Philippine Science Letters
vol. 4 | no. 1 | 2011
published online January 27, 2011


A matrix population model of
the "janitor fish" Pterygoplichthys
(Pisces: Loricariidae) in the Marikina River,
Luzon island, Philippines and the possibility of controlling this invasive species

by Benjamin Vallejo, Jr.* and Kristine A. Soriano

Institute of Environmental Science and Meteorology, College of Science, University of the Philippines, Diliman, Quezon City



A life stage-based Leftokovich matrix was used to model the population of the invasive "janitor fish" Pteryoplichthys in Marikina River, Luzon, Philippines. The matrix elements were derived from field and laboratory studies of life history and ecology, and the published literature. The population growth rate &lambda, rate of increase r and other life history parameters were derived from the model. The estimated &lambda is 1.079, and an r of 0.076 which suggests invasiveness. Matrix sensitivity and elasticity estimates suggest that the population is density independent and that juveniles are most prone to mortalities while adult and juvenile survivability is essential in ensuring population growth. Manipulation of survival probabilities in the model suggests that decreasing survival probabilities from 0.99 to 0.10 of juveniles and adults offers the best approach to controlling this population. The practicality of implementing management strategies are evaluated given the biological and ecological characteristics of the species.

*Corresponding author
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Submitted: October 31, 2010
Revised: December 28, 2010
Accepted: December 28, 2010
Published: January 27, 2011
Editor-in-charge: Eduardo A. Padlan