REGIONAL RESEARCH

KENYA RESEARCH

Collaborating Institutions

Kenya Fisheries Department, Ministry of Natural Resources

Oregon State University–Lead US Institution

Auburn University

University of Arkansas at Pine Bluff

Cooperating Institutions

Sagana Fish Farm

University of Nairobi

Note: Experimental Design has been revised. See Addendum to the Ninth Work Plan
Note: Schedule has been revised. See Addendum to the Ninth Work Plan
Note: Schedule for 9FFR2A (Objective 1 of 9FFR2) has been revised. See Addendum to the Ninth Work Plan

Objectives

Significance
Commercial fish culture in developed countries generally achieves greatest profits when high quality, nutritionally complete feeds are used to produce high fish yields. This strategy is often impossible or inappropriate in countries where high quality feedstuffs are limited. In Africa, nutritionally complete diets for tilapia are very expensive. However, poultry diets and some purchased inputs, such as brans, can be used to intensify fish production in ponds. Disadvantages are that commercial poultry rations are not nutritionally balanced for fish, containing more digestible energy per unit of protein than recommended for fish, and brans are nutritionally deficient and often unconsumed by the fish due to small particle size. Pelletizing reduces feed losses, especially when multiple ingredients are included in the formulation. There is a clear need to develop feed/fertilizer combinations that are appropriate for fish farming in Kenya (Ngugi and Wangila, 1996). Lower quality pelleted feeds formulated specifically for tilapia, combined with fertilization regimes to increase the availability of natural food organisms, may be an economically appropriate approach for intensification of tilapia culture in Africa.

This research is feasible in Kenya. Poultry diets and dairy meal are sometimes used in Kenya to feed tilapia. There is one commercial fish feed manufacturer in Kenya. They make trout feeds and small amounts of tilapia feeds and are willing to formulate other feeds.

Fertilization is often practiced to increase the abundance of natural food organisms in fish ponds receiving nutritionally deficient feeds. Assessment of the relative contribution of natural food organisms to fish growth in fed ponds would be a valuable contribution in the development of management practices involving nutritionally incomplete feeds. This assessment can be accomplished by analyzing the stable isotope ratios of N and C in the natural foods, feeds, and fish flesh.

Anticipated Benefits
Collaboration with a local feed manufacturer can lead to a viable partnership with private enterprise to develop the most cost-effective tilapia feed for ponds in Kenya and the region. The development of cost-effective feeds in Africa may increase the profitability of fish farming in the region and stimulate commercial aquacultural enterprises. The production of natural food organisms in feed-fertilizer management practices is often highly variable across sites; the need to evaluate this more intensive fish production practice under different environmental conditions would likely stimulate future intra-regional collaboration.

Research Design
Standard CRSP protocols will be used in all pond experiments.

Location of Work: CRSP research ponds, Sagana Fish Farm, Sagana, Kenya.

Pond Facilities: Three treatments will be replicated in four ponds of 800m² each:

Culture Period: Six months

Stocking Rates: All ponds will be stocked at densities of 30,000 fish/ha: (90% sex reversed male Oreochromis niloticus and 10% Clarias gariepinus). These proportions were used successfully in previous CRSP experiments. Average weight at stocking: 15 g for tilapia and 5 g for Clarias. Twenty-five tilapia will be stocked in cages in each pond and will not be fed. (These fish will be analyzed for C and N isotopes and compared to those in the open pond, which have access to feed.)

Test Species: O. niloticus and Clarias gariepinus

Nutrient Inputs: Feed and fertilizer treatments as described above. Feeding rates will be based on estimated biomass of tilapia: 3% of body weight per day for fish less than 50 g, 2% of body weight per day for fish between 50 and 150 g, and 1% of body weight per day thereafter. (These rates are approximately the same rates as used in Thailand when fish were fed at 50% satiation.) Depending on the diet composition, it may be necessary to feed the experimental animals a diet that is isotopically distinct from those diets to be used during the experiment for a period of 2—3 months prior to initiation of the trial.

Water Management: Water lost through seepage or evaporation will be replaced weekly.

Sampling Schedule: Fish will be sampled monthly by seining to determine average weight for adjustment of feeding rates. Thirty fish of each species will be weighed and measured individually to obtain standard deviations. Water quality will be sampled according to standard CRSP sampling protocol. For isotope analyses, fish and food/feed samples will be collected at stocking, at harvest, and every 1.5 to 2 months after stocking. Gut contents of caged and free-swimming fish will also be collected at least twice to back up results of the fish tissue analyses. This will be done in case the prepared feeds are not isotopically distinct from the natural foods, and visual distinction of consumed food items is necessary. Harvest data will include fish yield (fish weights & fish numbers), water quality data, percent of market-size fish, and reproduction. Proximate analysis of fish and feeds also will be conducted using standard methods.

Statistics: Null hypotheses: The nutrient input regimes tested do not differ significantly with respect to their effects on fish growth, yield, feed conversion, or C or N stable isotope ratios. Statistical analyses: ANOVA

Regional Integration
Fertilizer-enhanced natural pond productivity, required to supplement the nutritional deficiencies of lower quality fish feeds, will likely be variable within a region. The most profitable feeding-fertilizing regime under the test conditions at the Sagana station may be substantially more or less profitable at other sites. Assuming that the expected increased fish yields generate regional aquacultural interest, this topic could be a focus for future regionally integrated research.

Schedule
July to November 1999

UAPB personnel will arrange for isotope analysis of samples, interpret isotope data and compare it to production data from feeding trials in Kenya (in collaboration with Kenyan scientists and students), and conduct proximate analysis of fish and feed samples. Kenyan and Auburn personnel at Sagana fish farm will conduct the feeding trial, collect and process samples for isotope analysis and collect production data. Some proximate analysis also may be conducted at Sagana (depending on availability of equipment).

Report Submission
Final report: June 2000

References
Anderson, R.K., P.L. Parker, and A. Lawrence, 1987. A 13C/12C tracer study of the utilization of presented feed by a commercially important shrimp Penaeus vannamei in a pond growout system. Journal of the World Aquaculture Society, 18:148-155.

Diana, J.S., C. Kwei Lin, and Y. Yi, 1997. Stocking density and supplemental feeding. In: D. Burke,
B. Goetze, D. Clair, and H. Egna (Editors), Fourteenth Annual Technical Report, 1996. Pond Dynamics/Aquaculture Collaborative Research Support Program, Oregon State University, Corvallis, Oregon, pp. 133-138.

Lilyestrom, C.G., R.P. Romaire, and P. Aharon, 1987. Diet and food assimilation by channel catfish and Malaysian prawns in polyculture as determined by stomach content analysis and stable carbon isotope ratios. Journal of World Aquaculture Society, 18:278-288.

Lochmann, R. and H. Phillips, 1996. Stable isotopic evaluation of the relative assimilation of natural and artificial foods by golden shiners Notemigonus crysoleucas in ponds. Journal of the World Aquaculture Society, 27:168-177.

Ngugi, C.C. and B.C.C. Wangila, 1996. Aquaculture in Kenya: Status and constraints. In: Fisheries for Sustainable Development. Technical Report No.1, Department of Fisheries, Moi University, Eldoret, Kenya, pp. 33-42.