Assessment of species composition and the genetic population structure of the endemic fishes in the Rufiji River Basin, Tanzania
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Date
2024-03
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Sokoine University of Agriculture
Abstract
The Rufiji River Basin (RRB) is the largest river basin in East
Africa and is home to many endemic fish species that are
important for local livelihoods and food systems. However,
unsustainable fishing practices driven by rapid population
growth and high consumer demand have led to a concerning
decline in these endemic fishes. In response two protected
sites were established including, the Kilombero Valley
Floodplain Ramsar site in 2002 and Nyerere national park to
protect the endemic fish species from overexploitation. Yet,
fish stocks are declining, and it is still unknown whether the
implemented measures are consistent with the genetic stock
structure of endemic fishes in the basin. Therefore, the aim
of this study was to assess the composition of endemic fishes
and the genetic stock structure of endemic fish Bagrus
orientalis in the RRB. This study used fishers, and the key
informant’s interviews, Focus Group Discussion (FGDs), and
fishery surveys to assess the composition of endemic fishes.
DNA barcoding was also employed to confirm species
identities. Tissue samples of 46 different endemic fish
species and 182 of B. orientalis were collected from fishers
at six landing sites in the RRB including Kivukoni, Mofu,
Dinari, Ngalimila, Kidatu, and Zombe and preserved in 99.9%
ethanol. Genomic DNA was extracted from each sample
using the TIANamp Genomic DNA kit (TIANGEN Biotech,
Beijing) and fragments (620 base pairs) of the cytochrome
oxidase subunit I gene were amplified. The results showed
33 different fish species, out of which 54.55% are endemic
and 45.45% are exotic. Additionally, it was revealed that
Heterobranchus longifilis (Mjongwa), Citharinus congicus
(Mbala), Labeo congoro (Ningu), Mormyrus longirostris
(Sulusulu), and Labeobarbus leleupanus (Mkuyu) are very
rare in the catch, despite being classified as Least Concern
by IUCN. This suggests that rare species needs
reassessment and reclassification by IUCN because their current criteria does
not reflect their actual status on the ground.
Furthermore, the results revealed significant genetic
divergence between the populations of B. orientalis in the
RRB (FST = 0.33, p < 0.01). Hierarchical AMOVA revealed
that populations in the Ramsar site are genetically connected
with those from other sites within the Kilombero Valley Flood
Plain (KVFP), but genetically distinct from the populations in
Ruaha and Rufiji. This implies that conservation efforts within
the Ramsar site might not directly benefit the population in
Ruaha and Rufiji. Therefore, it is recommended to establish
the protected sites in Ruaha and Rufiji to rescue this
population from further decline. The findings also showed
that the low genetic diversity among population in Kidatu is
due to restricted genetic connectivity, highlighting the need
for enhancing habitat connectivity in the area. Moreover, the
poor body condition and small sized fish were observed in
Kidatu population. This does not conclude overfishing in the
area but further studies on population dynamics and fishing
pressure should be conducted to understand factors
affecting size structure of the fish.
Description
MSc Dissertation
Keywords
Fish identification, genetic connectivity, genetic diversity, population genetic structure, DNA barcoding