Browsing by Author "Mohotti, C.R.W.C."

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Acute toxicity test of aqueous extract of white hoary pea, Tephrosia candida (Papilionoideae) on Nile tilapia, Oreochromis niloticus (Cichlidae) fingerlings
(Sri Lanka Association for Fisheries and Aquatic Resources, 2015) Epa, U.P.K.; Mohotti, C.R.W.C.
Tephrosia candida was introduced to Sri Lanka as a legume live mulch for weed control and to protect soil surface. It is a source of flavonoids and rotenoids a including rotenone, tephrosin, and deguelin. Fishermen add large amount of grounded plant matter to the water that kills almost all the fish in the stream within a short period of time. This method of unregulated fishing may have a long term negative effect on fish diversity and abundance in the country. A 96hr static renewal toxicity bioassay was carried out in the laboratory to determine the median lethal concentration (LC50) of aqueous extract of T. candida leaves on Nile Tilapia (Oreochromis niloticus) fingerlings. Experimental fish were exposed to test water in 20L glass aquaria with concentrations of aqueous extract of 5, 7.5, 10, 15 and 20 mgL-1. All five treatments and the control aquaria were triplicated. Temperature, pH, total dissolved solids, conductivity and dissolved oxygen (DO) in water in all the aquaria were monitored using multi parameter water quality checker before and after the addition of toxicant, 24, 72 and 96hr of fish stocking thereafter. The median lethal concentration (LC50) values and its corresponding 95% confidence limits were calculated by Probit analysis. The LC50 values at various exposure periods were 10.83mgL-1 for 24h; 8.61mgL-1 for 48h; 7.26mgL-1 for 72h and 6.43mgL-1 for 96h. Symptoms of toxicity observed included, initial inactivation, agitated swimming, turning movement, air gulping, increased opercular beat, then erratic swimming, loss of reflex, slow opercular movement, setting at the bottom motionless and knockdown before death. The gills of the dead fishes were damaged, swollen and external bleedings were observed. Lower concentrations of the extracts had sub lethal effects which manifested as zigzag movement, air gulping, increased opercular movement and some fish gathered near the air stones. It could be concluded that the application of T. candida extract causes lethal toxic effects on fish at even very low concentrations.
Impact of fishing by white hoary pea Tephrosia candida (Fabales, Fabaceae) on diversity and abundance of fish in the streams at the boundary of Sinharaja Man and Biosphere forest reserve, Sri Lanka
(Revista de Biologia Tropical/ International Journal of Tropical Biology and Conservation, 2016) Epa, U.P.K.; Mohotti, C.R.W.C.
Local communities in some Asian, African and American countries, use plant toxins in fish poisoning for fishing activities; however, the effects of this practice on the particular wild fish assemblages is unknown. This study was conducted with the aim to investigate the effects of fish poisoning using Tephrosia candida, on freshwater fish diversity and abundance in streams at the boundary of the World Natural Heritage site, Sinharaja Forest Reserve, Sri Lanka. A total of seven field trips were undertaken on a bimonthly basis, from May 2013 to June 2014. We surveyed five streams with similar environmental and climatological conditions at the boundary of Sinharaja forest. We selected three streams with active fish poisoning practices as treatments, and two streams with no fish poisoning as controls. Physico-chemical parameters and flow rate of water in selected streams were also measured at bimonthly intervals. Fish were sampled by electrofishing and nets in three randomly selected confined locations (6 x 2 m stretch) along every stream. Fish species were identified, their abundances were recorded, and Shannon-Weiner diversity index was calculated for each stream. Streams were clustered based on the Bray-Curtis similarity matrix for fish composition and abundance. Physico-chemical parameters of water were not significantly different among streams (P > 0.05). A total of 15 fish species belonging to four different orders Cypriniformes, Cyprinodontiformes, Perciformes and Siluriformes were collected; nine species (60 %) were endemic, and six (40 %) were native species. From these, 13 fish species were recorded in streams with no poisoning, while five species were recorded in streams where poisoning was practiced. Four endemic and one native fish species were locally extinct in streams where fish poisoning was active. Fish abundance was significantly higher in control streams (32-39/m2) when compared to treatment streams (5-9/m2) (P < 0.05). We concluded that fish poisoning with T. candida may have resulted in a significant reduction in species richness, total abundance and Shannon-Weiner diversity index of fish species in the studied streams at the boundary of Sinharaja forest. We recommend that this fishing practice should be strictly regulated, and to inform local communities about the legal status of fish poisoning, its consequences and the importance of fish diversity for local livelihoods and conservation purposes.
Impact of fishing using exotic plant, white hoary pea Tephrosia candida (Papilionoideae) on diversity & abundance of fish in the streams at the boundary of Sinharaja Man and Biosphere forest reserve, Sri Lanka
(Sri Lanka Association for Fisheries and Aquatic Resources, 2015) Epa, U.P.K.; Mohotti, C.R.W.C.
Fish poisoning using exotic plant, Tephrosia candida is currently taking place in streams in southern part of Sri Lanka. This study was carried out to investigate the impact of this fishing activity on fish diversity and abundance in streams at the boundary of the Sinharaja forest. The Sinharaja forest that is located in south west part of the country is one of the most important watersheds in the country with number of streams draining into ‘Kalu Ganga’ and ‘Gin Ganga’ rivers. Three streams that were subjected to fish poisoning served as treatments while two streams that did not subject to fish poisoning served as controls. Physico-chemical parameters of water in streams were measured in bimonthly intervals for six times. Fish were sampled in three randomly selected locations (6 x 2m stretch) along each stream using electro fishing device, hand net and cast net. Number of fish species and their abundance in the streams were recorded and Shannon-Weiner diversity index for each stream was calculated. Physico-chemical parameters of water were not significantly different among streams. Out of fifteen fish species recorded, nine were endemic, Aplocheilus dayi, Belontia signata, Clarias brachysoma, Dawkinsia singhala, Garra ceylonensis, Schistura notostigma, Pethiya nigrofasciatus, Puntius titteya and Systomus pleurotaenia while six were indigenous, Glossogibius giuris, Devario malabaricus, Puntius bimaculatus, Puntius dorsalis, Puntius vittatus and Rasbora dandia. All fifteen fish species were recorded in two control streams while only six species were recorded in treatment streams. The total fish abundance of the control streams (30-39) were significantly higher than the treatment streams (4-9). The Shannon-Weiner diversity index was significantly higher in the control streams (1.98-2.04) than the treatment streams (0.99-1.52). According to the cluster analysis based on Bray-Curtis similarity matrix of fish composition, mainly two clusters were formed. The fish composition in three treatment streams was more or less similar to each other while fish composition in control streams clustered together. The two clusters were significantly different from each other (one way ANOSIM; p<0.05). Fish community composition of treatment streams has changed as a result of fish poisoning using T. candida. Therefore fishing using T. candida poses a great threat to freshwater fish diversity, abundance and species richness in the country.
Toxicity of aqueous extract of white hoary pea, Tephrosia candida (Papilionoideae) on Nile tilapia, Oreochromis niloticus (Cichlidae) fingerlings
(Sri Lanka Association for Fisheries and Aquatic Resources, 2016) Mohotti, C.R.W.C.; Epa, U.P.K.
Fish poisoning using Tephrosia candida, which is an exotic plant to Sri Lanka is taking place in streams in the boundary of the Sinharaja forest, a tropical forest range, designated as a world heritage site by UNESCO in 1988. T. candida is a source of flavonoids and rotenoids including rotenone, tephrosin, and deguelin. Fishermen add large amounts of grounded plant matter to kill almost all the fishes in the stream within a short period of time. This method of unregulated fishing may have a long term negative effect on fish diversity and abundance in the area. A 96 h static renewal toxicity bioassay was carried out in the laboratory to determine the median lethal concentration (LC50) of aqueous extract of T. candida leaves on Oreochromis niloticus fingerlings. Experimental fish were exposed to test water in 20 L glass aquaria with concentrations of plant extract of 5, 7.5, 10, 15 and 20 mg L-1. All five treatments aquaria and the control aquaria without plant extract were triplicated. Fish exposed to plant extract showed symptoms of toxicity including, initial inactivation, agitated swimming, turning movement, air gulping, increased opercular movement followed by erratic swimming, loss of reflex, slow opercular movement, setting at the bottom motionless and knockdown before death. The gills of the dead fishes were damaged, swollen and external bleeding were observed. Lower concentrations of the extracts had sub lethal effects which manifested as zigzag movement, air gulping, increased opercular movement and some fish gathered near the air stones. The LC50 values at various exposure periods were 10.83 mg L-1 for 24 h; 8.61 mg L-1 for 48 h; 7.26 mg L-1 for 72 h and 6.43 mg L-1 for 96 h. It could be concluded that the application of T. candida extract causes lethal toxic effects on fish even at very low concentrations.