Introduced or exotic fishes are those that have been imported from other countries for food, recreation and other purposes. Many introduced fishes have become invasive or harmful for causing ecological damage, economic loss and even human injury.
Based on a study of existing records and observations, 59 freshwater fishes were found to have been introduced into the Philippines from various countries since 1905 for various reasons such as for aquaculture (44 percent of the fishes), ornamental purpose (42 percent), recreational fishing (seven percent) and mosquito control (seven percent). Many other fishes are believed to have been introduced without a permit from the Bureau of Fisheries and Aquatic Resources (BFAR) and remain undocumented. In the evaluation of the introduced fishes, 47 (80 percent of the fishes) were found to be beneficial or non-harmful, eight (13 percent) were invasive and four (seven percent) are considered as potentially invasive species.
Of the 29 fishes introduced for aquaculture (food), 26 (90 percent) have been beneficial and only three (10 percent) have become invasive. Eighteen (62 percent) fishes have become established by successfully breeding in open waters (rivers and lakes) while three others have been artificially bred for culture. Eight (28 percent) of the introduced fishes have not become established because of their inability to spawn in the wild.
Among the introduced freshwater fishes that have significantly contributed to food fish production in the country are the cultured tilapias (mainly the Nile tilapia), carps (particularly the common carp and bighead carp) and the catfishes (African catfish and striped catfish). According to the Bureau of Agricultural Statistics, such fishes supplied 258,922 metric tons or 42 percent of the total farmed fish produce of the country with a value of P82.8 billion in 2010. From freshwater inland waters, the introduced fishes (tilapia, carp, mudfish, Thai catfish and gourami) added 78,335 metric tons or 42 percent of the total inland fisheries production with a value of P4.4 billion for the same year.
The three fishes introduced for aquaculture in the country that have become invasive are the mudfish (Channa striata), the Thai catfish (Clarias batrachus) and the rice paddy eel (Monopterus albus). The mudfish is considered a pest in freshwater ponds for being predaceous on cultured fish like the Nile tilapia. The C. batrachus has ecologically displaced the indigenous catfish (Clarias macrocephalus) in Laguna de Bay and other water bodies where it was introduced. The M. albus is reported to be infesting rice paddies in Cagayan Valley by burrowing into the dikes and causing water loss.
Of the 22 fishes introduced for the aquarium trade, 12 (54 percent) are considered beneficial or non-invasive while six (27 percent) have become invasive upon escaping accidentally or intentionally into open waters from commercial and/or private keepers, and four (18 percent) others are regarded as potentially invasive. The six invasive fishes are the “janitor fish†(Pterygoplicthys disjunctivus and P. pardalis), the “jaguar guapote†(Parachromis managuensis), the “clown knife fish†(Chitala chitala), the giant snakehead (Channa micropeltes), and the black-chin tilapia (Sarotherodon melanotheron). Of the six, only the “janitor fish†and the “clown knife fish†have been authorized by the BFAR.
The P. disjunctivus, as a nuisance fish, has caused economic losses for fisherfolk using gill nets and fish corrals in Laguna de Bay and Agusan Marsh by reducing their fish catch. On the other hand, the burrowing habit of the P. pardalis has eroded the banks of the Marikina River, a tributary of Laguna de Bay. The piscivorous P. managuensis has predated on and competed for the niche occupied by native fishes in Lake Taal in Batangas. The C. chitala, believed to have escaped into Laguna de Bay after a flooding event brought about by Typhoon Ondoy in 2009, is now wreaking havoc on the milkfish and Nile tilapia industries of the lake. Fortunately, the invasiveness of the C. micropeltes, now present in the Pantabangan reservoir in Nueva Ecija, and the S. melanotheron, first observed in Laguna de Bay but which has now spread to the brackish water ponds of Bulacan, is still not very serious.
Four introduced fishes for ornamental purposes which are presently still confined in private and/or commercial aquarium establishments are deemed potentially invasive because of their predatory habit, capability of spawning in tropical waters and known bio-invasive record in other countries. These fishes are the “arapaima†(Arapaima gigas), the “peacock bass†(Cichla occularis), “red-bellied piranha†(Pygocentrus nattereri), and “clown featherback†(Chitala ornata), a related species of the dreaded “clown knife fish.†The C. occularis and P. nattereri have not been approved for introduction by the BFAR. Because of their potential invasiveness and possibility of escaping into open waters, such fishes should be on the “Watch List†and closely monitored.
For the mitigation of the invasive fishes now in our open freshwaters, various measures are being considered for their economic utilization for food, raw materials for value-added products, and other beneficial uses. On a positive note, the M. albus has surprisingly found a big market as a food commodity in other countries. According to BFAR, more than P517 million worth of the fish was exported last year.
A review of the national policies and regulations on the introduction of imported live fishes showed that the required processes are adequate and in place as embodied in Fisheries Administrative Order No. 221 (series of 2003) of the Department of Agriculture implemented by the BFAR. Among the regulations are the conduct of an Import Risk Analysis prior to the issuance of a Sanitary and Phytosanitary Certificate for introduction of the fishes, their quarantine and health inspection. The BFAR is also empowered to confiscate and destroy “high risk and prohibited species†that have already entered the country without a valid import permit and impose the penalties of imprisonment and fine for offenders.
Besides the strict enforcement of regulations, there is an urgent need to strengthen the monitoring, surveillance and control measures to prevent the spread of the six invasive ornamental fishes now established in some of our inland waters and to forestall the escapes of the potentially invasive species. The regular inspection and possible registration of aquarium pet shops and a massive information, education and communication campaign to stir up public awareness for responsible aquarium pet care and environmental protection are recommended.
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Dr. Rafael D. Guerrero III is an academician of the National Academy of Science and Technology (Philippines) and a professorial lecturer at the University of the Philippines Los Baños, School of Environmental Science and Management. He holds a Ph.D. in Fisheries Management from Auburn University, Alabama, USA. He is the former executive director of the Philippine Council for Aquatic and Marine Research and Development of the Department of Science and Technology. This article is based on a research fellowship grant of the NAST. He may be contacted through email: rafaeldg7@gmail.com.