Introduction
Freshwaters constitute ~3% of the Earth’s water (WWF
2020) and occupy <1% of the Earth’s surface area
(Garcia-Moreno et al. 2014), but is habitat to about 40% of all
described fish species (Lundberg et al. 2000). The benefits of these
freshwater resources to society are immense. For example, 21 largest
lakes in the world provide about 1.3 million tons of fish annually, 62.5
GW of hydropower, 5 billion m3 of potable drinking
water, and 815 million m3 of water for irrigation
(Sterner et al. 2020). Also, freshwater systems replenish estuarine,
oceans, and seas with nutrients and water (Matthews 2016); for example,
Nile River deposits 1318 and 212 kg km−2yr−1 of nitrogen and phosphorus, respectively, into
the Mediterranean Sea (Yasin et al. 2010).
Freshwater species are more susceptible to human-induced threats such as
climate change, pollution, habitat alteration, overexploitation, and
alien species introductions compared with marine and terrestrial species
(Darwall et al. 2018; WWF 2020). For example, while marine and
terrestrial species have declined by 39% in the last 50 years,
freshwater counterparts have reduced by 76% higher than the global
average of 52% (WWF 2014). Freshwater fish species might be the most
threatened vertebrates assessed by IUCN (Reid et al. 2013). The species
are affected by the high levels of exploitation to support about 158
million people worldwide who derive animal protein from freshwater fish
species (McIntyre et al. 2016).
Approximately 500 fish species are reported in all water bodies in
Uganda (NEMA 2007; Natugonza & Musinguzi, 2020). However, several
non-native fishes, including Nile perch (Lates niloticus), Nile
tilapia (Oreochromis niloticus ), redbelly tilapia (Coptodon
zillii) , blue-spotted tilapia (Oreochromis leucostictus ), and
redbreast tilapia (Coptodon rendalii ) were introduced into
various lakes and rivers within the Victoria and Kyoga lake basins
(Kishe-Machumu et al. 2018). These introductions especially for Nile
perch coincided with the collapse of most native fish species
(Ogutu-Ohwayo 1990). In Lake Victoria, ~300+
haplochromine cichlids were extirpated (Kaufman 1992; Ogutu-Ochwayo
1990), and similar destructive ecological changes were observed in lakes
Kyoga and Nabugabo (Ogutu-Ohwayo 1990; Chapman et al. 1996). This loss
in haplochromine cichlids is believed to be the worst vertebrate species
extinction observed in recent times (Kaufman 1992), placing Nile perch
among the 100 top worst alien invasive species in the world (Lowe et al.
2000). Other native species such as Singidia tilapia (Oreochromis
esculentus ) and Ningu (Labeo victorianus ), which previously
dominated in fish catches from Lake Victoria and its affluent rivers
(Kudhongania et al. 1992) are currently classified as critically
endangered (IUCN 2020). The catfishes, including Semutundu (Bagrus
docmak Forsskål, 1775), Lake Victoria deepwater catfish
(Xenoclaris eupogon ), Clarias spp. ,Synodontis spp., and Silver catfish (Schilbe intermedius )
were also affected by Nile perch establishment in Lake Victoria
(Goudswaard & Witte 1997; Balirwa 1998; Balirwa et al. 2003). Riverine
species were mostly affected by overexploitation and habitat
degradation, while the native tilapines declined mostly through
interspecific competition and hybridization (Cadwalladr 1965;
Kudhongania et al. 1992).
The reduction in fish species diversity in Uganda has led to numerous
studies focussing on the species diversity, abundances, distribution,
taxonomy, and biology of the remnant species to facilitate their
recovery and reduce further extinctions (Witte & Van Oijen 1990;
Kaufman & Ochumba 1993; Ogutu-Ohwayo 1993; Ogutu-Ohwayo et al. 1999;
Mbabazi et al. 2004). In particular, small lakes, swamps, rivers,
streams, and wetlands were documented as the main structural refugia for
these fishes (Ogutu-Ohwayo et al. 1999; Mwanja et al. 2001; Chapman et
al. 2002; Mbabazi et al. 2004; Balirwa et al., 2003; Wakwabi et al.
2006; Olwa et al., 2020). However, these studies were waterbody-specific
with limited information to rank the waterbodies for site-based
conservation given the limited available resources. Analysis of the
distribution of fishes at a broader scale has been limited in the past
due to the paucity of data, which have been scattered in many research
institutions in unusable formats. Recently, substantial amounts of data
on the occurrence of fishes for Uganda have been made available through
the Global Biodiversity Information Facility portal (GBIF) (GBIF, 2020).
This study aims to develop a Conservation Priority Index (CPIw) for
inland water bodies to prioritize their selection for site-based fish
conservation, especially when resources are limiting. We use data on the
distribution, diversity, and conservation status of the fish species in
Uganda, which are freely accessible through GBIF and IUCN databases.