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Biodiversity and Conservation 3, 808-827 ( 1994)
Biogeographical considerations of fish diversity in Bioko
RAMON CASTELO Asociacidn Amigos de Doriana. Cl Panamri No. 6, 41080, Sevilla, Spain
Received 4 July 1994; accepted 12 August 1994
The present study on the fish fauna of Bioko reports a total of 43 species of 21 families; 18 of which are new records for the island. Bioko’s icthyofauna is made up of 17 freshwater and 26 saltwater and brackish water species. Freshwater fishes are primarily restricted to a narrow belt along the north and west of the island, similar to the adjacent volcanic region around Mount Cameroon. The rest of the island, however, is inhabited by salt tolerant fishes, as found in SLo Tome, Principe and Annobon. Fish communities also vary according to elevation since rivers on Bioko are characterized by steep gradients from source to sea. Pressures on Bioko’s river systems are not alarmingly high but may increase in the future because of the use of toxic products (lime and insecticides) for fishing. There is no doubt that this is having a significant effect on northern and western rivers which are precisely the most species-rich. Aphyosemion oeseri, which is endemic to Bioko, and which has a distribution restricted to the small northern rivers is in great danger of extinction. P. monkei is in a similarly precarious situation, given that it is extremely rare and will probably disappear altogether in a few years from the island’s rivers. Before the situation becomes irreversible urgent measures must be taken to improve matters through educational campaigns as well as through cleaning up heavily-polluted rivers and re-stocking them with fish species from neighbouring river basins.
Keywords: fishes, Bioko, endemisms, biogeography, distribution
Introduction
According to Trewavas (1974) and Roberts (1975), Bioko and Mount Cameroon form part of a subregion within the Lower-Guinea icthyological province. This province en- compasses Equatorial Guinea as well as coastal Gabon, Cameroon and SE Nigeria. Roberts’ (1975) empirical analysis of freshwater fish diversity coincides with the recent study by Hugueny (1990). However, Roberts includes the river basins in the Ivory Coast and Gambia in the ‘Upper Guinea’ province, whereas Hugueny considers them part of a Sahelo-Sudanese province. Likewise, rivers between the Ogun and Cross Rivers, which are classified by Roberts within the ‘Lower Guinea’ province, are regarded by Hugueny as also belonging to the Sahelo-Sudanese province. In this evaluation, the Bioko-Mount Cameroon subregion is considered to be between the Sahelo-Sudanese and the East Guinea regions.
Since the short and rather incomplete Bioko expeditions by Thys van den Aude- naerde (1967), Scheel (1968a,b) and Eisentraut (1973), little work has been done on the island’s rivers or on their fish fauna. Thys van den Audenaerde (1967, 1968), in fact, re-
0960-3115 ~CI 1994 Chapman & Hall
Fish diversity in Bioko go9
cognized the importance of additional investigations on Bioko’s icthyofauna and the need to study further some newly described species.
A research project, initiated in 1985, set out to investigate the epicontinental icthyo- fauna of Equatorial Guinea, including Bioko island. A seven-month study of the dis- tribution and ecology of fishes in Bioko was undertaken between November 1988 and June 1989. This paper presents some results on the species richness and biogeography of the fishes encountered. All specimens are deposited in the scientific collection at the Asociacion Centro de Estudios Tropicales (Asociacion Amigos de Doiiana), Sevilla, Spain.
Survey methods
The present study is based on approximately 1800 specimens collected from 34 sampling stations in most of the main Bioko rivers (Fig. 1). Most fish were caught with the use of gill nets (1 and 1.5 cm) or with long-pole nets. In some instances, hook and line and traditional fishing methods were also employed. Fish specimens were fixed in 10% form01 and preserved in 70% alcohol.
Water samples were taken from 41 different localities. Water analyses consisted of pH determination using an ORION (Model SA 250) with a 91-06 electrode. Conductivity was measured with an INSTRAN (Model 10) and dissolved oxygen concentrations and temperature with a SYLAND (Model Simplair-S).
The aquatic environments
Bioko’s icthyofauna is restricted to rivers since there are not fishes present in the crater lagoons (Lago Biao, Lago Loreto etc.). Aquatic biotopes are similar to those found in the adjacent Mount Cameroon area and may be subdivided into three main types, as shown in Table 1. Not of all Bioko’s rivers are composed of these basic physical features; some have only the first part (Type I) because their slopes are extremely steep and they cascade directly into the sea; others have no middle section but have an estuary (Type II); and Type III are rivers that possess all three features.
Because of Bioko’s abrupt relief and relatively small size, the island has numerous, fast-flowing rivers (or, more aptly called, mountain torrents) radiating from the two main systems around Pica Basil& and the Southern Highlands (Fig. 1). There are abundant gullies, rapids and falls. Some rivers flow only a few kilometres to the sea, often descending from heights of over 1000 m. Heaviest flows are typical of the southern parts of the island where rainfall can be as high as 11 m per year (Fa, 1991). Monthly flow data from three different rivers in southern Bioko (Fig. 2), illustrate how maxima are typical between September and October and minima between April and May; a sharp drop occurs in August when precipitation decreases. During the dry season, the smallest rivers may dry up completely and, in many cases, (especially in the south), estuaries can remain separated from the sea by sand barriers that form on the beaches.
River beds are lined with rough gravel and large basaltic boulders derived from volcanic lava; most rivers are between I-10 m wide and 0.5 m deep. Water properties (analysed at the end of the dry season between 20 February 1990 and April 1990) differ significantly from continental waters in Rio Muni (personal observations) as well as
Caste10
Figure 1. Distribution of the main river systems in Bioko.
from those in the Cross River, Nigeria-Cameroon (Teugels et al., 1992) due to contrasts in the underlying geology. Oxygen levels in Bioko rivers fluctuate between 4.7 (25.3”C) mg I-’ and 8.6 mg I -- ’ (21,8”(Z) and pH values vary from slightly acid (6.60) to alkaline (8.33) (average pH 7.5). Characteristically, electrolyte content is very high; conductivity differing with river length from between 36.5 to 260 microsiemens cm-‘. Water tem- perature averages around 24°C but may range from 17.5”C at high altitudes to 25.8”C in the lower regions.
Fish diversity in Bioko
Table 1. Classification of the main biotopes found in rivers in Bioko
811
Upper reaches: Found at high elevations. Usually long stretches of very steep slopes and correspondingly fast-flowing waters. These parts are not suitable for coloni- zation by any fish species except those of the genus Sicydium. There is prac- tically no submerged vegetation except for some colonies of Anubias heterophylla. Plants, such as Impatiens spp. may be found along the banks.
Middle reaches: These are narrow stretches of water, usually found 100 m above sea level. Currents are often slow and banks provide sandy sheltered areas with rotting vegetation. The most common aquatic plant is Crinum natans and Apomogetum sp. occurs to a lesser extent. The most common vegetation is Commelina sp. and, particularly, Anubias heterophylla; along sheltered river- banks there may be some floating Pistia stratoides with Nimphaes lotus in some stagnant areas or muddy riverbeds. These are the richest parts of the rivers in terms of epicontinental icthyofauna and are inhabited by all fresh- water fishes.
Lower reaches: Some of Bioko’s rivers form estuaries. As with most rivermouths in the adjacent continental areas, Bioko’s northeastern river vegetation is primarily mangroves with species such as Avicenna nitida, Laguncularia racemosa, Dal- bergia ecastophyllum, Drepanocarpus lunatus and Rhizophora mangle and, in places (e.g. the mouth of the Bosao river), associated halophytic Cyperaceae. Crinum natans occurs in some faster-flowing parts of the estuaries whereas the dominant riverbank vegetation consists of Cyperus spp., Kyllinga c$ odorata, Echinocloa spp., Cyrtosperma senegalensis and Raphia vintfera. Lep- toderris brachyptera is also very common in river estuaries and there are small colonies of Pandalus candelabrum in some scattered areas (e.g. Riaba, Ureca). This is the favoured stretch of river of Group II fishes (see Compo- sition of fish fauna).
Composition of the fish fauna
A total of 43 species of 21 families within nine fish groups was collected during the present study. Most of the families are represented by l-3 species, the largest family, the Gobiidae, being composed of seven species (Fig. 3). Although some nomenclature changes have altered Thys van den Audenaerde’s species list (1967, 1968), the present inventory adds another 18 new taxa to the island’s icthyofauna. All species collected by Thys van den Audenaerde (1967, 1968), except Arius latiscutatus, were recovered. Although the present study has added to the number of species found by Thys van den Audenaerde, his observation still holds that fish species richness in Bioko is much lower than in continental waters due to the ‘island factor’. Thys van den Audenaerde (1968) argued that it is because of the relatively small size of Bioko (many species may have become extinct after isolation from the continent) and the restricted range of biotopes, that fish fauna on and around the island is considerably poorer relative to the continent.
Thys van den Audenaerde (1967) divided the fish species in Bioko into two main groups: fishes of little or no saltwater tolerance (Group I) and marine and coastal fishes (Group II). Following this classification, the actual species list is composed of 17 Group I taxa and 26 Group II species.
Caste10
JAN FEE MAR APR MAY JUN JUL AUG SEF’ GCT NOV DEC
Figure 2. Flow fluctuations in three rivers in southern Bioko. (Source: Electricit& de France Inter- national
Group I: freshwater jishes
In Bioko, these fishes are primarily restricted to the lower parts of the permanent freshwater river basins in the NW and W of the island, along a narrow margin to the Bay of Luba. According to Hugueny (1990) six main subgroups can be recognized (Table 2):
Subgroup 11: Species endemic to Bioko and species common to the volcanic sub- region of Bioko and Mount Cameroon (three species).
Subgroup 12: Species restricted to the Lower-Guinea region (six species). Subgroup 13: Species restricted to the coastal regions of northern Lower-Guinea and
southern Nigeria (Sahelo-Sudanese icthyological region) (one species). Subgroup 14: Species inhabiting the Lower and Upper Guinea coastal strip and
southern Nigeria (two species). Subgroup 15: Species found in the Lower Guinea, Southern Nigeria (Sahelo-Sudanese
region) and Middle Zaire areas (one species). Subgroup 16: Species of a wide geographical distribution (four species).
Fish diversity in Bioko 813
Gobildae
I ARIIDAE
BAGRIDAE
CARANGIDAE
CLARIIDAE
CHARACIDAE
DASYATIDAE
GERREIDAE
HAEMULIDAE
KYPHOSIDAE
MALAPTERLJRIDAE
MASTACEMBELIDAE
MONODACTILIDAE
Families with more than one species
Figure 3. Distribution of species according to fish families in Bioko.
Group II: saltwater and brackish water fishes
Species in this group (Table 3) are found in saltwater or brackish water areas adjacent to freshwater river mouths around most of the island. From Senegal to Angola the composition of this fish fauna is relatively homogeneous, thus Thys van den Aude- naerde (1967) argues that this group of fishes is of little local zoogeographical im- portance. This statement is probably valid for all species except A. m. scheeli, which is an endemic subspecies in the Lower Guinea coast. Subdivisions of this group, following the categories and terminology used by Thys van den Audenaerde (1967), are as follows:
Subgroup 111 Shore fishes. Only P. barbarus is included. This species inhabits the in- tertidal areas.
Subgroup 112 Lagoon fishes. These are fishes which spend a large part of their lives in coastal saltwater lagoons and estuaries (14 species).
Subgroup 113 Sporadic freshwater fishes. These are marine fishes tolerant of fresh or brackish water (eight species). It is certain that the number of species included in this group will probably increase with future explorations, since Osorio (1898) and Gunther (1859- 1870) have reported Cephalopholis nigri (Serranidae), Selene dorsalis, Trachinotus goreensis (Carangidae), Lutjanus fulgens, L. griseus (Lutjanidae). Surveys by the author in intertidal pools have revealed Abubdefduf analogus (Pomacentridae) and Hypleur- ochilus langi (Blennidae), all of which have been cited by other authors (Quero et al., 1990; Schneider, 1990; Leveque et al., 1992) in brackish water estuaries in different parts of West Africa.
Subgroup 114 Complementary fishes. These are species which live in freshwater except during their larval stages which develop at sea.
Tabl
e 2.
Gro
up
I fis
hes
in
Biok
o
Geog
raph
ical
distri
butio
n Fa
mily
Sp
ecies
Isl
and
distri
butio
n Co
mm
ents
Biok
o Cy
prino
dont
idae
Aphy
osem
ion
oese
ri (S
chm
idt.
1928
) Al
In
Bi
oko,
A.
oe
seri
is sy
mpatr
ic wi
th
A.
volca
num
, bo
th
of
which
ar
e pr
esen
t in
riv
ers
in
the
NW
of
the
islan
d.
Biok
o/M
ount
Ca
mer
oon
Cypr
inida
e
Cypr
inodo
ntida
e
Barb
us
thysi
(Tre
wava
s, 19
74)
Aphy
osem
ion
volca
num
(R
adda
an
d W
ildek
amp,
19
77)
A Al
Thys
va
n de
n Au
dena
erde
(1
967.
19
68)
iden
tifie
d a
three
- sp
otte
d ba
rbus
as
B.
tri
spilo
s bu
t po
inte
d to
th
e hig
her
posit
ion
of
the
seco
nd
spot
. La
ter
Trew
avas
(1
974)
su
gges
ted
that
th
is sp
ecies
, to
geth
er
with
th
ose
in
Mun
go
and
Mem
e riv
ers
be
nam
ed
Barb
us
thysi.
In
Bi
oko,
it
is pr
esen
t in
th
e low
er
parts
of
th
e M
irupu
ruru
, Ol
sina,
M
opob
ill an
d Ba
supu
riv
ers
in
the
north
we
st as
we
ll as
in
th
e so
uthwe
st (T
iburo
nes).
Radd
a an
d Fu
rzl(l9
87)
conc
luded
th
at
the
Chro
map
hyos
emion
sp
ecies
in
Bi
oko
and
Mou
nt
Cam
eroo
n we
re
Aphy
osem
ion
volca
num
. Th
ey
claim
it
to
be
ende
mic
to
the
Kake
riv
er
basin
an
d ot
her
sprin
gs
in
the
Mou
nt
Cam
eroo
n ar
ea,
altho
ugh
they
did
not
spec
ify
Biok
o.
They
be
lieve
it
to
be
symp
atric
with
A.
oe
seri
and
its
habit
at
‘smal
l str
eams
an
d sw
ampy
pa
rts
of
broo
ks
and
river
s in
th
e ra
infor
est
on
volca
nic
soils
’. In
Bi
oko,
A.
vo
lcanu
m
is pr
esen
t wi
th
A.
oerse
ri in
riv
ers
in
the
NW
of
the
islan
d.
Lowe
r Gu
inea
regio
n Cy
prini
dae
Cypr
inida
e
Bagr
idae
Barb
us
camp
taca
nthu
s (B
leeke
r. Al
18
63)
Barb
us
bate
sii
(Bou
lenge
r. 19
03)
A2
Para
uche
nogla
nis
mon
kei
(Keil
hack
, 19
10)
Al
Foun
d in
Bi
oko
in
some
NW
riv
ers
(Tim
babe
, Os
ina,
Cons
ul)
Foun
d in
fo
reste
d ar
eas
from
S. C
amer
oon/
N.
Gabo
n to
th
e Ch
ad
syste
m an
d Ti
besti
(D
aget
er
al.
. 19
84);
in
the
latte
r pla
ced
with
B.
by
nni
occid
enta
lis
(Bou
lenge
r, 19
11)
by
Leve
que
and
Gueg
an
(199
0).
In
Biok
o re
strict
ed
to
Rio
Tibu
rone
s.
Foun
d in
S.
Cam
eroo
n.
In
Biok
o it
is ve
ry ra
re
in
the
Osina
an
d Ba
sapu
riv
ers
in
the
NW.
Cypr
inod
ontid
ae
Cypr
inod
ontid
ae
Proc
atop
us
similis
(A
hl,
1927
)
Cich
lidae
Lowe
r-Gui
nea/
Sout
h Ni
geria
Ci
chlid
ae
Lowe
r-Gui
nea/
Sout
h Ni
geria
/Mid
dle
Zaire
M
asta
cem
belid
ae
Epipl
aiys
sexfa
rciatu
s ra
rhke
i (R
adda
, 19
71)
Chro
mid
otila
pia
finley
i (T
rewa
vas,
19
74)
Pelvi
cach
romi
s ta
eniat
us
(Bou
leng
er,
1901
)
Caec
omas
tace
mbe
luF
crypla
canr
hus
(Gun
ther
, 18
67)
A Le
vequ
e et
al
. (1
992)
rec
ogni
zes
two
subs
pecie
s of
E.
sexf
asci
atus
Gill
(186
3) f
or W
. Af
rica.
E.
s.
rath
kei
occu
rs
from
th
e Ku
mba
re
gion
to
Rio
M
uni
and
E.
s. to
golen
sis
from
S.
Tog
o to
Ben
in
and
Nige
ria
(Cro
ss R
iver).
The
two
diffe
r in
the
ir co
lour
pa
ttern
s.
E.
s. ra
thke
i ha
s a
blac
k ba
nd
in i
ts u
neve
n fin
s, a
s fo
und
in B
ioko
sp
ecim
ens.
In
Biok
o,
the
spec
ies
is fo
und
in t
he l
ower
re
ache
s of
som
e riv
ers
in t
he N
W
and
W (
Tibu
rone
s-
Luba
).
Al
Base
d on
the
pos
ition
of t
he p
elvic
fin
s,
shap
e of
fe
mal
es a
nd
no y
ello
w on
the
bac
k, T
rewa
vas
(197
4)
conc
lude
d th
at t
his
spec
ies
was
close
to
P.
glauc
icaud
us.
Radd
a (1
972)
an
d W
ildek
amp
et a
l., (
in
Dage
t et
al.,
19
86)
and
Rom
and
(in
Leve
que
et
al.,
1992
) pl
ace
it wi
th
P.
similis
.
Al
Acco
rdin
g to
Dag
et e
t al.
, (1
991)
, C
. finl
eyi
is r
estri
cted
to
the
Mun
go
and
Mem
e riv
ers
in M
ount
Ca
mer
oon,
Bi
oko
and
the
Krib
i riv
er b
asin
. In
Bio
ko,
it is
foun
d in
th
e lo
wer
area
s of
som
e N
W
river
s.
Al
Lim
ited
to t
he c
oast
al a
reas
of
S. N
iger
ia
and
S.
Cam
eroo
n.
In B
ioko
, it
has
been
cau
ght
in t
he O
sina
and
Basu
pu
river
s in
the
NW
of
the
isla
nd.
Al
Larg
er
spec
imen
s ha
ve a
rou
nded
ca
udal
fin
com
pare
d to
a p
oint
ed
one
in s
mal
ler
ones
(< 2
02 m
m).
Prea
nal
leng
th
diffe
rs r
elat
ive
to t
he p
osta
nal
betw
een
0.65
in
the
larg
er
spec
imen
s to
up
to 0
.85
in t
he s
mal
ler
ones
. Th
is
varia
tion
may
poi
nt
to t
he l
arge
r sp
ecim
ens
bein
g C
. lon
gicau
da
as s
ugge
sted
by
Trav
ers
(198
4a).
Foun
d in
the
M
iddl
e Za
ire
river
a
cent
ral
west
Afri
can
subl
ittor
al
rain
fore
st
zone
fro
m
the
Ntem
(R
io
Mun
i) riv
er
basin
to
the
Oue
me
(Ben
in)
river
but
exc
ludi
ng
the
Nige
r ba
sin.
In B
ioko
, it
has
only
been
fou
nd
in t
he u
nder
wate
r ve
geta
tion
of s
helte
red
river
bank
s in
NW
riv
ers
(Bas
upu,
O
sina
and
Miru
puru
ru).
Tabl
e 3.
Gro
up I
I fis
hes
in
Biok
o
Type
Fa
mily
Sp
ecies
Isl
and
distri
butio
n Co
mm
ents
Shor
e fis
hes
Gobii
dae
Perio
phth
almus
ba
rbar
us
(Linn
aeus
. 17
66)
A-B1
Th
is ge
nus
was
first
cons
idere
d in
th
e fa
mily
Pe
rioph
thal
mid
ae
but
Murd
y (1
989)
pla
ces
it wi
thin
th
e fa
mily
Go
biida
e.
Base
d on
os
teolo
gy,
Bird
song
et
al.
, (1
988)
de
scrib
es
this
grou
p as
un
ique
wi
thin
th
e fa
mily
, sin
ce
P.
barb
arus
is
a re
lict
spec
ies
foun
d in
W
est
Afric
a,
of
an
esse
ntial
ly we
stern
In
do-P
acific
dis
tribu
tion
This
spec
ies
is fo
und
in
brac
kish
water
s an
d so
met
imes
fre
shwa
ters
betw
een
Sene
gal
and
Ango
la.
In
Biok
o,
it wa
s fo
und
arou
nd
the
river
mouth
s al
ong
the
north
-wes
t.
Estu
arine
an
d la
goon
fis
hes
Cypr
inodo
ntiad
ae
Aploc
heilic
hthy
s sp
ilauc
hen
(Dum
eril.
1861
) A-
B1
Aploc
heilit
chhy
s m
acro
phth
almus
A2
sc
heeli
(R
oman
. 19
71)
Thys
va
n de
n Au
dena
erde
(1
967)
hi
ghlig
hted
th
e lar
ger
size
(max
imum
le
ngth
92
.5
mm
) of
th
is sp
ecies
in
Bi
oko
comp
ared
to
co
ntine
ntal
forms
. In
th
e pr
esen
t stu
dy
a m
ale
mea
surin
g 10
3 m
m
was
colle
cted.
Rom
and
(Lev
eque
et
al.
, 19
92)
cons
idere
d th
is a
subs
pecie
s be
caus
e of
co
loura
tion
diffe
renc
es
and
geog
raph
ical
distri
butio
n.
Wild
ekam
p et
al.
, (in
Da
get
ef
al.,
1986
) lis
ted
it as
a
full
spec
ies.
Ther
e ar
e no
sig
nifica
nt
diffe
renc
es
in
the
mer
istico
-mor
pholo
gical
relat
ions
given
by
Ro
man
(1
971)
for
th
e su
bspe
cies
and
thos
e of
Da
get
(197
9)
and
Radd
a an
d Pu
rzl(l9
87).
Howe
ver,
ther
e ar
e re
giona
l va
riatio
ns
that
dis
tingu
ish
this
subs
pecie
s in
Bi
oko:
it
is mu
ch
large
r (to
tal
leng
th
50
mm
) an
d gr
eate
r nu
mbe
r of
ra
dii
in
the
anal
fin
(1
3m
15).
It wa
s fo
und
in
fresh
an
d sa
ltwat
er
river
m
outh
s in
co
asta
l Ca
mer
oon
and
Rio
Mun
i. In
Bi
oko
it inh
abits
so
me
river
s ar
ound
th
e Lu
ba
area
,
Syng
nath
idae
Enne
ucam
pus
anso
rgii
(Bou
lenge
r, 19
10)
A-B1
Le
vequ
e et
al.
, (1
992)
re
ports
th
e sp
ecies
as
fo
und
alon
g co
asta
l W
est
Afric
a fro
m Se
nega
l to
An
gola
. Bi
oko
spec
imen
s wa
s co
llecte
d at
Ur
eca
and
in
Rio
Tibu
rone
s.
Tabl
e 2.
Con
tinue
d
Geo
grap
hica
l di
strib
utio
n Fa
mily
Sp
ecie
s Is
land
di
strib
utio
n Co
mm
ents
Lowe
r-Upp
er
Gui
nea/
So
uth
Nige
ria
Mor
myid
ae
Char
acid
ae
Isich
thys
henr
yi (G
ill,
1863
)
Bryc
inus
long
ipin
nis
(Gun
ther
, 18
64)
Al
Al
In B
ioko
, fo
und
in t
he B
asup
u an
d M
irupu
ruru
riv
ers.
Pres
ent
in t
he l
ower
re
ache
s of
som
e N
W
river
s in
Bi
oko.
Wid
e di
strib
utio
n Cy
prin
idae
Bu
rbus
ca
llipte
rus
(Bou
leng
er,
1907
) Al
Clar
ias
came
rune
nsis
(Lon
nber
g,
A 18
95)
This
spe
cies
is fo
und
in p
ract
ically
th
e en
tire
Suda
nese
pr
ovin
ce,
inclu
ding
th
e Ch
ad
river
bas
in,
sout
hern
Up
per
Gui
nea
and
north
ern
Lowe
r G
uine
a.
Repo
rted
in B
ioko
in
the
low
er M
irupu
ruru
riv
er
(Thy
s va
n de
n Au
dena
erde
, 19
67,
1968
) an
d in
the
Olsi
na
and
Basu
pu
river
bas
ins
in t
his
stud
y.
Clar
iidae
Th
ys v
an d
en A
uden
aerd
e (1
967)
ide
ntifie
d fiv
e sp
ecim
ens
from
Bi
oko
as C
. wa
lkeri.
G
unth
er
(189
6)
plac
ed
this
spe
cies
with
C
. poe
nsis
(de&
bed
as a
Bio
ko
ende
mic)
. Te
ugel
(19
86),
on t
he o
ther
ha
nd,
inclu
des
C.
came
rune
nsis
with
C.
wa
lkeri.
Th
is s
pecie
s is
foun
d th
roug
hout
th
e co
asta
l re
gion
fro
m
Togo
to
the
mou
th
of t
he Z
aire
riv
er.
In B
ioko
, it
was
foun
d in
the
low
er
north
ern
river
s fro
m
Cons
ul
west
to T
ibur
ones
.
Mal
apte
rurid
ae
Mala
pter
urus
ele
ctricu
s (G
mel
in,
1789
)
Hem
ichro
mis
bimac
ulatu
s (G
ill,
1862
)
Al
Cich
lidae
A2
This
spe
cies i
s di
strib
uted
th
roug
hout
Af
rica.
Re
porte
d on
ly in
the
NW
riv
ers
in B
ioko
.
Biok
o sp
ecim
ens
are
larg
er
(37-
43%
) as
opp
osed
to
3 l-
37%
fou
nd
in T
euge
ls (1
986)
and
Thy
s va
n de
n Au
dena
erde
(L
eveq
ue
et
al.,
1992
). Bi
oko
figur
es
are
simila
r to
tho
se r
epor
ted
by D
aget
(1
954)
for
the
Upp
er
Nige
r. Tb
e sp
ecie
s is
wid
ely
dist
ribut
ed
alon
g th
e co
asts
fro
m
the
Zaire
riv
er
to S
eneg
al a
nd t
he N
ile b
ut
not
in
Rio
Mum
. In
Bio
ko,
it is
onl
y fo
und
in t
he T
ibur
ones
riv
er
basin
in
the
sout
hwes
t.
Tabl
e 3.
Con
tinue
d
Type
Fa
mily
Sp
ecies
Isl
and
distri
butio
n Co
mm
ents
Syng
nath
idae
Micr
ophis
br
achy
urus
ac
uleaiu
s (K
aup,
18
56)
A-B1
Th
is sp
ecies
is
cons
idere
d an
adro
mou
s by
M
cDow
all
(198
8).
Thys
va
n de
n Au
dena
erde
(1
967)
fo
und
the
spec
ies
in
Biok
o.
Spec
imen
s we
re
colle
cted
from
weste
rn
and
sout
hern
riv
ers
durin
g th
e pr
esen
t stu
dy
beca
use
of
its
pref
eren
ce
for
vege
tatio
n ar
ound
br
ackis
h wa
ter
estu
aries
. Pr
obab
ly pr
esen
t th
roug
hout
th
e co
ast
arou
nd
Biok
o.
Cich
lidae
Ti
lapi
a gu
ineen
sis
(Blee
ker,
1862
) Al
Mon
odac
tylida
e Mo
noda
crylu
s se
bae
(Cuv
ier,
1829
) A-
B1
Mug
ilidae
Mug
ilidae
Mug
ilidae
Liza
falci
pinnis
(V
alenc
ienne
s, 18
36)
A-B1
Liza
gran
disqu
amis
(Vale
ncien
nes,
1836
)
Mug
il cu
rema
(V
alenc
ienne
s, 18
36)
A-B1
A-B1
This
spec
ies
occu
rs al
ong
the
W.
Afric
an
coas
t fro
m Se
nega
l to
An
gola
. In
Bi
oko,
it
has
been
ca
ught
in
th
e NW
of
th
e isl
and
in
fresh
an
d br
ackis
h wa
ter
area
s. It
prob
ably
occu
rs th
roug
hout
riv
er
estua
ries
in
the
north
west.
This
is th
e on
ly re
pres
enta
tive
of
this
typica
lly
Indo
- Pa
cific
fam
ily
in
Afric
a.
It ha
s a
wide
dis
tribu
tion
alon
g th
e ea
stern
At
lantic
co
ast
from
Cape
Ve
rde
to
Ango
la.
In
Biok
o,
it is
prob
ably
foun
d in
mo
st es
tuar
ies.
This
spec
ies
was
foun
d in
th
e m
outh
of
th
e Ba
supu
riv
er.
Cata
drom
ous
spec
ies
(McD
owall
, 19
88)
which
inh
ibits
both
fre
sh
and
salt
wate
r al
ong
all
river
es
tuarie
s an
d ad
jacen
t ar
eas
at
sea
level.
Ve
ry co
mm
on
betw
een
Sene
gal
and
the
Zaire
riv
er.
Acco
rding
to
Qu
ero
et
al.
(199
0)
the
rang
e of
th
is sp
ecies
is
from
Sene
gal
to
Cam
eroo
n.
Leve
que
et
al.
(199
2).
in
agre
emen
t wi
th
Sere
t an
d Op
ic (1
981)
ex
tends
its
dis
tribu
tion
to
the
Zaire
riv
er.
Restr
icted
to
co
asta
l fri
nge
from
Sene
gal
to
Zaire
. In
Bi
oko,
on
ly on
e sp
ecim
en
has
been
ca
ught
in
th
e no
rth
of
the
islan
d alo
ngsid
e L.
falc
ipinn
is.
The
spec
ies
is pr
obab
ly fo
und
in
an
area
sim
ilar
to
L. f
alcipi
nnis.
Gob
iidae
Gob
iidae
Gob
iidae
Eleo
trida
e Bo
stryc
hus
afric
amu
(Ste
inda
chue
r, 18
80)
Eleo
trida
e El
eotri
s vit
tata
(D
umer
il,
1858
)
Spor
adic
fresh
wate
r fis
hes
Dasy
atid
ae
Barh
ygob
ius
sopo
rator
(V
alen
cienn
es,
1837
)
Nem
atog
obius
br
achy
nemu
s (P
faff,
19
33)
Nem
atog
obius
m
aindr
oni
(Sau
vage
, 18
80)
A-B1
A-B1
A-B1
A-B1
A-B1
Dasy
atis
mar
garit
a (G
unth
er,
1870
) A-
B1
Mille
r an
d Sm
ith (
1989
) co
nsid
er
this
spe
cies
to b
e di
stin
ct
from
ot
her
cong
ener
ics
foun
d in
the
reg
ion.
Th
is
is a
n ea
st A
tlant
ic sp
ecie
s wh
ich
has
colo
nize
d th
e Af
rican
co
asts
from
M
aurit
ania
to
Ang
ola.
Spec
imen
s co
llect
ed
far
exce
ed th
e m
axim
um
size
re
porte
d fo
r th
e sp
ecim
ens
by M
iller
(199
0).
Biok
o sp
ecim
ens
mea
sure
d 11
9-15
3 m
m a
s op
pose
d to
57
mm
. Un
til
now,
N.
brac
hyne
mus
had
neve
r be
en f
ound
ou
tsid
e m
arin
e ha
bita
ts.
In B
ioko
an
d SH
o To
mb,
sp
ecim
ens
have
bee
n ca
ught
in
tidal
wa
ters
as
well
as in
pe
rman
ent
fresh
wate
r se
ctio
ns o
f st
rong
cur
rent
s.
Biok
o sp
ecim
ens
were
fou
nd
in m
outh
of
the
016
rive
r in
S.
Biok
o.
Harri
son
(199
0) c
onsid
ers
this
spe
cies
as s
ynon
ymou
s to
N.
an
sorg
ii; th
e on
ly tw
o sp
ecie
s re
stric
ted
to f
resh
wate
rs
in t
he c
entra
l an
d we
ster
n tro
pica
l Af
rica.
Q
uero
et
al.
(199
0) r
ecor
ds t
he s
pecie
s as
a b
enth
ic,
insh
ore
mar
ine,
es
tura
ine
and
fresh
-wat
er
fish
foun
d fro
m
Sene
gal
to
Cong
o an
d th
e G
ulf
of G
uine
a isl
ands
.
Durin
g th
is s
tudy
, tw
o sp
ecim
ens
were
col
lect
ed
burie
d in
the
ben
thic
mud
on
the
edg
e of
the
Tib
uron
es
river
.
This
fis
h is
foun
d al
ong
the
lowe
r re
ache
s of
mos
t riv
ers
from
Se
nega
l to
Zai
re
as w
ell
as in
all
Gul
f of
Gui
nea
islan
ds.
Acco
rdin
g to
Ser
et (
in l
eveq
ue e
t al.,
19
92)
this
spe
cies i
s co
mm
on
in t
he c
oast
of W
. Af
rica
but
less
abu
ndan
t th
an
D.
mar
garit
ella.
It
rang
es f
rom
Cab
o Bl
anc0
to
Ang
ola.
O
ne s
pecim
en w
as c
olle
cted
in
the
Elo
belo
riv
er
(Ure
ca),
200
m fr
om
the
river
’s m
outh
, at
a d
epth
of
1 m
.
Tabl
e 3.
Con
tinue
d
Type
Fa
mily
Sp
ecies
Isl
and
Distr
ibutio
n Co
mm
ents
Cara
ngida
e Ca
ranx
hip
pos
(Linn
aeus
, 17
66)
A-B1
Th
is sp
ecies
is
wide
ra
nging
in
bo
th
sides
of
th
e At
lantic
an
d in
th
e M
edite
rrane
an.
In
W.
Afric
a,
it oc
curs
as
far
sout
h as
S.
Ang
ola.
Bi
oko
samp
les
were
co
llecte
d at
Ur
eca
but
are
prob
ably
this
spec
ies
foun
d in
al
l es
tuarie
s an
d riv
er
mou
ths
on
estu
aries
.
Lutja
nida
e
Gerre
idae
Haem
ulid
ae
Ariid
ae
Lutja
nus
ende
caca
nthu
s (B
leeke
r, A-
B1
1863
)
Lutja
nus
gore
ensis
(V
alenc
ienne
s, 18
30)
A-Bt
l
Gerre
s m
elano
pter
us
(Blee
ker,
1863
) A-
B1
Pom
adaq
s ro
gerii
(Cuv
ier,
1830
) A-
B1
Arius
lat
iscut
atus
(G
unthe
r. 18
64)
A-B1
Very
com
mon
al
ong
the
coas
tal
strip
of
the
Gulf
and
in
Biok
o.
It is
foun
d in
es
tuarie
s an
d ad
jacen
t fre
shwa
ter
area
s. In
S.
Bi
oko,
th
is fis
h ca
n of
ten
be
seen
tra
pped
in
po
ols
in
small
riv
ers
which
ar
e se
para
ted
from
the
sea
by
sand
ba
rrier
s du
ring
the
dry
seas
on.
They
als
o co
me
in
from
the
sea
at
high
tid
e.
In
Leve
que
et
al.
‘Bau
chot
(in
19
92)
cons
iders
this
fish
to
be
distri
bute
d al
ong
the
west
Afric
an
coas
tal
area
s in
th
e Gu
lf of
Gu
inea
as
well
as
arou
nd
the
Cape
Ve
rde
islan
ds.
Alth
ough
th
is fis
h is
a m
arine
litt
oral
spec
ies
it of
ten
pene
trate
s es
tuarie
s es
pecia
lly
durin
g ris
es
in
river
lev
els.
It is
wide
ly dis
tribu
ted
from
Sene
gal
to
Ango
la
as
well
as
alon
g th
e W
ester
n At
lantic
.
This
is a
mar
ine
fish
which
inh
abits
th
e co
asta
l ar
eas
from
Sene
gal
to
Ango
la.
Spec
imen
s we
re
colle
cted
in
saltw
ater
ar
eas
in
S.
Biok
o.
This
spec
ies
(A.
gamb
ensis
) wa
s no
t fo
und
durin
g th
e pr
esen
t stu
dy.
Com
plem
enta
ry
fishe
s Go
biida
e
Kyph
osida
e
Gobii
dae
Gobii
dae
Kyph
osus
se
ctator
(L
innae
us,
1766
) A-
B1
Chon
opho
rus
busta
man
tei
(Gre
eIT,
1882
) A-
B1
Sicy
dizzm
br
evzji
le (O
gilvie
- Gr
ant,
1884
) A-
B1
Sicy
dium
bu
rtam
ante
i (G
reeff
, 18
82)
A-B
This
littor
al sp
ecies
, ha
s hit
herto
be
en
reco
rded
on
ly in
m
arine
en
viron
ment
s bu
t ha
s a
wide
dis
tribu
tion
alon
g th
e W
. Af
rican
co
ast,
in
the
Gulf
of
Guine
a no
rthwa
rds,
inclu
ding
th
e M
edite
rrane
an
(Ser
et
and
Opic,
19
81).
A sp
ecim
en
was
foun
d ab
out
200
m
near
th
e El
obel
o riv
er
mou
th
poss
ibly
brou
ght
in
by
the
tide.
Mau
ge
(198
6)
desc
ribes
th
is sp
ecies
as
fo
und
in
fresh
water
an
d re
strict
ed
to
Biok
o,
SBo
Tom
e an
d Ro
las.
Acco
rding
to
hi
m,
this
spec
ies
and
S.
bzzs
tama
ntei
are
ende
mic
to
the
Gulf
of
Guine
a isl
ands
bu
t th
is as
certi
on
may
be
incor
rect
since
th
eir
life
cycle
is
partl
y de
pend
ent
on
a m
arine
sta
ge,
will
enab
le
the
spec
ies
to
be
mor
e wi
dely
distri
bute
d.
Obse
rvatio
ns
from
the
pres
ent
study
, ind
icate
th
at
it ma
y liv
e in
fre
sh
and
saltw
ater
ar
eas
alon
g riv
er
mou
ths,
altho
ugh
its
first
stage
s de
velop
at
se
a. Sa
mple
s we
re
colle
cted
in
the
inter
tidal
zone
sw
imm
ing
upcu
rrent
from
the
sea
towar
ds
Eola
-Bai
ta.
Juve
nile
stage
s ar
e tra
nspa
rent
an
d on
ly de
velop
co
lour
when
the
y en
ter
fresh
water
, as
in
th
e ge
nus
Sicy
dium
.
Alth
ough
Ri
sch
and
Thys
va
n de
n Au
dena
erde
(1
979)
lim
it th
is sp
ecies
’ ra
nge
to
the
coas
tal
river
ba
sins
arou
nd
the
Gulf
of
Guine
a,
it is
foun
d in
th
e low
er
and
mid
dle
parts
of
al
l riv
ers
in
the
Gulf
islan
ds.
Its
life
cycle
is
prob
ably
simila
r to
S.
bu
stama
rzte
i.
Very
little
is
know
n ab
out
this
genu
s in
Af
rica.
It
has
an
amph
idrom
us
life
cycle
, sim
ilar
to
Pacif
ic an
d W
. In
dian
Oc
ean
cong
ener
ics.
Adult
s sp
end
most
of
their
liv
es
in
river
s, ev
en
durin
g sp
awnin
g.
The
larva
e ar
e ca
rried
to
by
cu
rrents
to
th
e se
a, wh
ere
they
rem
ain
until
po
st-
larva
l sta
ges
when
th
ere
is a
mass
m
igrat
ion
towar
ds
the
end
of
the
dry
seas
on.
Shoa
ls of
th
is fis
h ha
ve
been
ob
serve
d to
sw
im
from
the
sea
into
th
e Ol
e an
d Ru
ma
river
s. S.
bu
stam
ante
i sh
ares
ha
bitat
s wi
th
S.
brev
zfile.
It
is als
o th
e on
ly fis
h sp
ecies
pr
esen
t in
th
e ste
eper
hig
her
zone
B2
. It
inhab
its
area
s of
str
ong
curre
nts
and
well
wash
ed
rocks
in
wh
ich
it liv
es
and
feed
s.
822 Castelo
Geographical zonation of Bioko’s fish fauna
The distribution of fresh and saltwater fish in Bioko can be classified into two main ic- thyological zones (Zones A and B) (Fig. 4).
ZONE A
Within this zone, most rivers are Type III and resemble those of the continental mainland. The zone encompasses the river mouths west of the island from below 100 m above sea level (depending on orogeny), north to Rebola and as far south as Luba. All first and second group fishes are present. The zone extends onto a littoral platform (at 50-100 m in depth), which has been the only connecting bridge between the continent and the island during the various geological stages. Zone A is therefore an area which has acquired its fish fauna as a result of migration of forms when Bioko was connected to the mainland. An important distinguishing geomorphological feature of this zone is the gentler sloping ground present when compared to the rest of the island. Because of this feature, vegetation is more abundant and this favours the development of life cycles of the different fish species.
This zone can be subdivided at the narrowing of contours around Basacato de1 Oeste at (3”35’35”N, 8”37’25”E) into a northern (Subzone Al) and a southern sector (Subzone A2).
Subzone AI This zone contains the majority of Group I species (12 species exclusive to it and another three - C. walkeri, E.s. rathkei and B. thysi. - shared with subzone A2).
Subzone A2 or centre- West Only two species are exclusive to it (H. bimaculatus and B. batesii).
ZONE B
Rivers in this zone are typically Types I and II and are identical to those found in the other Gulf of Guinea islands (Sao Tome, Principe and Annobon). It can be further sub- divided altitudinally into an upper region (Subzone Bl) and a lower part (Subzone B2).
Subzone Bl This is a narrow coastal strip stretching from the sea to 100 m above sea level. It covers the northeastern, eastern, southern and southwestern perimeter of the island from Rebola to Luba. Only Group II fishes are present and in its steeper parts are only colo- nized by the genus Sycidium. In this subzone, the river basins have heavily undulating profiles and some cascade directly into the sea. There is no littoral platform here, so fishes are restricted from expansion into the interior by orographic barriers whilst fresh- water fishes must contend with the sea water as another barrier (Myers, 1949).
Subzone B2 This area covers the highest parts of Bioko where only S. bustamantei is able to colonise after overcoming the steep slopes of the river basins, impassable to the other species.
Fish diversity in Bioko 823
41’30’
4%2
3030
7”: i 1000
1 Q , 2Km
I I I
8030’ 9000 9030’
Figure 4. Map of Bioko and adjacent regions showing the different icthyological zones, considered in the text.
824 Castelo
Status and conservation of species
In Bioko there are two factors which affect important icthyological areas making them extremely vulnerable to the extinction of species. These are: (i) the small size of the island and (ii) the fact that the two most densely populated towns, Malabo and Luba, are within icthyological subzones Al and A2, respectively. Human activity in the lower reaches of Bioko’s most important rivers (zone A) has, for decades, been direct and very intense since the surrounding areas are used almost exclusively for cocoa growing. However, it does not appear to have damaged the fish communities excessively despite the almost complete replacement of primary forest in the area and the periodic use of potentially toxic agents in the plantations e.g. copper sulphate and pesticides. Similarly, neither the hydroelectric plant in Semu (Musola river) nor the recently constructed one in Riaba (Ruma river) have affected fish communities, thanks to their particular design which does not stop water-flow and to their location, which in the case of the Semu plant is in the higher reaches of the river. The Riaba plant is outside any icthyological area of relevance.
Pollution of Bioko’s river systems is not alarmingly high but fishing pressures - ex- pressly forbidden by Equatorial Guinea’s laws -- using toxic products like lime and in- secticides are all too common (according to our observations) in the dry season. There is no doubt that this is having a significant effect on northern and western rivers which are precisely the most species-rich. Indeed, the endemic Cyprinodont A. oeseri restricted to the small northern rivers is in great danger of extinction. P. monk& is in a similarly precarious situation, given its rarity. It will probably disappear altogether in a few years from the island’s rivers if no action is taken.
Before the situation becomes irreversible urgent measures must be taken to improve matters: (i) public education campaigns to make local people aware of the dangers of indiscriminate use of toxins and the abuse of the environment in general; (ii) the conservation of species in danger of extinction as well as (iii) the cleansing of heavily-polluted rivers and their re-stocking with fish species from neighbouring river basins.
Acknowledgements
The present study was undertaken as part of a project directed by Drs Benign0 Roman Gonzalez and Javier Castroviejo Bolivar within the Programa de Investigation y Con- servacion de la Naturaleza en Guinea Ecuatorial (Estacibn Biologica de Doiiana- Agencia Espafiola de Cooperation International). This study would not have been possible without the encouragement and help of the Ministerio de Cultura, Turismo y Promotion Artesanal and its Minister, Exmo Sr D. Leandro Mbomio Nsue.
I would like to acknowledge the assistance received from colleagues at the Asociacion Amigos de Dofiana at Huevar (Sevilla) in organizing the collection. My thanks also go to Dr Raymond Romand for assistance in identifying fish species and to Mr Manuel Fidalgo de Carvalho for help with plants. To Dr John E. Fa, I am grateful for his comments and assistance in reviewing first drafts of the manuscript and to MS Monique Williamson for translation of the paper from Spanish to English.
Fish diversity in Bioko 825
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Fish diversity in Bioko
Appendix
Vernacular names of$sh species in Bioko
Abat (F): Acung (F): Aferec (F): Afve-ngo (F): Aiieng (F): Dodo (Bu):
Ebabo (Bu): Ebome (C): Econo (F): Ec6-mb6 (F): Edaaduma (F): Efutbele (Bu): Esuale (Bu): Lobi (Bu):
Meloco (Bu):
Modoco (Bu): MO&h (Bu): Motond6 (C): Musongo (C):
Ndora (F): Ndoo (FN): NfvPa (F):
Nfvoga (F): Nfvon (FO): Nfvong (F):
Ngoo (F): Nguala (F):
Noco (Bu):
Ntotom (F): Nwong (F): Nyobo (F): Nyoc (F): fiuma (Bu): Sibith-sadola-dola (Bu): Sibith-sihilo (Bu): Siquellh (Bu):
(F): Fang (FO): Fang Okak (FN): Fang Ntumu (C): Combe (Bu): Bubi
Brycinus longipinnis Tilapia guineensis Chromidotilapiajinleyi Monodactylus sebae Malapterurus electricus Nematogobius brachynemus Nematogobius maindroni Aplocheilichthys spilauchen Caranx hippos (Juv.) Tilapia guineensis Gerres melanopterus Aplocheilichthys spilauchen Kyphosus sectator Eleotris vittata Liza falcipinnis Liza grandisquamis Mugil curema Sicydium brevtjile Sicydium bustamantei Periophthalmus barbarus Chonophorus bustamantei Caranx hippos Enneacampus ansorgii Microphis b. aculeatus Epiplatys s. rathkei Parauchenoglanis monkei Barbus camptacanthus Barbus thysi Barbus batesii Parauchenoglanis monkei Aphyosemion oeseri Aphyosemion volcanum Aplocheilichthys m. sheeli Procatopus similis Clarias camerunensis Hemichromis bimaculatus Pelvicachromis taeniatus Bostrychus africanus Eleotris vittata Isichthys henryi Caecomastacembelus cryptacanthus Barbus callipterus Bathygobius soporator Dasyatis margarita Lutjanus goreensis Lutjanus endecacanthus Pomadasys rogerii
827
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