FABE 652
Ecosystems for waste treatment

Lecture #9
Manure and Fish Farming

Wohlfarth, G.W., Schroeder, G.L. 1979. Use of manure in fish farming--A review. Agricultural Wastes. 1:279-299.

CLASS ACTIVITY: Divide the class into 3 groups to summarize and discuss the 3 following topics related to the above article.

1) On page 281 the authors state that they ‘are not aware of any study starting with the manure as it enters the pond and following its components through the aquatic system to harvesting by the fish. In addition to summarizing information in the article related to this topic, you are to draw a food web that illustrates the movement of manure from addition to fish biomass.

2) The authors cite many past studies of aquaculture with manure applications (Tables 2 and 3). However, many of these results conflict with one another. Please summarize these results, and, based on your conclusions design an optimal fish farm.

3) An interesting explanation of when it is most profitable to feed fish manure and when it is more profitable to use fish feed is included. Please summarize this discussion, and provide at least 4 real-world examples that support or do not support their conclusions.

Some points to consider in your summary:

• What are the implications for our present system and the future use of similar systems?

• How have things changed since 1979? Will this affect your conclusions?

• Do you agree with the findings of the paper?

• What are weaknesses of the paper?

• What are the main points?

SOME SUMMARY POINTS:

Maximum yields per unit area are higher with higher with high-protein foods, than with manure, but are obtained at a greater cost.

Profits per unit time are higher with the use of feedstuffs when fish are relatively expensive, but when fish are cheap higher profits are obtained with manure.

Best results with manure occur when it is applied frequently.

Polyculture vs. monoculture—advantages are listed on page 281.

How does the manure flow through the system? What is the total food chain that is being supported by the manure?

Ducks and pigs were most common in 1979—‘In principle, any intensive livestock unit cold be integrated with fish farming to the mutual benefit of both units.’

The amount of manure used and especially the frequency of application are probably more critical than the source of manure. Complete manure breakdown described on page 283.

Summarize findings of applying manure to fish ponds:

• Higher yields with feed than manure
• Higher yields with fertilizers than manure
• Large yield when manure and fertilizer combined
• Relatively high yields produced with only manure with polyculture (page 288)
• Little difference in manure types (page 288)
• Yields with manure, although lower, have a much lower cost
• Adding manure to other type of feed not really helpful for fish growth (page 291)

Economic Comparisons

• Growing fish with manure is not always more profitable than using fish feeds (page 291)
• When fish are valued much more than feed per weight, it is more profitable to use the fish feeds. If fish are cheap, best to use manure. Manure is always cheap.

Modes of Action for Manure

• Direct consumption—Usually the addition of manure to feed pellets reduces fish growth. This may be due to lower energy and protein content of manure compared to pellets
• Manure as fertilizer for autotrophic production—through photosynthesis or heterotrophic production mineral fraction of manure can be used for cellular production—this fuels food chain. 5 units of carbon in feed result in one unit being fixed as fish flesh.
• Manure as base for heterotrophic production—1) direct consumption of manure by fish, 2) fish eat microbial slimes on detritus or flocs in water, 3) fish eat bacteria and protozoa.

Oxygen concentration and pH are higher and diurnal oxygen cycles more stable in manured ponds with fish than ponds without fish—WHY?