Ecological and Demographic Characteristics of Synodontis koensis, an Endemic Species of the Sassandra River Basin (Côte d'Ivoire)

 Co esponding au ho : N’DRI Olga Rosemonde
Copy igh © 2025 Au ho (s) e ain he copy igh o his a icle. This a icle is published unde he e ms o he C ea i e Commons A ibu ion License 4.0.
Ecological and Demog aphic Cha ac e is ics o Synodon is koensis, an Endemic
Species o he Sassand a Ri e Basin (Cô e d’I oi e)
N’DRI Olga Rosemonde 1, *, MONNEY A oubé ida 1, ALLOUKO Jean Renaud 1, ABO Kouakou Jean-Bap is e 1,
KONAN Kouassi Raphael 2 and KONE Tidiani 1
1 Labo a o y o Biodi e si y and Sus ainable Managemen o T opical Ecosys ems, Uni e si é Jean Lo ougnon Guédé, BP
150 Daloa, Cô e d’I oi e.
2 Cen e o Con inuing Educa ion, Uni e si é Jean Lo ougnon Guédé, BP 150 Daloa, Cô e d’I oi e.
GSC Biological and Pha maceu ical Sciences, 2025, 33(01), 252-260
Publica ion his o y: Recei ed on 14 Sep embe 2025; e ised on 22 Oc obe 2025; accep ed on 25 Oc obe 2025
A icle DOI: h ps://doi.o g/10.30574/gscbps.2025.33.1.0409
Abs ac
This s udy in es iga ed he ecological and demog aphic cha ac e is ics o Synodon is koensis (Pelleg in, 1934), an
endemic species o he Sassand a Ri e Basin (Cô e d’I oi e), in o de o p o ide baseline da a o i s conse a ion and
sus ainable habi a managemen . Sampling was conduc ed om No embe 2024 o Ma ch 2025 a i e s a ions along
he N’Zo Ri e , a majo ibu a y o he Sassand a. Physico-chemical pa ame e s o he wa e ( empe a u e, pH,
conduc i i y, o al dissol ed solids, and dep h) we e measu ed in si u, and a o al o 329 indi iduals we e collec ed o
mo phome ic and weigh analyses. Resul s e ealed a o able en i onmen al condi ions o aqua ic li e, wi h wa e
empe a u e anging om 27.3 o 29.5 °C, sligh ly alkaline pH (7.65–7.95), and low conduc i i y (51–68 µS/cm).
S anda d leng hs o ish anged om 35 o 110 mm (mean = 77.48 ± 13.63 mm) and body weigh s om 2 o 31 g (mean
= 11.71 ± 5.73 g), indica ing a unimodal size s uc u e domina ed by medium-sized classes (60–90 mm). The leng h–
weigh ela ionship ollowed he model P=aLbP, wi h b=1.93b = 1.93b=1.93, showing a nega i e allome ic g ow h
pa e n (b < 3), meaning ha body leng h inc eases as e han weigh . The condi ion ac o (K) anged om 1.10 o
9.26 (mean = 2.59 ± 1.57), sugges ing good o e all physiological condi ion. These indings indica e ha S. koensis
inhabi s an en i onmen ha emains a o able bu is inc easingly a ec ed by an h opogenic p essu es. The s udy
p o ides essen ial baseline in o ma ion o guide conse a ion s a egies and sus ainable managemen o endemic ish
popula ions wi hin he Sassand a Basin.
Keywo ds: Synodon is Koensis; N’Zo Ri e ; Sassand a Basin; Allome ic G ow h; Condi ion Fac o
1. In oduc ion
Sus ainable managemen o ishe y esou ces in Wes A ica elies on a sound unde s anding o he biological and
ecological cha ac e is ics o exploi ed species, pa icula ly hose ha a e endemic [1,2]. In A ican i e basins, and
especially in Cô e d’I oi e, inc easing an h opogenic p essu es such as in ensi ied ishing, de o es a ion, and
ag icul u al expansion a e h ea ening he long- e m iabili y o ish popula ions [3,4]. These p essu es a e u he
exace ba ed by clima e change, which al e s hyd ological egimes and deg ades aqua ic habi a s [5]. Among he majo
i e sys ems in Cô e d’I oi e, he Sassand a Ri e hos s a ich ich hyo auna, including se e al endemic species such as
Synodon is koensis (Pelleg in, 1934), a membe o he Mochokidae amily [6,7]. This ben hic ca ish plays a key ecological
ole in o ganic ma e ecycling and occupies a cen al posi ion in aqua ic ood webs [8,9]. A he same ime, i has
conside able socioeconomic impo ance as a sou ce o income and ood o local communi ies [10,11]. Despi e i s
ecological and economic ele ance, S. koensis aces mul iple h ea s. Habi a deg ada ion, i e agmen a ion, and
o e ishing jeopa dize he su i al o i s popula ions [12,13]. Consequen ly, he species is cu en ly lis ed as Nea
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Th ea ened on he IUCN Red Lis [13]. The implemen a ion o e ec i e conse a ion measu es, howe e , equi es
de ailed in o ma ion on i s biology, demog aphy, and ecological in e ac ions [14,31].
Resea ch on he Synodon is genus in A ica has been la gely domina ed by he wo ks o Gowe e al. on axonomy [15],
Lé êque on ishe ies biology [16], and Paugy and Lé êque on biogeog aphy [9]. Ye , ecological and demog aphic
pa ame e s o S. koensis emain poo ly documen ed, pa icula ly in he Sassand a Ri e Basin. I is he e o e essen ial
o in es iga e i s en i onmen al condi ions, popula ion s uc u e, and g ow h pa e ns o iden i y he key pa ame e s
in luencing i s popula ion dynamics and o p o ide a ounda ion o sus ainable managemen .
The p esen s udy con ibu es o his objec i e by assessing he ecological and demog aphic cha ac e is ics o
Synodon is koensis in he N’Zo Ri e , a majo ibu a y o he Sassand a Basin. Speci ically, i aims o (i) analyze he
physico-chemical pa ame e s o i s habi a , (ii) desc ibe i s popula ion s uc u e h ough size and weigh dis ibu ions,
and (iii) es ablish he leng h–weigh ela ionship and condi ion ac o o his endemic and h ea ened species. This
in eg a i e app oach is expec ed o enhance ou unde s anding o S. koensis popula ion dynamics wi hin i s na u al
habi a and o p o ide scien i ic insigh s suppo ing he sus ainable managemen o ishe y esou ces in he Sassand a
Ri e Basin.
2. Ma e ials and me hods
2.1. S udy A ea
The s udy was conduc ed in he N’Zo Ri e , a majo le -bank ibu a y o he Sassand a Ri e loca ed in sou hwes e n
Cô e d’I oi e. The N’Zo Basin co e s app oxima ely 4,310 km², wi h a main i e cou se 124 km long and a hyd ological
egime cha ac e ized by al e na ing high-wa e (July–Oc obe ) and low-wa e (No embe –June) pe iods [17]. The
egion has a sub-equa o ial clima e, wi h an annual ain all exceeding 2,000 mm [18]. Fi e sampling s a ions (S1–S5)
we e selec ed along he i e cou se based on habi a di e si y and accessibili y (Figu e 1). These si es ep esen
dis inc ecological g adien s, anging om ups eam headwa e s o downs eam a eas nea he Buyo Rese oi .
Figu e 1 Loca ion o he i e sampling si es along he N’Zo Ri e (Cô e d’I oi e).
2.2. Fish Sampling
Specimens o Synodon is koensis we e collec ed be ween No embe 2024 and Ma ch 2025 using a isanal ishing
echniques in collabo a ion wi h local ishe s. Mul iple ishing gea s we e employed, including gillne s, beach seines,
hand lines, longlines, aps, and adi ional bamboo po s. A o al o 329 indi iduals we e cap u ed and analyzed.
Gggg
Sub-p e ec u e
headqua e
Road
N’Zo Ri e
Guiglo Sub-
P e ec u e
Si es
Fo es a ea
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Specimens we e immedia ely p ese ed in ice a e cap u e and la e p ocessed in he labo a o y o mo phome ic
measu emen s.
2.2.1. Mo phome ic and Weigh Measu emen s
Fo each specimen, s anda d leng h (SL, mm) and o al leng h (TL, mm) we e measu ed wi h an ich hyome e o he
nea es 1 mm, while o al weigh (TW, g) was eco ded using a p ecision balance (Toledo PB810, ± 0.1 g).
2.2.2. Physico-Chemical Pa ame e s o Wa e
Wa e quali y pa ame e s we e measu ed in si u a each o he i e si es on a bimon hly basis, be ween 07:00 and 09:00
a.m. A mul ipa ame e me e (HACH HQ30d) was used o eco d empe a u e (°C), pH, conduc i i y (µS/cm), and o al
dissol ed solids (TDS, ppm). Wa e dep h was measu ed using a weigh ed g adua ed co d.
2.2.3. Size S uc u e Analysis
Popula ion size s uc u e was desc ibed based on equency dis ibu ions o s anda d leng h. Leng h classes we e
de e mined acco ding o S u ges’ ule [19]. The coe icien o a ia ion (CV) o size was calcula ed o assess popula ion
homogenei y:
• CV < 2 % = highly homogeneous
• 2 % ≤ CV ≤ 30 % = homogeneous
• CV > 30 % = he e ogeneous
2.3. Leng h–Weigh Rela ionship
The leng h–weigh ela ionship was exp essed by he o mula: 𝑃 = 𝑎𝐿𝑏
whe e P is o al weigh (g), L is s anda d leng h (cm), a is he in e cep , and b is he allome ic coe icien . A e
loga i hmic ans o ma ion, linea eg ession was pe o med as:
log P = log a + b log L
The es ima ed allome ic coe icien (b) was s a is ically compa ed o he heo e ical alue o 3 (isome ic g ow h) using
a s uden ’s - es .
2.4. Condi ion Fac o
The condi ion ac o (K) was calcula ed o each indi idual o e alua e i s physiological s a e:
𝐾 = (𝑇𝑊/𝑆𝐿3) × 100
Whe e TW is o al weigh (g) and SL is s anda d leng h (cm). Spa ial and empo al a ia ions in K we e analyzed o
assess indi idual well-being in ela ion o si e and sampling pe iod.
2.5. S a is ical Analyses
Da a we e analyzed using STATISTICA 7.1. No mali y o dis ibu ions was e i ied using he Shapi o–Wilk es . In e -
s a ion di e ences we e assessed wi h he K uskal–Wallis es (p < 0.05). The co ela ion coe icien ( ) and
de e mina ion coe icien ( ²) we e calcula ed o e alua e he s eng h and eliabili y o he leng h–weigh ela ionships.
3. Resul s
3.1. Physico-Chemical Pa ame e s o he Wa e
The physico-chemical pa ame e s measu ed a he i e si es o he N’Zo Ri e a e p esen ed in Table 1. Wa e
empe a u e luc ua ed be ween 27.3 °C (si e S2) and 29.5 °C (si e S5). S a is ical analysis (K uskal–Wallis es ) e ealed
no signi ican di e ences among s a ions (p > 0.05). The pH anged om 7.65 (si e S2) o 7.95 (si e S1), indica ing
sligh ly alkaline wa e . These a ia ions we e no signi ican (K uskal–Wallis, p > 0.05).
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The concen a ion o o al dissol ed solids (TDS) a ied be ween 24 ppm (si es S3, S4, and S5) and 32 ppm (si e S1),
wi h no signi ican di e ences among si es (K uskal–Wallis, p > 0.05). Likewise, elec ical conduc i i y luc ua ed om
51 µS/cm (si es S3, S4, and S5) o 68 µS/cm (si e S1), again wi h no signi ican di e ences (K uskal–Wallis, p > 0.05).
In con as , wa e dep h showed ma ked a iabili y among si es, anging om 371 cm (si e S1) o 875 cm (si e S3).
Unlike he o he pa ame e s, hese a ia ions we e s a is ically signi ican (K uskal–Wallis, p < 0.05).
Table 1 Physico-chemical pa ame e s measu ed (mean ± s anda d de ia ion) a he i e sampling si es o he N’Zo
Ri e .
Si es
Tempe a u e (°C)
pH
TDS (ppm)
Conduc i i y (µS/cm)
Dep h (cm)
S1
27,8 ± 0,4
7,95 ± 0,05
32,0 ± 2,1
68,0 ± 3,2
371 ± 25
S2
27,3 ± 0,6
7,65 ± 0,07
28,0 ± 1,8
60,0 ± 2,7
500 ± 30
S3
28,5 ± 0,5
7,80 ± 0,04
24,0 ± 1,5
51,0 ± 2,0
875 ± 40
S4
28,7 ± 0,3
7,85 ± 0,06
24,0 ± 1,7
51,0 ± 1,9
820 ± 35
S5
29,5 ± 0,5
7,90 ± 0,05
24,0 ± 1,6
51,0 ± 2,1
790 ± 28
3.2. Popula ion s uc u e
A o al o 329 indi iduals o Synodon is koensis we e collec ed om he i e sampling si es o he N’Zo Ri e be ween
No embe 2024 and Ma ch 2025 (Table 2). S anda d leng hs o specimens anged om 35 mm o 110 mm, wi h a mean
o 77.48 ± 13.63 mm. Indi idual body weigh s anged om 2 g o 31 g, wi h an a e age o 11.71 ± 5.73 g.
The equency dis ibu ion by leng h class e ealed a unimodal s uc u e domina ed by he 70–80 mm class (Figu e 2).
The majo i y o indi iduals (93.31 %) ell wi hin he 60–90 mm ange. The calcula ed coe icien o a ia ion (CV = 17.59
%) o he o al sample indica es a ela i ely homogeneous popula ion in e ms o size. Analysis by si e e ealed no able
di e ences in demog aphic composi ion
• Si e S1: Indi iduals be ween 50 mm and 75 mm ep esen ed 65.39 % o he o al ca ch.
• Si e S2: 79.82 % o ish measu ed be ween 65 mm and 90 mm.
• Si e S3: 76.08 % o specimens belonged o he 80–105 mm class, e lec ing a highe p opo ion o la ge
indi iduals.
• Si e S4: Dominan size classes anged om 70 mm o 100 mm, accoun ing o 73.68 % o he ca ch.
• Si e S5: Fish be ween 60 mm and 85 mm cons i u ed 61.25 % o he sampled popula ion.
These da a indica e ha , al hough he o e all popula ion is ela i ely homogeneous and domina ed by medium-sized
classes, ce ain spa ial di e ences exis —pa icula ly he p edominance o smalle indi iduals a si e S1 and la ge ones
a si e S3.
Table 2 Demog aphic pa ame e s o ish collec ed om he N’Zo Ri e .
Si es
S1
S2
S3
S4
S5
T
S anda d
Leng h
(mm)
Min
52
55
70
35
42
35
Max
110
109
110
103
95
110
Mean ± SD
72,4214,69
76,2511,34
93,418,96
79,2314,17
72,4610,78
77,4813,63
Weigh (g)
Min
5
5
9
2
2
2
Max
21
23
31
26
18
31
Mean ± SD
13,575,15
10,074,10
19,155,66
11,895,72
8,433,55
11,715,73
Numbe o indi iduals (N)
52
114
46
38
79
329
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a
b
c
d
e
Si e 1; b) Si e2; c) Si e 3; d) Si e 4; e) Si e 5; N: Numbe o indi iduals
Figu e 2 F equency dis ibu ion o ish cap u ed a each sampling si e om No embe 2024 o Ma ch 2025.

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3.3. Leng h–Weigh Rela ionship and Condi ion Fac o (K)
The s udy o he ela ionship be ween body leng h and weigh in Synodon is koensis om he N’Zo Ri e e ealed
signi ican esul s in e ms o allome ic g ow h (Figu e 3). The coe icien o de e mina ion ( ²) was es ima ed a 0.50,
indica ing ha leng h explains app oxima ely 50 % o he obse ed a iabili y in body weigh .
The eg ession equa ion was exp essed as
Log P = log a+b log L
whe e a = −2.61 and b = 1.93.
A S uden ’s - es was applied o assess he signi icance o he di e ence be ween he obse ed b alue and he
heo e ical alue o 3 (isome ic g ow h). The es indica ed ha b was signi ican ly di e en om 3 (p < 0.05),
con i ming ha he g ow h o S. koensis in his i e de ia es om isome ic g ow h.
This species hus exhibi s nega i e allome ic g ow h, meaning ha inc eases in leng h exceed inc eases in weigh as
indi iduals de elop.
Rega ding he condi ion ac o (K), which assesses he physiological s a e o indi iduals, alues anged om 1.101 o
9.259, wi h a mean o 2.59 ± 1.57. These da a, p esen ed in Table 3, e lec he gene al physical condi ion o he
specimens and indica e signi ican a iabili y likely linked o en i onmen al o physiological ac o s.
Figu e 3 Leng h–weigh ela ionship o Synodon is koensis in he N’Zo Ri e (No embe 2024 – Ma ch 2025).
Table 3 Pa ame e s o he leng h–weigh ela ionship and condi ion ac o o Synodon is koensis in he N’Zo Ri e (N
= 329).
Species (N = 329)
2
b
S uden ’s - es
G ow h ype
Condi ion ac o
Min
Max
Mean ± SD
Synodon is koensis
0.50
1.93
-3.6295891
A-(nega i e allome ic)
1.101
9.259
2.591.57
4. Discussion
The s udy conduc ed on Synodon is koensis in he N’Zo Ri e p o ides a comp ehensi e unde s anding o he ecological
and demog aphic dynamics o an endemic and h ea ened species whose su i al depends closely on he quali y o
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aqua ic habi a s wi hin he Sassand a Basin. The physico-chemical pa ame e s eco ded indica e ha he N’Zo Ri e
o e s a o able condi ions o aqua ic li e, wi h wa e empe a u es anging om 27 o 29 °C, sligh ly alkaline pH (7.65–
7.95), and mode a e conduc i i y (51–68 µS·cm⁻¹), which a e ypical cha ac e is ics o opical o es i e s ha emain
ela i ely undis u bed [22,33]. These esul s demons a e hyd ological and chemical s abili y, which p omo es he
g ow h and ep oduc ion o ben hic ish species such as Synodon is koensis [9]. The absence o signi ican di e ences
be ween sampling si es o mos pa ame e s, excep dep h, e lec s a ela i ely homogeneous ecological en i onmen
and sugges s ha popula ion a iabili y is mo e likely d i en by biological ac o s han by abio ic cons ain s.
Ne e heless, he ma ked a ia ion in wa e dep h among si es may in luence he spa ial dis ibu ion o indi iduals, as
deepe a eas may se e as e uges o p e e ed g ow h habi a s o adul s [20,21].
F om a demog aphic s andpoin , he unimodal s uc u e obse ed in S. koensis popula ions indica es a ela i ely s able
popula ion wi h balanced ec ui men . The dominance o medium size classes (60–90 mm) and he ela i ely low
coe icien o a ia ion (17.6%) e eal a homogeneous popula ion s uc u e, well es ablished in he ecosys em and
p obably ep oducing egula ly. A simila demog aphic pa e n has been obse ed in ela ed species wi hin he Nige
Basin [29], sugges ing ha he N’Zo Ri e ecosys em s ill unc ions e ec i ely despi e inc easing human p essu es.
Howe e , he si e-speci ic size a ia ions obse ed—smalle indi iduals ups eam and la ge ones downs eam—
illus a e spa ial o ganiza ion linked o hyd omo phological condi ions and he a ailabili y o ood esou ces [8,6]. This
spa ial dis ibu ion pa e n is consis en wi h he Ri e Con inuum Concep p oposed by Vanno e e al. [32], which
s a es ha he composi ion and s uc u e o aqua ic communi ies a y along he longi udinal g adien o he i e
acco ding o changes in dep h, cu en eloci y, and o ganic ma e inpu .
The analysis o he leng h–weigh ela ionship e ealed a nega i e allome ic g ow h pa e n, wi h an allome ic
coe icien b = 1.93 signi ican ly lowe han he heo e ical alue o 3. This indica es ha S. koensis g ows mo e in leng h
han in weigh , sugges ing an ene gy alloca ion s a egy a o ing linea g ow h o e biomass accumula ion. Such a
g ow h s a egy is common among ish species inhabi ing en i onmen s whe e ood a ailabili y luc ua es seasonally
[25,26]. Simila indings we e epo ed by Kab é and Illé [30] in Lake Buyo and by Io cho e al. [29] o Synodon is
schall in he Lowe Benue Ri e , Nige ia, suppo ing he idea ha species o he genus Synodon is display a high deg ee
o ecological plas ici y. The obse ed g ow h pa e n may also esul om selec i e ishing p essu e a ge ing la ge
indi iduals, a phenomenon equen ly no ed in Wes A ican a isanal ishe ies [31,12]. The condi ion ac o (K), which
anged om 1.10 o 9.26 (mean = 2.59 ± 1.57), con i ms he good adap a ion o S. koensis o i s en i onmen . Values
abo e 2 gene ally indica e good physiological condi ion and a o able en i onmen al condi ions [26,27]. Howe e , he
in e -indi idual a iabili y obse ed sugges s local luc ua ions in ood esou ce a ailabili y o ep oduc i e cycles. The
highes K alues, eco ded a he deepes si es, poin o mo e p oduc i e habi a s o e ing be e access o ben hic
o ganic ma e , which is he main ophic sou ce o his species [28]. These esul s co obo a e he indings o B emme
e al. [5] and T ao é and Koné [4], who emphasized he impo ance o main aining habi a quali y o sus ain heal hy ish
popula ions.
O e all, he N’Zo Ri e emains a unc ional ecosys em capable o suppo ing his endemic species. Howe e , he
p edominance o medium-sized indi iduals and he sca ci y o la ge specimens sugges a non-negligible ishing
p essu e ha could, in he medium e m, a ec popula ion enewal. This obse a ion aligns wi h he b oade issue o
sus ainable ishe y managemen in Wes A ica, whe e de o es a ion, ag icul u al expansion, and o e ishing
collec i ely unde mine he esilience o endemic species [3,1].
5. Conclusion
The p esen s udy on Synodon is koensis in he N’Zo Ri e p o ides new insigh s in o he ecology and popula ion
dynamics o an endemic species om he Sassand a Basin ha emains poo ly documen ed despi e i s ecological and
socioeconomic impo ance. The eco ded en i onmen al condi ions— empe a u es anging om 27.3 o 29.5 °C,
sligh ly alkaline pH (7.65–7.95), and low elec ical conduc i i y (51–68 µS/cm)—indica e a gene ally heal hy aqua ic
en i onmen capable o suppo ing a balanced ish popula ion.
Among he 329 indi iduals collec ed, s anda d leng hs anged om 35 o 110 mm, wi h a mean o al weigh o 11.71 ±
5.73 g. This pa e n e lec s a homogeneous demog aphic s uc u e domina ed by medium-sized classes (60–90 mm).
The leng h–weigh ela ionship e ealed an allome ic coe icien (b = 1.93) signi ican ly lowe han 3, indica ing
nega i e allome ic g ow h, whe e inc eases in body leng h p edomina e o e weigh gain. The condi ion ac o (K),
which anged om 1.10 o 9.26 (mean = 2.59 ± 1.57), sugges s an o e all good physiological s a e o he popula ion,
al hough local a ia ions may e lec en i onmen al he e ogenei y o ep oduc i e cycles.
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O e all, hese indings demons a e ha S. koensis h i es in an ecosys em ha emains ela i ely unc ional and
a o able o i s de elopmen , bu ha is inc easingly ulne able o an h opogenic p essu es. The p edominance o
medium-sized indi iduals and he ela i e sca ci y o la ge ish poin o po en ial ishing impac s ha may a ec long-
e m popula ion sus ainabili y.
The da a ob ained om his s udy p o ide a solid scien i ic basis o de eloping sus ainable managemen s a egies o
he Sassand a Basin, pa icula ly in e ms o habi a conse a ion, egula ion o ishing e o , and long- e m ecological
moni o ing o S. koensis popula ions. As an indica o o ben hic ecosys em heal h, his species ep esen s a aluable
biological model o assessing he esilience o aqua ic en i onmen s in Cô e d’I oi e and h oughou Wes A ica.
Compliance wi h e hical s anda ds
Disclosu e o con lic o in e es
No con lic o in e es o be disclosed.
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