Pterygoplichthys Gill

Joel M. Chavez, Reynaldo M. de la Paz, Surya Krishna Manohar, Roberto C. Pagulayan & Jose R. Carandang Vi, 2006, New Philippine record of south american sailfin catfishes (Pisces: Loricariidae)., Zootaxa 1109, pp. 57-68 : 57-66

[[ Genus Pterygoplichthys Gill ]]

In 2002, news reports of an introduced suckermouth armored catfish being caught in the waters of Laguna de Bay were published. The reports said that the fish was proliferating in the lake and was interfering in fishing-related activities. Apparently, the fish was being blamed for the decrease in the marketable fish catch from the lake either by replacing the usual fishes harvested or by destroying fishing nets and cages. Some national and local government agencies have also expressed concern over this problem because of the possible negative effects the fish may have on the lakes ecosystem.

The Laguna de Bay is the largest inland body of water in the Philippines and one of the largest lakes in Southeast Asia. It serves a number of agro-industrial purposes that benefit about 11 million Filipinos. Fisheries are its main use, and approximately 3 million people depend upon the lake for a living.

The fish is locally known as “janitor fish”, a moniker the fish earned because of its habit of eating algae in the tank, thus keeping the glass clean. Some reports putatively identified the janitor fish as Hypostomus plecostomus . No taxonomic records of the janitor fish in Laguna de Bay have been published, and locally available materials on the fish are minimal. A taxonomic and biogeographic investigation on the janitor fish in Laguna de Bay was conducted.

Methodology

Specimens were collected from five sites in and around the Laguna de Bay basin: Marikina River in Marikina and Pasig Cities; Pasig River in the City of Manila; Catmon Creek in Bay, Laguna; Banilad Creek in Siniloan, Laguna; and Laguna de Bay in San Pedro, Laguna. The institutional abbreviation DLSU ZC-F, which stands for De La Salle University Zoological Collection-Fishes, was used to catalog specimens.

Nineteen meristic and 37 morphometric characters of the specimens were examined in accordance with the methods of Armbruster (2003a) and Armbruster and Page (1996). When possible, counts and measurements were made on the left side of the body. Distances were measured in millimeters using dial calipers and were converted to ratios of the standard length or head length. Data collected were compared with published and online literature (Armbruster 1997, 1998, 2002a, 2002b, 2003a, 2003b, 2004; Armbruster & Hardman, 1999; Armbruster & Page, 1996; Armbruster & Provenzano, 2000; Armbruster et al, 2000; Weber, 1992) on Loricariidae . To compare our morphometric data with those of Weber (1992), the ratios of standard length or head length over the measured distances were computed. Other external features and coloration were also examined and compared.

Results and Discussion

The genus of the janitor fish was determined using the key by Armbruster (2002b) to the genera of family Loricariidae . Use of the key suggested that the janitor fish from Laguna de Bay belongs to the genus Pterygoplichthys (Gill 1858) and is not Hypostomus plecostomus as reported earlier. The identification of species was based on the key to the genus Pterygoplichthys sensu lato of Weber (1992) and other descriptions by Drs. Jonathan Armbruster and Claude Weber (personal communication). Nomenclature of species follows Armbruster (2004). Based on the observed coloration of 193 specimens, apparently two species of Pterygoplichthys (Gill 1858) can be found in the Laguna de Bay basin: Pterygoplichthys disjunctivus (Weber 1991) and Pterygoplichthys pardalis (Castelnau 1855) (Figs. 1 and 2).

Table 1 summarizes the range of variation of 16 meristic characters for the two species. Adipose fin is present in all specimens. Dentary teeth are as follows: P. disjunctivus 3-37 (mode=18); P. pardalis 3-42 (mode=24). Premaxillary teeth: P. disjunctivus 6-40 (mode=20); P. pardalis 3-40 (mode=25). Selected morphometrics of the fish samples are shown in Table 2.

Little variation in meristic counts and morphometric measurements for the two species was found when compared to data reported by Weber (2002), although a larger orbital diameter was noted among specimens of P. disjunctivus collected from Marikina River (Table 3).

Most of the samples have a base color of light gray usually becoming lighter towards the ventral side. Some have a dark brown base color while a few are light brown. Pterygoplichthys disjunctivus was distinguished from P. pardalis by the typical dark vermiculations on a light background (Fig. 3A). However, some variations on this pattern were observed. Some specimens exhibit variations in the thickness of the light and dark patterns (Fig. 3B) (n=14). Some specimens have the coalescent patterns on the abdomen only, these becoming spots towards the head or vent or both (Fig. 3C) (n=21). Pterygoplichthys pardalis has body coloration, particularly on the abdomen, consisting of dark spots on an otherwise light background (Fig. 4). The heads of both species exhibit linear patterns forming geometric shapes.

Both species of Pterygoplichthys were collected from the five study sites except in Pasig River in the City of Manila where only P. disjunctivus was noted. Current distributions of the two Pterygoplichthys species are shown in Fig. 5.

The fishes caught from Pasig River, Marikina River, Banilad Creek, and Catmon Creek were collected from medium-velocity rivers no more than two meters deep near the riverbanks. Specimens were caught with cast nets except those from Pasig River, which were hand-caught. Most of the drainages where specimens were collected have a muddy and murky bottom. Water quality in these areas can be characterized generally as polluted because these drainages receive waste materials and even sewage from households and industries. Breeding burrows were observed along the banks of Marikina River and Catmon Creek. Fishes in Marikina River were noted to move upstream during high tide to avoid the intrusion of saline water from Manila de Bay. Specimens from San Pedro, Laguna, were collected from fish traps about 2-4 meters deep in the lake waters. This collection site is also situated near heavily populated communities. All fishes were caught during daytime.

Our results do not dispel the presence of Hypostomus plecostomus as local reports claimed. However, our results establish the fact that the janitor fish commonly encountered in the Laguna de Bay basin are species of the genus Pterygoplichthys .

Species of Pterygoplichthys , commonly known as sailfin catfishes, are native to South America. When and how sailfin catfishes were introduced into Philippine waters are unknown. We suspect that the first individuals were imported from the United States as aquarium fishes, where species of Pterygoplichthys have been introduced in Texas, Florida, Nevada, and Hawaii (Hoover et al., 2004, Sabaj & Englund 1999).

Sailfin catfishes are popular in the Philippines as aquarium pets. Local aquarium dealers have used its local moniker as a selling point and over the years the misconception -that a “janitor fish” cleans uphas risen. Anecdotal reports say this misconception might also be a reason for the high incidence of sailfin catfishes particularly in the Marikina and Pasig Rivers. These drainages have been subjects of clean up drives by local government agencies and private organizations in the past.

Species of Pterygoplichthys are not the first non-native species of fishes introduced in Philippine waters through the ornamental fish trade (Juliano et al., 1989). We suspect a wider distribution of Pterygoplichthys species outside of the Laguna de Bay basin due to its popularity and the extent and briskness of the aquarium fish trade in the Philippines. We have received reports of “janitor fish” sightings in streams and rivers in Zamboanga City (about 850 Km south of the City of Manila) and Aparri Cagayan (about 420 Km north of the City of Manila).