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Perspectives on sustainable management of the Poso Lake (Indonesia)

endemic ricefish, Oryzias nigrimas (Actinopterygii: Adrianichthyidae)

Novalina Serdiati

*, Diana Arfiati

, Maheno Sri Widodo

, Tri Djoko Lelono

, Samliok Ndobe

Kasim Mansyur

& Abigail Mary Moore

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

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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

(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

Parameter (unit)

Secondary data - Year This study (May 2017 to April 2018) - Station

2007

2010

2011

2013

1 2 3

Temperature (ºC) 27.9-28.8

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

) 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

na = data not available;

Lukman (2007);

Mamondol (2018);

Makmur et al. (2011);

Gundo (2015);

mean value from

0-50 m; temperature ≈27 ºC at 60 m and 29-29.5 ºC from 0-10 m depth.

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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

Gundo (2015);

IUCN Red List;

Nursangaji et al. (2014);

Lukman & Ridwansyah (2009);

Mamondol (2018);

Nontji

(2016);

Gundo (2010);

Herder et al. (2012);

Mokodongan (2019n);

Mokodongan (2019h);

Parenti & Soeroto (2004).

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TABLE 3

Life history parameters of Poso Lake ricefishes

Parameter (unit)

Oryzias

nigrimas

orthognathus

nebulosus

Xenopoecilus

oophorus

poptae

Adrianichthys

kruyti

roseni

Main source (s) other

than FishBase

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)

58.5TL

52.5SL

65TL 50.1SL 33 SL 85 TL

69.3SL

171SL

192SL

160TL

109SL

90SL

Length at first

maturity L

(mm)

50.8 M; 47.5 F

na na na na na na

Estimated longevity na na na na na na na

Fecundity (eggs) 143-243

na na 33-135 na na na

Spawning pattern partial

partial na partial na na na

Spawning season

(month, abbreviated)

Jun, Sept, Nov,

Dec, Feb

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

na na isometric na na na

Phototaxis

Positive Positive Positive Positive Positive Positive Positive

na = data not available; bold characters indicate data from this study;

Froese & Pauly (2020);

Serdiati (2019);

Mokodongan (2019h);

Mokodongan (2019g);

Parenti & Soeroto (2004);

Gundo, Rahardjo, Batu, & Hadie (2016);

Mokodongan (2019m);

Mokodongan (2019c);

Parenti (2008);

Mokodongan (2019p);

Mokodongan (2019q);

TL = total

length; SL = standard length;

From field data on light fishing.

TABLE 4

Ecology, conservation status and exploitation of Poso Lake endemic ricefishes

Parameter/Aspect

Oryzias

nigrimas

orthognathus

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

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

E W E W N E W na na na

Main threats

IN, HL, IF

IN, HL IN, HL, IF, OT

IN, HL, IF IN, HL IN IN

Known to be fished -

food fish

yes yes

yes

Aquarium trade yes

yes

proposed

na na na

na = data not available; bold characters indicate data from this study;

Froese & Pauly (2020);

The IUCN Red List;

Serdiati et al. (2019a);

Parenti (2008);

Parenti & Soeroto (2004);

Gundo (2015);

S = stable; I = increasing; D = declining,

U = unknown; U/EX: unknown, possibly extinct;

Predominantly herbivorous;

This study: all three survey stations (W, NE

and SE; Fig. 1): Mokodongan (2019n): only West (W);

IN = invasive species; HL = habitat loss/degradation; IF = intensive

fishing; OT = other (infestation with parasitic copepods, Lernaea sp.);

Mokodongan (2019h);

Mokodongan (2019m);

Mokodongan (2019c);

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

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

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

8 Tambaqui, pacu

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

10 Auratus cichlid

Melanochromis auratus Cichlid Afrika

INV, PR, HB, FF, U

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

13 Bichir

Polypterus sp. Ikan palmas

African origin

14 Guppy

Poecilia reticulata Ikan seribu

INV, CP, U

15 Swordtail

Xiphophorus helleri Ikan pedang

INV, U, IU

16 Platyfish

Xiphophorus maculatus Ikan platy

INV, U, IU

17 Janitor fish

Family Locariidae

Ikan sapu-sapu

INV, PR, HB, U

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

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;

Synonym O. hasselti;

Taxonomy

of this family is confused; most likely Hypostomus sp. or Pterygoplichthys sp.;

Parenti & Soeroto (2004);

Gundo (2015);

Whitten, Henderson, & Mustafa (2002);

Gundo pers. com (2018);

Herder et al. (2012);

Makmur et al. (2011);

IUCN

Red List;

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

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

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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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