*Corresponding Author: ZPO Yébé, Laboratory of Environment and Aquatic Biology, NANGUI
ABROGOUA University, 02 BP 801, Abidjan 02, Ivory Coast. Email: [email protected]. 58
International Journal of Zoology and Applied Biosciences ISSN: 2455-9571
Volume 10, Issue 5, pp: 58-66, 2025 http://www.ijzab.com
https://doi.org/10.55126/ijzab.2025.v10.i05.008
Research Article
DIRECTIONAL ASYMMETRY OF OTOLITHS OF CHRYSICHTHYS
NIGRODIGITATUS (LACEPEDE 1803) INDICATOR OF ENVIRONMENTAL
STRESS IN THE COMOE RIVER BASIN (IVORY COAST)
ZPO Yébé, MK Konan, WY Koné and N. Konaté
Laboratory of Environment and Aquatic Biology, Nangui Abrogoua University, 02 BP 801, Abidjan 02, Ivory Coast.
Article History: Received 29th July 2025; Accepted 30th August 2025; Published 30th September 2025
ABSTRACT
The impact of pollution on the otoliths of Chrysichthys nigrodigitatus organisms from the middle course of the Comoé
River was assessed through the study of asymmetry. Quarterly sampling of 201 specimens of Chrysichthys nigrodigitatus
was carried out over one year, from February 2021 to March 2022 at five sampling stations (M’Basso, Manzan, YèrèYèrè,
Abradinou and Bettié). The otoliths were extracted and then measured. The Shapiro-Wilk test was performed to
statistically verify the normality of the variables (weight, area, width, length and perimeter). Asymmetry was assessed
through the AF1 and AF2 indices. After this assessment, analysis of variance (ANOVA) and the Tukey-Kramer post-hoc
test were used to test for differences in directional asymmetry between sites. Directional asymmetry values varied
significantly between sampling sites. Otolith analysis revealed marked directional asymmetry, predominantly oriented
toward the right side. The Manzan, Bettié, Abradinou, and YèrèYèrè stations displayed the highest average directional
asymmetry, while M'Basso recorded the lowest values.
Keywords: Chrysichthys nigrodigitatus, Echantillonnage, Erreur de mesure, Points aberrants, Pollution.
INTRODUCTION
Directional asymmetry (DA) is defined as a mean of d = r -
l that is significantly different from zero (Baamrane et al.,
2018). It is a difference between sides, but where the more
developed side is always the same for the entire population
(Baamrane et al., 2018). It represents small directional
deviations from perfect symmetry in bilateral structures
expressed by a genome (Møller, 1990). These deviations
may arise due to variations in the ability of individuals to
develop both sides of the body identically following
possible exposure to environmental stress (Baamrane et al.,
2018). The use of otoliths, which are paired structures,
could therefore be an appropriate tool for studying
directional asymmetry. Otoliths are complex
polycrystalline structures composed of calcium carbonate
(approximately 96%) and trace elements embedded in a
protein matrix (Wright et al., 2002). These structures are in
the inner ear of fish and play a role in hearing and
maintaining balance (Popper & Lu, 2000). They are
enclosed within three terminal organs of the inner ear of the
teleost fish (Popper & Lu, 2000). The saccular otolith
(sagitta) is the largest pair in most teleost families and is
therefore used in most studies (Mahé, 2019). Otolith
morphometry and morphology have been widely used to
identify fish species. Fortunato et al. (2014) used otolith
morphometry to identify mullet species (Mugilidae) from
the Northeast Atlantic and the Mediterranean Sea, while
Tuset et al. (2008) characterized 348 fish species using
otolith morphometry. Otolith morphometry has also been
used for fish stock identification (Avigliano et al., 2014).
However, studies related to otolith directional asymmetry
of Chrysichthys nigrodigitatus populations are lacking in
the middle reaches of the Comoé River. In this work, we
describe for the first time the directional asymmetry of
otoliths in Chrysichthys nigrodigitatus populations caused
by environmental stress in the middle reaches of the Comoé
River. Otolith asymmetry is considered a potentially
ZPO Yébé et al. Int. J. Zool. Appl. Biosci., 10(5), 58-66, 2025
www.ijzab.com 59
important tool for assessing the level of environmental
stress.
MATERIALS AND METHODS
Study environment
Figure 1 shows the map of sampling stations. The study
area is located in the south-east of Ivory Coast. It is
bordered by the middle course of the Comoé River. Five
stations from upstream to downstream were selected on the
Comoé River. These are : M’Basso, Manzan, YèrèYèrè,
Abradinou and Bettié.
Sampling ichthyological
Figure 2 represents a specimen of Chrysichthys
nigrodigitatus. The quarterly sampling method was carried
out over one year, from March 2021 to March 2022. The
catches were made using nets of different mesh sizes (7, 10,
12, 13, 18, 20, 25, 28, 30, 35, 50, 60 and 70 mm) in order to
capture the maximum number of specimens of
Chrysichthys nigrodigitatus The initial biological material
consisted of 201 specimens of Chrysichthys nigrodigitatus.
However, due to losses during handling and laboratory
extraction, 40 otoliths corresponding to 20 specimens could
not be included in the final analysis. Therefore, the final
sample of C. nigrodigitatus was 181 individuals, or 362
otoliths
Figure 1. Sampling map of the study stations.
Figure 2. Specimen of Chrysichthys nigrodigitatus.
www.ijzab.com 59
important tool for assessing the level of environmental
stress.
MATERIALS AND METHODS
Study environment
Figure 1 shows the map of sampling stations. The study
area is located in the south-east of Ivory Coast. It is
bordered by the middle course of the Comoé River. Five
stations from upstream to downstream were selected on the
Comoé River. These are : M’Basso, Manzan, YèrèYèrè,
Abradinou and Bettié.
Sampling ichthyological
Figure 2 represents a specimen of Chrysichthys
nigrodigitatus. The quarterly sampling method was carried
out over one year, from March 2021 to March 2022. The
catches were made using nets of different mesh sizes (7, 10,
12, 13, 18, 20, 25, 28, 30, 35, 50, 60 and 70 mm) in order to
capture the maximum number of specimens of
Chrysichthys nigrodigitatus The initial biological material
consisted of 201 specimens of Chrysichthys nigrodigitatus.
However, due to losses during handling and laboratory
extraction, 40 otoliths corresponding to 20 specimens could
not be included in the final analysis. Therefore, the final
sample of C. nigrodigitatus was 181 individuals, or 362
otoliths
Figure 1. Sampling map of the study stations.
Figure 2. Specimen of Chrysichthys nigrodigitatus.
ZPO Yébé et al. Int. J. Zool. Appl. Biosci., 10(5), 58-66, 2025
www.ijzab.com 60
Extraction and photography of otoliths
Figure 3 shows the otolith extraction steps. The saccular
otoliths were extracted by turning the fish's ventral side
upward to remove the gills and hypobranchial apparatus,
exposing the base of the skull. Fine forceps were used for
extraction. To remove the thin membrane covering the
otoliths, they were carefully cleaned with distilled water
and 70% ethanol (Panfili & Ximenes, 1992). They were
air-dried and stored in numbered plastic tubes. The two (2)
sagittal otoliths from each fish were photographed and then
coded (Figure 4). According to the terminology used by
Avigliano et al. (2014), morphometric variables such as,
otolith length (Lo, mm), otolith width (lo, mm), otolith
perimeter (Po, mm), otolith area (Ao, mm2) were measured
using the software (ImageJ version 1.52a).
Figure 3.Otolith extraction steps (A: ventral side of the fish and cutting of the lower jaw, B: exposure of the otolithic
chamber, C: opening of the otolithic chamber, D: highlighting the otolith).
Figure 4. Pair of sagittal otoliths of Chrysichthys nigrodigitatus after photography (L: left, R: right).
A
D
C
B
www.ijzab.com 60
Extraction and photography of otoliths
Figure 3 shows the otolith extraction steps. The saccular
otoliths were extracted by turning the fish's ventral side
upward to remove the gills and hypobranchial apparatus,
exposing the base of the skull. Fine forceps were used for
extraction. To remove the thin membrane covering the
otoliths, they were carefully cleaned with distilled water
and 70% ethanol (Panfili & Ximenes, 1992). They were
air-dried and stored in numbered plastic tubes. The two (2)
sagittal otoliths from each fish were photographed and then
coded (Figure 4). According to the terminology used by
Avigliano et al. (2014), morphometric variables such as,
otolith length (Lo, mm), otolith width (lo, mm), otolith
perimeter (Po, mm), otolith area (Ao, mm2) were measured
using the software (ImageJ version 1.52a).
Figure 3.Otolith extraction steps (A: ventral side of the fish and cutting of the lower jaw, B: exposure of the otolithic
chamber, C: opening of the otolithic chamber, D: highlighting the otolith).
Figure 4. Pair of sagittal otoliths of Chrysichthys nigrodigitatus after photography (L: left, R: right).
A
D
C
B
ZPO Yébé et al. Int. J. Zool. Appl. Biosci., 10(5), 58-66, 2025
www.ijzab.com 61
Statistical processing
First, for each site studied and for each parameter analyzed,
the otolith pairs (sagittae) were subjected to an outlier
elimination process. Potentially outlier individuals were
then statistically evaluated using the Grubbs test (Rohlf &
Sokal, 1995; Palmer & Strobeck, 2003). This test allows us
to objectively determine whether the exclusion of these
points is statistically justified. Furthermore, measurement
errors were considered in this study on a subset of 30
individuals, in accordance with Pither & Taylor, (2000). To
assess whether the variation between sides significantly
exceeded the measurement error, a mixed-model ANOVA
(side x individual) was performed for each trait studied,
considering two factors: sides and individuals. In addition,
the normality of the variables was verified using a Shapiro-
Wilk statistical test using R Studio software (Bertrand et
al., 2019). Finally, to detect directional asymmetry, a t-test
was used to test whether the means (d = r - l) differed from
zero. A mean distribution of traits significantly different
from zero would then indicate directional asymmetry
(Palmer & Strobeck, 1986). Meanwhile, in the present
study, antisymmetry was examined using the Kolmogorov-
Smirnov test applied to the frequency distribution of
deviations between right and left sides (Palmer &Strobeck,
1986). We used analysis of variance (ANOVA) to compare
asymmetry between sides and sampling sites. To precisely
determine significant differences between sites, we then
applied the Tukey-Kramer post-hoc (HSD) test.
Determination of asymmetry
Among the different indices for measuring asymmetry
proposed by the literature (Palmer, 1994) , we opted for the
AF1, AF2 indices. The AF1 index is frequently used for its
simplicity of calculation. It quantifies the average
difference between the right and left sides for a specific
character and treatment (Palmer, 1994) . This index makes
it possible to obtain a numerical measure of asymmetry. It
is obtained by the following relationship:
To account for the potential influence of otolith size on
asymmetry measurements, we applied a correction to our
calculations. Instead of simply using the raw difference
between the right and left otolith (AF1), we employed the
following formula (AF2) for the meaning of each character
This approach allows us to normalize the difference in total
otolith size, including biases related to size variations
between individuals (Palmer, 1994) .
Organic pollution index versus asymmetry
Table 1 illustrates the class boundaries of the organic
pollution index. Here, we used the organic pollution index
(Leclercq & Vandevenne, 1987) calculated from
ammonium, nitrite, and orthophosphate measurements. The
organic pollution level according to Buhungu et al. (2018)
is:
IPO = 5.0 - 4.6: no organic pollution.
IPO = 4.5 - 4.0: low organic pollution.
IPO = 3.9 - 3.0: moderate organic pollution.
IPO = 2.9 - 2.0: high organic pollution.
IPO = 1.9 - 1.0: very high organic pollution.
To analyze the relationship between the OPI and the
asymmetry of each sampling site, we used Pearson
correlation.
RESULTS AND DISCUSSION
Figure 5 illustrates the distribution of normal and outlier
values within C. nigrodigitatus populations. Of 362 otoliths
analyzed, 11 (3.04%) were identified as outliers (p < 0.05).
Grubb 's test confirmed the statistical significance of the
outliers (p < 0.05). This outlier data was excluded from
further analyses to ensure the reliability of the results.
Table 2 presents the results of the mixed analysis of
variance (ANOVA), carried out on a subsample of 30
specimens of Chrysichthys nigrodigitatus.
Table 1. Limits of the classes of the organic pollution index (Buhungu et al., 2018).
Classes NH4+ (mg/l) NO 2- ( ug /l) PO 3-4 ( ug / l )
5 <0.1 <5 <15
4 0.1-0.9 6-10 16-75
3 1-2.4 11-50 76-250
2 2.5-6 51-150 251-900
1 >6 >150 >900
The precision of the measurements was found to be
remarkable, with a measurement error between otolith
replicates of less than 1%. Figure 6 presents the
distributions of each parameter of the Chrysichthys
nigrodigitatus populations. The histograms show a shape
that appears to be that of a normal distribution. The
Shapiro-Wilk test revealed a normal distribution (P > 0.05)
in all stations and all parameters. Figure 7 represents the
intra-population variation of the directional asymmetry of
otoliths Chrysichthys nigrodigitatus according to the side.
Graphically we observe that the directional asymmetry is
more pronounced on the right side (R) of the otoliths in the
studied population. The ANOVA shows a very significant
difference between the right and left sides (p < 0.001) for
www.ijzab.com 61
Statistical processing
First, for each site studied and for each parameter analyzed,
the otolith pairs (sagittae) were subjected to an outlier
elimination process. Potentially outlier individuals were
then statistically evaluated using the Grubbs test (Rohlf &
Sokal, 1995; Palmer & Strobeck, 2003). This test allows us
to objectively determine whether the exclusion of these
points is statistically justified. Furthermore, measurement
errors were considered in this study on a subset of 30
individuals, in accordance with Pither & Taylor, (2000). To
assess whether the variation between sides significantly
exceeded the measurement error, a mixed-model ANOVA
(side x individual) was performed for each trait studied,
considering two factors: sides and individuals. In addition,
the normality of the variables was verified using a Shapiro-
Wilk statistical test using R Studio software (Bertrand et
al., 2019). Finally, to detect directional asymmetry, a t-test
was used to test whether the means (d = r - l) differed from
zero. A mean distribution of traits significantly different
from zero would then indicate directional asymmetry
(Palmer & Strobeck, 1986). Meanwhile, in the present
study, antisymmetry was examined using the Kolmogorov-
Smirnov test applied to the frequency distribution of
deviations between right and left sides (Palmer &Strobeck,
1986). We used analysis of variance (ANOVA) to compare
asymmetry between sides and sampling sites. To precisely
determine significant differences between sites, we then
applied the Tukey-Kramer post-hoc (HSD) test.
Determination of asymmetry
Among the different indices for measuring asymmetry
proposed by the literature (Palmer, 1994) , we opted for the
AF1, AF2 indices. The AF1 index is frequently used for its
simplicity of calculation. It quantifies the average
difference between the right and left sides for a specific
character and treatment (Palmer, 1994) . This index makes
it possible to obtain a numerical measure of asymmetry. It
is obtained by the following relationship:
To account for the potential influence of otolith size on
asymmetry measurements, we applied a correction to our
calculations. Instead of simply using the raw difference
between the right and left otolith (AF1), we employed the
following formula (AF2) for the meaning of each character
This approach allows us to normalize the difference in total
otolith size, including biases related to size variations
between individuals (Palmer, 1994) .
Organic pollution index versus asymmetry
Table 1 illustrates the class boundaries of the organic
pollution index. Here, we used the organic pollution index
(Leclercq & Vandevenne, 1987) calculated from
ammonium, nitrite, and orthophosphate measurements. The
organic pollution level according to Buhungu et al. (2018)
is:
IPO = 5.0 - 4.6: no organic pollution.
IPO = 4.5 - 4.0: low organic pollution.
IPO = 3.9 - 3.0: moderate organic pollution.
IPO = 2.9 - 2.0: high organic pollution.
IPO = 1.9 - 1.0: very high organic pollution.
To analyze the relationship between the OPI and the
asymmetry of each sampling site, we used Pearson
correlation.
RESULTS AND DISCUSSION
Figure 5 illustrates the distribution of normal and outlier
values within C. nigrodigitatus populations. Of 362 otoliths
analyzed, 11 (3.04%) were identified as outliers (p < 0.05).
Grubb 's test confirmed the statistical significance of the
outliers (p < 0.05). This outlier data was excluded from
further analyses to ensure the reliability of the results.
Table 2 presents the results of the mixed analysis of
variance (ANOVA), carried out on a subsample of 30
specimens of Chrysichthys nigrodigitatus.
Table 1. Limits of the classes of the organic pollution index (Buhungu et al., 2018).
Classes NH4+ (mg/l) NO 2- ( ug /l) PO 3-4 ( ug / l )
5 <0.1 <5 <15
4 0.1-0.9 6-10 16-75
3 1-2.4 11-50 76-250
2 2.5-6 51-150 251-900
1 >6 >150 >900
The precision of the measurements was found to be
remarkable, with a measurement error between otolith
replicates of less than 1%. Figure 6 presents the
distributions of each parameter of the Chrysichthys
nigrodigitatus populations. The histograms show a shape
that appears to be that of a normal distribution. The
Shapiro-Wilk test revealed a normal distribution (P > 0.05)
in all stations and all parameters. Figure 7 represents the
intra-population variation of the directional asymmetry of
otoliths Chrysichthys nigrodigitatus according to the side.
Graphically we observe that the directional asymmetry is
more pronounced on the right side (R) of the otoliths in the
studied population. The ANOVA shows a very significant
difference between the right and left sides (p < 0.001) for
ZPO Yébé et al. Int. J. Zool. Appl. Biosci., 10(5), 58-66, 2025
www.ijzab.com 62
all characters. Figure 8 illustrates the spatial differences in
the average directional asymmetry of otoliths. Statistical
analyses (ANOVA and Tukey HSD test) revealed
significant effects of stations on otolith directional
asymmetry (DA) (p < 0.05). Station Manzan has the
highest DA (14.92%), indicating more asymmetric otoliths.
Then, stations Bettié, YèrèYèrè and Abradinou show
intermediate values. M' Basso stands out for the lowest DA
values, about five times lower than the observed
maximums.
Figure 5. Results of outliers (red dots) of Chrysichthys nigrodigitatus.
The values of the organic pollution index (IPO), and the
average directional asymmetry are represented in table 3.
Overall, the values of the index oscillate between 1 (very
high organic pollution) and 2.8 (high organic pollution). It
is noted that the stations (Manzan, Betié, Abradinou and
YèrèYèrè) which are polluted with very high values of
pollution have a high average directional asymmetry. The
result of the Spearman correlation test between the
pollution index (IPO) and the directional asymmetry (AD)
indicates a strong negative correlation (-0.73) between IPO
and AD. This relationship is statistically significant
(P=0.0009) for the populations.
We analyzed otolith pairs of Chrysichthys nigrodigitatus
from five sites in the Comoé River, measuring various
morphological parameters (weight, area, width, length, and
perimeter). The Shapiro-Wilk test confirmed the normality
of the data, allowing for skewness analysis. The t-test and
ANOVA revealed significant directional skewness,
consistently oriented toward the right side (p < 0.001) for
all the characters studied. The directional skewness of
Chrysichthys nigrodigitatus otoliths appears to result from
ecological adaptation and varies among sampling stations.
ANOVA and the Tukey HSD test revealed that the Manzan
station exhibited significantly higher skewness than the
others, while M'Basso displayed the lowest values.
Table 2. Mixed model ANOVA result performed on a subsample of 30 individuals of Chrysichthys nigrodigitatus.
Area
Source of variation Df Sum Medium square F P
Side 29 0.7 0.69 0.012 0.913
Individual 29 57.06 57,056 0.085 0.0002
www.ijzab.com 62
all characters. Figure 8 illustrates the spatial differences in
the average directional asymmetry of otoliths. Statistical
analyses (ANOVA and Tukey HSD test) revealed
significant effects of stations on otolith directional
asymmetry (DA) (p < 0.05). Station Manzan has the
highest DA (14.92%), indicating more asymmetric otoliths.
Then, stations Bettié, YèrèYèrè and Abradinou show
intermediate values. M' Basso stands out for the lowest DA
values, about five times lower than the observed
maximums.
Figure 5. Results of outliers (red dots) of Chrysichthys nigrodigitatus.
The values of the organic pollution index (IPO), and the
average directional asymmetry are represented in table 3.
Overall, the values of the index oscillate between 1 (very
high organic pollution) and 2.8 (high organic pollution). It
is noted that the stations (Manzan, Betié, Abradinou and
YèrèYèrè) which are polluted with very high values of
pollution have a high average directional asymmetry. The
result of the Spearman correlation test between the
pollution index (IPO) and the directional asymmetry (AD)
indicates a strong negative correlation (-0.73) between IPO
and AD. This relationship is statistically significant
(P=0.0009) for the populations.
We analyzed otolith pairs of Chrysichthys nigrodigitatus
from five sites in the Comoé River, measuring various
morphological parameters (weight, area, width, length, and
perimeter). The Shapiro-Wilk test confirmed the normality
of the data, allowing for skewness analysis. The t-test and
ANOVA revealed significant directional skewness,
consistently oriented toward the right side (p < 0.001) for
all the characters studied. The directional skewness of
Chrysichthys nigrodigitatus otoliths appears to result from
ecological adaptation and varies among sampling stations.
ANOVA and the Tukey HSD test revealed that the Manzan
station exhibited significantly higher skewness than the
others, while M'Basso displayed the lowest values.
Table 2. Mixed model ANOVA result performed on a subsample of 30 individuals of Chrysichthys nigrodigitatus.
Area
Source of variation Df Sum Medium square F P
Side 29 0.7 0.69 0.012 0.913
Individual 29 57.06 57,056 0.085 0.0002
ZPO Yébé et al. Int. J. Zool. Appl. Biosci., 10(5), 58-66, 2025
www.ijzab.com 63
Individual side 29 0.84 0.841 0.0001 0.992
Measurement error 116 23.16 0.0023
Width
Source of variation Df Sum Medium square F P
Side 29 0.009 0.009 0.018 0.892
Individual 29 6,261 6,260 12,467 0.0005
Individual side 29 0.92 0.916 0.1824 0.6701
Measurement error 116 58,254 0.0022
Length
Source of variation Df Sum Medium square F P
Side 29 0.065 0.0651 0.140 0.708
Individual 29 5,343 5,342 11,524 0.0009
Individual side 29 0.6 0.58 0.0124 0.911
Measurement error 116 53,777 0.0036
Perimeter
Source of variation Df Sum Medium square F P
Side 29 0.002 0.0021 0.281 0.992
Individual 29 129.96 129,962 9,081 0.0003
Individual side 29 0.61 0.612 0.0004 0.984
Measurement error 116 16.15 0.009
Figure 6. Normality graphs of populations Chrysichthys nigrodigitatus.
www.ijzab.com 63
Individual side 29 0.84 0.841 0.0001 0.992
Measurement error 116 23.16 0.0023
Width
Source of variation Df Sum Medium square F P
Side 29 0.009 0.009 0.018 0.892
Individual 29 6,261 6,260 12,467 0.0005
Individual side 29 0.92 0.916 0.1824 0.6701
Measurement error 116 58,254 0.0022
Length
Source of variation Df Sum Medium square F P
Side 29 0.065 0.0651 0.140 0.708
Individual 29 5,343 5,342 11,524 0.0009
Individual side 29 0.6 0.58 0.0124 0.911
Measurement error 116 53,777 0.0036
Perimeter
Source of variation Df Sum Medium square F P
Side 29 0.002 0.0021 0.281 0.992
Individual 29 129.96 129,962 9,081 0.0003
Individual side 29 0.61 0.612 0.0004 0.984
Measurement error 116 16.15 0.009
Figure 6. Normality graphs of populations Chrysichthys nigrodigitatus.
ZPO Yébé et al. Int. J. Zool. Appl. Biosci., 10(5), 58-66, 2025
www.ijzab.com 64
Figure 7.Variations in directional asymmetry of otoliths Chyrsichthys nigrodigitatus depending on the side ( P: weight,
Lo: length, lo: width, Po: perimeter, Ao: area, D: right and G: left).
Figure 8. Spatial variations in mean directional asymmetry (AD) of otoliths from the population Chrysichthys
nigrodigitatus (stations with common letters do not differ, ABR: Abradinou, BET: Bettié, MAN: Manzan, MBA:
M’Basso, YER: YèrèYèrè).
www.ijzab.com 64
Figure 7.Variations in directional asymmetry of otoliths Chyrsichthys nigrodigitatus depending on the side ( P: weight,
Lo: length, lo: width, Po: perimeter, Ao: area, D: right and G: left).
Figure 8. Spatial variations in mean directional asymmetry (AD) of otoliths from the population Chrysichthys
nigrodigitatus (stations with common letters do not differ, ABR: Abradinou, BET: Bettié, MAN: Manzan, MBA:
M’Basso, YER: YèrèYèrè).
ZPO Yébé et al. Int. J. Zool. Appl. Biosci., 10(5), 58-66, 2025
www.ijzab.com 65
Table 3. Relationship between organic pollution index (OPI) and average directional asymmetry (DA) of the studied fish
populations (Cn: Chrysichthys nigrodigitatus).
Site Esp Class NH4+ Class NO2- Class PO4- IPO Pollution AD Horn P
My C,n 3 1 1 1 Very strong 0.149 -0.73 0.00
Be C,n 4 3 1 1.6 Very strong 0.078 -0.73 0.00
Ab C,n 4 3 2 1.8 Very strong 0.069 -0.73 0.00
Ye C,n 4 2 1 1.4 Very strong 0.068 -0.73 0.00
Mb C,n 5 5 4 2.8 Strong 0.013 -0.73 0.00
These results can be explained by several environmental
and biological factors (Mille et al., 2015). First,
environmental conditions, such as temperature, pH, and
substrate nature, play a crucial role in otolith formation and
morphology. Nasreddine (2010) and Mahé (2019)
demonstrated that temperature accelerates otolith
morphogenesis and changes their growth trajectory, which
can lead to more pronounced directional asymmetry in
certain geographic areas. According to Tissot & Souchon,
(2010), water temperature can also influence fish
embryonic development, including otolith development.
According to these authors, abnormally high temperatures
can lead to abnormalities in otolith development, which can
have consequences on the fish's sensory function. Mille
(2015) demonstrated that diet composition contributes more
significantly to otolith morphological variability than
ingested quantity. Thus, differences in food availability and
type between the Manzan, Bettié, and M’Basso stations
could explain the variations related to otolith asymmetry.
Another hypothesis is that phosphate exerts indirect
chemical stress effects on otolith pairs (Perennou &
Aufray, 2007). The presence of high phosphate
concentrations in a freshwater environment can lead to
excessive algal blooms, which can degrade water quality
and lead to eutrophication. This eutrophication
phenomenon can generate significant stress on living
organisms, particularly fish, and potentially increase their
asymmetry rate. The observation of the presence of algae at
the Bettié and Manzan sites, as well as the poor water
quality observed during the sampling periods, support this
hypothesis. Such an indirect effect of phosphate could thus
contribute to the increase in the level of otolith asymmetry.
Our hypotheses corroborate the findings of Østbye et al.
(1997). Their research revealed that perch from acidic lakes
rich in phosphate and aluminum showed a more
pronounced asymmetry than those from non-acidified
lakes. Similarly, it is possible that the polluted environment
and the stress experienced by C. nigrodigitatus populations
in the waters of Bettié and the Manzan River are sufficient
to generate a strong asymmetry of the otoliths. This idea is
supported by the organic pollution index (OPI) calculated
in our study, which indicates very strong organic pollution
in Manzan, YèrèYèrè, Abradinou and Bettié.
CONCLUSION
This study highlighted the significant influence of human
activities on the morphology of Chrysichthys nigrodigitatus
fish in the middle reaches of the Comoé River. Otolith
analysis revealed significant directional asymmetry
oriented towards the right side. The Manzan, Bettié,
Abradinou and YèrèYèrè stations showed the highest
average directional asymmetry, while M’Basso had the
lowest values. The results of this study highlight the
urgency of implementing conservation and sustainable
management measures to preserve aquatic biodiversity.
ACKNOWLEDGMENT
The authors would like to thank the Sustainable
Management of Fisheries Resources Support Program
(PAGDRH) of the Directorate of Aquaculture and Fisheries
(DAP) for the funding provided to carry out this work.
Indeed, this study was carried out within the framework of
the DAP/PAGDRH-UNA project on the assessment of the
impact of agricultural and gold mining on the water quality
and fishery resources of the Comoé River. The authors also
thank the researchers and others who participated in the
data collection and writing of this article.
CONFLICT OF INTERESTS
The authors declare no conflict of interest
ETHICS APPROVAL
Not applicable
FUNDING
This study received DAP/PAGDRH-UNA project on the
assessment of the impact of agricultural and gold mining on
the water quality and fishery resources of the Comoé River.
AI TOOL DECLARATION
The authors declares that no AI and related tools are used to
write the scientific content of this manuscript.
www.ijzab.com 65
Table 3. Relationship between organic pollution index (OPI) and average directional asymmetry (DA) of the studied fish
populations (Cn: Chrysichthys nigrodigitatus).
Site Esp Class NH4+ Class NO2- Class PO4- IPO Pollution AD Horn P
My C,n 3 1 1 1 Very strong 0.149 -0.73 0.00
Be C,n 4 3 1 1.6 Very strong 0.078 -0.73 0.00
Ab C,n 4 3 2 1.8 Very strong 0.069 -0.73 0.00
Ye C,n 4 2 1 1.4 Very strong 0.068 -0.73 0.00
Mb C,n 5 5 4 2.8 Strong 0.013 -0.73 0.00
These results can be explained by several environmental
and biological factors (Mille et al., 2015). First,
environmental conditions, such as temperature, pH, and
substrate nature, play a crucial role in otolith formation and
morphology. Nasreddine (2010) and Mahé (2019)
demonstrated that temperature accelerates otolith
morphogenesis and changes their growth trajectory, which
can lead to more pronounced directional asymmetry in
certain geographic areas. According to Tissot & Souchon,
(2010), water temperature can also influence fish
embryonic development, including otolith development.
According to these authors, abnormally high temperatures
can lead to abnormalities in otolith development, which can
have consequences on the fish's sensory function. Mille
(2015) demonstrated that diet composition contributes more
significantly to otolith morphological variability than
ingested quantity. Thus, differences in food availability and
type between the Manzan, Bettié, and M’Basso stations
could explain the variations related to otolith asymmetry.
Another hypothesis is that phosphate exerts indirect
chemical stress effects on otolith pairs (Perennou &
Aufray, 2007). The presence of high phosphate
concentrations in a freshwater environment can lead to
excessive algal blooms, which can degrade water quality
and lead to eutrophication. This eutrophication
phenomenon can generate significant stress on living
organisms, particularly fish, and potentially increase their
asymmetry rate. The observation of the presence of algae at
the Bettié and Manzan sites, as well as the poor water
quality observed during the sampling periods, support this
hypothesis. Such an indirect effect of phosphate could thus
contribute to the increase in the level of otolith asymmetry.
Our hypotheses corroborate the findings of Østbye et al.
(1997). Their research revealed that perch from acidic lakes
rich in phosphate and aluminum showed a more
pronounced asymmetry than those from non-acidified
lakes. Similarly, it is possible that the polluted environment
and the stress experienced by C. nigrodigitatus populations
in the waters of Bettié and the Manzan River are sufficient
to generate a strong asymmetry of the otoliths. This idea is
supported by the organic pollution index (OPI) calculated
in our study, which indicates very strong organic pollution
in Manzan, YèrèYèrè, Abradinou and Bettié.
CONCLUSION
This study highlighted the significant influence of human
activities on the morphology of Chrysichthys nigrodigitatus
fish in the middle reaches of the Comoé River. Otolith
analysis revealed significant directional asymmetry
oriented towards the right side. The Manzan, Bettié,
Abradinou and YèrèYèrè stations showed the highest
average directional asymmetry, while M’Basso had the
lowest values. The results of this study highlight the
urgency of implementing conservation and sustainable
management measures to preserve aquatic biodiversity.
ACKNOWLEDGMENT
The authors would like to thank the Sustainable
Management of Fisheries Resources Support Program
(PAGDRH) of the Directorate of Aquaculture and Fisheries
(DAP) for the funding provided to carry out this work.
Indeed, this study was carried out within the framework of
the DAP/PAGDRH-UNA project on the assessment of the
impact of agricultural and gold mining on the water quality
and fishery resources of the Comoé River. The authors also
thank the researchers and others who participated in the
data collection and writing of this article.
CONFLICT OF INTERESTS
The authors declare no conflict of interest
ETHICS APPROVAL
Not applicable
FUNDING
This study received DAP/PAGDRH-UNA project on the
assessment of the impact of agricultural and gold mining on
the water quality and fishery resources of the Comoé River.
AI TOOL DECLARATION
The authors declares that no AI and related tools are used to
write the scientific content of this manuscript.
ZPO Yébé et al. Int. J. Zool. Appl. Biosci., 10(5), 58-66, 2025
www.ijzab.com 66
DATA AVAILABILITY
Data will be available on request
REFERENCES
Avigliano, E., Martinez, C, F, R., & Volpedo, A, V, (2014).
Combined use of otolith microchemistry and
morphometry as indicators of the habitat of the silverside
(Odontesthes bonariensis) in a freshwater-estuarine
environment, Fisheries Research, 149, 55‑60,
Baamrane , M, A., Znari , M., & Abáigar , T, (2018).
Comparative study of fluctuating cranial asymmetry in
two subspecies of the dorcas gazelle (Gazella dorcas
massaesyla vs. G, d, Neglecta), Bulletin of the Scientific
Institute, Rabat, 40, 01‑09,
Bertrand, F, Claeys, E, & Maumy -Bertrand, M, (2019).
Statistical modeling through practice with R: Course and
corrected exercises, Dunod,
Buhungu , S., Montchowui , E., Barankanira , E.,
Sibomana, C., Ntakimazi , G., & Bonou , C, (2018).
Spatio-temporal characterization of the water quality of
the Kinyankonge River, a tributary of Lake Tanganyika,
Burundi, International Journal of Biological and
Chemical Sciences, 12 (1), 576-595.
Fortunato, R, C., Dura, V, B., & Volpedo, A, (2014). The
morphology of saccular otoliths as a tool to identify
different mugilid species from the Northeastern Atlantic
and Mediterranean Sea, Estuarine, Coastal and Shelf
Science, 146, 95‑101.
Leclercq, L., & Vandevenne , L, (1987). Impact of a
discharge of salt-laden water and organic pollution on
diatom populations in the Gander (Grand Duchy of
Luxembourg), Cahiers de Biologie Marine, 28 (2), 311-
318.
Mahé, K. (2019). Sources of variation in otolith shape:
Implications for fish stock discrimination. University of
the Littoral Côte d'Opale.
Mille, T. (2015). Sources of intra- population variation in
otolith morphology: directional asymmetry and diet (PhD
thesis, University of Lille 1-Sciences and Technologies).
Mille, T., Mahe, K., Villanueva, M., De Pontual , H., &
Ernande , B, (2015). Sagittal otolith morphogenesis
asymmetry in marine fishes, Journal of Fish Biology, 87
(3), 646‑663.
Møller, A. (1990). Fluctuating asymmetry in male sexual
ornaments may reveal male quality, Mamm Rev, 5,
121‑172.
Nasreddine, K. (2010). Signal registration and pattern
recognition. Application to the analysis of fish otoliths
(Doctoral dissertation, University of Western Brittany-
Brest).
Østbye, K., Øxnevad, S, A., & Vøllestad, L, A, (1997).
Developmental stability in perch (Perca fluviatilis) in
acidic aluminium-rich lakes, Canadian Journal of
Zoology, 75(6), 919‑928.
Palmer, A. R. (1994). Fluctuating asymmetry analyses: a
primer. In Developmental instability: its origins and
evolutionary implications: proceedings of the
international conference on developmental instability: its
origins and evolutionary implications, Tempe, Arizona,
14–15 June 1993 (pp. 335-364). Dordrecht: Springer
Netherlands.
Palmer, A, R, & Strobeck, C, (1986). Fluctuating
asymmetry: Measurement, analysis, patterns, Annual
review of Ecology and Systematics, 391‑421.
Palmer, A, R., & Strobeck, C, (2003), CH 17. Fluctuating
asymmetry analyses revisited, Developmental Instability:
Causes and Consequences, Oxford University Press,
Oxford, 279‑319.
Panfili, J., & Ximenes, M, (1992). Measurements on
ground or sectioned otoliths: Possibilities of bias, Journal
of Fish Biology, 41 (2), 201‑207.
Perennou , C., & Aufray , R, (2007). Observatoire
Camargue, Evolution de la Camargue: chasse, pêche,
protection .
Pither, J., & Taylor, P, D. (2000). Directional and
fluctuating asymmetry in the black-winged damselfly
Calopteryx maculata (Beauvois) (Odonata:
Calopterygidae), Canadian Journal of Zoology, 78(10),
1740‑1748.
Popper, A, N., & Lu, Z. (2000). Structure–function
relationships in fish otolith organs, Fisheries research,
46(1‑3), 15‑25.
Rohlf, F, J., & Sokal, R, R. (1995). Statistical tables,
Macmillan.
Tissot, L., & Souchon, Y. (2010). Summary of thermal
tolerances of the main fish species in the rivers and
streams of the lowlands of western Europe, Applied
Hydroecology , 17, 17-76.
Tuset, V, M., Lombarte , A., & Assis, C, A, (2008). Otolith
atlas for the western Mediterranean, north and central
eastern Atlantic, Scientia Marina, 72 (S1), 7‑198.
Wright, P., Panfili, J., Morales-Nin, B., & Geffen, A,
(2002). Different types of calcified piece, A/the otoliths,
Handbook of fish sclerochronology ( eds J, Panfili , Hd
Pontual , H, Troadec & PJ Wright), 31‑57.
www.ijzab.com 66
DATA AVAILABILITY
Data will be available on request
REFERENCES
Avigliano, E., Martinez, C, F, R., & Volpedo, A, V, (2014).
Combined use of otolith microchemistry and
morphometry as indicators of the habitat of the silverside
(Odontesthes bonariensis) in a freshwater-estuarine
environment, Fisheries Research, 149, 55‑60,
Baamrane , M, A., Znari , M., & Abáigar , T, (2018).
Comparative study of fluctuating cranial asymmetry in
two subspecies of the dorcas gazelle (Gazella dorcas
massaesyla vs. G, d, Neglecta), Bulletin of the Scientific
Institute, Rabat, 40, 01‑09,
Bertrand, F, Claeys, E, & Maumy -Bertrand, M, (2019).
Statistical modeling through practice with R: Course and
corrected exercises, Dunod,
Buhungu , S., Montchowui , E., Barankanira , E.,
Sibomana, C., Ntakimazi , G., & Bonou , C, (2018).
Spatio-temporal characterization of the water quality of
the Kinyankonge River, a tributary of Lake Tanganyika,
Burundi, International Journal of Biological and
Chemical Sciences, 12 (1), 576-595.
Fortunato, R, C., Dura, V, B., & Volpedo, A, (2014). The
morphology of saccular otoliths as a tool to identify
different mugilid species from the Northeastern Atlantic
and Mediterranean Sea, Estuarine, Coastal and Shelf
Science, 146, 95‑101.
Leclercq, L., & Vandevenne , L, (1987). Impact of a
discharge of salt-laden water and organic pollution on
diatom populations in the Gander (Grand Duchy of
Luxembourg), Cahiers de Biologie Marine, 28 (2), 311-
318.
Mahé, K. (2019). Sources of variation in otolith shape:
Implications for fish stock discrimination. University of
the Littoral Côte d'Opale.
Mille, T. (2015). Sources of intra- population variation in
otolith morphology: directional asymmetry and diet (PhD
thesis, University of Lille 1-Sciences and Technologies).
Mille, T., Mahe, K., Villanueva, M., De Pontual , H., &
Ernande , B, (2015). Sagittal otolith morphogenesis
asymmetry in marine fishes, Journal of Fish Biology, 87
(3), 646‑663.
Møller, A. (1990). Fluctuating asymmetry in male sexual
ornaments may reveal male quality, Mamm Rev, 5,
121‑172.
Nasreddine, K. (2010). Signal registration and pattern
recognition. Application to the analysis of fish otoliths
(Doctoral dissertation, University of Western Brittany-
Brest).
Østbye, K., Øxnevad, S, A., & Vøllestad, L, A, (1997).
Developmental stability in perch (Perca fluviatilis) in
acidic aluminium-rich lakes, Canadian Journal of
Zoology, 75(6), 919‑928.
Palmer, A. R. (1994). Fluctuating asymmetry analyses: a
primer. In Developmental instability: its origins and
evolutionary implications: proceedings of the
international conference on developmental instability: its
origins and evolutionary implications, Tempe, Arizona,
14–15 June 1993 (pp. 335-364). Dordrecht: Springer
Netherlands.
Palmer, A, R, & Strobeck, C, (1986). Fluctuating
asymmetry: Measurement, analysis, patterns, Annual
review of Ecology and Systematics, 391‑421.
Palmer, A, R., & Strobeck, C, (2003), CH 17. Fluctuating
asymmetry analyses revisited, Developmental Instability:
Causes and Consequences, Oxford University Press,
Oxford, 279‑319.
Panfili, J., & Ximenes, M, (1992). Measurements on
ground or sectioned otoliths: Possibilities of bias, Journal
of Fish Biology, 41 (2), 201‑207.
Perennou , C., & Aufray , R, (2007). Observatoire
Camargue, Evolution de la Camargue: chasse, pêche,
protection .
Pither, J., & Taylor, P, D. (2000). Directional and
fluctuating asymmetry in the black-winged damselfly
Calopteryx maculata (Beauvois) (Odonata:
Calopterygidae), Canadian Journal of Zoology, 78(10),
1740‑1748.
Popper, A, N., & Lu, Z. (2000). Structure–function
relationships in fish otolith organs, Fisheries research,
46(1‑3), 15‑25.
Rohlf, F, J., & Sokal, R, R. (1995). Statistical tables,
Macmillan.
Tissot, L., & Souchon, Y. (2010). Summary of thermal
tolerances of the main fish species in the rivers and
streams of the lowlands of western Europe, Applied
Hydroecology , 17, 17-76.
Tuset, V, M., Lombarte , A., & Assis, C, A, (2008). Otolith
atlas for the western Mediterranean, north and central
eastern Atlantic, Scientia Marina, 72 (S1), 7‑198.
Wright, P., Panfili, J., Morales-Nin, B., & Geffen, A,
(2002). Different types of calcified piece, A/the otoliths,
Handbook of fish sclerochronology ( eds J, Panfili , Hd
Pontual , H, Troadec & PJ Wright), 31‑57.