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\begin{document}

\title{Diet overlap and feeding preference of Oreochromis niloticus (Linnaeus,
1758) versus two native cichlids of the upper Kabompo River, northwest
of Zambia.}



\author[1]{Arthertone Jere}%
\affil[1]{Lilongwe University of Agriculture and Natural Resources Faculty of Natural Resources}%


\vspace{-1em}



  
  \date{May 22, 2024}


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\selectlanguage{english}
\begin{abstract}
Evaluating the food and feeding habits of fish is fundamental in
fisheries and conservation biology research. In this study, the diet of
exotic Oreochromis niloticus was compared with the 2 most abundant and
aquaculture preferred native cichlids of native species (Orochromis
macrochir and Coptodon rendalli) in the upper Kabompo River, Zambia. We
hypothesized that exotic and native cichlids would show no dietary niche
overlap. We analyzed the stomach contents of 114 specimens of the fishes
sampled. Fishes were grouped into 3 major feeding groups: microphages,
macrophages and carnivores, and omnivores. They were also grouped into
size classes of \textless{}50, 51-100, 101-150, and 151-302 mm total
length (TL). O. niloticus had a larger dietary niche than two native
species (71\% and 22\%, respectively). The dietary niche overlap between
O. niloticus and native C. rendalli species in size classes
\textless{}50 was significant (F (2, 45) = 0.084, p \textless{} 0.05).
Dietary niche overlap between the native O. macrochir species in size
class \textless{}50 mm was low (F (2, 33) = 2.13, p \textgreater{}
0.05), while as in size classes 51-100 mm and 101-150 mm was high (F (2,
35) = 0.27, p \textless{} 0.05) for C. rendalli. There was no clear
evidence of ontogenetic diet shift of native cichlids, with the
exception of O. macrochir, which showed ontogenetic diet shifts within
the 51-100 mm size class. The dietary overlap results indicate
interspecific competition between exotic O. niloticus and native O.
macrochir, which may have major impacts on food web structure in the
upper Kabompo River and may explain population decreases of some native
species.%
\end{abstract}%



\sloppy


\textbf{1. INTRODUCTION}

Exotic species have become a major threat to many native species and
whole ecosystems over the world (Agostinho et al., 2015; Jere et al.,
2021; Zengaya et al., 2020). Nile tilapia, \emph{Oreochromis
niloticus}(Linnaeus, 1758), is the most widely distributed exotic fish
species in Sub Saharan Africa. In Zambia, it was introduced in the late
1980's by Department of Fisheries for research and development in
aquaculture (Bbole at al\emph{.,} 2014; DoF, 2018; FAO, 2012). However,
the introduction of \emph{O. niloticus} poses a major threat to native
fishes as it is known to cause trophic cascades with potential impacts
on the entire fish community, particularly in highly diverse regions
such as the Northwestern Province of Zambia (AES, 2014; Bok \& Bills,
2012; Jere et al, 2021).

Partitioning of resources between coexisting species has been suggested
as one of the processes responsible for structuring populations and,
con- sequently, communities (Figueredo \& Giani, 2005; K\selectlanguage{polish}ı\selectlanguage{english}ran kaya \&
Ekmek\selectlanguage{ngerman}çi, 2013). Studies conducted by Gozlan et al. (2010) showed that,
in contrast to terrestrial organisms which partition resources mainly
through habitat segregation, for assemblages of fishes and other aquatic
animals trophic separation is more important. Partitioning of food
resources is the main factor in the development of fish communities in
nearly all aquatic habitats (Bwanika et al., 2004; Canonico et al.,
2005; Eloranta et al., 2015).

The degree of trophic adaptability of certain fish species may limit
feeding preferences when confronted with environmental changes. Changes
in re source availability may influence changes in the as semblage of
fish species in a community (Miller \& Crowl, 2006; K\selectlanguage{polish}ı\selectlanguage{english}rankaya \&
Ekmek\selectlanguage{ngerman}çi, 2013). For instance, direct competition for food resources
between exotic and native species may result in diet shifts and affect
native species' fitness (Eloranta et al, 2015). In certain cases, native
species can also be affected indirectly by exotic species. For example,
cichlids may influence a trophic cascade by either decreasing or
increasing the availability of nutrients such as phosphorus and
nitrogen, which may promote plankton blooms and lead to fluctuation in
the dissolved oxygen content of water (Ke et al., 2008; K\selectlanguage{polish}ı\selectlanguage{english}rankaya \&
Ekmek\selectlanguage{ngerman}çi, 2013). Furthermore, Nile tilapia in some cases may increase
turbidity through sediment resuspension (Zengeya et al., 2015). These
suspended solids in water have the capacity to reduce macrophyte
survival, which may result in a shortening of the trophic pathways of
native species (Scheffer et al., 2006; Agostinho et al., 2015).
Moreover, studies by other investigators have appropriate and practical
approaches to assessing possible impacts of exotic species on native
fishes (Figueredo \& Giani, 2005; Zengeya et al., 2015).

The use of stomach content analysis (SCA) to infer feeding strategies
and habits of native and exotic fish species within a food web is an
effective tool in the conservation of native populations (Pilger et al.,
2010). For example, stomach content analysis of \emph{Serrasalmus
marginatus} and \emph{S. maculatus} in the upper Parana River in Mexico
revealed high trophic niche overlap between the species, which both
consume fish fragments, detritus and plankton (Agostinho et al., 2015;
Philippsen et al., 2015). SCA is useful for understanding the functional
role of organisms in a food chain and is an important tool for
elucidating trophic differences between phylogenetically related fishes
(Keet al., 2008). The results of SCA can be used to define trophic
niches (Agostinho et al., 2015), and have become an important predictor
of the impacts of invasive alien species (Pilger et al., 2010; Agostinho
et al., 2015).

This study evaluated the dietary preferences of exotic \emph{O.
niloticus} and 2 most abundant and aquaculture preferred native fish
species \emph{(Oreochromis macrochir and Coptodon rendalli} ) in the
upper Kabompo River, Zambia. A Known population of exotic \emph{O.
niloticus} is established in the study area, and decreases in
populations of native species \emph{(O. macrochir and C. rendalli)} have
been reported (AES 2014; DoF 2018; Jere et al., 2021). Understanding the
dietary preferences of these species may help explain these decreases
and clarify how exotic species impact native species. \emph{O.
niloticus} and native species have generally similar feeding behavior
(Kenzo \& Mazingaliwa, 2002; Zengeya et al., 2015), although \emph{O.
niloticus} are assumed to show somewhat more generalist foraging
behaviour, feeding on a greater diversity of food items than native
species (Marshall, 2011; Zengeya et al., 2020). Thus, we hypothesized
that \emph{O. niloticus} and native species in upper Kabompo River would
show no dietary niche overlap with the two major native species. We used
SCA to test our hypothesis, the results of which should provide new
insight regarding coexistence of species in the environment and help to
develop strategic management plans for the conservation and management
of native species in the upper Kabompo River.

\textbf{2. MATERIAL AND METHODS}

\textbf{2.1 \emph{Description of study site}}

The study was undertaken in the upper Kabompo River, located on the
border of Kalumbila and Mwinilunga districts in Zambia. Kalumbila
District includes major mining towns in the Northwestern Province. The
study area lies approximately 60 km from the source of the Kabompo River
(12.1845°S, 25.1765°E to 12.3691°S, 25.0442°E).The water surface area is
approximately 1473 km\textsuperscript{2}, with numerous fish landing
sites. The study site (Figure 1) was chosen because of its frequent
fishing activity and high fish diversity. The fishery (covering all the
native species caught in this study) is also of economic importance to
local communities as a livelihood and a source of brood fish for the
Aquaculture Breeding Programme.

\textbf{2.2 \emph{Data collection and analysis}}

The study area covered approximately 15 km of the river with a total of
3 sampling points 7.2 km apart. At each sampling point, a 200 m stretch
of river was sampled, encompassing all 5 available microhabitat types
(runs, riffles, vegetative thickets , open pools (near fisheries landing
area) and the tributaries) of the river. Surveys were conducted for a
period of 1 month in the hot, dry season (December 2019) and 1 month in
the hot, wet season (January\selectlanguage{english}-February 2020). The sample periods were
chosen because temperatures are conducive to abundant food resources at
these times (AES 2014). Fish were collected using fishery independent
methods with gill nets 3 m deep and 30 m long, mesh size ranging from 1
to 3.5 inch; Fyke nets 3 m deep and 30 m long; an electrofisher; and a
beach seine net 3 m deep and 25 m long. The specimens were identified
immediately after capture according to Kenzo \& Mazingaliwa (2002). The
specimens were then measured (total length {[}TL{]} +- 1.0 mm) and
weighed (wet mass +- 0.1 g).

A total of 3 species were selected for SCA, based on the most abundant
fish species caught in the river (capture frequency \textgreater{}10\%)
according to Eloranta et al. (2015). The species selected were the
exotic \emph{O. niloticus} (n = 201) and two natives; \emph{O.
macrochir} (n = 110) and \emph{C. rendalli (} N=56). The fishes caught
from five aforementioned distinct habitats at different times of the day
(6 a.m., 12 afternoon and 5 p.m. to comprehensively understand effective
feeding period of the day) (Table 1). Indices used for diet
interpretation included; vacuity index (VI) is the quantity of unfilled
as number of empty stomachs and the gut fullness (GF) is average number
of relatively full stomachs investigated on scale of 0 for empty to 4
for fully distended with food and lastly the diet diversity was
evaluated according to Hyslop (1980). The frequency of occurrence method
was used to determine the percentage of stomachs containing a particular
food item relative to the total number of stomachs containing food
(Hyslop 1980). The fish were first grouped into 3 major feeding groups:
microphages, macrophages and carnivores, and omnivores, and then later
grouped into lower taxonomic or functional categories for quantitative
comparisons. Diet categories were chlorophytes, cyanophytes, diatoms,
microfauna (zooplankton, insects and protozoa), fish, macrophytes,
detritus, and unidentified items. The area occupied by each food item in
the stomach of a specimen was transformed into a percentage of each food
category. Numerical analysis was not used to categorize broader food
items because (1) lumping resource states often in- flates niche overlap
values, and (2) broader categories generally represent one or more
renewable resources (Winemiller 1989).

Dietary overlap between \emph{O. niloticus} and the native species was
calculated using the symmetric niche overlap coefficient of Pianka
(1973), in which values are constrained between near 0 (specialized
diets with almost no overlap) and 1 (similar use of food resources or
complete overlap). Overlap was categorized as low (0.0\selectlanguage{english}-0.29), moderate
(0.30\selectlanguage{english}-0.59), or high (0.6\selectlanguage{english}-1.00), with high overlap indicating biological
significance (Langton 1982). The dietary niche width was estimated using
Levins' (1969) standardized index of niche breadth, in which values near
0 indicate a specialized diet, and values near 1 signify generalist
diets.

To understand dietary preference, analysis of the diets of \emph{O.
niloticus} and native fish species in the upper Kabompo River was
conducted to understand pattern of dietary overlap. To achieve this,
results of the indices (vacuity, stomach fullness and Levin's
standardized niche breath) were collated via spreadsheets using
Microsoft Excel 2007 (summation, percentage and mean functions).
Further, principal component analysis (PCA) was performed to identify
the patterns in dietary similarity between \emph{O. niloticus} and the
two native fish species. Scatter plots from the first factors (component
with absolute values equals to or greater than 0.6) were used to
visualize the variation in diets among species. Principal component
analysis uses matrix algebra to model a correlation matrix as a set of
orthogonal (perpendicular) axes. The PCA axis (dietary gradient)
corresponds to an eigingvector. Thus, eigenvalues describes the variance
accounted for by the corresponding axis. The first principal components
indicated the largest percentage of total variation that can be modeled
by the algorithm (Sagar \emph{et al} ., 2019). Thereafter, an analysis
of variance (ANOVA) was then conducted on mean values from the dietary
indices to detect significant difference at 0.05 signficance level
(Sokal \& Rohlf, 1995). These statistical analyses were performed using
R software version 3.6.0 (R Core Team, 2019).

\par\null

\textbf{3. RESULTS}

Analysis of 114 stomachs of exotic and native fish species ranging in TL
from 21 to 302 mm showed that they employed similar feeding habits. The
largest species, \emph{O. niloticus} and \emph{O. macrochir} , were
found in all 4 class sizes. Smaller catches of species \emph{C.
rendalli} and\emph{O. macrochir} were found in size classes
\textless{}50, 51\selectlanguage{english}-1 00, and 101\selectlanguage{english}- 150 mm. \emph{O. niloticus} and larger
native species \emph{(O. macrochir)} did not significantly differ (F =
(2, 44) 0.48, p \textgreater{} 0.05) in size class. \emph{O. niloticus}
and smaller native species \emph{(C. rendalli)} were significantly
different in size class \textless{}51 mm (F (2, 51) = 0.27, p
\textless{} 0.05) (Table 1).

Therefore, the two native species showed a significantly higher degree
of individual dietary specialization than \emph{O. niloticus} (F (2, 35)
= 0.084, p \textless{} 0.05) (Figure 3). The mean number of food items
observed did not differ significantly among stomachs of native species,
but exotic \emph{O. niloticus} showed a larger volume and number
of\emph{C. rendalli} presented significant peaks (F = 5.31, food items
than native species in size class \textless{}50 mm p \textless{} 0.05,
at 5 pm) of higher feeding intensity at 12:00 h (F = 0.63, p
\textgreater{} 0.05). For juveniles of both exotic \emph{O.
niloticus}between the smaller and the larger species, fewer \emph{O.
niloticus}stomachs were empty and fewer insect food and native species
(\emph{O. macrochir} and \emph{C. rendalli} grouped according to larger
food items class sizes), feeding patterns were discontinuous and
cephalus than of exotic \emph{O. niloticus} (Figure. 2).significantly
different (F(2,35) = 2.71, p \textless{} 0.05 and F = 11.62, Dietary
overlap among the native species was p \textless{} 0.05, respectively),
with a distinct peak at 12:00 h varied and significantly low (F (2,27) =
2.13, p \textgreater{} 0.05) in size when the stomachs were fullest
(Tables 1).

Analysis of dietary preferences of exotic and native species showed that
mean SF was relatively high in \emph{O. niloticus, O. macrochir}
and\emph{C. rendalli} (between 3.0 +- 0.9 and 4.0 +- 0.1), while VI was
low in the largest size class (151--302 mm) and high in size classes
\textless{}150 mm (Table 2). The results showed that adult
exotic\emph{O. niloticus} fed continually (F (2,18) = 0.34, p
\textgreater{}0.05), while adults of native \emph{O. macrochir}
and\emph{C. rendalli} , and smaller species (in size class \textless{}51
mm) of \emph{C. rendalli} , fed on algae, diatoms and detritus (Figure.
2). The diet for fish in the \textless{}50 mm size class consisted
mainly of algae, while diet shifted in the 51\selectlanguage{english}-100 mm size class, with
fish and microfauna becoming the most important food items (Figure 2).
In general, \emph{O. niloticus} had a more diverse diet than native
fishes resulting from foraging on algae, chlorophytes, diatoms,
microfauna, and detritus in all size classes, while native species fed
selectively on different food items in different size classes,
indicating a slight ontogenetic diet shift.

Dietary overlap between exotic \emph{O. niloticus} and natives was
significantly high (F (2, 25) = 0.08; p \textless{} 0.05) for size class
\textless{}50 mm (Table 3). \emph{Oreochromis. niloticus} in the
\textless{}50 mm size class consumed mainly diatoms and algae, while
individuals in the 101\selectlanguage{english}-150 mm and 151\selectlanguage{english}- 302 mm size classes consumed
mostly zooplankton, chlorophytes, and algae, dominated by Micro cyst is,
Gonium, and Phacus. There were some significantly low dietary overlaps
among smaller native species at \textless{}50 and 101--150 mm size
classes, except for \emph{O. macrochir,} among which significantly high
diet overlap was observed (niche breath coefficients 0.625, 0.691, and
0.782, respectively) (Table 3\emph{). Coptodon rendalli} is
predominantly herbivorous, but its diet consisted of zooplankton and
insects in the 151\selectlanguage{english}-302 mm size class, and there was a low dietary
overlap with \emph{O. niloticus} for fish 151--302 mm in length (niche
breath coefficient 0.211).

Similarly, results for the first principal component axis indicated a
high positive correlation with food items such as microfauna, others and
fish, and a high negative correlation with cyanophytes, chlorophytes and
macrophytes (Table 4). This axis presents 53.2\% of the variation
explained from omnivorous species (\emph{O. niloticus} and \emph{O.
macrochir)} . The second principal component axis showed a strong
positive correlation with diatoms, microfauna and zooplanktons, and a
strong negative correlation with others and fish (Figure 4). This axis
presents 18.3\% of the variation explained from omnivorous fish species
of \emph{O. niloticus} and \emph{O. macrochir} . \emph{Oreochromis
niloticus} and native \emph{O. macrochir} grouped closely in dietary
space as defined by PCA axes 1 and 2, and did not significantly differ
(F(2,33) = 0.36, \emph{p} \textgreater{} 0.05) in their diet using ANOVA
test, indicating dietary overlap (Figure 4. and Table 4).

A weak association was observed between \emph{O. niloticus} and
native\emph{C. rendalli} fish species in the diets (Table 5). The first
principal component axis has strong positive correlations with food
items such as diatom, cyanophytes, chlorophytes and macrophytes. This
axis presents 50.7\% of the variation explained herbivorous \emph{C.
rendalli} and omnivorous \emph{O. niloticus} (Figure 5 and Table 5). The
second principal component axis showed a strong negative correlation
with microfauna, other and zooplanktons. This axis presents 15.8\% of
the variation explained \emph{O. niloticus} and native \emph{C.
rendalli} . \emph{Oreochromis niloticus} and native \emph{C.
rendalli}grouped closely in dietary space as defined by PCA axes 1 and
2, was significantly different (F(2,45) = 2.28, \emph{p} \textless{}
0.05) in their diet, indicating no dietary overlap.

\textbf{4. DISCUSSION}

Although the food resources of \emph{O. niloticus} and native species
were quite specific and similar (algae, diatoms, zooplankton, and
detritus), algae and diatoms were the most important items in the diet
of native species; individuals in the size class \textless{}50 mm fed
mainly on these resources. The principal difference between the diets of
exotic Nile tilapia and the native species was the size above which a
particular item came to be more important, since natives utilize algae
as food over a longer period of time. Our results also indicated that
\emph{O. niloticus} were more generalist with respect to diet
composition and the abundance of food items, and relied more heavily on
zooplankton and chlorophytes in the \textgreater{}151 mm size class than
native species. This more generalist foraging on microphages,
macrophages, microfauna, and detritus probably explains the high
abundance of \emph{O. niloticus}relative to native species in the river.

Contrary to our main hypothesis, the stomach content analysis data
provided no evidence of niche segregation between native species and
exotic \emph{O. niloticus} in the upper Kabompo River. \emph{O.
niloticus} evidently used more diverse food resource than native
species. When dominating fish communities, \emph{O. niloticus} have been
observed to have a wide trop hic niche but generally prefer zooplankton
and detritus (Werner \& Gilliam, 1984; Winemiller, 1989; Mason et al.,
2008; K\selectlanguage{polish}ı\selectlanguage{english}rankaya \& Ekmek\selectlanguage{ngerman}çi, 2013; Zengeya et al., 2015). However,
competitive inter actions and dietary overlap with natives such
as\emph{O. macro chir} may force \emph{O. niloticus} to occupy a wider
trophic niche (Kenzo \& Mazingaliwa, 2002; Marshall, 2011; Zengeya et
al., 2015). Hence, the observed narrow niche use of native species may
partly result from inc reased competition for food resources following
the invasion of \emph{O. niloticus} . In Lake Chivero, exotic \emph{O.
niloticus} and natives presented a low dietary overlap and wide niche
areas, while omnivores had a high trophic niche overlap where food
sources were limited (Junor, 1969; Marshall, 2011). However, \emph{O.
niloticus} feeds on larger quantities of food than native species in
Lake Victoria (Trewavas, 1983; Marshall, 2011; Zengeya et al., 2015).
Inclusion of more detritus and the algae \emph{Microcystis}
,\emph{Gonium} , and \emph{Phacus} in the diet of \emph{O. niloticus}
may also indicate differences in foraging tactics relative to native
species.

Our results from SCA suggested that the wide dietary niche of \emph{O.
niloticus} is largely due to marked size class differences in niche use.
Some size classes of \emph{O. niloticus} had exceptionally wide or
narrow trophic niches, indicating low or high levels of interspecific
competition in diets, respectively, and high individual variation in
feeding habitats (Werner \& Gilliam, 1984; Zengeya et al., 2015). The
small number but high quantity of food items consumed by \emph{O.
niloticus} in the 151\selectlanguage{english}-302 mm size class is probably due to specialized
foraging on abundant food sources in certain habitats, whereas the
relative importance of food items consumed by most native species and
also some \emph{O. niloticus} in the \textless{}101 mm size classes
probably indicates a diet dominated by algae chlorophytes and diatoms.
The selection of these food items at size class 151--302 mm of the
species is likely associated with their high abundance in the upper
Kabompo River, as reported for a nearby section of the river outside the
sampled area (Bok \& Bills, 2012; AES, 2014).

Previous studies suggest that dietary niche overlap between species can
be interpreted as evidence of multiple shared food sources (Helfman et
al., 1997; Pilger et al., 2010) and therefore as an indicator of
potential competition (Eloranta et al., 2015). The exotic
species\emph{O. niloticus} and the native species \emph{T.
sparrmanii}exhibited high trophic niche overlap. However, their wider
trophic niche area suggests that the \emph{O. niloticus} are
opportunistic and can change to overcome possible competition in trophic
position or diet composition, and may explain the coexistence of these 2
species (Lowe-McConnell, 1987; Winemiller, 1991, Winemiller \&
Kelso-Winemiller, 2003; Agostinho et al., 2015). In contrast, all native
species in our study had narrower dietary niches. For example, although
cichlids might include many species, individual species demonstrate a
narrow dietary niche area, suggesting that these species are
specialists.

\emph{Orochromis macrochir} and \emph{C. rendalli} less abundant of
smaller size class caught during the study. The species are of similar
size classes, feeding mainly on filamentous algae, benthic
invertebrates, and diatoms (Kenzo \& Mazingaliwa 2002). Thus, the
dietary niche of these species may overlap with that of \emph{O.
niloticus} at the base of the trophic web. Nowadays these native species
are 3 of the less abundant species in the upper Kabompo River (DoF
2018). In contrast, the \emph{O. niloticus} population has greatly
increased in the last decade, and abundant Nile tilapia was recorded
during this study. \emph{C. rendalli} is a native pelagic herbivore
which feeds mainly on fish, invertebrates (in size classes
\textgreater{}51 mm), and algae (in size class \textless{}50 mm),
suggested a potential dietary niche overlap with \emph{O. niloticus} in
the smallest size class (Kenzo \& Mazingaliwa 2002, Marshall 2011,
Zengeya et al., 2015).

Niche differentiation can explain how species co-exist in an ecosystem,
but empirical support has been sparse (Mason et al., 2008; Zengeya et
al., 2015). However, niche specialization has been regarded as a common
phenomenon in fish community assemblages (Pilger et al., 2010; Eloranta
et al., 2015). In the upper Kabompo River, there seems to be dietary
niche specialization among native species, supported by their relatively
low trophic niche overlap. The only substantial overlaps among native
species were observed between \emph{O. macrochir} and \emph{C.
rendalli.}

\emph{O. macrochir} and \emph{C. rendalli} in the 51\selectlanguage{english}-100 mm size class,
which are ecologically similar (Minshull, 1969; Junor, 1969; Kenzo \&
Mazingaliwa, 2002; Zengeya et al., 2015). In contrast, the high dietary
niche overlap between the native species in all size classes and\emph{O.
niloticus} suggests potential competition for food resources (Brendonck
et al., 2003; Marshall, 2011; Zengeya et al., 2015). The presence of
\emph{O. niloticus} can also affect populations of native species
indirectly. In many studies, invasion by \emph{O. niloticus} has been
related to a decrease in numbers of aquatic plants and phytoplankton
biomass, and a reduction in macroinvertebrate and macrophyte populations
(Moriarty \& Moriarty, 1973; Marshall, 2011). For example, in the
Olifants River in the Western Cape Province of South Africa, Nile
tilapia became the dominant species within a few years of introduction
and eliminated macrophytes within a few years of establishment,
coinciding with significant declines in previously abundant native
species within the community. As a result, natives are now confined to
smaller tributaries and headwaters (Zengeya et al., 2015). Furthermore,
the presence of \emph{O. niloticus} can lead to trophic cascades
(Marshall, 2005; AES, 2014; Zengeya et al., 2020).

The narrow dietary niche of native species suggests that a small change
in food resource abundance could generate a big shift in native species
population sizes. This narrow dietary niche could con tribute to
population de creases of native species, particularly\emph{, O.
macrochir} and \emph{C. rendalli} , which showed a relatively high
degree of dietary overlap with \emph{O. niloticus} , in contrast to our
hypothesis. This may be because the system has been changing rapidly
over the last few years due to mining activities in the surrounding
area, as predicted by a 2010 biological monitoring study (Bok \& Bills,
2012; DoF, 2018). Mining activities may affect fish habitat condition
and affect populations of native fishes. Another factor is dietary niche
overlap among natives, suggesting shared resource use and potential
competition. However, as indicated by wide dietary niches, both \emph{O.
niloticus} and native species are able to switch food sources depending
on the abundance of these sources, while native species that feed only
on a small range of food sources are more vulnerable to changes in
resource abundance.

There is a need for detailed studies on the biology of all native fish
species in the upper Kabompo River and also data from the dry cold
season, when food resources are limited in the river. This will help to
increase our understanding of the impacts of \emph{O. nilo ticus} on
native fish communities.



\textbf{5. ACKNOWLEDGMENT}

The research was supported by the Germany Exchange Service (DAAD), the
Ministry of Fisheries and Livestock in Zambia, and the Africa Center of
Excellence in Aquaculture and Fisheries (Aquafish ACE) as part of a
doctoral dissertation by A.J. We appreciate the expert support from the
Aquaculture and Fisheries Department staff at Lilongwe University of
Agriculture and Natural Resources.

\textbf{6. AUTHORS' CONTRIBUTIONS AND CONFLICT OF INTEREST}

Arthertone Jere-Lead in data collection, data analysis, writing and
manuscript editing, Dr Wilson W. L. Jere - Lead and supervisor in
research design, data analysis and editing; Dr Austin Mtethiwa-Lead and
supervisor in writing and editing; Professor Daud Kassam-Lead and
supervisor in writing and manuscript editing.

\textbf{7. DATA ACCESSIBILITY}

The data that has been used in this study is available and the Dryad
data repository will be used to archive the data. The authors cited in
this document have acknowledged that data should be stored in the Dryad
data repository at https://doi.org/10.5061/dryad.sj3tx9661.

.

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\textbf{Table 1} . Abundance of the fishes caught and time of capture in
upper Kabompo River, December 2019- February 2020 survey.\selectlanguage{english}
\begin{longtable}[]{@{}lllll@{}}
\toprule
\textbf{Species} & \textbf{Common names} & \textbf{Status} &
\textbf{Individuals caught} & \textbf{Time of Capture}\tabularnewline
\midrule
\endhead
\emph{0reochromis niloticus} & Nile tilapia & Exotic & 14 & 6:00
AM\tabularnewline
& & & 161 & 12:00 AM\tabularnewline
& & & 40 & 5:00 PM\tabularnewline
\emph{Oreochromis macrochir} & Greenhead tilapia & Native & 5 & 6:00
AM\tabularnewline
& & & 10 & 12:00 AM\tabularnewline
& & & 95 & 5:00 PM\tabularnewline
\emph{Coptodon rendalli} & Redbreast tilapia & Native & 9 & 6:00
AM\tabularnewline
& & & 44 & 12:00 AM\tabularnewline
& & & 3 & 5:00 PM\tabularnewline
\bottomrule
\end{longtable}

\textbf{Table 2} . Mean stomach fullness and \% Vacuity index of
stomachs of the fish collected by total length class in upper Kabompo
River, December 2019- February 2020. N = total number of stomachs
examined, SF = mean stomach fullness (\selectlanguage{ngerman}± = Standard Deviation) and
VI=vacuity index.\selectlanguage{english}
\begin{longtable}[]{@{}lllll@{}}
\toprule
\begin{minipage}[b]{0.17\columnwidth}\raggedright\strut
\textbf{Species}\strut
\end{minipage} & \begin{minipage}[b]{0.17\columnwidth}\raggedright\strut
\textbf{Size class (mm.TL)}\strut
\end{minipage} & \begin{minipage}[b]{0.17\columnwidth}\raggedright\strut
\textbf{N}\strut
\end{minipage} & \begin{minipage}[b]{0.17\columnwidth}\raggedright\strut
\textbf{SF}\strut
\end{minipage} & \begin{minipage}[b]{0.17\columnwidth}\raggedright\strut
\textbf{VI (\%)}\strut
\end{minipage}\tabularnewline
\midrule
\endhead
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
\emph{Oreochromis niloticus}\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
151-302\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
2\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
3.8 \selectlanguage{ngerman}± 0.4\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
13\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
101-150\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
5\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
3.5 \selectlanguage{ngerman}± 0.5\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
7.4\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
51-100 \textless{}50\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
9 4\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
3.0 \selectlanguage{ngerman}± 0.9 1.9 ± 1.4\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
31 51.4\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.19\columnwidth}\raggedright\strut
\emph{Oreochromis macrochir}\strut
\end{minipage} & \begin{minipage}[t]{0.19\columnwidth}\raggedright\strut
151-302 101-150 51-100 \textless{}50\strut
\end{minipage} & \begin{minipage}[t]{0.19\columnwidth}\raggedright\strut
4 2 9 5\strut
\end{minipage} & \begin{minipage}[t]{0.19\columnwidth}\raggedright\strut
3.7 \selectlanguage{ngerman}± 0.5 2.6 ± 1.2 1.5 ± 1.0 2.9 ± 1.1\strut
\end{minipage} & \begin{minipage}[t]{0.19\columnwidth}\raggedright\strut
41.2 20.8 16 51.4\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
\emph{Coptodon rendalli}\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
101-150\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
6\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
3.5 \selectlanguage{ngerman}± 0.6\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
16.7\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
51-100\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
4\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
3.6 \selectlanguage{ngerman}± 0.5\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
21.4\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
\textless{}50\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
10\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
2.5 \selectlanguage{ngerman}± 1.2\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
21.5\strut
\end{minipage}\tabularnewline
\bottomrule
\end{longtable}

\textbf{Table 3}. Mean values of the dietary overlap of exotic and
native species in size classes (\textless{}50 mm TL: upper left panels
and 51-100 mm and 101-150mm TL: lower right panels) in upper Kabompo
River, December 2019- February 2020. The values are Pianka`s (1973)
symmetrical measure of niche. Breadth coefficients with significant
values (\textgreater{}0.60) in bold font. Dash (-) = not comparable.\selectlanguage{english}
\begin{longtable}[]{@{}lllll@{}}
\toprule
\textbf{Status} & \textbf{Species} & \emph{C. rendalli} & \emph{O.
macrochir} & \emph{O. niloticus}\tabularnewline
\midrule
\endhead
Exotic & \emph{O. niloticus} & \textbf{0.625} & \textbf{0.691} &
\textbf{-}\tabularnewline
Native & \emph{O. macrochir} & 0.551 & \textbf{-} &
\textbf{0.782}\tabularnewline
Native & \emph{C. rendalli} & \textbf{-\_} & 0.211 &
0.465\tabularnewline
\bottomrule
\end{longtable}

\textbf{Tables 4.} Loadings from principal components analysis
of\emph{O. niloticus} and \emph{O. macrochir} fish species based on
dietary characters in the upper Kabompo River.\selectlanguage{english}
\begin{longtable}[]{@{}lll@{}}
\toprule
\textbf{Food Item} & \textbf{PCA axis} & \textbf{PCA
axis}\tabularnewline
\midrule
\endhead
& \textbf{1} & \textbf{2}\tabularnewline
Eigenvalue & 4.259 & 1.461\tabularnewline
Percent of variance explained & 53.242 & 71.503\tabularnewline
Cyanophytes & 0.630 & -0.137\tabularnewline
Chlorophytes & 0.094 & 0.856\tabularnewline
Diatoms & 0.807 & 0.297\tabularnewline
Macrophytes & 0.836 & -0.117\tabularnewline
Microfauna & 0.898 & 0.198\tabularnewline
Detritus & 0.891 & -0.173\tabularnewline
Others & 0.919 & -0.056\tabularnewline
Zooplanktons & -0.239 & -0.731\tabularnewline
Fish & 0.000 & 0.000\tabularnewline
\bottomrule
\end{longtable}

\textbf{Table 5.} Loadings from principal components analysis of\emph{O.
niloticus} and \emph{C. rendalli} fish species based on dietary
characters in the upper Kabompo River.\selectlanguage{english}
\begin{longtable}[]{@{}lll@{}}
\toprule
\textbf{Food Item} & \textbf{PCA axis} & \textbf{PCA
axis}\tabularnewline
\midrule
\endhead
& \textbf{1} & \textbf{2}\tabularnewline
Eigenvalue & 4.058 & 50.226\tabularnewline
Percent of variance explained & 1.261 & 66.485\tabularnewline
Cyanophytes & 0.778 & -0.002\tabularnewline
Chlorophytes & 0.039 & -0.249\tabularnewline
Diatoms & -0.854 & 0.082\tabularnewline
Macrophytes & -0.874 & 0.164\tabularnewline
Microfauna & 0.874 & 0.082\tabularnewline
Detritus & 0.676 & 0.551\tabularnewline
Others & 0.858 & -0.233\tabularnewline
Zooplanktons & -0.022 & 0.894\tabularnewline
Fish & 0.000 & 0.000\tabularnewline
\bottomrule
\end{longtable}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image1/image1}

\end{center}
\end{figure}

\textbf{Figure 1.} Map of the study area - upper Kabompo River

{[}CHART{]}{[}CHART{]}{[}CHART{]}

\textbf{Figure 2} . A comparison of the the diets (\% volume) of exotic
and native fish species in the upper Kabompo River. December 2019 --
February 2020. Microfuna= Insects, Zooplankton and protozoa.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image2/image2}

\end{center}
\end{figure}

\textbf{Figure 3.} PCA ordination of \emph{O. niloticus} and
native\emph{O. macrochir} fish species based on dietary characters in
the upper Kabompo River.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image3/image3}

\end{center}
\end{figure}

\textbf{Figure 4.} PCA ordination of \emph{O. niloticus} and
native\emph{C. rendalli} fish species based on dietary characters in the
upper Kabompo River.

\selectlanguage{english}
\FloatBarrier
\end{document}

