Journal of Threatened Taxa |
www.threatenedtaxa.org | 26 August 2022 | 14(8): 21579–21587
ISSN 0974-7907 (Online) | ISSN 0974-7893
(Print)
https://doi.org/10.11609/jott.7621.14.8.21579-21587
#7621 | Received 18 August 2021 | Final
received 12 July 2022 | Finally accepted 30 July 2022
Can the Sri Lankan
endemic-endangered fish Labeo fisheri (Teleostei: Cyprinidae) adapt to a new habitat?
Dinelka Thilakarathne
1 & Gayan
Hirimuthugoda 2
1,2 Department of
Zoology, Faculty of Science, University of Peradeniya, Peradeniya, Sri Lanka.
1 Postgraduate
Institute of Science, University of Peradeniya, Peradeniya, Sri Lanka.
1 Department of
Zoology, Faculty of Science, University of Ruhuna, Matara,
Sri Lanka.
1 dinelkat@yahoo.com
(corresponding author), 2 nadeela@lankamail.com
Editor: J.A. Johnson, Wildlife Institute
of India, Dehradun, India. Date of publication:
26 August 2022 (online & print)
Citation: Thilakarathne, D. & G. Hirimuthugoda (2022). Can the Sri Lankan endemic-endangered fish Labeo fisheri (Teleostei: Cyprinidae) adapt to a
new habitat? Journal of Threatened Taxa 14(8): 21579–21587. https://doi.org/10.11609/jott.7621.14.8.21579-21587
Copyright: © Thilakarathne & Hirimuthugoda
2022. Creative
Commons Attribution 4.0 International License.
JoTT allows unrestricted use, reproduction,
and distribution of this article in any medium by providing adequate credit to
the author(s) and the source of publication.
Funding: Self-funded.
Competing interests: The authors declare no competing interests.
Author details: Dinelka Thilakarathne (BSc and MPhil) is a
Lecturer (Probationary) in the Department of Zoology, Faculty of Science,
University of Ruhuna, Sri Lanka. She is currently a Ph.D. student at University
of Nebraska-Lincoln, USA. Animal ecology and wildlife conservation are her main
research interests and she is currently conducting biodiversity and animal
ecology related research in Sri Lanka. Gayan Hirimuthugoda is a Technical
officer at Department of Zoology, University of Peradeniya for 10 years and was
OIC of the Department’s Aquarium. He is currently working as an Educator and
Scientific illustrator. In relation to his interests in biodiversity, he is
currently engaged in research work related to fish breeding, embryology and
rearing, especially of endemic, Endangered species.
Author contributions: DT—specimen
identification and measuring, data analysis and manuscript writing; GH—specimen
collection, measuring and manuscript writing.
Abstract: Labeo fisheri
is an endemic and endangered freshwater fish of Sri
Lanka. Mainly restricted to the upper reaches of the Mahaweli River basin, it
has been previously reported living in deep rapids and among large rocks and
boulders. An accidental record of a Labeo fisheri specimen from Victoria Reservoir led us to
further study this habitat during the period from January to August 2017. This
study was carried out to confirm the presence of a population of Labeo fisheri within
the Victoria Reservoir and report its new habitat type in deep stagnant waters.
We further investigated the food habits by analyzing
the gut contents of L. fisheri in the Victoria
Reservoir. Seven individuals were recorded from fishermen’s gill net catch in
three fish landing sites along Victoria Reservoir, with an average total length
of 24.80 ± 4.30 cm, average standard length of 19.70 ± 3.86 cm and average body
weight of 197.69 ± 107.12 g. Based on gut content analysis, only phytoplankton,
especially diatoms and cyanobacteria, were found in the gut of L. fisheri. This new population is facing the direct
threat of fishing. Effective conservation measures are doubtful, since a
fishery is well established in the Victoria Reservoir and the fishing gear used
is not species-specific. More research is necessary to understand the
population dynamics of L. fisheri in the
Victoria Reservoir. In order to conserve it at this locality, community-based
conservation measures are recommended.
Keywords: Adaptation, habitats,
feeding habit, freshwater fish, gut analysis, Labeo
fisheri, new locality, stagnant water, Victoria
Reservoir.
INTRODUCTION
Sri
Lanka and the Western Ghats of India collectively are one of the 34
biodiversity hotspots in the world (Bossuyt et al.
2004; Gunawardene
et al. 2007). Sri Lanka is situated at the southeastern tip of the Indian peninsula
between 6o & 9o north of the equator and 79o &
82o east of the Greenwich mean line. It is a small island (65,610 km2)
with rich biological diversity. Its proximity to the equator, heterogeneity of
topography and climatic conditions help to support vast diversity of both flora
and fauna (Weerakoon 2012). Sri Lanka harbors a rich
ichthyofaunal diversity comprising 127 species, including 61 endemics and 30
introduced species (De Silva et al. 2015; Goonatilake
et al. 2020). Exotic species have been introduced to the island mainly to
increase the inland fisheries, and the rest are from aquarium escapes (Goonatilake 2007). According to the distribution patterns
of freshwater fish, four major zones have been identified: transition,
southwestern, Mahaweli, and dry (Senanayake &
Moyle 1982). Of these four zones, the Mahaweli zone and southwestern zone have
the highest species diversity. This is due to the high heterogeneity of the
habitats, rainfall patterns and the topography of these regions. Although the
fish of the Mahaweli zone are relatively well known, it continues to produce
significant discoveries despite widespread habitat destruction (Senanayake & Moyle 1982).
Taxonomic
nomenclature is an important tool to identify fish species. Nomenclature of Sri
Lankan freshwater fish has been extensively revised during the past two
decades. For example, the genus Rasbora (Silva
et al. 2011; Sudasinghe et al. 2020), genus Rasboroides (Batuwita et
al. 2013; Sudasinghe et al. 2018), genus Puntius
(Pethiyagoda et al. 2012; Sudasinghe
et al. 2020, 2021), genus Devario (Batuwita et al. 2017; Sudasinghe
et al. 2020), genus Labeo (Sudasinghe
et al. 2018), and genus Esomus (Sudasinghe et al. 2019) were revised and new species have
been described. Taxonomy has been always important as scientists struggle to
identify species in order to understand the evolutionary relationships and
complex interactions of ecosystems threatened due by anthropogenic activities.
The genus Labeo is one such fish group that
was recently revised by Sudasinghe et al. (2018).
Labeo
fisheri (Jordan
& Starks, 1917), commonly called Sri Lankan Mountain Labeo,
is an endemic and endangered freshwater fish species (MOE 2012; Goonatilake et al. 2020). It is mainly confined to the
upper reaches of the Mahaweli River, and is also recorded at a few locations of
the lower reaches of the river. It has not been recorded from any other river
basin in Sri Lanka (Sudasinghe et al. 2018). It is found in deep, rocky areas with rock
crevices where the water current is strong with rich oxygen. It is reported
that L. fisheri is highly sensitive to these
microhabitat conditions (Pethiyagoda 1991). The
alteration of river morphology as a result of different hydropower projects
since the 1980s has caused habitat loss for L. fisheri.
This has probably led to a population fragmentation. In the inland fishery
sector, there is a high demand for this fish not only for its delicacy, but
also for perceived aphrodisiac effect of its flesh (NARA 2017). Initially an
accidental observation of a specimen of L. fisheri
in a fisherman’s catch was made in 2017 from the Victoria Reservoir. This catch
was otherwise composed of Oreochromis niloticus
(around 30 individuals) and a 9 cm stretched mesh size gill net was used by the
fishermen. This accidental finding prompted us to investigate the presence of L.
fisheri in Victoria Reservoir, with the aim of
establishing a new distribution record and determining diet preference in the
new habitat.
MATERIALS AND METHODS
Study
Site and study period
Fieldwork
was conducted from January to August 2017. The study sites were in the Victoria
Reservoir between Thennekumbura (7.281 N, 80.666 E)
and Anuragama (7.247 N, 80.731 E), Sri Lanka (Figure
1; Image 1). These sites are located in the intermediate zone with elevation
ranging 641–764 m. The mean annual rainfall in this area is 50–200 mm.
Survey
of Labeo fisheri
in the Victoria reservoir
Fishermen
were advised to collect any specimens of L. fisheri
found in their daily catch and inform the members of our research team, who in
turn collected the specimens during the study period. Specimens collected by
fishermen were photographed using a Nikon (5300) digital camera and brought to
the aquarium in the Department of Zoology, University of Peradeniya for further
study. Caudal fin samples of each individual specimen were collected into 100%
ethanol vials onsite, and stored at 4oC for molecular analysis.
After taking the meristic and morphometric measurements, the collected
specimens were dissected and the gut was separated into 90% ethanol containers
for diet analysis.
Taxonomic
identification
The
fish were identified using available fish guides and literature (Pethiyagoda 1991; Goonatilake
2007; De Silva et al. 2015; Sudasinghe et al.
2018). Taxonomic analysis was done for further confirmation of the L. fisheri captured from Victoria Reservoir.
The
morphometric measurements (total body length, standard body length, body depth,
caudal peduncle depth, caudal peduncle length, pre-dorsal length, length of
dorsal fin base, length of anal fin base, height of dorsal fin, height of anal
fin, length of pectoral fin, length of pelvic fin, length of longest dorsal
fin, spine, head length, head width, snout length, suborbital width, length of
orbit to pre-opercular angle, eye diameter, upper jaw
length, and gape width) of the collected fish were measured using a digital
Vernier caliper. The following meristic characters (dorsal fin spines, dorsal
fin rays, anal fin spines, anal fin rays, pectoral fin rays, scales along
lateral line, scales above lateral line, scales below lateral line, scales
before dorsal fin and scales around caudal peduncle) of the fish were also
noted (Armbruster 2012). These morphometric measures were used in principal
component analysis (PCA) in Minitab® 17.1.0 (©2013 Minitab Inc.) to compare the
morphometric characters of individuals collected from Victoria Reservoir.
Analysis
of food habit of Labeo fisheri
The
anterior part of the gut was crushed adding distilled water and the gut content
was extracted. The crushed solution was used to analyze the food habit of the
fish. The gut solution was mixed well and 0.05 ml was pipetted onto a clean
glass slide, covered with a cover slip and observed under a Primo-star light
microscope. Ten drops (0.05 ml each) of gut solution were analyzed for each
individual captured from the Victoria Reservoir. Types of plankton species
present in the samples were identified using plankton guides (Fernando & Weerewardhena 2002; Yatigammana
& Perera 2009) and photographed using a Zeiss
Primo star inverted microscope attached with camera. The relative abundance of
each plankton species was calculated as follows:
Number of individuals of
a particular plankton species
Relative
abundance = –––––––––––––––––––––––––––––––––––––– X 100%
Total number of
individuals of all plankton species
Comparisons
were determined using one-way ANOVA in R version 3.6.1 (R foundation for
statistical computing) using 95% confidence intervals (α = 0.05).
RESULTS
A
total of seven Labeo fisheri
specimens were collected during this period. The specimens showed two distinct
coloration patterns. Adults with olive green body coloration dorso-laterally, the color becoming lighter in the ventral
region. Sub adults (<~220 mm snout length) have yellowish-brown color dorso-laterally and white ventrally. Base of the fins show
dark green color and it eventually turn into the reddish-orange color towards
the top. All specimens have a black blotch at the base of the caudal peduncle
which is 6–7 scales long and 4–5 scales high. There is a single pair of barbels which is maxillary in position. Its mouth is
ventrally positioned and has a well-developed rostral fold with thick fleshy
lips. The snout was covered with white color tubercles (Image 2).
The
average total body length of the seven specimens collected was 24.80 ± 4.30 cm
and the average standard length was 19.70 ± 3.86 cm (Table 1). The maximum
recorded standard length and the body weight of Labeo
fisheri from Victoria reservoir was 24.00 cm and
333.00 g, respectively. The average body weight of the seven specimens was
197.69 g. Morphometric characters
expressed as a ratio to the standard length are given in the Table (2).
Principal component analysis (PCA) carried out for the Victoria population
revealed that this population share the same morphometric characters compared
to the L. fisheri populations in some
other Mahaweli tributaries such as Moragolla and Gatambe (Figure 2).
The
dorsal fin comprised of two simple rays and 10–12 branched rays. The anal fin
had two simple rays and five branched rays. The pectoral fin comprised of one
simple ray and 15–18 branched rays. Ventral fins composed of one simple and
eight branched rays. The lateral line is complete with 38–39 lateral line
scales. There are 16–18 scales along the pre dorsal region. The formula for
meristic characters could be given as; D ii/10-12; A ii/5; P i/15-18; V i/8; LL 38-39; L. lat 7 ½ / 5½.
According
to the food habit analysis, a total of 21 phytoplankton species belonging to
five classes were identified in the gut contents of Labeo
fisheri recorded from the Victoria Reservoir. Bacillariophyceae (diatoms) and Cyanophyceae
(cyanobacteria) were the dominant classes, although the preference for species
each differed (F = 3.01; p <0.05). The most preferred were Aulacoseira sp., followed by Chlorococcus
sp. and Staurastrum cingulum. It
is also found that the diatoms Closterium sp.,
Cyclotella sp., Lyngbya
sp., Merismopedia sp., Nostoc
sp., Oscillatoria sp., Staurastrum
megacanthum, and Tabellaria
sp. were least preferred (Image 3; Figure 3).
DISCUSSION
Labeo
fisheri has been
exclusively recorded from Mahaweli river basin and mostly in the upper reaches
of the river. Highest recorded elevation is Ulapane-Gampola
at 562 m and lowest is Angammedilla-Polonnaruwa at 80
m (NARA 2017; Sudasinghe et al. 2018). It had been
earlier recorded along the Mahaweli River (upstream of the Victoria Reservoir)
at Ulapane-Gampola, Getambe,
Lewella, Polgolla, and Digana. They were also earlier recorded downstream of the
Victoria reservoir at Randenigala, Minipe anicut, and Badulu Oya (Sudasinghe et al. 2018). Labeo fisheri was
also recorded in the Mahaweli tributaries at Heen
Ganga, Thelgamu Oya, and
Amban Ganga (NARA 2017; Sudasinghe et al. 2018). Labeo fisheri was
last recorded in 1952 at Lewella (type locality) and
in 1991 at locations around Victoria Reservoir such as Randenigala,
Digana, and Polgolla. In
this study, for the first time we confirm a presence of a well-established
population of L. fisheri in the Victoria
Reservoir.
In
the past L. fisheri was found in lentic
habitat conditions. This is a strong indication that L. fisheri
can change habitat from lotic to lentic, and introduction of exotic species
such as Tilapia and tank cleaners may have played a role. L. fisheri was earlier recorded in deep rapids among large
rock crevices and boulders, whereas juveniles and sub-adults were common in
shallow regions with a moderate, non-turbulent flow (Sudasinghe
et al. 2018). Specimens in this study were collected from the middle of the
reservoir in stagnant waters, and the depth they were entangled in the net is
around 10 m. It is possible that there are more recordings of L. fisheri from the Victoria Reservoir, because we only
collected specimens from three landing sites out of a total of ten around the
Reservoir. Therefore, more research work has to be done to confirm the presence
of a viable population in the reservoir. Since fisheries in the reservoir are
being monitored by National Aquaculture Development Authority (NAQDA), Sri
Lanka, they are able to collect such extensive fisheries data.
Gut
content analysis is the best method to get a proper understanding of fish
feeding habits. Previous studies have shown that L. fisheri
scrapes submerged rocks using thick and horny lips in the ventral mouth.
Earlier Pethiyagoda (1991) reported that they only
feed on algae. It is believed that L. fisheri
in Ulapane and Gatambe feed
on an aquatic plant belonging to the family Podostemaceae
(NARA 2017). However, according to our findings they mainly feed on diatoms and
cyanobacteria. This may be due to inadequate submerged vegetation and algae in
the Victoria Reservoir.
Water
entering to the Victoria reservoir during the rainy season is highly turbid due
to wash off from upstream areas. At the reservoir where water is stagnant, soil
particles start to settle at the bottom. Sedimentation increases and reduces
the production of algae and macrophytes due to lack of oxygen in the bottom of
the reservoir. Sedimentation also increases eutrophication of the reservoir.
Both these factors affect the transparency of the water and limit sunlight
penetration to the bottom, which can damage the food source of L. fisheri.
Many
people use Mahaweli River for washing, bathing and dumping garbage. All these
pollutants are collected and concentrated at the reservoir. Thus water
pollution is observable in the reservoir. The gut content analysis of L. fisheri also confirmed that this reservoir was highly
polluted because Aulacoseira sp. and
some cyanobacteria were the most prominent phytoplankton species in the gut of
the L. fisheri. Aulacoseira
sp., and Navicula sp. often attain high
biomass in eutrophic rivers and reservoirs (Akinyemi et al. 2007). Thus, it is
a useful indicator species for trophic conditions (Akinyemi et al. 2007). So,
this is a clear indication that water in the Victoria Reservoir is polluted and
it may have adverse effects on the native species living there. Some of the
areas of Victoria Reservoir have been used as dumping sites for garbage which
also contributes to the water pollution of the reservoir.
Sometimes
illegal small-meshed gill nets were used to capture fish, especially at the
shallow areas and at mouths of tributaries. These are potential habitats of
juveniles and sub adults of L. fisheri though
they migrate up streams for spawning and they are subjected to be caught. This
new population is facing the direct threat of inland fisheries. Effective conservation
measures are doubtful since fisheries are well established in the Victoria
reservoir and the fishing gear is size specific but, not species specific.
During the dry season from February to September, the reservoir water level
goes down and they are highly vulnerable to be captured by the gill nets.
Victoria
Reservoir has several invasive species of fish such as Pterygoplichthys
disjunctivus (tank cleaner), potentially invasive
Oreochromis mossambicus and Oreochromis niloticus. Pterygoplichthys
sp. was initially an aquarium escapee, which later became well-established
in the river and reservoir systems of the country. They have a high rate of
reproduction and high rate of survival during harsh environmental conditions. Pterygoplichthys sp. is piscivorous and feeds
on the native species, especially fry, fingerling and juvenile stages (Bambaradeniya et al. 1999). Oreochromis mossambicus and Oreochromis niloticus
were introduced in to reservoirs as food fish and to encourage a commercial
capture fishery (De Silva 1988). They are competitive species for the food and
space in the reservoir. Due to their high natality rates, survival rate and
voracious feeding habit, the native fish populations declined. In the dry zone,
Oreochromis mossambicus is considered
responsible for the extinction of L. lankae,
due to overlapped habitats and niches in the dry zone reservoirs (Pethiyagoda 2006). In the same way Oreochromis sp.
might pose risk for the extinction of Labeo
fisheri as well due to the niche overlapping. Unlike
the Oreochromis sp., L. fisheri cannot
adapt well to the new habitats. They
have to compete for their usual food and other resources in the reservoir. That
may cause the population reduction of Labeo
fisheri from the reservoir in the future. Other
than the L. fisheri, L. rohita
was recorded from the Victoria reservoir and Labeo
heladiva was recorded from the Rantambe reservoir downstream of the Mahaweli River. This
indicates that the some of the species in the genus Labeo
can adapt to the lentic conditions.
Most
of the endemic and threatened freshwater fish are found outside protected areas
with high anthropogenic activities. Therefore, they need to be protected by
protecting habitats (their catchment areas and the quality of water). Any type
of development that cause harm to these habitats (such as mini hydro projects)
needs to be clearly assessed. Species oriented and habitat-oriented
conservation programs should be established at least for the endangered
species. When the species are located outside of the protected areas, the local
communities must be made aware and have to be involved in conservation
programs. Such community awareness program has been successfully implemented
for Pethia bandula
(MOE 2012; Goonatilake et al. 2020). Ex situ
breeding programs, translocation, reintroduction should be established with the
aim of increasing the wild population. Some of these translocation programs
have been highly successful while others have failed (Goonatilake
2012; Sudasinghe et al. 2018). Therefore, we need to
find proper conservation measures and implement early to help safeguard the Labeo fisheri in
the Victoria Reservoir.
CONCLUSIONS
Endemic
and endangered Labeo fisheri
is recorded in a new locality (Victoria Reservoir) where it has not been
previously recorded and this appears to be a new habitat. It is interesting
that this fish was able to adapt for stagnant water apart from its original
habitat (fast flowing waters). Not only that, their food habit is slightly
changed from algae to diatoms and cyanobacteria due to the availability in this
reservoir. However, more research work has to be done to ensure the existence
of a viable population in the reservoir and since fisheries in the reservoir is
being monitored by National Aquaculture Development Authority (NAQDA), they are
in a better position to collect such extensive fisheries data. Water pollution
and direct exposure to the fisheries poses greatest threat to its survival.
Community based conservation efforts should be taken if this species needs to
be conserved at this locality.
Table 1. Body length
and body weight of captured Labeo fisheri in Victoria Reservoir, Sri Lanka (N = 7).
|
Average total body
length / cm |
Average standard
length / cm |
Average body weight
/ g |
Mean |
24.80 |
19.70 |
197.69 |
SD |
4.31 |
3.86 |
107.12 |
SE |
0.62 |
0.55 |
15.30 |
SD—Standard Deviation
| SE—Standard Error
Table 2. Morphometric
characteristics of Labeo fisheri in Victoria Reservoir, Sri Lanka (N = 7).
|
Ratio to standard
length |
||||||||||||||||||
Body depth |
Caudal peduncle
depth |
Caudal peduncle
length |
Pre-dorsal length |
Length of dorsal
base |
Length of anal base |
Height of dorsal
fin |
Height of anal fin |
Length of pectoral
fin |
Length of pelvic
fin |
Length of longest
dorsal spine |
Head length |
Head width |
Snout length |
Suborbital width |
Length of orbit to
pre-opercula angle |
Eye diameter |
Upper jaw length |
Gape width |
|
Mean |
0.30 |
0.14 |
0.16 |
0.44 |
0.20 |
0.08 |
0.19 |
0.16 |
0.23 |
0.19 |
0.11 |
0.23 |
0.16 |
0.09 |
0.05 |
0.09 |
0.09 |
0.06 |
0.14 |
SD |
0.02 |
0.01 |
0.02 |
0.02 |
0.01 |
0.01 |
0.02 |
0.02 |
0.01 |
0.01 |
0.03 |
0.02 |
0.01 |
0.01 |
0.01 |
0.01 |
0.13 |
0.01 |
0.01 |
SE |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
0.02 |
0.00 |
0.00 |
SD—Standard deviation
of sample | SE—Standard error of sample.
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