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Janitor Fish

Page history last edited by PBworks 14 years ago
Janitor Fish


Description and Rationale


The janitor fish is not a native fish of the Philippines; it was originally imported as a helpful fish to clean the algae and debris in tropical fish enthusiasts’ aquariums.  It has now been introduced, either accidentally or deliberately, into the Marikina River and other freshwater lakes and rivers in the Philippines.  It has adapted very well and its populations are increasing. 


What is the janitor fish’s impact on the local ecology and fish populations?  Is it a predator of catfish, tilapia, milkfish and other native fish or their eggs? Is it a competitor for food resources with other aquatic organisms?  How is its presence affecting the people’s livelihood who depend of the resources of the rivers or lakes for their livelihood?  Does the fish’s sharp fins damage the fishing nets?  Or are they simply ugly and therefore an eyesore to eliminate?  Are there legitimate reasons why such a plentiful resource is being discarded?


Might there be new ways to utilize the janitor fish for food or livelihood?  Recent observations at the King’s Garden Organic Farm near the Payatas Dump area by the Marikina River show that the fisherfolk and other poor people living on the banks regard the janitor fish as a pest or threat to discard in rotting piles on the riverbank.  What are the reasons for this disregard?  How much is based on experience and scientific observations and how much is based on superstition or assumption?  If beneficial uses of the janitor fish are found, such as food, fertilizer, livestock feed, leather handicrafts, or other livelihood-enhancing ventures, what would be the best way(s) to communicate the findings to the people and barangays along these waterways?


The initial purpose of this project will be to research the biology and ecology of the janitor fish living primarily in the Marikina River, through a search of the literature as well as firsthand observations and interviews with people living along the riverbank (with the assistance of a Tagalog-speaking interpreter).  These initial findings will help guide the experimental phase, where key variables in the janitor fish’s survivability and usefulness will be further explored.


It is hoped that new uses of the previously unwanted janitor fish might help improve the livelihood of the people living along the Marikina River through a more informed understanding of an abundant biological resource.


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Common Names and Synonyms

Hypostomus plecostomus is also called the suckermouth catfish.  To aquarium enthusiasts, it’s also known as the Janitor Fish, since it will often attach itself to a surface such as the glass walls, and use its sucker-like mouth to rasp at algae that has built up.  Other synonyms include Plecostomus (Philippines); Sea Hasar (Guyana); and Spotted Pleco (US).



Kingdom: Animalia

Phylum: Chordata

Class:  Actinopterygii (ray-finned fishes)

Order:  Siluriformes (catfish)

Family: Loricariidae (armored catfish)

Genus: Hypostomus  (sucker mouth)

Species: H. plecostomus (folded mouth)

There are many types of suckermouth armored catfish that science has not described.  As a result, they are given a common name and an L-number designation until a new scientific name for the fish is described.  An example is the flash plecostomus, L204, believed to be a species of Panaque.


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Morphology and Physical Description

The fish can grow to a maximum of over a foot or around 50 cm.  The body shape of the plecostomus is short and robust.  The fins are arranged as follows:   1 dorsal spine, 7 dorsal soft ray fins, 1 anal spine, 3-5 anal soft rays.  The caudal peduncle (or tail stalk) is not depressed.  An adipose fin is present.  Among the paired fins, the pectoral fins are spined and each has 6 rays.  They are positioned in the thoracic region.  It also has a pair of pelvic fins.


The upper parts of the head and body are encased in longitudinal rows of scutes, or armored plates; the lower surface of the head and abdomen is naked. During the day, their unusual omega irises ( Ω) block a lot of the light out of their eyes. The iris opens at night. Plecos can also wink by rolling the eye into the head.


Internally, the plecostomus has two interesting and unique features compared with other bony fishes.  The thin-walled stomach of Hypostomus plecostomus, with its rich network of capillaries, has a morphology suggesting it is an efficient organ for air breathing. Histological and ultrastructural investigations of the stomach shows that its structure is different from that typical of the stomachs of other bony fishes: the wall is thin and transparent, while the mucosal layer is smooth and devoid of folds. The epithelium lining the whole internal surface of the stomach consists of several types of cells, the most prominent being flattened respiratory epithelial cells.


Additionally, the gills seem adapted to extract chloride ions in typically ion-poor, murky Brazilian waters of its homeland.  The specialized cells and abundant mucous layer on the cells may slow down the uptake of dissolved oxygen, which is why it seems to have the ability to take in supplemental oxygen by gulping air into its stomach.


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Getting Food

Plecostomuses are omnivorous, but in the wild, feed mostly on plant material at night.  Benthic (bottom-dwelling) algae and weeds tend to make up most of its diet, but it also eats small crustaceans, insects, and detritus.  There also have been bizarre reports of the fish eating wood!

    "Every year when it rains[in Brazil], the waters rise up against the big trees in the jungle,    and the Hypostomus Catfish suck onto the trees and eat right through them, until trees start falling down everywhere. Not because the roots are wet, but because the Hypostomus are eating right through the trees, and any trees that fall into the water are eaten by the Hypostomus and completely disappear." (http://www.aquariumfish.net/catalog_pages/scavengers/our_mothers_burl.htm)



The plecostomus mates through external fertilization, where the female deposits eggs on smooth rocks, depressions or burrows in the river bank.  The eggs are then fertilized by the male.  Afterwards, the eggs are guarded by one or both parents.  In captivity, the most successful breedings have occurred in ponds with steep clay or mud banks.  The fish dig tunnels close to the water level and the males guard the eggs until they hatch.


Environmental Factors

The plecostomus is demersal, meaning that it sinks to or lies on the bottom; living on or near the bottom and feeding on benthic organisms.  It lives in freshwater with a pH range between 6.2 and 8.2.  It is best adapted to tropical water temperatures between 20-28o C. 

There are several disease organisms that may use the plecostomus as a host.  These include white spot disease, parasitic infestations (protozoa, worms, etc.), skin flukes (flatworm parasites), and  velvet disease.


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Origin and Distribution

The plecostomus is originally from South America, inhabiting the coastal drainages in Guiana and between 12°N - 25°S latitudes, 60°W - 51°W.  It has been introduced to several Asian countries for the aquarium trade, and is bred in captive pens in Florida for tropical fish enthusiasts in the States.  It has been able to survive and thrive in a variety of tropical environments at 20 – 28°C water temperature.


Importance to People

In some places in the southern US (Florida and Texas), this species has been introduced from its native range, probably dumped by aquarists into the local waters. They have been also been introduced to several Asian countries as well. Suckermouth catfish are often cultured in ponds in Singapore and Hong Kong, where it is very popular for the aquarium trade as an algae eater.

Suckermouth catfish are of little or no value as a food fish, although they are at least occasionally consumed over their native range in South America. However, they are of great value in the aquarium trade in the United States.  Locally in the waters around Manila, there are concerns that the plecostomus  may be competing with native catfish and other edible, marketable fish.  The fisher folk also complain of its sharp spines severing holes in their fishing nets.  Along the Marikina River the fisherfolk throw any captured plecostomus up on the banks to die. 

There are several intriguing ideas about using the abundant wild Plecostomus as a resource.  An organic farm next to the Marikina River is experimenting with using ground-up plecostomuses as a low-cost fertilizer amendment for vegetable production.  Also, two high school students have found that the cured hides of Plecostomus make a tough, resilient leather for key chains and other small craft items. 


Survivability and Endangered Status

The resilience of the suckermouthed catfish is medium.  It has a minimum population doubling time of between 1.4 and 4.4 years.  The suckermouthed catfish is now being considered an invasive alien species in the Philippines, due to its tolerance for a broad range of water conditions and food as well as a lack of predators.  It may be competing with more marketable, edible catfish, bangus, and tilapia in Laguna de Bay, the Marikina River, and an ecologically important Agusan marshland in Mindinao. 



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Potential Solutions


Is the janitor fish’s presence in the Marikina River good or bad?  It has not been established at this point by this researcher whether the janitor fish is an invasive species in the Marikina River that is interfering with normal fishing practices or whether it is simply an introduced species that may prove to be a valuable new resource.  Further research and field studies about the ecology and food webs in the Marikina River are necessary before determining if the janitor fish is an asset or liability to the fishing efforts of the poor families living in the area.

There seem to be several promising livelihood possibilities that involve new uses of the janitor fish that may be able to benefit the trash pickers and poor families living around the King’s Garden area of the Marikina River.  Below are 3 possibilities with an analysis of the advantages and disadvantages for each.  Along with each possibility is a current status report of progress made to date on each of the possibilities.


Possibility 1  FISH LEATHER


 From an article found in the January – February 2006 edition of Greenfields Magazine (“the Philippines’ longest running agricultural and agribusiness magazine”), there was a fascinating article about how three high school students at Manila Science High School, in fulfillment of requirements for their science project, took 25 janitor fish from the river, carefully scraped the flesh and other organs from the skin, cured and treated the fish skin, and discovered that the skin can be crafted into coin purses, key holders, and other small paraphernalia.  Skin from both Australian salmon and sharks have already been made into fish leather on a commercial basis.






1.    Income could be generated for the riverside families in several different ways.  Currently the King’s Garden pays 30 pesos (US $ .60) for a kilo of live janitor fish.  Also, through the sales of handicrafted fish leather products, both locally and at Manila boutiques and bazaars, an alternate source of income from the typical trash-picking and recycling endeavors.  A similar livelihood venture on a nearby island, called “Threads of Hope” has made a substantial positive impact on the lives of many poor families previously victimized in the sex trade of nearby tourist resorts by creating a market for their hand-woven bracelets and anklets.



2.    The reduction of janitor fish would relieve some of the competitive pressures on the fisher folk’s catches of tilapia, bangus, and catfish.  Additionally there would be less damage to the fishing nets from the janitor fish’s sharp fins.






1.    The size of the janitor fish needed for leather production would require more intensive fishing strategies; many of the fish caught in the nets are smaller than workable size.


2.    The logistics of finding these original student scientists and/or their research has been a challenge in itself.  A call to the reporter of the article last week referred me to the school.  I then tried several numbers of the science high school before finding a supervisor of curriculum in the office.  The fact that only minimum staffing are available at the school offices during their summer break prevented me from talking to the students’ supervising teacher.  Furthermore, the students are believed to have graduated already, so that tracking them down requires more time than I have available right now.  The results of their experiment where they tested three tanning procedures:   vegetable, chrome, and a combination of both, are consequently unavailable at this time.  Perhaps at some time in the future this fish leather option would be more viable.



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With the tremendous growth rate of the plecostomus and the large numbers caught in fishing nets, why not eat them? 






1.    The meat is edible.  Rey, the farm supervisor at King’s Garden, vouches that the meat is tastier than catfish and less smelly than the local tilapia.  The fish is eaten by the locals in the fish’s native range in Guyana.



2.    The meat would provide a much-needed protein source to the poor communities, especially for the brain development of younger children.







1.    The current polluted state of the Marikina River, both from organic waste from a nearby piggery, Payatas landfill, and run-off from a government relocation community, could all produce a meat that is high in coliform bacteria and other organic and inorganic contaminants.  Initial research did not cover any studies of the water quality of the river that would dispel doubts about the potential health risks of eating the fish.



2.    While people eat the local catfish, another bottom-feeder grown in the same waters without reported health disabilities, there doesn’t seem to be a similar receptivity to eating the janitor fish.  Is there some type of cultural taboo or superstition that prevents the local people from eating it?  Perhaps more questions need to be asked about the people’s aversion.



3.    The only plecostomus I have available that would probably be safe to eat is in my 70-gallon aquarium at home.  We’ve had Brutus, the largest, for over 2 years, and I’m simply reluctant to eat our pet!


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The benefits of using fish as plant fertilizer have been known for thousands of years.  Ray, the farm supervisor, has recently tried liquefying the fish, then boiling the slurry before extracting the fish oil.  A solution of beneficial microorganisms has been added to this pungent mixture.  I added about 20 ml of a diluted (15 ml to 1000 ml water solution) to a group of 6-week old pepper plant seedlings, while irrigating a similar group of control seedlings with the same volume of tap water.  I am measuring both height and number of leaves to determine if the liquefied plecostomus solution can act as an organic fertilizer.






  A B C D E   A B C D E
4/21/2007 24.6 29.7 27.2 23.2 29.4 4/21/2007 26.3 30.3 29.4 25.7 30.3
24-Apr 25 30.4 30.5 29.3 30.5 24-Apr 26.8 30.2 30 27 32
26-Apr 26.2 30 30.3 28.4 32.9 26-Apr 26.7 34 30.5 29.6 32.3
28-Apr 28.2 31.2 30 28 31.9 28-Apr 28.5 30.8 30.6 30.7 29.2
1-May 28.7 32.2 31.5 32.4 36.2 1-May 30.3 35 34.3 34.2 35.1
3-May 28.8 32.7 31.5 38.6 37.5 3-May 30.8 35.4 37.7 35 35.7
5-May 29.2 34.8 33.1 32.3 37.6 5-May 31.9 37.1 36.1 42.1 34.8
Height diff 4.6 5.1 5.9 9.1 8.2   5.6 6.8 6.7 16.4 4.5
avg          6.6           8
  A B C D E   A B C D E
4/21/2007 14 15 14 7 14 4/21/2007 12 7 8 8 7
24-Apr 14 15 15 9 15 24-Apr 12 7 8 9 7
26-Apr 14 16 16 9 13 26-Apr 13 7 9 10 8
28-Apr 14 16 16 10 15 28-Apr 14 8 9 9 8
1-May 16 16 29 10 19 1-May 16 8 10 11 9
3-May 18 22 33 11 22 3-May 17 8 10 10 8
5-May 19 29 41 11 29 5-May 15 8 10 10 9
increase 5 17 27 4 15   3 1 2 2 2
Avg         13           2











Although the increase in leaf number was less in the experimental plants, both the heights and the number of plants that had begun flowering was higher in the experimental plants.  It seems clear that plecostomus fertilizer can improve the height, photosynthetic efficiency, and budding/fruiting rate of pepper plants.







1.    If it can be shown that the solution acts as a growth enhancer, the production level of homegrown vegetables can be improved, along with people’s livelihood.  A comparative addition of chemical store-bought fertilizer is economically impractical for the local poor community.



2.    Since a Christian worldview emphasizes better stewardship of God-given resources, the ability to utilize the plecostomus as a beneficial cheap fertilizer rather than a annoying useless piece of trash honors God through creativity, innovation, and resourcefulness.






1.    The preparation of the janitor fish concoction involves a rather violent death process, and may raise concern from animal activists.  However, if there was a humane way of euthanizing the fish before liquefying the tissues, it may quiet some of the outcry.



2.    The amount of fish needed for a commercially-viable organic farm fertilizer would require a cost analysis.  Overhead in the fertilizer’s preparation includes paying local people around 30 pesos per kilo live weight of janitor fish.  Also, a bottle of EM (beneficial microorganisms) costs 200 pesos.  There may be additional fees for workers who are preparing and filtering and applying the mixture.  While there is a very good dilution factor that stretches the concoction farther, it would still need to be seen whether the anticipated profit yields at harvest can offset the costs of preparation.






In relating my pepper plant experiment findings to Dr. Corrie DeBoer, the director of the King’s Garden, I learned that she would like to develop more opportunities to train out-of-school youth in organic farming techniques, discipleship, and leadership training.  We talked about how Faith Academy’s biology students could partner with the ministry in developing curriculum, background research, and service opportunities as a result of these environmental challenge projects.


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Banos,  Mike. “Janitor Fish Threatens Asia's Largest Marshland”  American Chronicle  5     June 2006.



Crustado, Evangeline R. “Waste no more, pest no more (Inventions from the young).”         Greenfields   January – February 2006:  18-20.


DeBoer, Dr. Corrie. Telephone Interview. 12 April 2007.


Delos Reyes, R. 2003,  “Fish pen culture and its impact on the ecosystem of Laguna de Bay” in V. Christensen and D. Pauly, eds. Trophic models of aquatic ecosystems. International Center for Living Aquatic Resources Management, Manila, Philippines.




“Epithelial gill cells in the armored catfish, Hypostomus cf. plecostomus (Loricariidae).” Brazilian Journal of Biology.  February 2001;61(1):69-78.




Hilaron, Mr Rey. Personal Interview. 21 April 2007.


“Hypostomus plecostomus” in Fishbase.org March 2007.




“Hypostomus plecostomus.” Planetcatfish.com.  11 March 2007.




“Hypostomus plecostomus.” Wikipedia.org.  11 March 2007.




“Morphology of the air-breathing stomach of the catfish Hypostomus plecostomus.” Journal of  Morphology August 2003;257(2):147-63.




Santos-Borja, Adelina and Dolora N. Nepomuceno. “Experience and Lessons Learned Brief for Laguna de Bay”  Laguna Lake Development Authority. 13 January  2004.




Sinohin, Veronica O. and Wilma R. Cuaterno, “Invasive Alien Species Resource Directory for the Philippines” during the workshop on “The

Prevention and Management of Invasive Alien Species:  Forging Cooperation through South and Southeast Asia”  held from 14-16 August 2002 in Bangkok, Thailand.,+pest,+Philippines,+Plecostomus&hl=en&ct=clnk&cd=1&gl=ph&client=firefox-a


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