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Rev. Biol. Trop. (Int. J. Trop. Biol.) • Vol. 69(1): 139-152, March 2021
Perspectives on sustainable management of the Poso Lake (Indonesia)
endemic ricefish, Oryzias nigrimas (Actinopterygii: Adrianichthyidae)
Novalina Serdiati
1
*, Diana Arfiati
2
, Maheno Sri Widodo
2
, Tri Djoko Lelono
3
, Samliok Ndobe
1
,
Kasim Mansyur
1
& Abigail Mary Moore
4
1. Aquaculture Study Program, Tadulako University, Palu, Central Sulawesi, Indonesia; novalinaserdiati@untad.ac.id,
samliok@untad.ac.id, achim_dive9@yahoo.com
2. Department of Aquatic Resources Management, Brawijaya University, Malang, Indonesia; d-arfiati@ub.ac.id,
lynxpardel@yahoo.co.id
3. Department of Utilization of Fisheries and Marine Resources, Brawijaya University, Malang, Indonesia;
t.djoko@ub.ac.id
4. Postgraduate School, Hasanuddin University, Makassar, South Sulawesi, Indonesia; abigail@pasca.unhas.ac.id
* Correspondence
Received 22-VI-2020. Corrected 28-X-2020. Accepted 09-XI-2020.
ABSTRACT. Introduction: The endemic fishes of the ancient lakes of Sulawesi are under increasing threat.
Objective: To evaluate the data and information available from a holistic management perspective and to formu-
late measures to conserve the endemic ricefish Oryzias nigrimas in Poso Lake, Indonesia. Methods: Collection
of primary data from three stations around Lake Poso and literature study. Results: Threats to O. nigrimas
include habitat degradation and loss, introduced alien species, and exploitation as a locally important food fish.
Options to promote sustainable fisheries management include spatial and temporal limitations to minimise catch
of gravid or brooding fish. Habitat protection should include measures to minimise impacts from activities
which can reduce water quality and disturb or kill aquatic vegetation. Conclusion: Measures to prevent further
O. nigrimas population decline are considered urgent and further research is recommended to fill identified
knowledge gaps. Ex-situ conservation, including the development of captive breeding, could also contribute to
a holistic O. nigrimas conservation strategy.
Key words: endemism; lacustrine; Oryziinae; black buntingi; invasive species; light fishing.
Sulawesi Island, the largest landmass in
the Wallacea region, is renowned for high
levels of endemicity, including aquatic taxa
(Hadiaty, 2018; von Rintelen & Cai, 2009; von
Rintelen, Stelbrink, Marwoto, & Glaubrecht,
2014). The “ancient lakes” of Sulawesi, includ-
ing the Malili Lake complex in South Sulawesi
and Poso Lake in Central Sulawesi, are espe-
cially rich in endemic fishes and invertebrates
(Meisner, 2001; von Rintelen & Glaubrecht,
2006; Meixner et al., 2007; Schubart & Ng,
2008; Walter, Hogan, Haffner, & Heath, 2011;
von Rintelen & Cai, 2009; Mokodongan &
Yamahira, 2015; Vaillant, Bock, Haffner, &
Cristescu, 2013; von Rintelen et al., 2014)
The ricefishes (Adrianichthyidae) are a
family with 33 recognised (valid) species in
2013 (Kottelat, 2013), a number which has since
increased to at least 37 (Mandagi, Mokodon-
gan, Tanaka, & Yamahira, 2018), including the
Serdiati, N., Arfiati, D., Widodo, M.S., Lelono, T.D., Ndobe, S., Mansyur, K., & Moore,
A.M. (2021). Perspectives on sustainable management of the Poso Lake (Indonesia)
endemic ricefish, Oryzias nigrimas (Actinopterygii: Adrianichthyidae). Revista de
Biología Tropical, 69(1), 139-152. DOI 10.15517/rbt.v69i1.42404
ISSN Printed: 0034-7744 ISSN digital: 2215-2075
DOI 10.15517/rbt.v69i1.42404
140
Rev. Biol. Trop. (Int. J. Trop. Biol.) • Vol. 69(1): 139-152, March 2021
description of two new species from Sulawesi:
Oryzias soerotoi (Mokodongan, Tanaka, &
Yamahira, 2014); Oryzias dopingdopingensis
(Mandagi et al., 2018). Of these 37 species, 21
ricefishes are native to Sulawesi, a recognised
“hotspot” of biodiversity for this fish fam-
ily (Parenti, 2008; Mokodongan et al., 2014;
Hadiaty, 2018; Mandagi et al., 2018). While
Oryzias javanicus is widely distributed across
Southeast Asia (Mokodongan, 2019a), and O.
celebensis (previously considered endemic to
Sulawesi alone has also been reported from
East Timor (Parenti, 2008; Hadiaty, 2018;
Lumbantobing, 2019a), the majority (19 spe-
cies or 90.5 %) of the Sulawesi ricefishes are
endemic to one or more of the ancient lakes
and/or certain riverine systems in Sulawesi
(Parenti, 2008; Hadiaty, 2018; Mandagi et al.,
2018; Lumbantobing, 2019b; Lumbantobing,
2019c; Lumbantobing, 2019d; Mokodongan,
2019b; Mokodongan, 2019c; Mokodongan,
2019d; Mokodongan, 2019e; Mokodongan,
2019f; Mokodongan, 2019g; Mokodongan,
2019h; Mokodongan, 2019i; Mokodongan,
2019j; Mokodongan, 2019k; Mokodongan,
2019l; Mokodongan, 2019m; Mokodongan,
2019n; Mokodongan, 2019o; Mokodongan,
2019p; Mokodongan, 2019q).
Species with such restricted natural ranges
are intrinsically vulnerable to extinction (Wal-
ter et al., 2011). The 2019 version of The IUCN
Red List of Endangered Species (hereafter
referred to as the IUCN Red List) provides
assessments of the conservation status accord-
ing to the criteria of the International Union for
the Conservation of Nature (IUCN) for 36 rice-
fishes (Family Adrianichthyidae), including all
but one (O. dopingdopingensis) of the 21 rice-
fishes reported from Sulawesi. One Sulawesi
endemic (O. wolasi) is classed as Data Defi-
cient (DD), meaning the data available are
insufficient to assign a conservation status.
Globally, half of the assessed ricefishes
are classed within one of the IUCN Red
List categories indicating a significant risk
of extinction; it is remarkable that 89 % of
these are ricefishes endemic to Sulawesi. A
third of all assessed ricefishes are classed as
Least Concern (LC) including the Poso Lake
endemic Xenopoecilus oophorus (synonyms
Adrianichthys oophorus and Oryzias oopho-
rus) (Mokodongan, 2019m) and O. celebensis
(Lumbantobing, 2019a). However, concerns
have been expressed regarding the threats to
and urgent need for conservation of all Sulawe-
si endemic freshwater fishes (Parenti, 2011),
including X. oophorus (Gundo, 2010).
Among the ancient lakes of Sulawesi,
the ichthyofauna of Lake Poso is particularly
rich in ricefishes with seven endemic species
(Hadiaty, 2018). The taxonomy of ricefishes
at the genus and species levels is a matter of
ongoing research (Mokodongan et al., 2018;
Parenti, 2008), with several synonyms in cur-
rent use for some species (e.g. X. oophorus).
Using the taxonomy according to Kottelat
(2013), the ricefishes recorded in Poso Lake
are: Oryzias nigrimas (Parenti, 2008; Serdiati,
Arfiati, Widodo, Lelono, & Gosari, 2019a;
Serdiati et al., 2020), O. nebulosus (Parenti &
Soeroto, 2004; Serdiati, Arfiati, Widodo, Lelo-
no, & Toha, 2019b), O. orthognathus (Parenti
& Soeroto, 2004), Xenopoecilus oophorus and
X. poptae (Parenti, 2008), Adrianichthys kruy-
ti (Parenti, 2008), and A. roseni (Parenti &
Soeroto, 2004).
Anthropogenic activities pose many direct
and indirect threats to the environment in and
around Poso Lake (Nursangaji et al., 2014;
Mamondol, 2018), Despite their small size,
several ricefishes are exploited as food fish
(Gundo, 2010; Parenti & Soeroto, 2004), while
the remainder may well be caught as by-
catch in targeted (ricefish) and other fisheries.
Sulawesi ricefishes are also being proposed
as potential model organisms for research in
fields as diverse as the study of evolution,
behavioural, biological and medical research
(Mokodongan & Yamahira, 2015; Mokodon-
gan et al., 2018; Sari, Andriani, & Yaqin, 2018;
Hilgers & Schwarzer, 2019; Sutra et al., 2019).
Seven of the eight ricefish species assessed as
Near Threatened (NT) in the 2019 IUCN Red
List are endemic to Sulawesi, and three to Lake
Poso: O. nebulosus (Mokodongan, 2019g),
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O. orthognathus (Mokodongan, 2019h), and O.
nigrimas (Mokodongan, 2019n).
The purpose of this study was to evaluate
the Poso endemic ricefish O. nigrimas from
a holistic conservation management perspec-
tive. Based on primary survey data combined
with secondary data and information, the study
aimed to provide guidance on potential man-
agement measures to sustain this species.
MATERIALS AND METHODS
Field study site: Poso lake (Fig. 1) is
situated in Poso District, Central Sulawesi
Province, Indonesia (1º41’18.42”-2º18’3.41”
S & 120º21’27.10”-120º51’9.28” E) at an alti-
tude of approximately 657 m above sea level
(Nontji, 2016). Based on measurements made
in 2007 (Lukman & Ridwansyah, 2009), Poso
Lake covers an area of 368.9 km
2
(36 890 ha),
with a shoreline of 127 km, length and width
of approximately 35.9 km and 15.3 km. The
narrow shallow shelf around the shore reaches
depths of around 5-7 m then plunges steeply
to a maximum depth of 385 m, with a mean
depth of 194.7 m
and nearly 2m fluctuation in
water level between rainy and dry seasons.
Data collection: Primary data were col-
lected primarily at three survey stations around
Poso Lake (Fig. 1) on a monthly basis from
May 2017 to April 2018. These sites were
selected based on information from local fish-
ermen and data from previous surveys. Quan-
titative in situ measurements visibility (m,
Secchi disc), dissolved oxygen (DO) (mg/l,
Lutron DO-5510) temperature (ºC) and pH
(ATC Tri-meter) were supplemented by quali-
tative observations on habitat condition. As
no fisheries statistics were available for O.
nigrimas and other endemic fishes in Poso
Lake, qualitative data on O. nigrimas exploi-
tation and trends in abundance were obtained
Fig. 1. Map of Poso Lake showing Oryzias nigrimas observation stations and the surrounding sub-districts (adapted from
Serdiati et al., 2020).
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through direct observation and key informant
interviews (government officials, fishermen,
local residents). Secondary data were sourced
from the scientific literature and databases,
unpublished data (e.g. previous survey reports
by academics), and other documents available
online or from government agencies.
Data analysis: Data were analysed
descriptively. A synopsis of bioecological
parameters was compiled for of O. nigrimas
and related species, focused on aspects relevant
for conservation. Current and historical data on
fish populations, habitat and exploitation levels
were evaluated to identify actual or potential
threats and changes relevant to the conserva-
tion of Poso endemic species, especially O.
nigrimas. Management measures were for-
mulated to reduce the risk of extinction and
maintain or promote recovery of O. nigrimas
populations along with other endemic species
in Poso Lake.
RESULTS
Poso Lake ecosystem and O. nigrimas
habitat: A synopsis of data (primary and sec-
ondary) on the habitat of O. nigrimas in Poso
Lake is shown in Table 1. Table 2 presents an
overview of major threats to the Poso Lake
ecosystem in general and the habitat of O.
nigrimas in particular.
Biology, ecology, conservation status
and exploitation of O. nigrimas and other
Poso ricefishes: A synopsis of data on key life
history parameters for the black buntingi O.
nigrimas (including data obtained during this
study) and the other six Poso Lake endemic
ricefishes (Table 3) reveals major gaps in cur-
rent knowledge. Similar gaps are reflected in
a synopsis of data on the ecology, conserva-
tion status and exploitation of Poso ricefishes
(Table 4).
The fisheries targeting endemic fishes in
Poso Lake were not regulated or recorded
by any government agency. The field survey
revealed that O. nigrimas and other Poso
endemic ricefishes were among the species
targeted by night-time fisheries using lights
to attract phototaxis positive fish. The main
light fishing gears were a variety of lift nets
and gillnets; scoop nets were also used and
beach seines also caught ricefishes. Lift nets
generally operated 15-20 days per month,
avoiding the full moon period. The O. nigri-
mas fishing grounds were in shallow waters
close to the lake shore, and included all three
survey sites (Fig. 1) where the rocky substrate
TABLE 1
Physical and chemical parameters of Poso Lake
a
Parameter (unit)
Secondary data - Year This study (May 2017 to April 2018) - Station
2007
b
2010
c
2011
d
2013
e
1 2 3
Temperature (ºC) 27.9-28.8
f
30.4 26-30 27-28.5 26.5-28 26-28.5 27.5-28.5
pH 8.34-8.69 7.7 6.39-8.09 8.5-8.7 8.0-8.5 8.4-8.5 8.3-8.5
DO (mg/l) 5.91-7.80 4.67 5.24-9.55 5.86-5.99 6.0-6.9 6.0-6.8 6.4-6.7
Visibility (m) 10-11 na 5.5-9 7-11 7.2- 8.8 8.5-10.6 8.5-11.2
Nitrogen (mg/l) 0.14-0.68 0.42 0.07-0.15 na na na na
Phosphate (mg/l) 0.01-0.05 na 0.04-0.05 na na na na
Chlorophyll (mg/m
3
) 0.24-1.69 na na na na na na
N/P ratio 2.5-39 na na na na na na
Trophic status mesotrophic to mildly eutrophic oligotrophic indications of eutrophication
Hardness soft na na na na na na
Sedimentation high high na high generally high
a
na = data not available;
b
Lukman (2007);
c
Mamondol (2018);
d
Makmur et al. (2011);
e
Gundo (2015);
f
mean value from
0-50 m; temperature ≈27 ºC at 60 m and 29-29.5 ºC from 0-10 m depth.
143
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is particularly suitable as O. nigrimas habi-
tat. Fishermen and other locals consistently
reported a decline in ricefish abundance with
a decreasing trend in fisheries catch despite
an increase in effort, indicating overfishing of
O. nigrimas populations.
The mesh size of all liftnets and some
gillnets observed was very small, making them
intrinsically non-selective (size and species).
The ricefish O. nebulosus was visually identi-
fied in the catch of fishers targeting O. nigri-
mas. This was confirmed by molecular (DNA)
analysis (Serdiati et al., 2019b). Fishing activi-
ties targeting O. nigrimas were intensive and
ricefishes in all age-size classes were caught.
Very few captured ricefishes were in a fit
condition to survive if certain categories (e.g.
juvenile fish, egg-bearing females or specific
species) were released.
Invasive alien species in Poso Lake: A
growing number of non-native (alien invasive)
species have been reported in Poso Lake. The
list of introduced species reported in Poso Lake
in Table 5 is likely incomplete.
The field survey revealed that local com-
munities do not like eating these introduced
fishes; with little fishing pressure, they have
become established and spread. While the
origins of some alien species (Table 5) are
known (e.g. releases under government proj-
ects), others are speculative. The bony-lipped
bard (Osteochilus vittatus) and Java barb (Bar-
bonymus gonionotus), called nilem and tawes
locally, are thought to have been released by
migrants under the government “transmigrasi
program to reduce over-population in Java (and
Bali). Nilem were the most abundant fish visible
during a survey on Poso anguillid eels (Ndobe
TABLE 2
Major threats to the Poso Lake ecosystem, including Oryzias nigrimas habitat
Type of threat Details
Actual/potential impact on O.
nigrimas
References
Sedimentation, reduced
depth
Erosion due to degradation
of the watershed, particularly
deforestation
Degradation or loss of shallow-
water habitat, including hard
substrate and aquatic plants
This study and
a,b,c,d,e,f
Lakeside development
including reclamation
Growth of Tentena (the main
lakeside town) and other
settlements; tourism
Pollution (sewage, run-off, plastic
and other garbage) and loss of
habitat, especially ecologically
important seasonally flooded
riparian areas
This study and
a,b,c,d,e,f,g
Aquaculture of non-
native species
Mostly in net cages (fixed or
floating) in the Lake; some in Poso
River and tributaries
Pollution, damage to habitat, and
accidental releases
This study and
a,g,h,i,j
Introduced (alien)
invasive species
Government projects and private
initiatives (species: see Table 3)
Competition for habitat and food;
predation; degradation of habitat;
parasites and disease
This study and
a,b,h,k
Spread of modern
farming and plantations
Use of fertilisers and agricultural
chemicals; increased erosion and
changes in hydrology
Eutrophication and other pollution
(e.g. pesticides); intensification of
floods, droughts and sedimentation
affecting water quality and water
level patterns
This study and
a,b,c,d,e,f,k
Poso dam and
hydroelectric power
plants
Effect on water level/ water flow
patterns and retention of sediments
Potential impacts on seasonal
conditions; exacerbation of
problems related to sedimentation
This study and
a,b,h
a
Gundo (2015);
b
IUCN Red List;
c
Nursangaji et al. (2014);
d
Lukman & Ridwansyah (2009);
e
Mamondol (2018);
f
Nontji
(2016);
g
Gundo (2010);
h
Herder et al. (2012);
i
Mokodongan (2019n);
j
Mokodongan (2019h);
k
Parenti & Soeroto (2004).
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TABLE 3
Life history parameters of Poso Lake ricefishes
a
Parameter (unit)
Oryzias
nigrimas
O.
orthognathus
O.
nebulosus
Xenopoecilus
oophorus
X.
poptae
Adrianichthys
kruyti
A.
roseni
Main source (s) other
than FishBase
b
This study,
c d
This study,
e,f g,h i,j f,k f,j,l
Maximum length L
max
(mm, TL or SL)
m
58.5TL
c
52.5SL
c
65TL 50.1SL 33 SL 85 TL
69.3SL
171SL
192SL
160TL
109SL
90SL
Length at first
maturity L
m
(mm)
50.8 M; 47.5 F
c
na na na na na na
Estimated longevity na na na na na na na
Fecundity (eggs) 143-243
c
na na 33-135 na na na
Spawning pattern partial
c
partial na partial na na na
Spawning season
(month, abbreviated)
Jun, Sept, Nov,
Dec, Feb
c
na na Nov, Jan,
Feb, Apr
na na na
Sexual dimorphism yes yes yes yes na na na
Parental care: external
(pelvic brooder)
none (eggs laid
on vegetation)
na none (eggs
laid on vegetation)
yes yes yes na
Growth pattern allometric negative
c
na na isometric na na na
Phototaxis
n
Positive Positive Positive Positive Positive Positive Positive
a
na = data not available; bold characters indicate data from this study;
b
Froese & Pauly (2020);
c
Serdiati (2019);
d
Mokodongan (2019h);
e
Mokodongan (2019g);
f
Parenti & Soeroto (2004);
g
Gundo, Rahardjo, Batu, & Hadie (2016);
h
Mokodongan (2019m);
i
Mokodongan (2019c);
j
Parenti (2008);
k
Mokodongan (2019p);
l
Mokodongan (2019q);
m
TL = total
length; SL = standard length;
n
From field data on light fishing.
TABLE 4
Ecology, conservation status and exploitation of Poso Lake endemic ricefishes
a
Parameter/Aspect
Oryzias
nigrimas
O.
orthognathus
O.
nebulosus
Xenopoecilus
oophorus
X. poptae
Adrianichthys
kruyti
A, roseni
Main source (s)
other than
b,c
This study,
d e f, g g e e e
Prior Red List status VU EN none EN CR CR none
2019 Red List status NT NT NT LC EN CR CR
Population status
h
S
c
or D S S S U U/EX U/EX
Pelagic (PL) or
Benthopelagic (BP)
PL BP/PL PL PL PL PL na
Feeding guild omnivore
d,i
na na na na na na
Areas in Poso Lake
(cardinal points)
W NE SE
j
E W E W N E W na na na
Main threats
k
IN, HL, IF
f
IN, HL IN, HL, IF, OT
f
IN, HL, IF IN, HL IN IN
Known to be fished -
food fish
yes yes
l
yes
f
yes
m
yes
n
yes
o
yes
f
Aquarium trade yes
b
yes
b
proposed
f
proposed
f
na na na
a
na = data not available; bold characters indicate data from this study;
b
Froese & Pauly (2020);
c
The IUCN Red List;
d
Serdiati et al. (2019a);
e
Parenti (2008);
f
Parenti & Soeroto (2004);
g
Gundo (2015);
h
S = stable; I = increasing; D = declining,
U = unknown; U/EX: unknown, possibly extinct;
i
Predominantly herbivorous;
j
This study: all three survey stations (W, NE
and SE; Fig. 1): Mokodongan (2019n): only West (W);
k
IN = invasive species; HL = habitat loss/degradation; IF = intensive
fishing; OT = other (infestation with parasitic copepods, Lernaea sp.);
l
Mokodongan (2019h);
m
Mokodongan (2019m);
n
Mokodongan (2019c);
o
Mokodongan (2019p).
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and Moore, unpublished data, 2008), in an area
where endemic (native) species were abundant
during surveys a decade earlier (Ndobe, unpub-
lished data, 1996-2001). Several species seem
to have been introduced through escape from
aquaculture facilities or through well-meaning
but misguided release to the wild of ornamen-
tal fishes (Parenti & Soeroto, 2004; Samliok
Ndobe & Abigail Moore, unpublished data,
2008). One of the more recent and potentially
most dangerous introductions for endemic fish
species, the janitor fish (ikan sapu-sapu), Fam-
ily Locariidae, was documented in Poso Lake
in 2018 (Gundo, pers. com., 2018).
Management options for O. nigrimas.
Based on the data presented above, proposed
priorities, interventions and anticipated ben-
efits are outlined in Table 6. One potential
intervention is the development of captive
breeding followed by restocking. The national
guidelines for restocking threatened aquat-
ic (marine and freshwater) species (Sadili,
Haryono, Kamal, Sarmintohadi, & Ramli,
2015) and their relevance to O. nigrimas are
summarised in Table 7.
DISCUSSION
Need for a holistic approach: The direct
and indirect threats to Oryzias nigrimas (e.g.
habitat degradation and loss, introduced
alien species, and intensive exploitation as a
locally important food fish) are complex and
TABLE 5
Non-native species reported in Poso Lake
No Common name Scientific name Local name Remarks
a
Reference
1 Nile tilapia
Oreochromis niloticus Ikan nila
INV, PR, CP, HB, FF, G
d,e,f,i,j
2 Tilapia
O. mossambicus Ikan mujair
INV, PR, CP, HB, FF, G
d,e,j
3 Common carp
Cyprinus carpio Ikan mas
INV, CP, HB, FF, G
d,f,j
4 Bonylip barb
Osteochilus vittatus
b
Ikan nilem
INV, CP
d,e,f,i
5 Java barb
Barbonymus gonionotus Ikan tawes
INV, CP
d,e,f
6 Catfish
Clarias sp. Ikan lele
INV, PR, HB, FF, G
d,f,h,j
7 Pangasius
Pangasius sp. Ikan patin
INV, PR, HB, FF, G
e
8 Tambaqui, pacu
k
Colossoma macropomum Bawal air tawar
INV, PR, HB, FF, G
d,e
9 Flowerhorn cichlid none: hybrid cichlid
Flowerhorn
INV, PR, HB, FF, U A
e
10 Auratus cichlid
Melanochromis auratus Cichlid Afrika
INV, PR, HB, FF, U
e
11 Three-spot gourami
Trichopodus trichopterus Ikan sepat
INV, PR, HB, FF, U
Possibly also T. pectoralis
e,f,
12 Blue panchax
Aplocheilus panchax Ikan kepala timah
INV, CP, U
e
13 Bichir
Polypterus sp. Ikan palmas
African origin
d
14 Guppy
Poecilia reticulata Ikan seribu
INV, CP, U
e
15 Swordtail
Xiphophorus helleri Ikan pedang
INV, U, IU
d
16 Platyfish
Xiphophorus maculatus Ikan platy
INV, U, IU
d
17 Janitor fish
Family Locariidae
c
Ikan sapu-sapu
INV, PR, HB, U
g
18 Climbing perch
Anabas testudineus Ikan betok
PN, PR
e,f,h,i
19 Striped snakehead
Channa striata Ikan gabus
PN, PR
e,f,h,i
a
INV = invasive; PN = possibly native; PR = known or suspected predator; CP = known or suspected competitor for
resources (e.g. food, habitat); HB = known/suspected to cause habitat degradation; FF = food fish (caught by local fishers);
G = introduced under government projects; U = unknown origin; IU = impact unknown;
b
Synonym O. hasselti;
c
Taxonomy
of this family is confused; most likely Hypostomus sp. or Pterygoplichthys sp.;
d
Parenti & Soeroto (2004);
e
Gundo (2015);
f
Whitten, Henderson, & Mustafa (2002);
g
Gundo pers. com (2018);
h
Herder et al. (2012);
I
Makmur et al. (2011);
j
IUCN
Red List;
k
may include other species of the genera Colossoma and Piaractus.
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interrelated with each other as well as with the
status of other species (native and introduced)
in Poso Lake. Ensuring the survival of this spe-
cies in its native (endemic) habitat therefore
requires a holistic approach, crossing socio-
political boundaries (e.g. between government
sectors, scientific disciplines, administrative
jurisdictions and community segments/actors),
as well as linking aquatic and terrestrial eco-
systems. Action to mitigate these threats should
benefit other endemic fish and invertebrate
species in Poso Lake. Proposed approaches
discussed below under four thematic groupings
would each benefit greatly from and should be
synergised with the other approaches.
Habitat conservation and rehabilitation:
Like other ancient lakes, Poso Lake was until
quite recently classified as oligotrophic (Gie-
sen, 1994). Various human activities around
the lake and throughout the watershed have
increased both nutrient levels and sedimenta-
tion rates in the lake (Nursangaji et al., 2014;
Nontji, 2016; Mamondol, 2018). Increased
nutrients are thought to arise from urbanisa-
tion around the Lake as well as the increased
use of fertiliser on arable and plantation crops
which have increasingly replaced the natural
forest vegetation and waste from cage cul-
ture of introduced fishes. The loss of around
50-60 m in maximum depth over four decades
(Lukman & Ridwansyah, 2009) is most likely
related to increasing rates of erosion in the
Poso Lake watershed (Lukman & Ridwansyah,
2009; Nursangaji et al., 2014; Mamondol,
2018). Erosion rates of 15-60 tonnes/ha/year
TABLE 6
Matrix of proposed O. nigrimas conservation priorities and interventions
No Priority Interventions Anticipated benefits/risks
1 Data for
management
Design and implement a comprehensive
baseline survey and monitoring program for
the ichthyofauna of Poso Lake, with focus on
endemic species
Spatial distribution of species and habitat use
Basis for stock assessments and fisheries
management as well as conservation planning
Basis for evaluation of management success
2 Reduce direct
threats (fishery-
related)
Immediate: spatial and temporal restrictions
on fishing/gear use based on existing data
Revisions based on outputs from point 1
Increased survival and reproductive potential of
O. nigrimas/ other endemic fishes
Potential economic impact: may need research
on selective gear to reduce endemic species
by-catch
3 Mitigate alien
species impacts
Strict regulations on release of aquatic
organisms in Poso Lake and watershed,
with effective surveillance and enforcement
(penalties)
Cessation of so-called “re-stocking” of alien
species
Encourage exploitation of introduced species
Control of alien species not used as food
fish (e.g. sapu-sapu), including research on
possible uses to encourage fishing
Increased survival and reproductive success of
endemic fishes, including O. nigrimas
Eradication of feral alien species unlikely
to succeed, so control measures will need to
be continuous and long-term; need to seek
profitable ways to control so that fishers will do
the work as part of their livelihoods
Need for research to ensure control measures do
not impact endemic fish/invertebrates
4 Reduce indirect
threats
Integrated watershed management: synergy
with Lake Rehabilitation Program (Nursangaji
et al., 2014) and relevant agencies/stakeholder
groups
Prevent (or at least minimise) decline in habitat
condition, especially water quality and impacts
of sedimentation
Potential for habitat rehabilitation
5
Ex-situ research
and breeding
In-depth research on O. nigrimas reproductive
biology/feeding habits o
Develop breeding and release protocols, with
due attention to guidelines (Table 7)
Improved understanding to inform in-situ
management
Captive population as genetic bank and potential
source of fish for eventual restocking
Potential as additional «model organism»
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have been reported in the watershed around
Poso Lake, with the highest rates in areas with
predominantly steep slopes and high rates of
deforestation (Mamondol, 2018). The data in
Table 1 and Table 2 indicate an ongoing deg-
radation of the Poso Lake ecosystem in general
and O. nigrimas habitat in particular.
On the positive side, there are initiatives
with potential to mitigate or even to some extent
reverse environmental degradation, as high-
lighted in Table 6. In particular, as Poso Lake is
one of 15 lakes in the national lake rehabilita-
tion program (Nursangaji et al., 2014), there are
many opportunities for synergy with this pro-
gram. A key recommendation is that this and
other Poso Lake watershed programs should
include endemic species as a priority factor.
Specific measures for endemic fish conserva-
tion should be synergised with this program,
including direct protection of key habitat and
habitat restoration through improved watershed
management and restoration.
Sustainable ricefish fisheries in Lake
Poso: Data collection for fisheries purposes
(Poso Lake and surrounding watershed) has
concentrated on anguillid eels and introduced
food fish species (e.g. Makmur et al., 2011).
The 2019 IUCN Red List assessments refer-
ring to surveys in 2012 and 2017 (Mokodon-
gan, 2019c, 2019g, 2019h, 2019m, 2019n,
2019p, 2019q) and research on O. nigrimas
and Xenopoecilus oophorus (Gundo, 2010;
Gundo, 2015) confirm the field survey findings
that Poso endemic ricefishes in general are
target and/or bycatch species in light fisheries
which are of importance for local food security
and livelihoods.
The biology and ecology of most Sulawe-
si freshwater endemic species is still poorly
understood, including the Poso Lake ricefishes
in general and O. oryzias in particular (Table 3,
Table 4). Knowledge gaps include ecological
roles and interactions in the environments in
which they have evolved as well as parameters
TABLE 7
Summary of key considerations in the Indonesian national guidelines
for restocking threatened fishes (Sadili et al., 2015)
No Guideline component
Relevance to O. nigrimas
1 Where to restock: water bodies (marine or freshwater)
where threatened species occur naturally and native
species populations have declined severely
Poso Lake qualifies - for the native (especially endemic)
species in the lake
2 What to restock: native species, within parts of their native
range where they have been extirpated or populations have
declined to a level unlikely to permit natural recovery. In
the case of exploited species, restocking might also be
appropriate as part of a sustainable fisheries management
strategy
O. nigrimas qualifies as a threatened species, despite the
downgrading of Red List category in 2019 (Mokodongan
2019n); however, with the population assessed as «stable»
it does not qualify for restocking at present
3 When to restock: once the factors which caused
extirpation/drastic decline have been eliminated or
mitigated and measures are in place to promote survival/
sustainable management
These aspects have not yet been addressed for O.
nigrimas, but should include attention to habitat and
threats from introduced species.
4 Fish used for restocking: progeny of native fish,
representing maximum possible genetic variation in native
population; in good health (free of pests and diseases);
adapted for release and survival in the wild (e.g. not
acclimated to pelleted feed)
The necessary knowledge, technology and protocols for
breeding and release would need to be developed for O.
nigrimas, through fundamental and applied research.
5 Post-restocking: monitoring and evaluation are vital (and
require valid initial baseline data)
Baseline not yet available. Monitoring not yet in place.
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used in both traditional and ecosystem-based
approaches to fisheries management. Despite
these gaps, we recommend an assessment of
the Poso ricefish fisheries using the Ecosystem
Approach to Fisheries Management (EAFM)
indicators developed primarily for marine fish-
eries in Indonesia (NWG-EAFM, 2014; Pome-
roy et al., 2015) and currently being adapted to
freshwater fisheries.
As reported previously for the X. oophorus
fishery (Gundo, 2010; Gundo, 2015), the inten-
sive and currently unregulated light-assisted
liftnets arguably pose the most serious direct
fishing-related threat to Poso Lake endemic
fishes, including O. nigrimas. By their very
nature, these liftnets are unselective in terms
of species and size. Therefore, attempts to
reduce or manage the impact of these gears
on endemic fish populations need to focus on
temporal and spatial aspects. Specific priori-
ties include spatial (key feeding, spawning and
nursery grounds) and temporal (peak spawning
periods) protection for O. nigrimas popula-
tions. The current de facto temporal fishing
limitation to darker nights, during which light
fishing is most effective, could be adapted to
conserve fisheries resources, in particular the
phototaxis positive endemic ricefish popula-
tions in Poso Lake. November and February
appear to be key spawning seasons for both O.
nigrimas and X. oophorus (Table 3). Extending
the non-fishing period to the spawning peaks
of the ricefishes present at each fishing site
should increase the number of fish reproduc-
ing before capture, and thus help to maintain
stocks. Spatial restrictions could include fisher-
ies reserves (suaka perikanan in Indonesia), to
support the conservation (including sustainable
use) of O. nigrimas and other endemic fishes
in Poso Lake.
While data poor approaches could be
adopted now, we recommend multidisciplinary
studies to fill the many knowledge gaps, in par-
ticular to identify spawning periods, investigate
trophic ecology and map key habitats of Poso
Lake endemic species, as well as to collect
data on preferred fishing grounds and monitor
catch compositions. Such data would enable
the identification of times and places where
temporal and/or spatial restrictions could have
a maximum positive impact on endemic fish
resources while minimising negative impacts
on subsistence and commercial fisheries.
A routine monitoring program for O. nigri-
mas and other Poso Lake endemic species
is needed to build time series data sets as a
basis for science-based adaptive and holistic
management. Sustainable levels and patterns
of exploitation could support local livelihoods
including fisheries and other economic activi-
ties (e.g. eco-tourism) and maintaining local
culture, including culinary specialties based on
O. nigrimas and other endemic fishes.
The conundrum of alien species: Among
the threats to the endemic Ichthyofauna of
Poso Lake, introduced (alien) species are a par-
ticular concern. Government projects, mislead-
ingly called “restocking” programs, have (often
repeatedly) introduced non-native species. Sev-
eral of these are known to be invasive and have
negatively impacted native ichthyofauna in
Indonesia and other countries, including two
species of Tilapia (Oreochromis niloticus and
O. mossambicus); African catfish Clarias sp.;
and aggressive and omnivorous South Ameri-
can piranha relatives of the genera Colossoma
and Piaractus (Cagauan, 2007; Sadili et al.,
2015; Ndobe et al., 2019).
The status of two species, the striped
snakehead Channa striata (local name ikan
gabus) and climbing perch Anabas testudin-
eus (local name ikan betok), is unclear. Some
regard these species as native to (at least parts)
of Sulawesi (Kottelat, Whitten, Kartikasari,
& Wirjoatmodjo, 1996) while others consider
them introduced (Herder et al., 2012). Both
are considered at risk from introduced species
in some areas of Central Sulawesi (Ndobe
et al., 2019). If introduced by humans, their
place in local culture and cuisine indicates the
introductions must have occurred a long time
ago, centuries or even millennia. Considering
that all known Poso endemic fishes (including
those considered critically endangered or pos-
sibly even extinct) have been found in recent
149
Rev. Biol. Trop. (Int. J. Trop. Biol.) • Vol. 69(1): 139-152, March 2021
decades, it is unlikely that A. testudineus or C.
striata posed a significant threat to Poso rice-
fishes in the past. However, being predatory
fishes, they could potentially accelerate the
decline or impede recovery of ricefish popula-
tions severely depleted from other causes.
The national guidelines for restocking
threatened aquatic (marine and freshwater) spe-
cies (Sadili et al., 2015, summarised in Table
7) advocate precautionary approaches. It is
unfortunate that similar precautions have rarely
(if ever) been followed for the introduction of
non-native fishes (by government and non-
government parties) across Indonesia, most
of which have occurred without any scientific
evaluation of the risks to native biodiversity
(including locally important fisheries species)
and ecosystems. This paradigm is reflected in
the list of introduced (alien invasive) species in
Poso Lake (Table 5). It is vital to avoid further
introductions (of existing or new alien species),
and serious efforts should be made to mitigate
the impacts of past alien species introductions.
No reports could be found of successful
eradication after breeding populations were
established of the invasive species already
present in Poso Lake from any other natural
lakes. It seems logical that fisheries for alien
species should be encouraged to control (and
hopefully reduce) their abundance and envi-
ronmental impact. However, it is crucial that
such fisheries are operated (and regulated) in
ways which minimise negative impacts on
O. nigrimas and other endemic species, both
direct (e.g. as by-catch or through behavioural
disturbance) and indirect (e.g. through impacts
on habitat, such as lacustrine vegetation and
water quality).
While eradication of introduced species
is unlikely to be feasible on practical grounds
(and in some cases livelihood or food secu-
rity considerations), the prevention of further
introductions should be a priority. Govern-
ment should lead the way, ceasing so-called
“restocking” programs which are in fact alien
species introductions, and implementing miti-
gation measures. Education and public aware-
ness strategies need to be accompanied by
effective surveillance and enforcement, with
meaningful penalties strictly applied for any
violations such as the release of alien species.
Potential contribution of aquaculture
and ex-situ measures: In addition to in-situ
conservation measures, ex-situ research and
conservation-oriented breeding could be con-
sidered for O. nigrimas and other endemic rice-
fishes. The medaka O. latipes is widely-used
as a model organism, and ricefishes are con-
sidered relatively easy to maintain and breed in
captivity (Parenti & Soeroto, 2004; Hilgers &
Schwarzer, 2019). Several Sulawesi ricefishes
have been successfully bred in the laboratory
(Parenti & Soeroto, 2004). Recent research on
the food habits of O. nigrimas (Serdiati et al.,
2019a) provides data for the development of
captive breeding for this species.
Restocking is not considered necessary at
present for O. nigrimas, based on the condi-
tion of the endemic population. Furthermore,
the scientific/technical basis has not yet been
developed and the necessary knowledge is
not available regarding historical range of O.
nigrimas in Poso Lake. However, research to
develop the knowledge and tools to support
an eventual need for responsible restocking
is highly recommended, both as “insurance”
and as a means of learning and building the
scientific basis and human capacity to support
in-situ management. True restocking (sensu
Sadili et al., 2015) of native/endemic fish spe-
cies should follow the guidelines in Table 7.
The development of ex-situ breeding could also
potentially support aquaculture as an economic
activity, and reduce fisheries pressure.
ACKNOWLEDGMENTS
The authors acknowledge support from
the Indonesian Ministry of Research, Technol-
ogy and Higher Education of the Republic of
Indonesia through a doctoral scholarship to the
first author. The authors also wish to thank all
who in any way contributed to the research,
as well as the preparation and publication of
this manuscript. In particular, we acknowledge
150
Rev. Biol. Trop. (Int. J. Trop. Biol.) • Vol. 69(1): 139-152, March 2021
the valuable and insightful contribution of the
anonymous reviewers.
RESUMEN
Perspectivas sobre el manejo sostenible del pez
Oryzias nigrimas, endémico del Lago Poso en Indonesia
(Actinopterygii: Adrianichthyidae). Introducción: Los
peces endémicos de los antiguos lagos de Sulawesi están
cada vez más amenazados. Objetivo: Evaluar los datos y
la información disponible desde una perspectiva de gestión
holística y formular medidas para conservar el pez endémi-
co Oryzias nigrimas en el lago Poso, Indonesia. Métodos:
recopilación de datos primarios de tres estaciones alrededor
del lago Poso y revisión de la literatura. Resultados: Las
amenazas para O. nigrimas incluyen la degradación y pér-
dida del hábitat, la introducción de especies exóticas y la
explotación como producto pesquero de importancia local.
Las opciones para promover la ordenación pesquera sos-
tenible incluyen limitaciones espaciales y temporales para
minimizar la captura de peces grávidos o reproductores. La
protección del hábitat debe incluir medidas para minimizar
los impactos de las actividades que pueden reducir la cali-
dad del agua y perturbar o matar la vegetación acuática.
Conclusión: Las medidas para prevenir una disminución
de la población de O. nigrimas se consideran urgentes y
se recomienda realizar más investigaciones para llenar los
vacíos de conocimiento identificados. La conservación ex
situ, incluido el desarrollo de la cría en cautividad, también
podría contribuir a una estrategia de conservación holística
de O. nigrimas.
Palabras clave: endemismo; lacustre; Oryzae; medaka
negro; especies invasivas; pesca con luces.
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