Browsing by Author "de Silva, T.W.J.T."

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    Identification of invasive alien sailfin catfish (Pterygoplichthys, Loricariidae) in Sri Lanka based on morphological characteristics
    (Sri Lanka Association for the Advancement of Science, 2013) Epa, U.P.K.; de Silva, T.W.J.T.
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    Impact of sailfin catfish (Pterigoplichthys disjunctivus) on reproduction output of guppy Poecilia reticulata under laboratory conditions
    (Sri Lanka Association for the Advancement of Science, 2014) de Silva, T.W.J.T.; Epa, U.P.K.
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    The impact of three invasive alien fish species on the survival and larval production of Poecilia reticulata under laboratory conditions
    (Sri Lanka Foundation Institute, 2015) de Silva, T.W.J.T.; Epa, U.P.K.
    Interactions of native with non-native species rank second only to habitat modification as a threat to freshwater fish biodiversity in the world. These impacts of exotic fish populations may arise from predation, competition for resources, habitat and water quality alterations, hybridization, and importation of parasites and diseases. Aquaculture is the major industry that has introduced number of exotic fish species into freshwaters of Sri Lanka during last few decades. Although aquaculture confines fish in to reservoirs, ponds, cages, or tanks, accidental and intentional releases into natural waters are not uncommon. Perceptions of impacts of these introduced fish species on native fish fauna vary widely. Thus, a pilot scale laboratory study was conducted to investigate impacts of three introduced fish species, Oreochromis niloticus, Helestoma teminkii and Trichogaster tricopterus on Poecilia reticulata, another common exotic fish found in natural freshwater habitats in Sri Lanka. P. reticulate was selected for the study considering its smaller size (equivalent to other fish larvae), easiness to breed, rare in captivity and its availability in large numbers. It was further decided not to sacrifice large number of native fish or fish larvae in this pilot study. Study was conducted from June to August, 2014 in twelve glass aquaria with a size of 90x30x30 cm. Ten healthy and mature P. reticulata fishes (length 1.85±0.18 cm; width 0.3±0.03 cm) with male to female ratio of 2:3 and 20g of Hydrilla were introduced to all experimental tanks. Females without swollen bellies were only selected in the study. ExperimentI (EI): H. teminkii (length 15.5±0.43 cm; width 7.1±0.17 cm); one fish a tank; Experiment2 (E2): T. tricopterus fishes (length 6.5±0.5 cm; width 3.4±0.3 cm); three fishes a tank; Experiment3 (E3): O. niloticus (length 6.5±0.5 cm; width 3.4±0.3 cm); three fishes a tank. All experiments were conducted in triplicate. Three tanks only with guppy and Hydrilla were controls. Water quality parameters such as DO, temperature and pH were measured in all experimental tanks once a week. Fish were fed twice a day using a commercial fish feed, excess feed and fish excreta were siphoned out. Half of the water in tanks was exchanged with aged tap water twice a week. Fish behavior and emergence of guppy larvae were monitored daily. Larvae born in each tank were counted and removed twice a week. Water quality parameters measured were not significantly different among tanks (one way ANOVA, p>0.05). Average DO, pH and temperature in tanks were 8.4±0.31 mg/L,7.7±0.12 and 28.7±0.3 0C, respectively.O. niloticus chased and predated on all guppies introduced in E3 within an hour of introduction. Guppy larvae were observed in E1 and E2. Total number of larvae recorded in E1, E2 and control were 38, 15 and 39, respectively at the end of experimental period. Larval counts were significantly higher in control and E1 than E3 after experimental period (one way ANOVA, p<0.05). Larval numbers recorded in E2 decreased in consecutive days indicating predatory behavior of T. tricopterus. Number of larvae in E1 and control tanks did not decrease in consecutive days indicating non predatory behavior of kissing gouramy. O. niloticus showed high carnivorous behavior towards adult guppy and T. tricopterus fed only on larvae. H. teminkii had no impact on survival or reproductive output of P. reticulata. Research is warranted to study impact of O. niloticus and T. tricopterus on other fish species in wild environment.
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    Impact of three invasive alien fish species on the survival of tadpoles of Asian common toad, Duttaphrynusmelanostictus under laboratory condition
    (Sri Lanka Foundation Institute, 2015) de Silva, T.W.J.T.; Epa, U.P.K.
    On a global scale, alien invasive species have been identified as being one of the five most important direct causes of the world wide decline in biodiversity and ecosystem services. Large number of exotic species has deliberately been introduced to increase food security, to develop cash crop production, as biological control agents and for the ornamental purposes. However the impacts of these introductions are least studied. This laboratory study was conducted to investigate the impact of three introduced fish species, Oreochromis niloticus, Helestoma teminkii, and Trichogaster tricopterus on the survival of tadpoles of Duttaphrynus melanostictus. Study was conducted from July to September, 2014 in twelve glass aquaria with a size of 90 x 30 x 30 cm. Five, healthy tadpoles with an average length of 1.2 ±0.21 cmand 20g of Hydrilla plant were introduced to all experimental tanks. Experimental design: Experiment I (EI): H. teminkii (length 15.5±0.43 cm and width 7.1±0.17 cm), one fish in each treatment tank; Experiment 2 (E2): T. tricopterus (length 6.5±0.5 cm; width 3.4±0.3 cm); three fishes in each treatment tank; Experiment 3 (E3): O. niloticus (length 8.5±0.7 cm; width 5.2±0.3 cm); three fishes in each treatment tank. All the experiments were conducted in triplicate. Three tanks served as controls which only with tadpoles. Water quality parameters such as DO, temperature and pH were measured in all the tanks once a week. Fish were fed twice a day using a commercial fish feed and excess feed and fish excreta were siphoned out. Half of the water in tanks was exchanged with aged tap water twice a week. Fish behavior and number of tadpoles were carefully monitored daily. Tadpoles were reintroduced once a week up to five times into all the treatment tanks.Water quality parameters measured were not significantly different among tanks (one way ANOVA, p> 0.05). Average DO, pH and temperature were 8.4±0.32 mg/L, 7.7±0.12 and 28.7±0.3 0C, respectively. O. niloticus started to chase tadpoles once they were introduced in to the tanks in E3. They took tadpoles into the mouth and spitted out 1-3 times before they were swallowed. None of the tadpoles in E3 survived due to predation after 2 hrs of introduction. Number of tadpole mortalities in E1, E2 and control were 2, 3 and 2, respectively. Tadpole mortality counts were not significantly different among E1, E2 and control tanks (One way ANOVA, p< 0.05). According to the results presence of H. teminkii and T. tricopterus did not pose a threat to the existence of tadpoles. The existence of O. niloticus in fresh water habitats may be a great threat to the survival of tadpoles of D. melanostictus. A further study to investigate the predation of O. niloticus on the tadpoles of other species of amphibians in Sri Lanka is warranted.
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    A study on diversity and shell utilization of Hermit crabs (Families Coenobitidae and Diogenidae) in the Western coast of Sri Lanka
    (Sri Lanka Association for the Advancement of Science, 2011) Epa, U.P.K.; de Silva, T.W.J.T.