By: William Mebane
Published: 2009-10-20


Editors: We at ECHO have followed this project for the past few years as Bill Mebane often stops by ECHO on his way to or from visits to the project in Haiti. We recognized that he had made a breakthrough when he brought reports of success with a technique developed in Israel for growing “organically certified” tilapia by adding (1) submerged bamboo poles or palm fronds and (2) a submerged “compost pile” to fertilize the pond. Microscopic organisms collectively called “periphyton” grow on the surface of the submerged poles or fronds. This is the preferred food for tilapia. According to Bill Mebane, “If used properly, the method can produce high quality protein for human consumption using a minimum of precious human and natural resources.” We asked Bill to share some of this work with our readers.

According to the Marine Biological Laboratory (MBL) website, MBL in Woods Hole, Massachusetts (USA) is “an international center for research, education, and training in biology. The oldest private marine laboratory in the [USA], the MBL currently supports a year-round staff of more than 275 scientists and support staff working in such fields as cell and developmental biology, ecology, microbiology, molecular evolution, global infectious disease, neurobiology, and sensory physiology.”

Background

In 2002, we at the Marine Biological Laboratory were asked to help enhance fish (tilapia) production in more than 50 ponds that had been built in the Cormeir area of Haiti by CODEP missionaries (CODEP, Comprehensive Development Project, has been active in Haiti for more than 15 years, and works primarily in the area of reforestation). The concrete ponds were designed to be filled via rainwater runoff from mountains and roads during the rainy season, and the fish (provided by the CODEP mission in LaCul) were to be fed commercial feed imported from the states. Political turmoil and the difficulty and cost of importing commercial fish food were problems that plagued the productivity of the ponds. The concept was good but these unforeseen obstacles resulted in the ponds being unproductive or unused.

Method

Our initial approach was to formulate fish food using locally available plant material (leaves from cassava and from calliandra, moringa and leucaena trees). These efforts were successful and the formulation was capable of growing fish. However, the method was too burdensome on both human and plant resources. The science behind making fish food is complicated, but as we found out, not nearly as complicated as making the whole process fit with the culture of Haitian life. Life in rural Haiti is a day-by-day challenge. Families spend most of their waking hours hauling water, tending crops and gathering food; they simply do not have enough time to devote to growing and making feed for livestock that takes six months to be harvested. Thanks to advice and collaboration with colleagues who have worked in aquaculture in developing areas around the world, a decision was made to use a fish culture technique better suited for rearing fish in Haiti. The method involves using what has been termed periphyton aquaculture technology(PAT). Periphyton is the green slimy material that grows on the surface of almost anything submerged in water (Figure 1). Depending on the nutrients available in the water, periphyton can contain 100% of the essential amino acids necessary for fish to grow. Tilapia, the species of fish being grown in Haiti, are especially adapted to feed on periphyton and are extremely efficient at converting periphyton into high quality fish flesh. The quantity of fish produced using the PAT technique is directly proportional to the quality of the fertilizer (compost) added to the pond and to the availability of special surfaces that the periphyton need to grow on. If done properly, the growth rate of fish reared using the PAT technique can equal that of fish being fed expensive commercial fish food.

 

Figure 1. Periphyton growing on submerged bamboo. Photo by William Mebane
Figure 1. Periphyton growing on submerged bamboo. Photo by William Mebane

 

In March 2007 we worked with CODEP to conduct training seminars in Haiti, teaching Haitian animators how to rear fish using the PAT methods. (An animator is an agricultural extension agent; each of these animators is in charge of overseeing the work of 30 to 50 fellow Haitians in specific regions of Haiti.) The animators were then responsible for getting their fellow Haitians to implement the PAT techniques in the more than 50 ponds that were currently fallow due to lack of food for fish (Figure 2).

 

 

 

 

 

Figure 2. Animators demonstrating how to install bamboo substrate for periphyton to grow on. Photo by William Mebane.
Figure 2. Animators demonstrating how to install bamboo substrate for periphyton to grow on. Photo by William Mebane.

During our most recent visit to Haiti we witnessed the harvest of a pond that had been managed by two Haitians we had trained earlier. Fish in this pond were raised using the PAT technique. Manure, leaves and minimal human labor were the only inputs. Approximately two pounds of small fish were stocked into the pond and 25 pounds were harvested! A harvest of 25 pounds is only a fraction of what the pond was capable of producing, but it was a great start. The harvested fish were sold, traded, and eaten by many people. It was inspiring to see many people reap the benefits of a nutritious meal and to see the ponds generate some income, but what was most inspiring was the enthusiasm expressed by the farmers to repeat the process and try to do it even better!

Basic Guidelines for Successful PAT Fish Rearing

Ponds (rearing units). The ponds can be earthen, concrete, or built using a liner. The depth should be less than a meter, and water exchange rate should not exceed one turnover every two weeks. Every effort should be made to build the ponds in areas where they receive maximum sunlight.

Types of substrate for growing periphyton. Bamboo seems to be the best substrate. [In this context, the word “substrate” means “whatever surface is chosen on which the microscopic plants will grow.”] Palm or coconut fronds work well also. It is very important to position the substrate so it remains submerged and gets maximum exposure to sunlight. Many methods can be used to accomplish this goal: bundles of sticks can be stuck in the muddy bottom of a pond; pieces of substrate can be hung from wires strung across the pond; or large branches can simply be placed in the ponds. To facilitate the ease of harvesting fish, the substrate should be installed so that it can be easily removed if a seine is used to harvest. If the substrate begins to rot prior to fish harvest, additional substrate should be added.

Providing nutrients to enhance periphyton production. Construct simple submerged compost bins within each pond. The compost bins can be made of woven sticks, concrete blocks, or other material. There are some key criteria to keep in mind: the bins need to be permeable to water, strong enough to loosely retain several hundred pounds of organic matter, placed in an area with easy access for filling and mixing, and constructed to occupy approximately 1/20th the surface area of the pond (Figure 3). The compost bin basically serves as a giant “teabag,” oozing nutrients while retaining the solid materials. If inorganic fertilizers are available, the compost can be reduced in size or eliminated [though in this case the fish you harvest would no longer be considered “organic”]. Regardless of the source of nutrients for the periphyton, the optimum nitrogen to phosphate ratios appear to be about 6:1. In our experience using submerged compost in Haiti, keeping an equal balance of green (non-woody) plant material, non-meat food scraps and fresh (non-human) manure has worked well. Poultry manure is best for the latter component. The compost bins need to be kept full and stirred or mixed at least three times per week if possible.

 

Figure 3. A drained pond showing the compost bin in the top left corner. Photo by William Mebane.
Figure 3. A drained pond showing the compost bin in the top left corner. Photo by William Mebane.

Stocking ponds. Obtaining fingerlings for stocking can be done either of two ways: a) Collecting fry from existing ponds. Tilapia as small as 50 grams are sexually mature and will spawn every 30 to 40 days if they are healthy. Eggs are fertilized externally and are incubated and hatched in the mouths of adults. Young fry can be collected from almost any pond containing mature fish using a fine mesh net (window screen mesh size works well) on a long handle. Adults carrying eggs or young fry will not eat often and their lower jaw will appear distended. When agitated, or during brief times of feeding, these adults will discharge or spit out their cargo, which can be collected. One of the easiest ways to collect young fry is to walk quietly along the edge of a pond and look for plumes of young fry that hover near the surface while their parents forage nearby. A quick net and stealthy movements by the collector are key to successful fry capture (if the fry are startled they will quickly swim back into their parents’ mouths). This method should also be used to cull young fry from production ponds, to keep the fish from overpopulating the pond.

b) Producing fry from selected brood stock. Stocking adult fish in well-maintained smaller tanks at a ratio of 3:1 (female:male), is probably one of the easiest methods to produce fry. Careful observation of these brood stock fish will reveal when an adult is caring for eggs (distended lower jaw) and the harvesting of fry can be a bit more controlled. It is important to collect the fry as soon as they are able to swim, and to use large fish for brood stock. The quantity of eggs produced is directly proportional to the size of the adults.

If the fry were placed into the production pond, there would be equal numbers of male and female fish. Because they reach sexual maturity at such a young age, soon the pond would be filled with a harvest of thousands of small stunted fish. None would reach a good size. [It is quite possible that even very small fish might be fried until crisp and eaten whole, but large fish would be more profitable.]

Because of this, the most productive fish farmers use a process called “sex reversal.” It is easy to do even in remote settings without electricity. The collected young fry are placed into 40-liter plastic containers in the shade, where they are fed (for approximately three weeks) a commercial fish diet that has been treated with methyltestosterone. Methyltestosterone is a hormone that can be purchased in a powder form, which must be dissolved in isopropyl alcohol prior to mixing with the feed. Once the feed is mixed with the alcohol/hormone mixture, it is spread out to dry in the shade. The alcohol evaporates and the hormone remains. When fed to the fish, the hormone remains in the fish’s tissue for a very short period of time (days) but it “persuades” the sexual traits of the fish to be male.

Though used worldwide for sex reversing fish, methyltestosterone is not approved for such use in the USA. To locate the hormone for sex reversal of fish, check with the nearest fishery in your country or try asking a veterinarian. If you are unable to obtain the hormone, you can still avoid ending up with large numbers of very small fish by removing baby fish from the ponds as frequently as possible (using the method described in part (a) of “Stocking ponds”). For more information about sex reversal of tilapia, click here

During this period when fish are being treated with methyltestosterone, the water in the containers is exchanged twice a day. The surface area to depth ratio of the water should be maximized (it is better to have a shallow container with a lot of exposed surface area than a deep narrow container). 400 young fry per square meter of surface area can be safely stocked in a container of static water (i.e. without a system to mechanically add air to the water). The container should be kept partially shaded in a quiet area and fish should be fed using the “5 minute rule” (feed only what the fish will consume in a 5 minute time period) at least 3 times per day.

Debris and any dead fish must be removed several times per day if possible.

Stocking the grow-out pond. Stocking rates for the grow-out pond should not exceed two fish per square meter if periphyton is the only source of food. Three to five fish per square meter can be stocked if periphyton is supplemented with papaya leaves or moringa cast upon the pond surface. If possible, sex reversed fingerlings should be used to prevent stunted fish due to uncontrolled breeding. This is very important! (See description of sex reversing in previous paragraphs).

Harvesting. In our experience, a 10-gram fingerling will usually reach a size of 150 to 200 grams in six months. This growth rate is improving with each harvest, as improvements are made in substrate and compost management. According to the literature, a six-month growing period using the PAT technique can yield fish weighing 400 to 500 grams each. (Milstein et al, 2003).

All of the ponds we have been working with in Haiti are harvested by draining and collecting the fish. This process is not ideal, as it requires considerable time and is dependent upon rain to refill the ponds. A seine is the most efficient way to harvest. However, some of our Haitian fish farmers have been successfully experimenting with fish traps.

Problems and Pitfalls

********We have run into some problems. We hope that sharing our experiences will help prevent similar problems for those who experiment with PAT.

a.) Overpopulation of the ponds. Uncontrolled reproduction continues to be a problem if sex-reversed fish are not used. It is possible to solve this problem by introducing a predator species that selectively feeds on very small tilapia, but we have yet to find a good predator species in the areas where we work. As mentioned earlier, regular removal of small fish is another way to keep down the population if using sex-reversed fish is not an option.

b.) Proliferation of single cell algae may keep sunlight from reaching deeply enough into the pond. PAT is 100% dependent upon sunlight reaching the substrate. Introducing a filter feeder (perhaps silver carp?) to the ponds would help. Alternatively, using a flocculant (such as moringa seed powder) might help clear the water.

c.) Ownership of the ponds. The PAT method will grow fish at a rate similar to fish fed a commercial diet, but the total yield per pond is less. (This is because the poundage of periphyton produced—and consequently the poundage of fish that can be harvested—is limited by the size of the pond. In contrast, with a commercial feed, almost unlimited amounts can be used.) A problem we have encountered in Haiti (in many cases) is that too many people are involved in the ownership of a pond. The return per person at the end is too small to warrant even the little bit of work needed.

.d.) Keeping compost bins full can be challenging. People who do not own fish ponds now see value in their food scraps, manure etc., and are reluctant to give them away for use in composts.

e.) Failure to recognize the value of consuming fish. Fresh fish contains high-quality protein. It is also a valuable marketable product. Many farmers sell their harvest to purchase large quantities of less nutritious food, rather than consuming the fish themselves.

Conclusion

Periphyton aquaculture technology is a very low-cost, lowinput technique for raising fish. We hope the information in this article is helpful for those readers who wish to try it. If you experiment with the technique, please let ECHO know the results!

References

Milstein, A., M.E. Azim, M.A. Wahab, and M.C.J. Verdegem. 2003. The effects of periphyton, fish and fertilizer dose on biological processes affecting water quality in earthen fish ponds. Environmental Biology of Fishes 68: 247-260.

Further information about the PAT method can be found in the following article:

Milstein, A. and O. Lev. 2004. Organic Tilapia Culture in Israel. Proceedings of ISTA 6 (Sixth International Symposium on Tilapia in Aquaculture) Manila, the Philippines, Sept 12-16. Vol. 2, 657-660. http://ag.arizona.edu/azaqua/ista/ista6/ista6web/p…

The reference for the paper about sex reversal in tilapia that was referred to in the article is:

Phelps, R.P. and T.J. Popma. 2000. Sex reversal of tilapia. Vol. 2, Tilapia Aquaculture in the Americas, edited by B.A. Costa-Pierce and J.E. Rakocy (The World Aquaculture Society, Baton Rouge, Louisiana, United States), 34-59.