to North America. Additional farms are coming online in the region. In Honduras the demand for tilapia has increased in the past few years and several farms are focusing on local markets. No matter where they are sold, the purchase of feed for fattening these fish is the largest cost in the production budget for commercial tilapia farmers regionally.

Small-scale tilapia culture has not prospered locally. Fish culture is not a part of traditional agriculture in Central America. Local NGO run extension programs have had limited success in assisting rural farmers in growing tilapia. One important problem is the lack of knowledge in the proper management of costly inputs such as fish feed.

How farmers manage the feeding of their fish is often the key to success, or reason for the failure, of a particular farm. This paper discusses some of the biological aspects of tilapia in relation to its nutritional needs and practical feeding of fish in the culture environment.

This abstract was based on the original paper, which was published in D. Meyer (Editor), 6to Simposio Centroamericano de Acuacultura Proceedings: Tilapia Sessions, 22–24 August 2001. Tegucigalpa, Honduras, pp. 61–70.

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