Abstract:
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.
