Population dynamics of accidentally introduced Amazon sailfin catfish, Pterygoplichthys ardalis (Siluriformes, Loricariidae) in Pologolla reservoir, Sri Lanka
H.P. WATHSALA SUMANASINGHE and UPALI S. AMARASINGHE
Many fish species have been introduced either intentionally or accidentally into Asian freshwaters and some species have been disreputed as alien invasive species (AIS) due to their potential threats to the biodiversity. In Polgolla reservoir of Sri Lanka, there is an established population of Pterigoplichthys pardalis, which makes a significant negative impact on the commercial fishery targeting exotic cichlid species as this armored catfish damages gillnets of the fishery. In the present study, an attempt was made to investigate population dynamics of P. pardalis in Polgolla reservoir with a view to ascertaining possibilities for commercial level exploitation of the fish stock. The fish landing sites in the reservoir were visited 4-6 days a month from May to November 2004 to collect data on species composition of landings and length frequency data of P. pardalis. P. pardalis accounted for 21% of the landings and von Bertalanffy growth parameters estimated by length-based stock assessment methodologies using FISAT II software were asymptotic total length of 41.3 cm and growth constant of 0.3 yr-1. Total mortality, natural mortality and fishing mortality were 0.76 yr-1, 0.73 yr-1 and 0.03 yr-1 espectively. Relative yield-per-recruit analysis indicated that there would be a great potential to optimize the fishery by increasing exploitation ratio from the present level of 0.4 to 0.7, while increasing length at first capture from the present level of 17.8 cm to 23 cm. However, as the consumer demand for this species is presently very poor, intensification of the fishery is possible only if market demand for P. pardalis is established through value addition by post-harvest technology.
Keywords: AIS, armored catfish, FiSAT, inland fisheries, Loricariidae, Pterigoplichthys