Population dynamics of vermiculated sailfin catfish, <em>Pterygoplichthys disjunctivus</em>, Weber 1991 (Family Loricariidae) in Victoria (Central province) and Kalawewa (North-Central province) reservoirs, Sri Lanka

Abstract

Introduction of alien invasive species has created adverse impacts on biodiversity in many places in the world. Scientific studies on such populations are important to formulate control measures of invasive species. In this study, population dynamics of invasive P. disjunctivus were studied in Victoria reservoir and Kalawewa reservoir in Sri Lanka. Present study was based on the fish landing sites harvested with 80 mm meshed gill nets in two reservoirs. Fish samples: 2454 from Victoria and 1515 from Kalawewa were studied once a month in two years of duration from January 2015 to December 2017 and standard length (SL) frequency data (LFD) were recorded. LFD were analyzed for fitting von Bertalanffy growth model for growth. An initial estimate of asymptotic standard lengths (L∞) was obtained using Powell- Wetherall method as implemented in the FiSAT II (version 1.2.2) software package. Asymptotic standard length and growth constant (K, yearly basis) were then determined by ELEFAN routine which were consistent with L∞ estimated using Powell-Wetherall method. Total mortality (Z) was calculated using original LFD by the length-converted catch curve method. Natural mortality (M) was estimated. Initial estimate of asymptotic standard lengths (L∞) were Victoria: 33.15 cm and Kalawewa: 35.28 cm. Asymptotic standard length and growth constant (K, yearly basis) estimated by ELEFAN were: 34.13 cm and 34.87 cm in Victoria and Kalawewa reservoirs, respectively. Total mortality (Z) values were reported as 1.22/y in Victoria and 1.32/y in Kalawewa. Estimated natural mortality (M) values were 0.87/y in Vicoria and 0.80/y in Kalawewa. Relative yield-per-recruit analysis and probability of capture with FISAT II software indicated that relative yield-per-recruit was 0.075 and 0.065 in the current exploitation rate in Victoria and Kalawewa reservoirs, respectively. Probabilities of capture of fish for Victoria and Kalawewa were 50% at 16 cm and 50% of 20 cm, respectively. It also revealed that there will be a great potential to optimize the fishery by increasing exploitation ratio from the present levels by increasing length at first capture from the present levels of 16.2 cm to 20.0 cm and 20.1 cm to 21.0 cm for Victoria and Kalawewa reservoirs, respectively. Gill nets can be used to increase harvest potential by increasing fishing effort to control and to produce value added products this species.